ABSTRACT
This chapter considers the heterogeneous nature of macrophages when they participate in granulomatous inflammation. This variability in response is particularly well displayed in the various granulomas that occur in skin. The chapter reviews some aspects of monocyte maturation and macrophage development. Monocytes arise from pluripotential stem cells in the bone marrow, like all blood cells. During the past decade great advances have been made in understanding the factors and circumstances which determine hematopoiesis. Monocytes migrate into all tissues, including the bone as osteoclasts and brain as microglia. The macrophages develop extensive phagolysosomes and become stuffed with the foreign material. A simplistic view of granulomatous inflammation is to paint it either black or white, foreign body or immune granuloma response. Certainly, in infectious granulomas with humoral and cellular immune factors significantly in the play, one frequently sees sheets or groups of epithelioid cells.
