A purified protein fromSalmonella typhimuriuminhibits high-affinity interleukin-2 receptor expression on CTLL-2 cells

Previously, we have demonstrated that the immunosuppression induced by the purified substance Salmonella typhimurium-derived inhibitor of T-cell proliferation (STI) involves T-cell non-responsiveness to interleukin-2 (IL-2). In the present study, it was found that STI inhibited the growth of CTLL-2 cells, which are an IL-2-dependent cytotoxic T-cell line. Analysis of IL-2 receptor (IL-2R) function showed that STI inhibited high-affinity receptor expression and internalization by CTLL-2 cells. Furthermore, FACS analysis demonstrated that STI inhibited both beta chain and gamma chain expression of IL-2R on the cells. These results suggest that the suppression of T-cell proliferation induced by STI results from a defect in IL-2R function.