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Abstract: Interferon gamma (IFNγ) is important for immune resistance to herpes simplex virus (HSV) infection. To examine the influence of IFNγ on the development of HSV-specific immune responses and test for IFNγ-independent adaptive immune mechanisms of protection, IFNγ-deficient mice (IFNγ−/−) were immunized with thymidine kinase-deficient HSV-2 (HSV-2 333tk−). HSV-specific cellular and humoral responses were elicited in immunized IFNγ−/− mice resulting in increased resistance relative to non-immune C57BL/6J (B6) mice following challenge with fully virulent HSV-2. CD8+ T cells from IFNγ−/− mice displayed cytotoxic activity and secreted TNFα. HSV-specific CD4+ T cells from immunized IFNγ−/− mice secreted IL-4, TNFα, and IL-17, but unlike T cells from HSV-immune B6 mice, could not clear virus from genital tissue following adoptive transfer. HSV-immune IFNγ−/− mice produced predominantly IgG1 HSV-specific antibodies while immune B6 mice produced predominantly IgG2c antibodies. Transfer of equivalent amounts of HSV-specific antibodies from either strain to naïve mice imparted equivalent early resistance against infection of the genital epithelia. However, protection against neurological symptoms mediated by immune B6 antibodies was superior late in infection. Taken together, these results demonstrate that the limited resistance of HSV-immune IFNγ−/− mice to HSV-2 infection resulted from the action of HSV-specific Ab rather than IFNγ-independent effector functions of T cells. Further, protection against neurological manifestations of HSV-2 infection was superior in mice receiving Ab from immune B6 mice suggesting that Ab-mediated protective mechanisms involving IFNγ-induced IgG subclasses were more effective once virus had spread to neural tissues. [Copyright &y& Elsevier]

In primary infection, CD8+ T cells are important for clearance of infectious herpes simplex virus (HSV) from sensory ganglia. In this study, evidence of CD4+ T-cell-mediated clearance of infectious HSV type 1 (HSV-1) from neural tissues was also detected. In immunocompetent mice, HSV-specific CD4+ T cells were present in sensory ganglia and spinal cords coincident with HSV-1 clearance from these sites and remained detectable at least 8 months postinfection. Neural CD4+ T cells isolated at the peak of neural infection secreted gamma interferon, tumor necrosis factor alpha, interleukin-2 (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 that CD4+ T cells could mediate clearance of HSV-1 from neural tissue. To examine possible mechanisms by which CD4+ T cells resolved neural infection, CD8+ T cells were depleted from perforin-deficient or FasL-defective mice. Clearance of infectious virus from neural tissues was not significantly different in perforin-deficient or FasL-defective mice compared to wild-type mice. Further, in spinal cords and brains after vaginal HSV-1 challenge of chimeric mice expressing both perforin and Fas or neither perforin nor Fas, virus titers were significantly lower than in control mice. Thus, perforin and Fas were not required for clearance of infectious virus from neural tissues. These results suggest that HSV-specific CD4+ T cells are one component of a long-term immune cell presence in neural tissues following genital HSV-1 infection and play a role in clearance of infectious HSV-1 at neural sites, possibly via a nonlytic mechanism. [ABSTRACT FROM AUTHOR]

The effect of human immunodeficiency virus (HIV) infection and high-level HIV replication on the function of monocytes was investigated. HIV-positive patients had elevated levels of spontaneous production of some or all of the monocyte proinflammatory cytokines measured (interleukin-1β [IL-1β], IL-6, and tumor necrosis factor alpha [TNF-α]) compared to uninfected controls. In patients on therapy with high frequencies of monocytes producing proinflammatory cytokines, this frequency was diminished in the context of viremia during an interruption of therapy. Diminished production of proinflammatory cytokines during viremia was restored by culture with autologous CD4+ T cells or monocytes from an on-therapy time point or lipopolysaccharide (LPS). Microarray analysis demonstrated that diminished monocyte production of proinflammatory cytokines was correlated with elevated type I interferon-stimulated gene transcripts. The addition of exogenous alpha 2A interferon diminished the spontaneous production of IL-1β, IL-6, and TNF-α but did not affect responses to LPS, recapitulating the changes observed for HIV-viremic patients. These results suggest that monocyte function is diminished during high-level HIV viremia and that this effect is mediated by chronic stimulation by type I interferons. This effect on monocytes during viremia may play a role in diminished innate or adaptive immune system functions in HIV-infected patients. In addition, the restoration of these functions may also play a role in some immune reconstitution syndromes observed during initiation of therapy. [ABSTRACT FROM AUTHOR]

