Effector CD4+ T lymphocyte resolution of acute HSV infection at genital and neuronal sites, and the manipulation of CD4+ T cell responses via TLR ligand-induced proinflammatory cytokine milieus
Alison Joy Johnson
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In primary infection, CD8+ T cells are important for clearance of infectious HSV from sensory ganglia. We present evidence of CD4+ T-cell-mediated clearance of infectious HSV-1 from neural tissues. In immunocompetent mice, HSV-specific CD4+ T cells were present in sensory ganglia and spinal cords coincident with HSV-1 clearance and remained detectable at least 8 months post-infection. Neural CD4+ T cells isolated at the peak of neural infection secreted IFN-ã, TNF-á, IL-2, or IL-4 after stimulation with HSV antigen. HSV-1 titers in neural tissues were greatly reduced over time in CD8+ T-cell-deficient and CD8+ T-cell-depleted mice, suggesting CD4+ T cells could mediate clearance from neural tissue. Clearance of infectious virus from neural tissues was not significantly different in CD8+ T-cell-depleted, perforin-deficient or FasL-defective mice compared to wild-type mice. Virus titers in neural tissues of chimeric mice expressing both perforin and Fas or neither perforin nor Fas were significantly lower than in controls. Thus, perforin and Fas were not required for clearance of infectious virus from neural tissues. These results further define the HSV-specific CD4+ T cell response. To determine the influence of differential TLR activation of DCs in development of appropriate CD4+ T cell phenotype, magnitude, and memory, we established bone marrow-derived DCs that were 92.6% CD11c+CD11b+, and 94.0% CD11c+B220-Ly-6c- in vitro. Ligands for TLR3, -4, or -9 were applied to DCs, and cytokine and chemokine secretion was examined. Particular interest was paid to IL-12 and IFN-g (important for TH1 differentiation thought critical against HSV), and antiviral type I interferons. Proliferation and activation of the CD4+ T cells co-cultured with TLR-ligand-stimulated DCs were assessed. CD4+ T cell magnitude, effector function, and establishment of memory generated upon injection of TLR-ligand-stimulated peptide-pulsed DCs were examined. Stimulation of DCs through TLR3 enhanced CD4+ T cell production of large amounts of TH1-type cytokines and cytolytic molecules. Stimulation of DCs through TLR4 did drive this phenotype, and also enhanced memory CD4+ T cell population formation within the genital tract. A vaccine able to elicit a vigorous, long-lasting CD4+ T cell response may prove important in limiting disease and transmission of virus.