A CELL-FREE SALMONELLA-TYPHIMURIUM EXTRACT MODULATES INTERLEUKIN-2 (IL-2) RECEPTOR EXPRESSION BUT NOT IL-2-STIMULATED RESPONSES OF MURINE SPLENIC LYMPHOCYTES

In a previous study, we observed that a cell-free Salmonella typhimuri um extract induced suppression of mitogen-induced T-cell proliferation and this suppression involved non-responsiveness of T-cells to interl eukin-2 (IL-2). In this study, we found that a cell-free S. typhimuriu m extract modulated IL-2 receptor (IL-2R) expression on phytohemagglut inin (PHA)-stimulated murine spleen cells and this was a mechanism of T-cell non-responsiveness to IL-2, but did not affect IL-2 binding to IL-2R and the consequent responses. Western blotting using anti-phosph otyrosine antibodies showed that IL-2R-mediated tyrosine phosphorylati on of protein substrates in PHA-activated murine splenic T-cells, whic h express a high-affinity IL-2R (alpha- and beta-chains), was not affe cted by treatment with the S. typhimurium cell-free extract. Furthermo re, PHA-activated spleen T-cells responded to recombinant IL-2 and thi s was not inhibited by the extract. Surprisingly, IL-2R expression was augmented by treatment with the extract, although this was independen t of IL-2 production. These results suggest that the suppression of T- cell proliferation induced by the Salmonella cell-free extract was ass ociated with augmentation of IL-2R expression, rather than down-regula tion of the IL-2 response. This may be a mechanism responsible for the Salmonella extract-evoked suppression of mitogen-induced T-cell proli feration.