Lymphokine-Induced Modulation of Macrophage Functions

The role of mononuclear phagocytes not only in resistance to many infections but also in immune response as effector and regulatory cells is becoming increasingly recognized (van Furth 1975; Nelson 1976; Krahenbuhl & Remington 1971; Rosenthal et al. 1976; Rosenstreich & Oppenheim 1976; Gery & Waksman 1972). While it has been known for some time that macrophages from different compartments are functionally different, only in recent years has the functional heterogeneity of macrophages within the same compartment been described (Walker 1976). Exposure to various stimuli in vivo or in vitro results in macrophages with different sets of functions. In particular, it could be shown that lymphokines ‘activate’, that is, induce or modulate many functions in macrophages (David 1975). The mechanisms by which various stimuli produce macrophages with different functions is still obscure. Since it is well established that mononuclear phagocytes originate in the bone marrow (van Furth et al. 1972), two mechanisms are conceivable: in the course of maturation, macrophages either pass through all functional stages or differentiate into various subpopulations charactized by certain functions or their ability to respond to a particular stimulus.