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Macrophages Information and Courses from MediaLab, Inc.

These are the MediaLab courses that cover Macrophages and links to relevant pages within the course.

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Authentic and Spurious Causes of Thrombocytopenia
Increased platelet destruction

The most common cause of thrombocytopenia is increased destruction of platelets. Platelets are eliminated from peripheral circulation faster than the bone marrow can produce new platelets.Increased platelet destruction may be the result of immune or nonimmune mechanisms. Immune platelet destruction begins when antibodies coat platelets. These sensitized platelets are then destroyed by macrophages, mostly from the spleen but also from the liver. Disorders that are associated with immune mechanisms of destruction include: Idiopathic (or immune) thrombocytopenic purpura (ITP) Heparin-induced thrombocytopenia (HIT) Neonatal alloimmune thrombocytopenia (NAIT)Increased destruction of platelets is not always caused by the immune system. Platelet destruction can occur as a result of abnormal platelet aggregation or endothelial cell injury. Both of these occurrences can cause fibrin to form in arterioles and capillaries. This leads to platelet activation and consumption. Conditions associated with nonimmune destruction and consumptive thrombocytopenia include: Thrombotic thrombocytopenic purpura (TTP) Hemolytic uremic syndrome (HUS) Disseminated intravascular coagulation (DIC) All of these conditions are associated with significantly decreased platelet counts that may become life threatening. Restoration of platelet numbers is essential to promote clotting and vascular patency.

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Treatment for ITP

Treatment guidelines recommend that patients receive treatment if they have any of the following: Significant bleeding risk <20 x 109/L platelets and moderate bleeding <10 x 10 9/L platelets with no bleeding symptomsCorticosteroids are effective treatments for 50 - 80% of individuals with either acute or chronic ITP. Even with a reduction or discontinuation of corticosteroid treatment, remission can be maintained.Anti-D immunoglobulin, administered intravenously, may be an effective treatment for Rh-positive children or adults diagnosed with acute or chronic ITP. Anti-D immunoglobulin forms red blood cell complexes that block the destruction of platelets. This treatment cannot be used for patients who are Rh-negative or who have undergone a splenectomy. When a patient is refractory to the above treatments, other treatment possibilities include thrombopoietic drugs to stimulate the megakaryoblast or Rituximab, a treatment that targets CD 20-positive B-cells.Splenectomy may be a last resort treatment for chronic ITP sufferers if their platelet counts are below 30 x 109/ L or if symptoms warrant it. In ITP, antibodies develop that coat the platelets. The spleen produces macrophages whose Fc receptors recognize and destroy these antibody-coated platelets. Removing the spleen would decrease platelet destruction, but it is a last resort since the immunologic function of the spleen would also be lost.

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Body Fluid Differential Tutorial
Synovial Lining Cells

A joint space has a membranous lining similar to the mesothelium found in the pleural and peritoneal cavities. The synovial lining cells, which make up this membrane, produce synovial fluid which lubricates the joints.In a normal joint there is a minimal total volume of fluid present. With joint trauma, such as infection or inflammation, the volume will be increased and synovial lining cells may be noted on the cytospin preparation in addition to the cell types normally present with infection, inflammation or hemorrhage. Synovial lining cells (see arrows) resemble miniature mesothelial cells or small macrophages. They can be found singly or in clumps and can have "foamy"-looking cytoplasm.

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Adenocarcinoma in Peritoneal Fluid

This is a cytospin of an ascites fluid from a patient with widely metastatic adenocarcinoma.Notice the size of these tumor clumps (see arrows) when compared to the size of the background neutrophils, lymphocytes and macrophages.Also, note how close together the nuclei appear in the tumor clump. Think about the separation you would see in a mesothelial clump. These tumor cells are larger than mesothelial cells would normally be. They have a considerably larger and more dysplastic-looking nucleus and have much less cytoplasm than a mesothelial would normally have. These are key differentiating features in the identification of adenocarcinoma tumor clumps in fluids.

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Metastatic Tumors in Fluid Cytospins.

There are a wide variety of solid tumors that can metastasize and spread into body fluids. As with cytospins positive for leukemia or lymphoma, any smear with tumor or suspected tumor should be sent for pathology or hematologist review.Body fluids tend to be a good growth medium for metastatic tumors. These tumor cells tend to be present in sheets and clumps. Frequently there will be reactive changes with increased mesothelial cells and macrophages associated with metastatic tumors as well.Tumor cells, in general, typically appear large with fine/open chromatin patterns, dismorphic or dysplastic nuclei and prominent nucleoli. They will have varying amounts of basophilic cytoplasm depending on the tissue of origin.

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What is the identification of this cellular clump found in CSF? Note the presence of many similar-appearing nuclei without distinct lines of demarcation between cells.View Page
Monocytes and Macrophages

Monocytes and macrophages are frequently found together in body fluids. In fact, macrophages are actually monocytes that have arrived in the fluid earlier, and become more active than their more recently arrived brethren. The function of a monocyte or macrophage is to remove and recycle dead or dying cells so they do not become an irritant to the body. Macrophages (see arrows) are larger with much more cytoplasm which is frequently heavily vacuolated. The nucleus tends to be pushed to the edge of the cell and the cytoplasm may have ingested materials present. You may see ingested RBC's or WBC's, lipid droplets, hemosiderin and even ingested crystals.

