[Immunohistochemistry of the human mononuclear phagocytic system]

Monocytes and macrophages comprising the so called mononuclear phagocyte system are characterized by an astonishing diversity with respect to morphology as well as function. Lysosomal acid hydrolases, specially the unspecific acid esterase (EC 3.1.1.6) have been widely used to characterize and recognize this cell system. It was the aim of this study to further clarify the heterogeneity of the mononuclear phagocyte system using acid hydrolases and related typical intracytoplasmic structures, the lysosomes, as biochemical as well as immunological markers. The following results were obtained: 1. Human blood monocytes and their macrophage derivatives are characterized by an extraordinary isoelectric focusing pattern of the unspecific acid esterase, which could not be observed in all other normal human blood cells. 2. The monocyte specific isoelectric focusing pattern of unspecific acid esterase is also observable under neoplastic conditions: The typical pattern can be recognized in monocytic leukemias as well as in the permanent monocytic cell line U-937. 3. The isoenzymes of monocytic acid esterase as well as lysosomes of stimulated U-937 cell line are cell specific antigens: Polyclonal antisera raised against these structures recognize physiological functional forms, pathologic reaction forms, as well as neoplastic variants of the mononuclear phagocyte system applying immunohistochemistry. 4. The broad reactivity spectrum of polyclonal antibodies raised against lysosomes can be subdivided in different reactivity patterns by monoclonal antibodies. With the latter reagents it could be shown that monocytes not only differentiate in phagocytes but also in two populations of immune accessory cells thus mirroring the bipolarity of immune response as shown by T and B lymphocytes. The established biochemical as well as immunohistochemical markers open the possibility to characterize the different neoplasias originating from the mononuclear phagocyte system. Furthermore, it is hoped that the morphological as well as immunohistochemical heterogeneity is also paralleled by special functions expressed by the recognized subcohorts.