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Generation and partial characterization of a regulatory T cell phenotype following repeated in vivo treatement with the staphylococcal superantigen toxic shock syndrome toxin-1 Cameron, Scott

Abstract

Toxic shock syndrome induced by superantigens such as TSST-1 is characterized by the production of lethal proinflammatory cytokines associated with a T helper 1 (T[sub H]I1) response including IL-2, IFN-y, TNF-α and IL-12. However, repeated exposure to superantigens appears to upregulate production of the anti-inflammatory cytokine IL-10 by CD4⁺ T[sub R]1 cells. T[sub R]1 cells have been implicated in suppression of autoimmune diseases, and their mechanism of differentiation and polarization is currently unclear. Therefore, the objective of this study was to determine if the staphylococcal superantigen TSST-1 was capable of inducing IL-10 producing T[sub R]1 cells, and to further characterize these cells based on their cytokine profile, surface marker expression and functional activity both in vitro and in vivo. Utilizing a protocol of repeated subcutaneous injections of 4μg TSST-1 in BALB/c mice, we observed a significant decrease in serum levels of IL-2 and IFN-y, while IL-10 levels were enhanced. The decrease in serum IL-2 and IFN-y levels observed in vivo following repeated TSST-1 stimulation were transferable to naive mice by adoptive transfer of 1x10⁷ CD4⁺ T cells intravenously from mice treated repeatedly with TSST-1. The observed in vivo suppression of IL-2 was dependent on IL-10 production, as blockade of the IL-10 receptor abrogated IL-2 suppression induced by adoptive CD4⁺ T cell transfer. Repeated in vivo treatment with TSST-1 was accompanied by an increase in both IL-10⁺IL-4⁺ and IL-10⁺IFN-y⁺ CD4⁺ splenocytes as well as IL-10⁺ single-positive cells as revealed by intracellular cytokine staining. Concurrently, there was a decrease in IL-2+ CD4+ splenocytes. TSST-1 treatment also induced a significant increase in intracellular CTLA-4 expression, and surface expression of CD25. CD4⁺ T cells from mice treated repeatedly with TSST-1 had significantly higher proportion of IL-10⁺CTLA-4⁺ double positive and CD4⁺CD25⁺CTLA-4⁺ triple positive cells compared to control mice. CD4⁺CD25⁺ splenocytes from mice treated repeatedly with TSST-1 were potent in their ability to induce elevated levels of IL-10 and IFN-y, and suppressed IL-2 production when mixed with naive splenocytes in a ratio as low as 1:20 and restimulated in vitro with TSST-1. Our investigations of regulatory T cells induced by repeated TSST-1 administration have added new insights with potential therapeutic applications in the fields of autoimmune disease, cancer resistance, and infectious disease pathogenesis.

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