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Siderophage

The heavy black pigmentation in the macrophages present in this image (see arrow) is hemosiderin - a storage form of recycled iron. This is a bronchioalveolar lavage(BAL) sample from a patient that had pneumonia-like symptoms with two episodes of unexplained drops in hemoglobin without obvious external bleeding.The large amount of hemosiderin is a reflection of the amount of intra-alvelolar bleeding that was causing both the drop in hemoglobin and the pneumonia symptoms.

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Macrophages

The macrophages in this image have multiple large phagocytic vacuoles. This sample is a reactive pleural effusion in a patient with widely metastatic rhabdomyosarcoma. These particular macrophages have been removing some of the red blood cells (RBCs) that have been released into the pleural space due to the spread of this patient's tumor. While there are no intact RBCs in these cells, the size of the vacuoles is good indication of what they have most likely been phagocytizing.

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Histiocytes

The large multinucleate macrophage shown in this bronchialalveolar lavage image (see arrow) is a histiocyte. Notice the similar cytoplasm characteristics and chromatin texture and staining between the histiocyte and macrophages. If you were to fuse together 5 of the macrophages in this photo, it would not be easily distinguished from the histiocyte in the center.Note: The terms histiocyte and macrophage are sometimes used interchangeably. The choice of which term to use can be institution and pathologist dependent. Some institutions designate large multinuclear macrophages as histiocytes.

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Macrophages are actually lymphocytes that have entered the tissues and body fluids via diapedesis.View Page
Anaplastic Large Cell Lymphoma (ALCL)

This cytospin is from a patient who presented in respiratory distress and was found to have a large mediastinal mass and large bilateral pleural effusions.The lymphoid cells in this image are large and immature in appearance. These lymphocytes were initially believed to be consistent with lymphoma cells but, after immunophenotyping, were found to be reactive T-cells instead of lymphoma cells.The three larger cells in the image look similar. The two larger cells on the left are just macrophages. The one larger cell on the right is actually the malignant cell (see arrow). The malignant cell has a larger nucleus with softer more open chromatin and a slightly more prominent nucleoli. The cytoplasm is also more basophilic, and the vacuoles are atypical. They are not the typical round vacuoles seen in macrophages/histiocytes; these vacuoles are more elongated.The diagnosis of ALCL was confirmed when the cytogenetics proved positive for the specific translocation, t(2;5), that defines this lymphoma.

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Intracellular Diplococci

When intracellular bacteria are present in a body fluid cytospin, they classically appear within neutrophils (see arrows). When the bacterial burden is high, they may also be found in monocytes/histiocytes. It is important to note that monocytes are the less effective phagocytes of these two cell types, so they will never contain intracellular organisms if the neutrophils do not do so as well. If you think you are seeing bacteria in a monocyte/macrophage, and the neutrophils do not display intracellular bacteria, you may actually be observing granules of hemosiderin within the macrophages. Hemosiderin usually stains more green-blue or black than bacteria, and the granules are less regular in size than ingested bacteria. Comparing the Wright stain to the Gram stain, and performing an iron stain, will help with this distinction.

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Bronchial Lining Cells

Bronchial alveolar lavage (BAL) is a procedure performed to obtain cells from the lungs to evaluate the cause of lung disease. A fiber-optic scope is passed into the section of lung to be examined while a small amount of physiologic saline is instilled and then removed to be sent for examination.Macrophages are frequently found in Bronchial alveolar lavages and can be found singly or in clusters. This photo shows several macrophages (blue arrows).The elongated rectangular cell with the cilia at the end is a bronchial lining cell which is also frequently present in BAL samples (red arrow).

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Mesothelial Cells

The mesothelium is the name given to the membrane that lines most body cavities and surrounds the internal organs. Cells that shed from these membranes are commonly found in pleural, peritoneal and pericardial fluids. Mesothelial cells are large cells that may be found as single cells or in clusters and clumps. They tend to have a large round centrally placed nucleus with a generous amount of basophilic cytoplasm which can appear frayed at the edges. They will have one ore two small, well-defined, deeply staining nucleoli. While they may have small pinpoint vacuoles, they will not have the larger "foamy" vacuoles seen in macrophages or histiocytes.There are two mesothelial cells in the image below (see arrows). While they are different in size, they are definitely larger than the background lymphocytes and plasmacytoid lymphocytes. Notice the irregular frayed edge to the cytoplasmic membrane.

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Reactive Mesothelial Cells

Reactive mesothelial cells can be found when there is an infection or an inflammatory response present in a body cavity. This condition can be due to the presence of a bacterial, viral or fungal infection. It can also be the result of trauma or the presence of metastatic tumor.Reactive mesothelial cells tend to come in clusters and clumps and have a more washed out cytoplasm in body fluids. Notice in the image on the right, how indistinct the cytoplasmic borders are in this clump compared to normal mesothelial cells. The wide separation of the nuclei and the well defined nucleoli help to identify these as reactive mesothelial cells. However if there is any doubt, the smear should be sent for hematology or pathology review.Note: It is not uncommon for macrophages to be mixed into a reactive mesothelial clump.

