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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]

Reactivation of herpes simplex virus 2 (HSV-2) results in infection of epithelial cells at the neuro-epithelial junction and shedding of virus at the epithelial surface. Virus shedding can occur in either the presence or absence of clinical disease and is usually of short duration, although the shedding frequency varies among individuals. The basis for host control of virus shedding is not well understood, although adaptive immune mechanisms are thought to play a central role. To determine the importance of CD4+ T cells in control of HSV-2 shedding, this subset of immune cells was depleted from HSV-2-infected guinea pigs by injection of an anti- CD4 monoclonal antibody (MAb). Guinea pigs were treated with the depleting MAb after establishment of a latent infection, and vaginal swabs were taken daily to monitor shedding by quantitative PCR. The cumulative number of HSV-2 shedding days and the mean number of days virus was shed were significantly increased in CD4- depleted compared to control-treated animals. However, there was no difference in the incidence of recurrent disease between the two treatment groups. Serum antibody levels and the number of HSV-specific antibody-secreting cells in secondary lymphoid tissues were unaffected by depletion of CD4+ T cells; however, the frequency of functional HSV-specific, CD8+ gamma interferon-secreting cells was significantly decreased. Together, these results demonstrate an important role for CD4+ T lymphocytes in control of virus shedding that may be mediated in part by maintenance of HSV-specific CD8+ T cell populations. These results have important implications for development of therapeutic vaccines designed to control HSV-2 shedding. [ABSTRACT FROM AUTHOR]

The elderly are known to have enhanced susceptibility to infections and an impaired capacity to respond to vaccination. West Nile virus (WNV), a mosquito-borne flavivirus, has induced severe neurological symptoms, mostly in the elderly population. No vaccines are available for human use. Recent work showed that an attenuated WNV, a nonstructural (NS) 4B-P38G mutant, induced no lethality but strong immune responses in young (6- to 10-week-old) mice. While studying protective efficacy, we found unexpectedly that old (21- to 22-month) mice were susceptible to WNV NS4B-P38G mutant infection but were protected from subsequent lethal wild-type WNV challenge. Compared to responses in young mice, the NS4B-P38G mutant triggered higher inflammatory cytokine and interleukin-10 (IL-10) production, a delayed γδ T cell expansion, and lower antibody and WNVspecific T cell responses in old mice. Toll-like receptor 7 (TLR7) is expressed on multiple types of cells. Impaired TLR7 signaling in old mice led to dendritic cell (DC) antigen-presenting function compromise and a reduced γδ T cell and regulatory T cell (Treg) expansion during NS4B-P38G mutant infection. R848, a TLR7 agonist, decreased host vulnerability in NS4B-P38G-infected old mice by enhancing γδ T cell and Treg expansion and the antigen-presenting capacity of DCs, thereby promoting T cell responses. In summary, our results suggest that dysregulation of TLR7 partially contributes to impaired innate and adaptive T cell responses and an enhanced vulnerability in old mice during WNV NS4B-P38G mutant infection. R848 increases the safety and efficacy during immunization of old mice with the WNV NS4B-P38G mutant. [ABSTRACT FROM AUTHOR]

Recognition of conserved pathogen-associated molecular patterns (PAMPs) by host pattern recognition receptors (PRRs) results in the activation of innate signaling pathways that drive the innate immune response and ultimately shape the adaptive immune response. RepliVAX WN, a single-cycle flavivirus (SCFV) vaccine candidate derived from West Nile virus (WNV), is intrinsically adjuvanted with multiple PAMPs and induces a vigorous anti-WNV humoral response. However, the innate mechanisms that link pattern recognition and development of vigorous antigen-specific B cell responses are not completely understood. Moreover, the roles of individual PRR signaling pathways in shaping the B cell response to this live attenuated SCFV vaccine have not been established. We examined and compared the role of TLR3- and MyD88-dependent signaling in the development of anti-WNV-specific antibody-secreting cell responses and memory B cell responses induced by RepliVAX WN. We found that MyD88 deficiency significantly diminished B cell responses by impairing B cell activation, development of germinal centers (GC), and the generation of long-lived plasma cells (LLPCs) and memory B cells (MBCs). In contrast, TLR3 deficiency had more effect on maintenance of GCs and development of LLPCs, whereas differentiation of MBCs was unaffected. Our data suggest that both TLR3- and MyD88-dependent signaling are involved in the intrinsic adjuvanting of RepliVAX WN and differentially contribute to the development of vigorous WNV-specific antibody and B cell memory responses following immunization with this novel SCFV vaccine. [ABSTRACT FROM AUTHOR]

