[The monocyte-macrophage-system (author's transl)]

The importance of the monocyte-macrophage-system in specific and non-specific immune reactions is described. Macrophages are involved during both the afferent phase, e.g. antigen trapping, antigen processing, and the efferent phase, e.g. allograft rejection, tumour cell destruction, of the specific immune system. The monocyte-macrophage system can be activated by non-specific and - more important in vivo - by specific mechanisms via soluble factors produced by sensitized T-lymphocytes. Finally, some clinically important disorders of macrophage function are described.