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Bone Marrow Aspiration Part I: Normal Hematopoiesis and Basic Interpretive Procedures
Calculating and Reporting the Myeloid:Erythroid (M:E) Ratio

Once the bone marrow cell count is completed and recorded, the M: E ratio should be assessed. This is performed by calculating the total myeloid precursors in proportion to the total erythroid precursors. Remember that this does not use the total white blood cell tally; the myeloid cells alone are counted, excluding lymphocytes, monocytes, macrophages, plasma cells, megakaryocytes, osteoclasts, osteoblasts, and other non-myeloid cells. In most circumstances, it is quite simple to divide the myeloid total by the erythroid total to find the ratio. This is always reported as a whole number ratio, and is normally around 3:1 (reference range= 2:1 to 4:1). In some situations where the erythroid portion is increased, or the myeloid series is decreased, the M:E ratio is reversed. This would still be expressed as a whole number ratio (example: 1:2). A simple way to perform the calculation is to always divide the larger value by the smaller. Which side of the colon, the 1 is placed on, is dependent on which cell type was larger. The 1 always belongs on the side of the cell type found in lower numbers.For example:Myeloid total 120 : Erythroid total 40 M:E ratio = 120 ÷ 40 = 3 or 3:1 So, the M:E ratio is 3:1Another example:Myeloid total 30 : Erythroid total 150Divide the larger number by the smaller (notice that the placement is reversed).150 ÷ 30 = 5 So, the M:E ratio is 1:5

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Rules for Bone Marrow Differentials, continued

Bone marrow smears can be very cellular and it can be difficult to keep track of where you are on the smear while keeping your correct hand position on the keyboard . Having a good strategy to use when counting cells and performing differentials can make this less difficult. On peripheral blood differentials, it is easy to observe and count each cell individually as the stage is moved to bring the next field into view. However, with bone marrows, the total number of keys that need to be used on the differential counter is greater than the number that need to be used with a peripheral blood smear and the number of cells per field is also increased dramatically, making it easy to lose track of the cells on the smear or one's hand/keyboard placement. It can be simpler and less stressful to work on the quadrant system. There are two different ways to do this: Divide the field into quadrants. Count the individual cells in each quadrant separately. This decreases the number of cells into more manageable bites. However, you still have the increased number of cell types to deal with and possible keyboard frame-shifts. Divide your keyboard into quadrants. Search your field for a limited number of cell types and tally all you see before moving on to the next grouping of cell types. Once you tally all your groups then move on to the next field (e.g., lymphocytes, monocytes, macrophages, eosinophils, basophils, plasma cells, erythroids, segmented neutrophils, bands, etc). You can make these small groupings for any cells as long as you cover the entire list of cell types that your laboratory reports in its bone marrow differential protocol. Remember that blasts are identified by cell type and there will usually be a separate key for pronormoblasts, myeloblasts, lymphoblasts, and possibly monoblasts and plasmablasts. It is possible to combine both methods, using the keyboard quadrant technique with a restricted portion of the total microscope field. This is useful when you are getting close to your total tally and do not want to alter the balance by only counting one cell type for the last few cells.

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Iron Staining

Iron staining on bone marrow aspirate smears is commonly part of the standard order protocol for bone marrows aspirates. The iron staining procedure utilizes the Prussian Blue stain for ferric iron to assess bone marrow iron stores. This procedure is particularly helpful when evaluating patients with anemia, iron overload, myelodysplasia, etc. In the adult setting, it is commonly performed on the bone marrow biopsy, but can be requested on the aspirates as well.In the pediatric setting, it is less likely to be part of the standard order set since young children rarely have stainable iron stores. However, iron staining may be requested on patients with congenital anemia and possible mitochondrial defects to look for sideroblastic anemia.In this technique, iron will stain blue and will normally be found in bone marrow stromal/ macrophages, which are found in the spicules. On aspirate smears, without fragments/spicules, it is not possible to evaluate for iron stores. However, if there are nucleated red blood cells (NRBCs) present, it is still possible to look for the ringed sideroblasts, common in sideroblastic anemias.The image on the right is a field from a bone marrow slide from a patient with congenital sideroblastic anemia. The NRBC indicated by the red arrow is a normal siderocyte with few granules of hemosiderin scattered through the cytoplasm. The NRBC that is indicated by the blue arrow has a large number of hemosiderin granules concentrated in the mitochondria that surround the nucleus. This is a pathologic ringed sideroblast.

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Polychromatophilic Normoblast

In the polychromatophilic normoblast stage, the cytoplasm has begun to produce hemoglobin and, as a result, the color starts to shift from deep basophilic to a slate blue/gray shade. The cell continues to slowly shrink in size while the chromatin becomes much more knotted and clumped. The spoke-like pattern of the chromatin accentuates the nuclear membrane and the nuclear pores.The top image on the right shows a clump of polychromatophilic normoblasts. Notice they are all very similar in size, shape and stage of maturation. This is a classic pattern in erythroid development and these clusters are frequently associated with macrophages or histocytes in the marrow as they are the RBC precursors' source of iron. Note that the cytoplasm color is now a blue/gray rather than the deep midnight blue of the basophilic pronormoblast stage. The lower image on the right shows a range of RBC precursors. At the bottom is a cluster of basophilic normoblasts (see red arrow), one of which is binucleate. There are also two cells above the cluster: the top cell is an early polychromatophilic normoblast (blue arrow) while the lower is a late basophilic normoblast (green arrow). Note the difference in cytoplasm color. The polychromatophilic normoblast is slate blue/gray while the basophilic normoblast still maintains the midnight blue hue. Observe the nuclei and the chromatin pattern: the chromatin is much more condensed in the polychromatophic normoblast.