Unlabelled: The elderly are known to have enhanced susceptibility to infections and an impaired capacity to respond to vaccination. West Nile virus (WNV), a mosquito-borne flavivirus, has induced severe neurological symptoms, mostly in the elderly population. No vaccines are available for human use. Recent work showed that an attenuated WNV, a nonstructural (NS) 4B-P38G mutant, induced no lethality but strong immune responses in young (6- to 10-week-old) mice. While studying protective efficacy, we found unexpectedly that old (21- to 22-month) mice were susceptible to WNV NS4B-P38G mutant infection but were protected from subsequent lethal wild-type WNV challenge. Compared to responses in young mice, the NS4B-P38G mutant triggered higher inflammatory cytokine and interleukin-10 (IL-10) production, a delayed γδ T cell expansion, and lower antibody and WNV-specific T cell responses in old mice. Toll-like receptor 7 (TLR7) is expressed on multiple types of cells. Impaired TLR7 signaling in old mice led to dendritic cell (DC) antigen-presenting function compromise and a reduced γδ T cell and regulatory T cell (Treg) expansion during NS4B-P38G mutant infection. R848, a TLR7 agonist, decreased host vulnerability in NS4B-P38G-infected old mice by enhancing γδ T cell and Treg expansion and the antigen-presenting capacity of DCs, thereby promoting T cell responses. In summary, our results suggest that dysregulation of TLR7 partially contributes to impaired innate and adaptive T cell responses and an enhanced vulnerability in old mice during WNV NS4B-P38G mutant infection. R848 increases the safety and efficacy during immunization of old mice with the WNV NS4B-P38G mutant., Importance: The elderly are known to have enhanced susceptibility to infections and an impaired capacity to respond to vaccination. West Nile virus (WNV), an emerging mosquito-borne flavivirus, has induced severe neurological symptoms more frequently in the elderly population. No vaccines are available for human use. Here, we used an aged mouse model to investigate the protective efficacy of an attenuated WNV, the nonstructural 4B-P38G mutant, which was previously shown to induce no lethality but strong immune responses in young adult mice. Studies that contribute to a mechanistic understanding of immune defects in the elderly will allow the development of strategies to improve responses to infectious diseases and to increase vaccine efficacy and safety in aging individuals., (Copyright © 2016, American Society for Microbiology. All Rights Reserved.)

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.

The T-cell-mediated resolution of herpes simplex virus type 2 (HSV-2) genital infections is not fully understood. In these studies, the mechanisms by which CD8+ T cells clear virus from the genital epithelium were examined. Ovalbumin (OVA)-specific CD8+ T cells from OT-I transgenic mice cleared a thymidine kinase-deficient, ovalbumin-expressing HSV-2 virus (HSV-2 tk- OVA) from the genital epithelium of recipient mice, and clearance was abrogated by in vivo neutralization of gamma interferon (IFN-gamma). Further, CD8+ OT-I T cells deficient in IFN-gamma were unable to clear HSV-2 tk- OVA from the vaginal epithelium. The requirement for cytolytic mechanisms in HSV-2 tk- OVA clearance was tested in radiation chimeras by adoptive transfer of wild-type or perforin-deficient OT-I T cells to irradiated Fas-defective or wild-type recipients. Although a dramatic decrease in viral load was observed early after challenge with HSV-2 tk- OVA, full resolution of the infection was not achieved in recipients lacking both perforin- and Fas-mediated cytolytic pathways. These results suggest that IFN-gamma was responsible for an early rapid decrease in HSV-2 virus titer. However, either perforin- or Fas-mediated cytolytic mechanisms were required to achieve complete clearance of HSV-2 from the genital epithelium.