Early clearance of a thymidine kinase-deficient strain of herpes simplex virus type 2 from the female genital tract required T-cell-produced gamma interferon (IFN-γ). Transfer of activated CD8+ T cells to irradiated C57BL/6 mice resulted in rapid virus clearance, but clearance was greatly delayed in recipients deficient in the IFN-γ receptor (IFN-γ R). Early virus clearance was demonstrated in radiation chimeras in which IFN-γ R expression was limited to parenchymal cells, but resolution was significantly delayed in chimeras deficient in IFN-γ R expression and chimeras expressing IFN-γ R only on hematopoietic cells. Together, these results suggest that early IFN-γ-mediated protection was manifested mainly by stimulation of genital parenchymal cells. [ABSTRACT FROM AUTHOR]

Abstract: CD8+ T cells are important for resolution of HSV-2 lesions from the female genital epithelium. It is uncertain whether optimal clearance of viruses such as HSV-2 that cause a limited, non-systemic infection solely requires expression of effector functions by infiltrating CD8+ T lymphocytes, or if the clearance rate is reflective of the expression level of critical effector functions. To address this, CD8+ T cells from normal OT-I mice or OT-I mice deficient in IFNγ (IFNγ−/−) or the IFNγ receptor (IFNγR−/−) were activated in vitro in the presence of IFNγ or IL-4 to generate a series of effector populations (Tc1 and Tc2-like respectively) that secreted different levels of IFNγ and expressed different levels of HSV-specific cytolytic function. Compared with Tc1 cells, Tc2-like cells produced the type 2 cytokines IL-4 and IL-5, exhibited decreased IFNγ secretion, diminished proliferation in vitro, and decreased antigen-specific cytolysis in vivo. Clearance of an ovalbumin-expressing HSV-2 strain (HSV-2 tk− OVA) by adoptively transferred Tc2-like cells was delayed relative to Tc1 cell recipients. Because donor Tc2-like cells proliferated in vivo and infiltrated the infected genital epithelium similar to Tc1 cells, the diminished virus clearance by Tc2-like effector cells correlated with reduced expression of critical effector functions. Together, these results suggest that high level expression of protective T cell functions by effector T cells is necessary for optimal clearance of HSV-2 from the genital epithelium. These results have important implications for vaccines designed to elicit CD8+ T cells against viruses such as HSV-2 that infect the genital tract. [Copyright &y& Elsevier]

Human immunodeficiency virus type 1 (HIV-1) infection has been associated with perturbations of plasmacytoid dendritic cells (PDC), including diminished frequencies in the peripheral blood and reduced production of type I interferons (IFNs) in response to in vitro stimulation. However, recent data suggest a paradoxical increase in production of type 1 interferons in vivo in HIV-infected patients compared to uninfected controls. Using a flow cytometric assay to detect IFN-α-producing cells within unseparated peripheral blood mononuclear cells, we observed that short-term interruptions of antiretroviral therapy are sufficient to result in significantly reduced IFN-α production by PDC in vitro in response to CpG A ligands or inactivated HIV particles. The primary cause of diminished IFN- production was reduced responsiveness of PDC to de novo stimulation, not diminished per cell IFN-α production or migration of cells to lymphoid organs. Real-time PCR analysis of purified PDC from patients prior to and during treatment interruptions revealed that active HIV-1 replication is associated with upregulation of type I IFN-stimulated gene expression. Treatment of hepatitis C virus-infected patients with IFN-α2b and ribavirin for hepatitis C virus infection resulted in a profound suppression of de novo IFN-α production in response to CpG A or inactivated HIV particles, similar to the response observed in HIV-infected patients. Together, these results suggest that diminished production of type I interferons in vitro by PDC from HIV-1-infected patients may not represent diminished interferon production in vivo. Rather, diminished function in vitro is likely a consequence of prior activation via type I interferons or HIV virions in vivo. [ABSTRACT FROM AUTHOR]