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Monoblast

Monocytes progress through maturational stages in a similar fashion to the myeloid series before entering the peripheral blood circulation. The final stage of monocyte maturation into macrophages occurs after they have migrated out of the peripheral blood and into the surrounding tissues via diapedesis. Mature macrophages are also found in the bone marrow. The monocyte lineage does not maintain a maturational pool in the bone marrow as large as the myeloid pool. As a result, the monoblast stage is infrequently noted in most normal bone marrows.Monoblasts are the largest blasts of all the hematopoeitic cell lines present in the bone marrow. They have a large, round, centrally-placed nucleus with soft, fine-stranded chromatin. They normally have a single, large, prominent nucleolus. The cytoplasm is very generous and has a fine, grainy texture. In the monoblast stage, the cytoplasm will be basophilic, similar to other blasts, but will possess a slightly lighter shade of blue. In the monoblast, the color will shift to blue-gray as the cell matures into a monocyte.The top image on the right shows a single monoblast. Notice the large, round nucleus, the single large nucleolus and the generous blue, grainy cytoplasm. The second image shows a group of monocyte precursors. The large cell at the top is a monoblast (see red arrow). Notice the round and flat look of the nucleus in the blast compared to the other stages. Observe the nuclear shape becoming more folded and three-dimensional as the cell matures.

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Monocyte

The monocyte is the final stage of monocyte maturation found in the peripheral blood before it migrates into tissues and further develops into a macrophage (histiocyte).When seen in the bone marrow, a mature monocyte will look identical to its peripheral counterpart. It will have fine, lacy chromatin pattern with varying degrees of nuclear folding and condensation. The cytoplasm will be blue-gray in color with a slightly grainy texture. The cytoplasm may have a light sprinkling of fine pink cytoplasmic granules. The mature monocyte will be larger than mature segmented neutrophils, but not quite as large as promyelocytes or early myelocytes. The top image to the right shows several monocytes with varying degrees of nuclear folding (see red arrows). Notice that the chromatin clumping is not as dense as that found in neutrophils. Notice also that the cytoplasm is blue-gray and grainy, not the pink/tan of a neutrophil. Observe that the mature monocytes are slightly smaller than the promyelocytes in the image.The lower image to the right shows a monocyte (red arrow) adjacent to a segmented neutrophil (blue arrow). The monocyte is clearly larger. Notice the increase in size of the two monocytes below (green arrows) as they begin to transform into macrophages (histiocytes). The vacuolation is an indication of this transformation occurring.

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Macrophage (Histiocyte)

The macrophage is the final stage of development in the monocyte lineage. It is a phagocyte whose roles include the removal of dead and dying tissue and the destruction and ingestion of invading organisms. Macrophages (histiocytes) act as immune modulators as they will present antigens from ingested pathogens to helper T-cells.Their primary role in the bone marrow is the removal of cellular debris, including old red blood cells (RBCs). As a result, they become a source of iron for maturing RBC precursors. A histiocyte is a less phagocytic form of a macrophage with fewer lysosomal granules. Histiocytes may form clusters, or even fuse together into mulitnucleated giant cells. These giant cells are particularly evident on bone marrow biopsy from a patient with a marrow granuloma.The top image on the right shows the early transformation of a monocyte into a macrophage (see red arrow). Notice the increase in the amount of cytoplasm present as the cell begins to ingest debris in the bone marrow. This is demonstrated by the increasing vacuolization present in the cytoplasm. The larger the debris ingested, the larger the vacuoles will be.The lower image on the right shows a macrophage with large vacuoles (red arrow) adjacent to an RBC cluster (blue arrow). This is a common placement, since the macrophage is the iron source for these developing RBCs in the bone marrow.

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Hemophagocytosis

One of the normal roles of the marrow macrophage is to remove cellular debris. In a normal bone marrow, this includes the engulfment of extruded RBC nuclei and old, non-nucleated RBCs at the end of their lifespan. In some patients, macrophages lose their ability to distinguish self from non-self (i.e., invader/ pathogen) and good cells from old/senescent cells. This can happen because of an inborn error in the macrophages or by an infection-mediated transformation. When this change occurs, any cell in the vicinity of a defective macrophage become a target for engulfment. This term is called hemophagocytosis.The top image on the right shows two macrophages that have ingested several different cell types (see red arrows). There is the normally ingested non-nucleated RBC, but also the abnormally ingested segmented neutrophil and at least one early nucleated RBC precursor. Viable bone marrow precursors are not the usual diet of macrophages.The lower image on the right shows an even more impressive macrophage with at least a dozen or more ingested RBCs as well as three segmented neutrophils and a lymphocyte.

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Stromal Cells

Stromal cells are the cells that comprise the backbone of a bone marrow fragment. They provide the support matrix as well as some of the nutrients necessary for the growth of all cellular precursors found in the bone marrow.Stromal cells appear similar to macrophages and tend to be found in sheets. Usually, they are deep in the heart of a fragment. When the differential is counted in the areas adjacent to the fragments, they may not be noticed and should not be counted. While stromal cells may be present in clusters, it is important to recognize that these cells are normal bone marrow elements and are not tumor cells.In aplastic bone marrows, or bone marrows with decreased cellularity, they may be more apparent. However, since they are considered tissue cells, they are not included in the differential. The top image to the right demonstrates a typical stromal clump. The bottom image shows stromal cells mixed with phagocytic macrophages.

