Macrophages

MACROPHAGES (from Greek makros- large and phago- to eat), also called megaphages, macrophagocytes, large phagocytes. The term M. was proposed by Metchnikoff, who divided all cells capable of phagocytosis into small phagocytes, microphages (see), and large phagocytes, macrophages. Under the term macrophages, Metchnikoff implied a rather large and diverse group of phagocytic cells, excluding polymorphonuclear leukocytes. The distinguishing feature of all these cells is their absorption of various colloidal particles in the form of large grains (the phenomenon of macrophagy), especially well observed in experiments with the intravital introduction of colloidal dyes (Lithion-carmin, Trypanblau, Trypanrot, etc.) and colloidal solutions of metals (colloidal silver, solution of Ferri saccharati, etc.); The main role among the group of M. is played by wandering cells of connective tissue, designated as polyblasts, histiocytes, leukocytoid cells, and originating from the so-called adventitial cells of vessel walls (see Wandering cells). In nervous tissue, M. include cells of neuroglia and cells of Schwann's sheaths of nerve fibers. In muscular tissue, during processes of decay, M. acquire significance through the so-called free sarcolites, sarcoblasts. Also, cells of the epithelium of serous cavities and other coverings, especially when multiplying and detaching from the general complex, can become M. (for example, cells of the peritoneum, alveolar epithelium, etc.). In addition to all these cells, which exhibit the ability to phagocytose when separated from the tissue complex, M. also include a number of cells closely related to the tissue complex and being immobile (so-called immobile phagocytes); these include elements of the reticulo-endothelial apparatus (see). As can be seen from the above, the concept of M. is a collective one and combines very different cells capable of phagocytosis; on this basis, it appears more convenient to speak not of M., but of the 'macrophage system' (Lubarsch), which includes the reticulo-endothelial system. Based on their relationship to vital staining and their origin from the reticulo-endothelium, many consider the blood monocytes to be cells identical to M. of connective tissue, calling them blood M. (Blutmakrophagen, Aschoff). As for the physiological function of M., it concerns phagocytosis of bacteria to a comparatively lesser degree (in contrast to microphages). M. mainly phagocytose products of tissue decay, dead cells and their fragments, and various foreign particles; this includes phagocytosis of grains of protein decay, absorption of fat droplets with transformation of M. into xanthoma cells and granular spheres, phagocytosis of products of Hb decay with deposition of grains of hemosiderin, phagocytosis of erythrocytes, lymphocytes, and leukocytes (for example, in the spleen, in lymph glands, and in Peyer's patches in typhoid fever), absorption of pigment in malaria, absorption of various grains of exogenous origin (coal, etc.). In connection with this, although M. are a normal component of any tissue, they are found in particularly large quantities in cases where there is enhanced decay of various materials in the tissue; this occurs in inflammation, in necroses of various origins, in hemorrhages, etc. In addition, M. are constantly present in large quantities in any granulation tissue, and also participate in the formation of specific granulomas (in tuberculosis, syphilis, leprosy, actinomycosis, lymphogranulomatosis). In some granulomas, for example, in typhoid fever, the participation of M. is so predominant that one can speak of a 'macrophage granuloma'. In these cases, as well as in proliferations of the reticulo-endothelium in some metabolic diseases (Gaucher's disease, Niemann-Pick), one can speak of macrophagocytoses. In the resorption of dense materials, M. can transform into giant cells. The fate of M. that have phagocytosed one or another material is different; M. of the wandering cell type are often carried by the current of tissue fluid into the lymphatic pathways, are detained and die in the sinuses of lymph glands, where the material they have phagocytosed is captured by the sinus endothelium. In other cases, M. with phagocytosed material remain in place; this in particular applies to immobile M. of the reticulo-endothelial system, the elements of which, having phagocytosed one or another material, rarely detach and are carried away by the current into the blood or lymph. The material absorbed by M. undergoes reprocessing in them and changes its physicochemical properties; this circumstance underlies the recognition of M.'s participation in the intermediate metabolism. In addition, it is very probable that M., as very essential elements of mesenchyme, play a role in manifestations of local and general immunity (see) and in the implementation of various reactive abilities of the organism.