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This study highlights the importance of functional PMN, T-cell, and NK-cell immunity for the outcome of IA. Larger multicenter studies should address the potential use of NK-cell counts for the management of antifungal therapy.

Staphylococcus aureus infection elicits through its mature lipoproteins an innate immune response by TLR2–MyD88 signaling, which improves bacterial clearing and disease outcome. The role of dendritic cells (DCs) and T cells in this immune activation and the function of T and B cells in defense against S. aureus infection remain unclear. Therefore, we first evaluated DC and T cell activation after infection with S. aureus wild type (WT) and its isogenic mutant, which is deficient in lipoprotein maturation, in vitro. Lipoproteins in viable S. aureus contributed via TLR2–MyD88 to activation of DCs, which promoted the release of IFN-γ and IL-17 in CD4+ T cells. This strong effect was independent of superantigens and MHC class II. We next evaluated the function of T cells and their cytokines IFN-γ and IL-17 in infection in vivo. Six days after systemic murine infection IFN-γ, IL-17, and IL-10 production in total spleen cells were MyD88-dependent and their levels increased until day 21. The comparison of CD3−/−, Rag2−/−, and C57BL/6 mice after infection revealed that IFN-γ and IL-17 originated from T cells and IL-10 originated from innate immune cells. Furthermore, vaccination of mice to activate T and B cells did not improve eradication of S. aureus from organs. In conclusion, S. aureus enhances DC activation via TLR2–MyD88 and thereby promotes TH1 and TH17 cell differentiation. However, neither T cells and their MyD88-regulated products, IFN-γ and IL-17, nor B cells affected bacterial clearing from organs and disease outcome.

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