Phenotypic Characterization of Macrophages in Non-neoplastic Lymph Nodes

Lymphatic tissue in general, and lymph nodes in particular, are the physiological sites of the specific immune response to soluble and particulate foreign matter, where close interaction between macrophages, accessory cells, and immunocompetent lymphocytes is required. At least two types of antigen arrive at lymph nodes, where they are trapped, processed, and presented to the specific immunocompetent lymphocytes. The soluble molecules are conveyed by the lymph stream and can be directly bound by the accessory cells. In the case of complex or particulate antigens, preparatory digestion is necessary in order to resolve at least one part of the components and soluble molecules following the usual path of phagocytosis accomplished by the typical macrophages. A considerable fraction of the antigens is destroyed by lytic processes. Soluble fragments are bound by the accessory cells. This means that macrophages may be relevant to the development of a specific immune response (Unanue and Askonas 1968; Benacerraf 1988) and constitute a regular cellular component of normal and reactive lymph nodes. Nevertheless, in the absence of particulate antigens macrophages do not seem to be indispensable for the establishment of the specific immune response.