This MAb stains the cytoplasm of macrophages and histiocytes in hematopoietic organs, Kupffer s cells of the liver and Langerhan s cells of the skin. Macrophages comprise of many forms of mononuclear phagocytes found in tissues. Mononuclear phagocytes arise from hematopoietic stem cells in the bone marrow. After passing through the monoblast and pro-monocyte states of the monocyte stage, they enter the blood, where they circulate for about 40 hours. They then enter tissues and increase in size, phagocytic activity, and lysosomal enzyme content becoming macrophages. Among the functions of macrophages are nonspecific phagocytosis and pinocytosis, specific phagocytosis of opsonized microorganisms mediated by Fc receptors and complement receptors, killing of ingested microorganisms, digestion and presentation of antigens to T and B lymphocytes, and secretion of a large number of diverse products, including many enzymes including lysozyme and collagenases, several complement components and coagulation factors, some prostaglandins and leukotrienes, and many regulatory molecules (Interferon, Interleukin 1). LN-5 selectively stains human sebaceous glands in formalin-fixed, paraffin-embedded skin samples. Undifferentiated sebocyte progenitors are negative, and only sebocytes from the onset of their differentiation reveal positive cytoplasmic staining. Since there are very few selective and easy-to-use markers of sebaceous glands, LN-5 antibody can offer a simple and relatively specific way to detect human sebocytes from the onset of their.