A cell-free Salmonella typhimurium extract modulates interleukin-2 (IL-2) receptor expression but not IL-2-stimulated responses of murine splenic lymphocytes

Purified protein from Salmonella typhimurium inhibits the interleukin-2 response of murine splenic T-lymphocytes activated with anti-CD3 antibody

Previously, we demonstrated that the immunosuppression induced by a purified preparation of Salmonella typhimurium-derived inhibitor of T-cell proliferation (STI) can be observed in terms of suppression of the proliferation of murine spleen cells stimulated with a mitogenic lectin. In the present study, I observed that STI inhibited the interleukin-2 (IL-2) response of purified murine splenic T lymphocytes stimulated with anti-CD3 antibody. The flow cytometric analysis of IL-2 receptor (IL-2R) expression on T cells showed that STI specifically suppressed the expression of IL-2R beta and IL-2R gamma. Furthermore, when the IL-2-dependent T-cell line CTLL-2 was incubated with STI, the growth of CTLL-2 cells was significantly inhibited. These results suggest that the target cells for STI are T cells themselves, and that the suppression of T-cell proliferation induced by STI might involve a defect in the IL-2 receptor (IL-2R) function of T cells.

A purified protein from Salmonella typhimurium inhibits proliferation of murine splenic anti-CD3 antibody-activated T-lymphocytes

In previous study, we observed that the purified substance Salmonella typhimurium-derived inhibitor of T-cell proliferation (STI) had an immunosuppressive effect, demonstrated as the suppression of mitogenic lectin-induced proliferation of murine spleen cells. In the present study, we confirmed the immunosuppressive effect of STI, which suppressed the proliferation of murine splenic T-lymphocytes activated with the anti-CD3 antibody (Ab) and phorbol 12-myristate-13 acetate (PMA) and this phenomenon was accompanied by augmentation of interferon-gamma (IFN-gamma) secretion and inhibition of interleukin-2 (IL-2) secretion. Furthermore, the augmentation of IFN-gamma secretion caused IL-2 receptor alpha chain (IL-2R alpha) over expression on T-cells. However, the addition of an anti-IFN-gamma Ab and recombinant IL-2 (rIL-2) did not reverse the suppressed T-cell proliferation, although the level of IL-2R alpha expression on T-cells recovered to around normal. Furthermore, Western blotting using an anti-phosphotyrosine Ab showed that IL-2R-mediated tyrosine phosphorylation of protein substrates in T-cells was inhibited by incubation with STI for 48 h and this inhibition was not reversed by adding the anti-IFN-gamma Ab and rIL-2. These results suggest that STI-induced suppression of T-cell proliferation involves a defect in IL-2R function and/or IL-2 signaling pathway in T-cells.

Immunosuppression induced by Salmonella infection is correlated with augmentation of interleukin-2 receptor alpha chain expression in murine splenic lymphocytes

In a previous study, we observed that the suppression of T-cell proliferation induced by Salmonella cell-free extract was associated with augmentation of IL-2 receptor (IL-2R) alpha chain expression. In this study, we also observed this kind of augmentation of IL-2R alpha in Salmonella-infected mice. Phytohaemagglutinin (PHA)-stimulated proliferation of murine spleen cells was significantly suppressed when the mice were infected with Salmonella typhimurium. However, expression of the alpha chain but not the beta chain of IL-2R in lymphocytes was augmented by the infection. Analysis of the IL-2R-positive cell-population showed that the augmentation of IL-2R alpha was not specific to certain cell subpopulations. Furthermore, the inhibition of PHA-stimulated murine spleen cell proliferation and the augmentation of IL-2R alpha expression induced by the infection in lymphocytes was completely reversed by treatment with anti-interferon-gamma monoclonal antibody (anti-IFN-gamma Ab). These results suggest that the suppression of T-cell proliferation induced by Salmonella infection was associated with augmentation of IL-2R alpha expression in an IFN-gamma production-dependent manner in the same way as the suppression of T-cell proliferation induced by Salmonella cell-free extract.

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 NG-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.