Like the lymphocytes, monocytes cannot be identified with bright field microscopy. With the PAP stain, the cell is larger than a neutrophil and has a characteristic bean shaped nucleus. The macrophage is, after the fibroblast, the most abundant cell in connective tissue. The activated macrophage is difficult to describe because it has a very variable aspect. This cell often presents itself with so many cytoplasmic inclusions that the cell's structures are completely masked.
Inclusions are of several types, but the droplet is the most frequent.
A classic easy to identify macrophage, is the giant cell that contains one or two smaller phagocyted cells in its cytoplasm. The macrophages are frequent in acute inflammations. The macrophage loaded with fat droplets is frequently found in many body fluids. These are usually related to a chronic inflammation process. In urine, when these droplets form a maltese cross when viewed between crossed polarized filters, the macrophages are then called oval fat bodies.