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Cardiac Biomarkers (retired 12/6/2013)
Atherosclerosis

Atherosclerosis is one of the leading causes of heart disease and its presence is an important risk factor for events leading to acute myocardial infarction (AMI). In the past, atherosclerosis was described as a cholesterol and lipid storage event. Now we know it is a chronic inflammatory disorder of the arterial vessels with lipid components. Atherosclerosis begins with damage to the cells that line the blood vessels. Some possible causes of this cell injury are bacterial infection, hyperlipidemia, hypertension, glycosylated products of diabetes, cytokines from adipose tissue, or exposure to toxins such as pollution and second-hand smoke. Monocytes and lymphocytes adhere to the injured site; macrophages enter and ingest proteins and, along with modified lipoproteins, create foam cells. An inflammatory milieu results as cytokines and other inflammatory molecules become involved; foam cells and white blood cells begin secreting cytokines and metalloproteinases. Myeloperoxidase is also released by degranulated white blood cells and macrophages. As inflammation and accumulation of these products continues, fatty dots and streaks are formed on the vessel lining and the formation of plaque begins. As the atherosclerotic process continues, involved cells proliferate forming a complex extracellular matrix and a fibrous cap. If development continues, possibly over decades, the plaque formations are distributed throughout various vessels, become calcified or collagenized and make the vessel walls rigid. The risk to patients with significant atherosclerosis is that eventually a narrowing of the artery (stenosis) can cause a reduction in oxygen delivery to tissues and plaque rupture can lead to an acute coronary event.

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Myeloperoxidase

Myeloperoxidase (MPO) is an enzyme released by leukocytes and some macrophages and elevated levels indicate an ongoing inflammatory process. MPO is also involved in the degradation of the plaque matrix in atherosclerosis. Increased serum concentrations of MPO would indicate both an inflammatory process and plaque instability. An immunoassay for MPO has been approved for use in high risk patients with ACS. More study is required to learn if the MPO levels provide additional information than troponin levels in risk stratification.

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Which biomarkers of cardiac disease risk are inflammatory markers?View Page

Case Studies in Clinical Microbiology
Review 3

Rouquette C. Berche P. The pathogenesis of infection by Listeria monocytogenes Microbiologia. 12:245-58, 1996 Listeria monocytogenes is a Gram-positive bacterium responsible for severe infections in human and a large variety of animal species. It is a facultative intracellular pathogen which invades macrophages and most tissue cells of infected hosts where it can proliferate. The molecular basis of this intracellular parasitism has been to a large extent elucidated. The virulence factors, including internalin, listeriolysin O, phospholipases and a bacterial surface protein, ActA, are encoded by chromosomal genes organized in operons. Following internalisation into host cells, the bacteria escape from the phagosomal compartment and enter the cytoplasm. They then spread from cell to cell by a process involving actin polymerisation. In infected hosts, the bacteria cross the intestinal wall at Peyer's patches to invade the mesenteric lymph nodes and the blood. The main target organ is the liver, where the bacteria multiply inside hepatocytes. Early recruitment of polymorphonuclear cells lead to hepatocyte lysis, and thereby bacterial release This causes prolonged septicaemia, particularly in immunocompromised hosts, thus exposing the placenta and brain to infection. The prognosis of listeriosis depends on the severity of meningoencephalitis, due to the elective location of foci of infection in the brain stem (rhombencephalitis). Despite bactericidal antibiotic therapy, the overall mortality is still high (25 to 30%).

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Cerebrospinal Fluid (retired 7/17/2012)
The image is a stained smear of cerebrospinal fluid. What types of cells are present in this field?View Page
Cytospin Technique

The cytospin technique uses a high speed centrifuge to concentrate the cells on a slide in a uniform monolayer 6 mm in diameter. The monolayer distribution enhances the morphological appearance of the cells present.Allow the slides to dry in air for several minutes and then stain them with Wright-Giemsa stain. Cytospin slides may be placed in an automatic stainer or stained manually.Perform a 100 or 200 cell differential and record the number of neutrophils, eosinophils, basophils, lymphocytes, monocytes, macrophages, and blasts cells.Pathologists must review any slide which has tumor cells, unidentified cells, or immature stages of cells, such as blasts.Since criteria for review may vary from one laboratory to another, be sure to check the requirements in your laboratory before reporting the differential.

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Pia Arachnoid Mesothelial Cells (continued)

A reactive pia arachnoid mesothelial cell as noted by the darker cytoplasm is present in this field. Reactive cells are a common finding in cytospin smears from spinal fluid samples and are sometimes difficult to distinguish from tumor cells. Mesothelial cells are usually interspersed among the other cells, rather than appearing in clumps. They have a single distinct nuclei that may be eccentric. The macrophages (histiocytes) are seen next to the mesothelial cell. Macrophages are distinguished from circulating monocytes by the irregular appearing cytoplasm. Bacteria, red cells or other debris can often be seen in the cytoplasm of macrophages.

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What type is the indicated cell?View Page
Malignant Cells

Malignant cells that have broken away from a tumor within the brain or meninges may also be present in spinal fluid. Tumor cells may be difficult to distinguish from macrophages or pia arachnoid mesothelial cells. While blasts in the CSF also indicate malignancy, in particular leukemia, for the purposes of this discussion, they are considered separately.

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Match the condition on the left with associated CSF cells on the right.View Page
More Neutrophils and Lymphocytes

Two segmented neutrophils and a lymphocyte (indicated by an arrow) are in the center of this picture. Notice the mature chromatin structure in the nucleus of the lymphocyte. Three mature red cells are present around the lymphocyte. Two macrophages are also present in this picture.

