Pathogenic role of IL-6, gp130, and IL-17 on the innate immune response induced by SAgs of the egc operon.

NOLI TRUANT, SOFIA; IANNANTUONO LÓPEZ, LAURA; REDOLFI, DANIELA; SARRATEA, BELÉN; ANTONOGLOU, BELÉN; EMILIO L. MALCHIODI; JANCIC, CAROLINA; FERNÁNDEZ MARISA MARIEL

Ettal

Workshop; 15th Spring School on Immunology; 2019

German Society for Immunology

Bacterial superantigens (SAgs) are enterotoxins that bind to MHC-II and TCR molecules, activating as much as 20% of T cells and promoting a cytokine storm which enhances endotoxic shock and produces immunosuppression, hindering the immune response against bacterial infection. IL-17 is a crucial cytokine for the eradication of extracellular SAgs-producing bacteria. Here, we investigated the effect on the innate immunity and its IL-17 arm of four natural SAgs (SEG, SEI, SEO and SEM) encoded by the egc operon.SAgs were tested over human PBMCs, showing the ability to produce significantly higher concentrations of IL-6 respect to control, measured by ELISA. IL-6 acts directly to promote the development of Th17 by activating the gp130-STAT3 pathway. Despite all SAgs induced IL-6 production, only SEI, SEG and SEM significantly increased IL-17A. This profile was accompanied, too, by the production of IL-12, IFN-γ, TNF-α, and anti-inflammatory IL-10.Then, we evaluated the ability of these SAgs to bind to gp130 by Surface Plasmon Resonance. SEO and SEG showed a higher affinity, compared to SEI and SEM; besides, each SAg showed distinct kinetic behavior. Nevertheless, mutant SAg in TCR binding site did not display interaction. As possible participants of this pro-inflammatory profile, we evaluated the SAgs? effect on human γδ T cells by FC and ELISA. In contrast to the effect on αβ T cells, γδ T cells were differentially activated only by some SAgs, yet at high concentrations they became toxic. Besides, we found a significant production of IFN-γ and TNF-α and no detectable IL-17A. Notably, mutant SAg, lacking the ability to bind αβ TCR, activated γδ T cells as much as wild type SAg. At the same time, we evaluated the SAgs?s effect on PMN cells, and we detected the formation of structures compatible with NETS by fluorescent microscopy.We concluded that direct interaction of SAgs with gp130, a key participant in inflammation, immune regulation and the activation of the Th17 arm, may explain part of the wide effects of these toxins, and would have straight influence over γδ T lymphocytes and PMNs. Furthermore, SAgs promote early necrosis and apoptosis in γδ T cell, with the previous releasement of type 1 cytokines, and cell death of PMN, all which would conspire against the eradication of these extracellular bacteria.