We show, for the first time, that the transcription factor T-bet, which is implicated in IFN-γ production, is required for the induction of vaccine-induced antiviral immune protection. T-bet was found to be important in both the innate and acquired immune protection against genital HSV-2 infection. T-bet−/− and T-bet+/+ mice were infected vaginally with HSV-2 and examined daily for disease and mortality. T-bet−/− mice had significantly higher virus titers than T-bet+/+ mice following a primary HSV-2 infection, and succumbed significantly earlier to the infection. This result was associated with an impaired NK cell cytotoxic capacity and NK cell-mediated IFN-γ production in the T-bet−/− mice. To assess the induction of acquired antiviral immune protection, mice were vaccinated with an attenuated virus before infection. Vaccinated T-bet−/− mice could not control viral replication following an HSV-2 challenge and had significantly higher virus titers and mortality rates than vaccinated T-bet+/+ mice that remained healthy. The impaired acquired immune protection in T-bet−/− mice was associated with a significantly decreased HSV-2-specific delayed-type hypersensitivity response and a significantly reduced HSV-2-specific IFN-γ production from CD4+ T cells. However, T-bet deficiency did not impair either the IFN-γ production or the cytotoxic capacity of HSV-2-specific CD8+ T cells. We conclude that T-bet plays a crucial role in both the innate defense and the generation of vaccine-induced immunity against genital HSV-2 infection in mice.

Genital herpes, caused by herpes simplex virus type 2 (HSV-2), is the most common genital ulcer disease worldwide. HSV-2 infection causes a variety of symptoms, ranging from subclinical/silent infection to severe and recurrent episodes of genital blisters and ulcers, and the virus can also in rare cases cause meningitis. In primary infection, the virus sequentially enters and replicates in epithelial cells followed by local sensory neurons. In the latter, a life-long infection is established via the induction of viral latency or dormancy. Latent virus is however continuously reactivated, also in those with a silent infection, which results in a low-grade viral replication and shedding into the vaginal lumen. This reactivation can in many individuals be amplified following e.g. stress, hormonal variations or immune suppression, which results in recurrent genital disease.

Human natural killer (NK) cell differentiation, characterized by a loss of NKG2A in parallel with the acquisition of NKG2C, KIRs, and CD57 is stimulated by a number of virus infections, including infection with human cytomegalovirus (CMV), hantavirus, chikungunya virus, and HIV-1. Here, we addressed if HSV-2 infection in a similar way drives NK cell differentiation towards an NKG2A-NKG2C+KIR+CD57+ phenotype. In contrast to infection with CMV, hantavirus, chikungunya virus, and HIV-1, recurrent HSV-2 infection did not yield an accumulation of highly differentiated NK cells in human peripheral blood. This outcome indicates that human HSV-2 infection has no significant imprinting effect on the human NK cell repertoire.

Lack of Toll-like receptor 3 (TLR3) functional activity predisposes children to human herpesvirus 1 (HSV-1) encephalitis. In this study, we have investigated whether there is any link between TLR3 and adult HSV-2 infection by studying genetic variations in TLR3. The frequency of four singlenucleotide polymorphisms (SNPs) in the TLR3 gene in 239 patients with genital HSV-2 infection and 162 healthy controls, as well as the impact of these variants on TLR3 gene-expression levels, were compared. Two SNPs in the TLR3 gene (rs13126816 and rs3775291) were associated with a reduced incidence of HSV-2 infection. The minor allelic variants at both rs13126816 and rs3775291 were more common among healthy HSV-2-seronegative subjects than among HSV-2-infected individuals. This was even more apparent in HSV-1-seronegative individuals. There was, however, no association between any of the four TLR3 SNPs and HSV-2 disease severity, as they were expressed at similar proportions in asymptomatic and symptomatic HSV-2-infected patients alike. Furthermore, when assessing TLR3 mRNA expression in a limited number of HSV-2-infected individuals, we found that individuals carrying the homozygous genotypes for the minor alleles had significantly higher levels of TLR3 mRNA expression in peripheral blood mononuclear cells in response to HSV-2 stimulation than individuals that were homozygous for the major allele variants. Taken together, these results suggest that genetic variations in TLR3 may affect the susceptibility to HSV-2 infection in humans.

Intracellular DNA- and RNA-sensing receptors, such as the IFN-inducible protein Absent in Melanoma 2 (AIM2), serve as host sensors against a wide range of infections. Immune sensing and inflammasome activation by AIM2 has been implicated in innate antiviral recognition in many experimental systems using cell-lines and animal models. However, little is known about the expression and function of AIM2 in freshly isolated human cells. In this study we investigated the expression of AIM2 in different cell types derived from human cord and adult peripheral blood, in steady state and following in vitro-activation. Adult but not cord blood B-cells expressed high levels of AIM2 mRNA at steady state. In adults, AIM2 was primarily expressed in mature memory CD27+ B-cells. Both adult and cord blood derived B-cells could induce their transcription of AIM2 mRNA in response to type II IFN but not type I IFN or the AIM2 ligand poly dA:dT. Upon B-cell receptor stimulation, B-cells from adult blood expressed reduced levels of AIM2 mRNA. In addition, we show that adult B-cells were able to release IL-1β upon stimulation with synthetic DNA. We conclude that functional AIM2 is preferentially expressed in adult human CD27+ B-cells, but is absent in cord blood mononuclear cells.