Mononuclear phagocyte. Development, structure, function and involvement in immune response

An understanding of the ability of the mononuclear phagocyte (MNP) to develop an extensive repertoire of functions in many tissue areas requires continued evaluation of this cell. The membrane receptors for the Fc portion of IgG and complement, C3 as well as its nonspecific phagocytic capacity permit this cell to interact with many circulating particulate and nonparticulate materials. Since the immune response is dependent, in part, on initial antigen processing by MNP, any evaluation of disease syndromes with autoantibody or dysgammaglobulinemic responses, that is, hypogammaglobulinemia, requires evaluation of the role of the MNP in addition to the lymphocyte subpopulations. The identification of the role of the MNP in various disease processes, presumably as a defense mechanism, such as phagocytosis and antigen processing, is now well recognized. More recently, the presence of 'activated' macrophages in human disease has been delineated, that is, sarcoidosis, Crohn's disease, and tuberculosis. It remains to be determined whether these cells are detrimental or beneficial in these diseases. Investigation of MNP receptor activity and recognition of immunoprotein-coated erythrocytes in patients with autoimmune hemolytic anemia has suggested that patients' MNPs interact more with their homologous erythrocytes than MNPs from normal controls. In this instance 'activated' MNPs may contribute excessively to erythrocyte destruction. Similar analysis of MNPs in other illnesses may assist in further understanding the pathophysiology and therapy of certain diseases. The precise characterization of MNP receptor structure and function, metabolic and phagocytic capacity, mechanisms of homing to various tissue sites, its subsequent maturation and involvement in the immune response need a more complete understanding as regards the MNP. (167 references)