INHIBITION OF T-CELL PROLIFERATION INDUCED BY A CELL-FREE SALMONELLA-TYPHIMURIUM EXTRACT DOES NOT INVOLVE A NITRIC OXIDE-MEDIATED MECHANISM

In a previous study, we observed that a cell-free Salmonella typhimurium extract induced suppression of mitogen-induced T-cell proliferation and that this suppression involved nonresponsiveness of T-cells to interleukin-2 (IL-2) and augmentation of IL-2 receptor (IL-2R) expression. In this study, we found that inhibition of phytohemagglutinin (PHA)-stimulated murine spleen cell proliferation induced by a cell-free S. typhimurium extract was reversed by treatment with an anti-interferon-gamma monoclonal antibody (anti-IFN-gamma Ab), but not by interleukin-4 or N-G-monomethyl-L-arginine, which is known to inhibit nitric oxide (NO)-secretion from spleen cells in culture. However, IL-2R expression was augmented by treatment with the extract, although this was independent of an NO-mediated mechanism. Only anti-IFN-gamma Ab treatment reduced the augmented IL-2R expression to a normal level. These results suggest that the suppression of T-cell proliferation induced by the Salmonella cell-free extract is associated with augmentation of IL-2R expression in an NO production-independent manner.