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Monocytes

The arrow in this slide is pointing to a monocyte. The nucleus has an open chromatin pattern which gives it a spongy appearance. The other two nucleated cells could be classified as macrophages (histiocytes) because the nucleus in each cell is oval or kidney bean-shaped and the cytoplasm is very irregular. After circulating in the blood for one to three days, monocytes enter the tissues. The tissue form of the monocyte is called a macrophage or histiocyte.

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Lymphocytes

Many lymphocytes are present in this field. Two larger, reactive lymphocytes with intact cytoplasm and slightly indented nuclei are indicated by the blue arrows. Two other large cells with irregular, trailing cytoplasm are macrophages (histiocytes). These are indicated by the red arrows. Increased lymphocytes may be seen in viral meningoencephalitis, partially treated bacterial meningitis, multiple sclerosis, Guillian-Barre's syndrome, or polyneuritis.

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Neutrophils

Many neutrophils are present in this slide from a spinal fluid sample from a patient with bacterial meningitis. Several macrophages (histiocytes) which have engulfed some of the bacteria can also be seen among the neutrophils.

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Chemistry / Urinalysis Question Bank - Review Mode (no CE)
The cells faintly seen between the arrows are consistent with:View Page

Emerging Cardiovascular Risk Markers (retired 12/6/2013)
Atherosclerosis

Atherosclerosis is a clogging, narrowing and hardening of the body's large and medium-sized blood vessels. Atherosclerosis can lead to hypertension, stroke, myocardial infarction (heart attack), renal problems, etc. Not surprisingly, cardiovascular risk markers tend to reflect a person's degree of atherosclerosis.Atherosclerosis is actually a chronic inflammatory response within the walls of arteries. Small lipoproteins like LDL are able to diffuse through the endothelial wall of blood vessels and accumulate. The inflammatory component of atherosclerosis results from the migration of leukocytes (mainly macrophages) that enter the blood vessel walls. These macrophages seek to remove the deposited LDL as well as intermediate-density lipoproteins (IDL). As macrophages phagocytose these lipoproteins, they become foam cells that get trapped in the endothelial space. This eventually leads to "hardening" or "furring" of the arteries and plaque formation. Arteriosclerosis is a general term describing any hardening (loss of elasticity) of medium or large arteries whereas atherosclerosis is a hardening of an artery specifically due to plaque. The risk to patients with significant atherosclerosis is that eventually a narrowing of the artery (stenosis) can cause a reduction in oxygen delivery to tissues and plaque rupture can lead to an acute coronary event.

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LpPLA2

LpPLA2 refers to lipoprotein-associated phospholipase A2. This enzyme is also known as platelet-activating factor acetylhydrolase(PAF). The LpPLA2 enzyme is a lipase found predominantly on the surface of LDL particles. Note that LpPLA2 is a lipase enzyme and not an apolipoprotein. LpPLA2 is made by inflammatory cells (T cells, mast cells, macrophages) and then integrated onto the surface of lipoprotein particles. The enzymatic function of LpPLA2 is to hydrolyze oxidized phospholipids in LDL.LpPLA2 plays a corrective role in removing oxidized phospholipids. Thus, it might seem that having high levels of LpPLA2 would be good. However, although LpPLA2 has a positive role in removing oxidized lipids, it also generates inflammatory products in the process. So in fact, high levels of LpPLA2 are associated with increased cardiovascular risk. Researchers have identified high amounts of LpPLA2 in human atherosclerotic lesions. The LpPLA2 that accumulates in the vessel wall can come from LDL (which can carry LpPLA2 on its surface) or it can come from immune cells that have invaded the vessel wall. Since Lp-PLA2 is produced or localized in the plaque itself, it may be a more specific marker of cardiovascular function compared to systemic, more general inflammatory markers like hs-CRP.

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Oxidized LDL Physiology

Oxidized LDL leads to the release of chemotactic factors from nearby cells; factors which signal leukocytes to migrate to the site. Recall that atherosclerosis is believed to be caused by phagocytic cells such as macrophages, which ingest LDL particles and turn into stationary foam cells. Macrophages have been shown to have increased affinity for oxidized LDL. Thus, oxidation makes LDL more susceptible to phagocytosis and therefore more atherogenic.Since oxidized LDL is more atherogenic than native LDL it makes sense that oxidized LDL may be a cardiovascular risk marker. Indeed, many studies have now correlated increased levels of oxidized LDL with risk of cardiac events.

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Fundamentals of Hemostasis
Secondary Hemostasis: The Extrinsic Pathway

The extrinsic pathway is the shortest and least complex of the three pathways. The extrinsic pathway primarily involves the interaction of tissue factor with factor VII, leading to the activation of factor VII. Tissue factor initiates coagulation when plasma contained within the vessel walls leaks outside the broken vessel and comes into contact with these cells. The nomenclature, extrinsic pathway, comes from the fact that tissue factor is external to the vasculature. This pathway is sometimes referred to as the tissue factor pathway.Once a vessel has been breached, tissue factor is exposed to circulating factor VII, and the two substances bind to form a complex. The newly formed tissue factor/factor VII complex is thought to be the primary physiological stimulus for blood coagulation. In other words, more hemostatic activities are initiated by the extrinsic pathway than the intrinsic. This complex leads to the activation of factor VII (factor VIIa) which is now ready to catalyze the conversion of factor X to factor Xa as part of the common pathway.The extrinsic pathway is circled in red in the image below.

