The second group of cells are the leukocytes or white blood cells (WBC's). The leukocytes can be divided into two groups: granulocytes and mononuclear cells. Leukocytes are involved in various ways with the body's defense mechanisms. The cell shown by the red arrow is a mononuclear cell, in this case a monocyte. The cell shown by the blue arrow is a granulocyte, in this case a neutrophil. These cells will be presented in much more detail later.