Plasma cells and plasmacytoid lymphocytes can be found in any viral-reactive effusion. This image is a pleural fluid from a patient with viral pneumonia.
Notice the plasma cells (see arrows) which contain a large amount of cytoplasm compared to the smaller lymphocytes. The color is more basophilic and there is a noticeable clearing adjacent to the nucleus. Notice the dense and clumped chromatin pattern. Some of these cells have a hint of cytoplasmic vacuolation which can be prominent storage vacuoles.