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The p220 antigen is found on the high m.w. form of the T200 common leukocyte antigen family. Although T200 monoclonal antibodies (MAb) react with all hematopoietic cells, p220 MAb react only with B cells, NK cells, about 50% of CD4+ T helper cells, and about 90% of CD8+ T suppressor cells. The p220 antigen appears to play an important role in T cell activation, because anti-p220 MAb at doses as low as 5 ng/ml accelerate the proliferation kinetics of PHA-stimulated T cells and augment anti-CD3-driven proliferation when IL 2 is in excess. Fab fragments have no effect on PHA-stimulated cells but partially block proliferation in response to anti-CD3. Our data suggest that p220 is functionally related to expression of the IL 2 receptor. Anti-p220 MAb cause an increase in the number of T cells that express the IL 2 receptor early after activation. In addition, T cells begin to turn off expression of p220 after activation, and two-color immunofluorescence shows that by day 3 after activation the cells expressing the most IL 2 receptor have the least p220. The loss of p220 on T cells may reflect a post-thymic differentiation process related to cell activation. Our data are consistent with a model where the p220- T cells in peripheral blood are a more activated population of T cells that have lost p220 and its ability to regulate their IL 2 receptor expression.
Ledbetter et al. (Sun,) studied this question.