Inhibition of mitogen-induced proliferation of spleen lymphocytes is correlated with the induction of cell-mediated immunity in Salmonella infection in mice

Infection with Salmonella enterica Serovar Typhimurium Leads to Increased Proportions of F4/80+ Red Pulp Macrophages and Decreased Proportions of B and T Lymphocytes in the Spleen

Infection of mice with Salmonella enterica serovar Typhimurium (Salmonella) causes systemic inflammatory disease and enlargement of the spleen (splenomegaly). Splenomegaly has been attributed to a general increase in the numbers of phagocytes, lymphocytes, as well as to the expansion of immature CD71+Ter119+ reticulocytes. The spleen is important for recycling senescent red blood cells (RBCs) and for the capture and eradication of blood-borne pathogens. Conservation of splenic tissue architecture, comprised of the white pulp (WP), marginal zone (MZ), and red pulp (RP) is essential for initiation of adaptive immune responses to captured pathogens. Using flow cytometry and four color immunofluorescence microscopy (IFM), we show that Salmonella-induced splenomegaly is characterized by drastic alterations of the splenic tissue architecture and cell population proportions, as well as in situ cell distributions. A major cause of splenomegaly appears to be the significant increase in immature RBC precursors and F4/80+ macrophages that are important for recycling of heme-associated iron. In contrast, the proportions of B220+, CD4+ and CD8+ lymphocytes, as well as MZ MOMA+ macrophages decrease significantly as infection progresses. Spleen tissue sections show visible tears and significantly altered tissue architecture with F4/80+ macrophages and RBCs expanding beyond the RP and taking over most of the spleen tissue. Additionally, F4/80+ macrophages actively phagocytose not only RBCs, but also lymphocytes, indicating that they may contribute to declining lymphocyte proportions during Salmonella infection. Understanding how these alterations of spleen microarchitecture impact the generation of adaptive immune responses to Salmonella has implications for understanding Salmonella pathogenesis and for the design of more effective Salmonella-based vaccines.

A cell-free Salmonella typhimurium extract induces inhibition of tyrosine phosphorylation in murine splenic T-lymphocytes

In a previous study, we observed that suppression of T-cell proliferation induced by Salmonella infection is associated with inhibition of tyrosine phosphorylation in T-cells, and that a cell-free Salmonella typhimurium LT2 extract (LT2 extract) also suppressed mitogen-induced T-cell proliferation. In the present study, therefore, we attempted to clarify whether the T-cell suppression induced by LT2 extract involved inhibition of tyrosine phosphorylation in T-cells. Western blotting using anti-phosphotyrosine antibodies showed that the mitogen-induced tyrosine phosphorylation of 120-, 106-, 94-, 76-, 68-, 57- and 36-kDa proteins in murine splenic T-cells was inhibited by treatment with LT2 extract. These results suggest that the suppression of T-cell proliferation induced by LT2 extract is also associated with inhibition of tyrosine phosphorylation in T-cells.

Response to Salmonella enteritidis infection by the immunocompromised avian host

To develop knowledge of the avian immune response and improve the ability of chickens to resist infection by Salmonella enteritidis (SE), the role of the different components of the immune response against SE infection was examined. Birds were given treatments with cyclophosphamide, cyclosporine A, or testosterone propionate to induce immunological deficiency, and experiments were performed to determine the effects of each on the immune response. Each treatment reduced hatch rate, survival rate, and rate of weight gain. As measured by flow cytometry, treatments with cyclophosphamide and testosterone propionate decreased the percentages of B cells to background levels and increased the percentages of CT8 cells significantly above controls. The intestinal shed rate of SE increased after treatment with testosterone propionate and cyclophosphamide, but dissemination to the spleen of infected birds was not different from controls for any treatment. The SE infection was also immunosuppressive as measured by the proliferative response to mitogenic stimulation. Maximum lymphocyte proliferation occurred 1 wk after infection in response to .5 micrograms concanavalin A per 10(6) cells. By the 2nd wk, proliferation dropped 10-fold to almost no response. Results showed that immunocompetence relied on interdependent functions of multiple components of the immune response, i.e., aspects of both humoral and cell-mediated immunity.

A cell-free extract of Salmonella typhimurium inhibits mitogen-induced proliferation of murine splenic T lymphocytes

In this study, a cell-free extract of Salmonella inhibited T cell mitogen-induced proliferation of spleen cells from non-immunized mice. The proliferation of murine spleen cells stimulated with a T cell mitogen, such as phytohaemagglutinin (PHA) or concanavalin A (ConA) was suppressed significantly when the cells were treated with a sonicate of S. typhimurium, but not of E. coli. The agent(s) responsible for the suppressive effect existed mainly in the soluble fraction of S. typhimurium, whereas the membrane fraction possessed minimal activity. The T cell proliferation suppression paralleled the level of interleukin-2 (IL-2) secretion. Addition of phorbol 12-myristate-13 acetate (PMA) to the cultures restored IL-2 secretion to normal levels, although proliferation remained suppressed and was not reversed by treatment with recombinant IL-2. These results suggest that the suppression of T cell proliferation induced by a soluble Salmonella fraction is associated with inhibition of IL-2 secretion and the response of T cells to IL-2 and the former effect is dependent upon the inhibition of the stimulatory activity of protein kinase C on IL-2 secretion. This type of suppression may explain a mechanism of immunosuppression induced by murine typhoid fever.