Human T lymphocytes of inducer and suppressor type occupy different microenvironments.

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Distinct subsets of human peripheral T-cell populations have recently been characterized using mouse monoclonal antibodies and conventional hetero-antisera in functional tests in vitro1–6. ‘Inducer’ or ‘helper’ T cells have been shown to react with a monoclonal antibody termed OKT4. These OKT4+ cells respond to soluble antigens3, help B-lymphocyte differentiation into plasma cells in pokeweed mitogen stimulated cultures4 and assist the development of cytotoxic T cells in mixed lymphocyte cultures (MLC)3. In contrast, the ‘suppressor-cytotoxic’ T-cell subset is recognized by the monoclonal antibodies OKT55 and OKT86. The same subset can also be labelled with a conventional horse antiserum which (after extensive absorption) recognizes TH2 antigen5,7. These OKT8+, TH+2 cells fail to respond optimally to soluble antigen3 but contain the concanavalin-A induced suppressor cell population5,7 and the cells which develop cytotoxic activity in mixed lymphocyte reaction (MLR)-induced cell-mediated lympholysis3. The physiological role, tissue distribution and recirculation patterns of ‘inducer’ and ‘suppressor’ T cells are unknown, although changes in the proportion and activity of blood-borne T-ceU subsets have been observed in various immunoregulatory disorders8,9. We have therefore now analysed the distribution of these T-cell subsets in the lymphohaematopoietic organs and the gut. OKT4+, OKT8− cells of inducer type predominate in the thymic medulla, blood and T-cell traffic areas such as tonsillar paracortex and intestinal lamina propria. OKT4−, OKT8+; cells of suppressor-cytotoxic type, on the other hand, constitute the larger part of T-cell population in normal human bone marrow and gut epithelium. Furthermore, a close micro-anatomical relation can be seen between the OKT4+, OKT8−T cells and non-lymphoid cells expressing large amounts of la-like (p 28,33) antigens, for example, interdigitating (ID) cells and Ia+ macrophages, suggesting that Ia-like antigens may play a part in the local regulation of inducer T cell activity. Thus the T-cell subsets which have been shown to have different functions in vitro seem also to have different patterns of tissue distribution, implying different immunological functions in vivo.