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The Fibrinolytic System, continued

Fibrin strands woven into the clot structure are cleaved into soluble fibrin fragments and then removed by macrophages. The action of fibrinolysis also serves to restore blood flow into the area that had been sealed off, helping to promote further healing. Fibrinolysis is mediated by a proteolytic enzyme called plasmin (plasminogen is the inactive precursor form of plasmin that is found in plasma). Plasmin takes on fibrinolytic properties after activation, digesting both fibrin and fibrinogen. Inhibitors act to control the process, serving as a check and balance system for fibrinolytic activities.

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General Laboratory Question Bank - Review Mode (no CE)
Which of the following would not be considered a part of the body's cellular immune system:View Page

Hematology / Hemostasis Question Bank - Review Mode (no CE)
Which of the following cells are capable of producing antibodies and lymphokines:View Page
Phagocytosis is a function of which of the following types of cells:View Page

Hemolytic Disease of the Fetus and Newborn
Mechanism of Action

When first developed in the 1960s, RhIg was believed to work by a simple clearance mechanism, i.e., by coating D-positive fetal red cells with IgG anti-D, which resulted in clearance of the sensitized cells in the spleen by macrophages with receptors for IgG.Current research shows that a simple model of antigen clearance by antibody-sensitized D-positive RBCs is not the mechanism of anti-D suppression by RhIg. More is involved at the molecular level, possibly involving a down-regulation of antigen-specific B cells and related mechanisms.Regardless, if given soon enough following exposure to D+ red cells, and in a suitable dosage, RhIg has the ability to prevent immunization to D.

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Histology Special Stains: Connective Tissue
What is Connective Tissue?

Connective tissue offers structural and metabolic support structure for organs and tissue. It is the most abundant tissue type in the body and can be found throughout. Cells and extracellular material called connective tissue matrix make up connective tissue. Fibroblasts, mast cells, macrophages, adipose cells, blood leukocytes, and plasma cells can all be found to some degree in connective tissue. In addition to cells, the matrix has 3 different fibers present:Reticular fibers - Support soft organs and the network around nerve fibers, fats cells, lymph nodes, and muscle fibers.Collagenous fibers - Found in ligaments, tendons, cartilage, and bone.Elastic fibers - Allow tissue to expand and are typically located in skin and blood vessel walls.

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HIV Safety for Florida
Proteins Involved in Adsorption

The joining of the HIV and the host cell involves a spike on the HIV envelope and a CD4 molecule on the T-lymphocyte, macrophage, or brain cell.The molecule on the HIV spike is called glycoprotein 120 or gp120. The "120" refers to the molecular weight of the glycoprotein.While the CD4 site is important in viral binding, there is evidence that there are other molecules called co-receptors also involved.These molecules are embedded in the membranes of T-lymphocytes, macrophages, and brain cells. In the T-lymphocyte the abbreviated name of the protein molecule is CXCR4.

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HIV: Structure and Replication (retired 2/20/2013)
Proteins Involved in Adsorption

The joining of the HIV and the host cell involves a spike on the HIV envelope and a CD4 molecule on the T-lymphocyte, macrophage, or brain cell.The molecule on the HIV spike is called glycoprotein 120 or gp120. The "120" refers to the molecular weight of the glycoprotein.While the CD4 site is important in viral binding, there is evidence that there are other molecules called co-receptors also involved.These molecules are embedded in the membranes of T-lymphocytes, macrophages, and brain cells. In the T-lymphocyte the abbreviated name of the protein molecule is CXCR4.

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Introduction to Bone Marrow
These cells tend to occur in tight clusters. They may have prominent nucleoli, immature chromatin, and scant cytoplasm.View Page
Supporting Cells

Reticular cells (adventitial cells) provide structural support for the endothelial cells that line the venous sinus and the developing blood cells within the hematopoietic cord. The cytoplasm of the reticular cells is capable of extending itself in fiberlike strands deep into the hematopoietic cords. These strands provide a meshwork for the blood cells. Other types of cells which furnish support in the cord include macrophages and fat cells.

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Location of Cells within Cord

Within the hematopoietic cords each cell line has a specific location for development. Erythroid precursors are located near a venous sinusoid and cluster around a macrophage. This is referred to as an erythroblastic island. Developing red cells obtain iron needed for hemoglobin production from macrophages. Megakaryocytes are also located close to a venous sinus. They extend their cytoplasm in fingerlike projections through the sinus wall in order to release their platelets directly into the blood in the sinus. Immature granulocytes lie within the hematopoietic cords. The metamyelocyte stage is the first stage of the granulocyte series that is motile and able to move toward the sinus area. Mature neutrophils, eosinophils and basophils enter the sinusoidal blood through the basement membrane. As maturing erythrocytes also move toward the sinus wall any remaining nuclei are lost as the red cells move through small openings in the cells lining the sinus wall.

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Macrophage

The large cell in the center of this slide is a macrophage, which is normally present in low numbers in the marrow. Macrophages have a loose chromatin pattern and on some smears the nucleoli appear blue/green. The cytoplasm is irregular in shape and contains granules.

