Contrasting effect of transforming growth factor type beta 1 (TGF-beta 1) on proliferation and interleukin-2 receptor expression in activated and rapidly cycling immature (CD3-CD4-CD8-) thymocytes.

Transforming growth factor beta (TGF-beta) is a cytokine with immunoregulatory properties that acts negatively on T lymphocyte proliferation. However, with the EL 4-6.1 variant of the murine thymoma EL 4 activated with phorbol ester and/or interleukin-1 (IL-1), we recently found that it up-regulates interleukin-2-receptor (IL-2R) expression. Since EL 4-6.1 cells share phenotypic and functional characteristics with the immature thymic subset lacking CD4 and CD8 accessory molecules (DN), we investigated the effect of TGF-beta 1 on the IL-2R 55kD alpha chain expression and proliferation of activated DN cells and especially in DN cells that do not express CD3. We observed that TGF-beta 1 was able to increase both the percentage of CD3-DN cells expressing IL-2R alpha chains and the expression of IL-2R alpha chain in these cells. This stimulatory effect of TGF-beta 1 was distal from early transduction events. In addition, TGF-beta 1 was found to modulate CD3-DN cell proliferation. During differentiation in the thymus, CD3-DN cells transiently express the IL-2R alpha chain of the IL-2R and these IL-2R+ CD3-DN cells are preprogrammed to down-regulate the IL-2R alpha chain and up-regulate the CD4 and CD8 accessory molecule. We thus also tested the effect of TGF-beta 1 on IL-2R alpha chain expression in these in vitro differentiating CD3-DN cells. We found that TGF-beta 1 neither significantly affected IL-2R expression nor changed CD4 or CD8 expression. Hence, in CD3-DN cells, the effect of TGF-beta 1 on IL-2R expression seems to be restricted to proliferating cells.