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Metabolic Syndrome
TNF-alpha

TNF-alpha (TNF-α) produces different effects as it is secreted; many of these effects are immunological and result in increased inflammation. The original name for TNF, tumor necrosis factor, came from its first discovered activity, tumor regression. TNF-α is synthesized and secreted by adipocytes, macrophages, lymphoid cells, endothelial cells and other body cells.Adipocyte-secreted TNF-α stimulates adipocytes to increase their release of NEFAs and decrease adiponectin synthesis. TNF-α also inhibits insulin activity, leading to insulin resistance. Adipocyte TNF-α secretion is increased in obesity causing an increased insulin resistance in obesity.

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Resistin

Resistin is another inflammatory cytokine that is increased in obesity. It increases insulin resistance and enhances adhesion molecules present on endothelial cells. It is synthesized and secreted by macrophages and adipocytes.

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Adipokines and Atherosclerotic Inflammatory Process Continued

Adipokines play several roles in the atherosclerotic inflammatory process: TNF-a activity produces inflammatory changes in vascular tissue and adhesion molecules. This increases the ability of monocytes to adhere to vessel walls. Resistin also promotes cell adhesion. Angiotensin II from angiotensinogen enhances the adhesion process of monocytes and platelets to vessel walls. When glucose levels are increased, leptin assists in the incorporation of lipids by enhancing uptake of cholesterol by macrophages. IL-6 enhances the inflammatory process and increases CRP. If there are ruptured atherosclerotic plaques, PAI-1 increases probability of thrombus formation and inhibits fibrin clot lysis.

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Small Dense LDL Molecules

Small dense LDL molecules may be more atherogenic and harmful to the endothelium because they can more easily move through the basement membrane of the endothelium and into the arterial wall. They may also adhere to glucoproteins more readily and more easily bind to monocytes and macrophages in plaque formation. Thus, small dense LDL molecules would enhance the incorporation of lipid into the plaque.

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Microbiology / Serology Question Bank - Review Mode (no CE)
Which one of the following statements about Coxiella burnetii is not true:View Page

Normal Peripheral Blood Cells
Where is the main site of action for monocytes after diapedesis?View Page
Match the following cells with their corresponding characteristics:View Page
Monocytic Function

Monocytes are phagocytes which remove injured and dead cells, cell fragments, microorganisms and insoluble particles from the blood and body tissues. Monocytes also secrete substances that affect the function of other cells, especially lymphocytes. They are produced in the bone marrow, and when mature are released into the peripheral blood. Although they do serve a phagocytic role in the blood, their main site of action is the body tissues. The half-life for monocytes in the peripheral blood is approximately 8 hours. Monocytes migrate into the tissues, often to sites of inflammation, where they serve their primary purpose. Here they transform into fixed or free macrophages, and continue their function as avid phagocytes. When activated, macrophages may enlarge and have enhanced metabolism.Monocytes provide defense against mycobacteria, fungi, bacteria, protozoa and viruses. They respond to chemotactic factors, phagocytize and kill the microorganisms.

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Normal Peripheral Blood Cells (retired 6/20/2012)
Match cells with their characteristics.View Page
Monocytes

Monocytes are phagocytes which remove injured and dead cells, cell fragments, microorganisms and insoluble particles from the blood and body tissues.Monocytes also secrete substances that affect the function of other cells, especially lymphocytes.They are produced in the bone marrow, and when mature are released into the peripheral blood. Although they do serve a phagocytic role in the blood, their main site of action is the body tissues.The half-life for monocytes in the peripheral blood is approximately 8 hours. Monocytes migrate into the tissues, often to sites of inflammation, where they serve their primary purpose.Here they transform into fixed or free macrophages, and continue their function as avid phagocytes.When activated, macrophages may enlarge and have enhanced metabolism.

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Parasitology Question Bank - Review Mode (no CE)
I reside inside of macrophages.View Page

Rh negative female with anti-D at delivery: A case study
Mechanism of Action

When first developed in the 1960s, RhIg was believed to work by a simple clearance mechanism, i.e., by coating D-positive fetal red cells with IgG anti-D, which resulted in clearance of the sensitized cells in the spleen by macrophages with receptors for IgG.Current research shows that a simple model of antigen clearance by antibody-sensitized D-positive RBC is not the mechanism of anti-D suppression by RhIg. More is involved at the molecular level, possibly involving a down-regulation of antigen-specific B cells and related mechanisms (see Further Reading).

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Transfusion Reactions
In Vivo Red Cell Destruction

Important events that occur in an immune-mediated hemolytic transfusion reaction (HTR) include:Antibody binding to red blood cells Antibodies may be either IgM or IgG class. IgM antibodies activate complement and lead to intravascular hemolysis where free hemoglobin is released into the plasma. IgG antibodies rarely activate complement but they are often involved in effecting phagocytosis. The concentration of the antibody is directly related to the severity of the HTR. Activation of complement The end result of complement activation is red cell lysis. Activation of mononuclear phagocytes and cytokines Sensitized red cells are removed from circulation by mononuclear phagocytes. Macrophages in the spleen and Kupffner cells in the liver are active in this process. Activation of coagulation Antibody-antigen complexes may initiate coagulation and cause disseminated intravascular coagulation (DIC). Shock and Renal Failure Hemolysis can be intravascular or extravascular. In intravascular hemolysis, free hemoglobin, RBC stroma, and intracellular enzymes are released into the blood stream. This results in hemoglobinemia and hemoglobinuria, which can lead to kidney damage. In extravascular hemolysis, there is no release of free hemoglobin. Sensitized red cells are removed from the circulation by the monocytes and macrophages in the reticuloendothelial system.

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