HSV-2 replication sites, monocyte and lymphocytic cell infection and virion phagocytosis by neutrophils, in vesicular lesions on penile skin. Electronoptical studies of a biopsy

A sustained type I IFN-neutrophil-IL-18 axis drives pathology during mucosal viral infection

Neutrophil responses against pathogens must be balanced between protection and immunopathology. Factors that determine these outcomes are not well-understood. In a mouse model of genital herpes simplex virus-2 (HSV-2) infection, which results in severe genital inflammation, antibody-mediated neutrophil depletion reduced disease. Comparative single-cell RNA-sequencing analysis of vaginal cells against a model of genital HSV-1 infection, which results in mild inflammation, demonstrated sustained expression of interferon-stimulated genes (ISGs) only after HSV-2 infection primarily within the neutrophil population. Both therapeutic blockade of IFNα/β receptor 1 (IFNAR1) and genetic deletion of IFNAR1 in neutrophils concomitantly decreased HSV-2 genital disease severity and vaginal IL-18 levels. Therapeutic neutralization of IL-18 also diminished genital inflammation, indicating an important role for this cytokine in promoting neutrophil-dependent immunopathology. Our study reveals that sustained type I interferon (IFN) signaling is a driver of pathogenic neutrophil responses and identifies IL-18 as a novel component of disease during genital HSV-2 infection.

IL-36γ Is a Key Regulator of Neutrophil Infiltration in the Vaginal Microenvironment and Limits Neuroinvasion in Genital HSV-2 Infection

HSV-2 is a neurotropic virus that causes a persistent, lifelong infection that increases risk for other sexually transmitted infections. The vaginal epithelium is the first line of defense against HSV-2 and coordinates the immune response through the secretion of immune mediators, including the proinflammatory cytokine IL-36γ. Previously, we showed that IL-36γ treatment promoted transient polymorphonuclear cell infiltration to the vaginal cavity and protected against lethal HSV-2 challenge. In this report, we reveal that IL-36γ specifically induces transient neutrophil infiltration but does not impact monocyte and macrophage recruitment. Using IL-36γ^-/- mice in a lethal HSV-2 challenge model, we show that neutrophil counts are significantly reduced at 1 and 2 d postinfection and that KC-mediated mature neutrophil recruitment is impaired in IL-36γ^-/- mice. Additionally, IL-36γ^-/- mice develop genital disease more rapidly, have significantly reduced survival time, and exhibit an increased incidence of hind limb paralysis that is linked to productive HSV-2 infection in the brain stem. IL-36γ^-/- mice also exhibit a significant delay in clearance of the virus from the vaginal epithelium and a more rapid spread of HSV-2 to the spinal cord, bladder, and colon. We further show that the decreased survival time and increased virus spread observed in IL-36γ^-/- mice are not neutrophil-dependent, suggesting that IL-36γ may function to limit HSV-2 spread in the nervous system. Ultimately, we demonstrate that IL-36γ is a key regulator of neutrophil recruitment in the vaginal microenvironment and may function to limit HSV-2 neuroinvasion.

Alternative entry receptors for herpes simplex virus and their roles in infection and disease

Herpes simplex virus (HSV) infections are highly prevalent in human populations. Clinical manifestations are often not apparent or are limited to mucocutaneous lesions, at least in persons other than neonates or the immunocompromised. The virus establishes latent infections in peripheral neurons, cannot be eliminated by the immune system once acquired and can periodically reactivate to cause recurrent skin lesions even in persons with apparently normal immune systems. Additionally, the virus can spread to the CNS, causing life-threatening encephalitis. Multiple alternative entry receptors for HSV have been identified. This review will focus on recent studies designed to investigate which of these receptors are exploited by the virus for infection of its various target cell types, whether each receptor contributes equally to disease, and whether HSV strains differ in receptor usage, perhaps influencing their pathogenicity.

Macrophages and cytokines in the early defence against herpes simplex virus

Herpes simplex virus (HSV) type 1 and 2 are old viruses, with a history of evolution shared with humans. Thus, it is generally well-adapted viruses, infecting many of us without doing much harm, and with the capacity to hide in our neurons for life. In rare situations, however, the primary infection becomes generalized or involves the brain. Normally, the primary HSV infection is asymptomatic, and a crucial element in the early restriction of virus replication and thus avoidance of symptoms from the infection is the concerted action of different arms of the innate immune response. An early and light struggle inhibiting some HSV replication will spare the host from the real war against huge amounts of virus later in infection. As far as such a war will jeopardize the life of the host, it will be in both interests, including the virus, to settle the conflict amicably. Some important weapons of the unspecific defence and the early strikes and beginning battle during the first days of a HSV infection are discussed in this review. Generally, macrophages are orchestrating a multitude of anti-herpetic actions during the first hours of the attack. In a first wave of responses, cytokines, primarily type I interferons (IFN) and tumour necrosis factor are produced and exert a direct antiviral effect and activate the macrophages themselves. In the next wave, interleukin (IL)-12 together with the above and other cytokines induce production of IFN-gamma in mainly NK cells. Many positive feed-back mechanisms and synergistic interactions intensify these systems and give rise to heavy antiviral weapons such as reactive oxygen species and nitric oxide. This results in the generation of an alliance against the viral enemy. However, these heavy weapons have to be controlled to avoid too much harm to the host. By IL-4 and others, these reactions are hampered, but they are still allowed in foci of HSV replication, thus focusing the activity to only relevant sites. So, no hero does it alone. Rather, an alliance of cytokines, macrophages and other cells seems to play a central role. Implications of this for future treatment modalities are shortly considered.

A proinflammatory peptide from herpes simplex virus type 2 glycoprotein G affects neutrophil, monocyte, and NK cell functions

We have identified a synthetic peptide derived from the secreted portion of HSV type 2 glycoprotein G, denoted gG-2p20, which has proinflammatory properties in vitro. The gG-2p20 peptide, corresponding to aa 190-205 of glycoprotein G-2, was a chemoattractant for both monocytes and neutrophils in a dose-dependent fashion, and also induced the release of reactive oxygen from these cells. The receptor mediating the responses was identified as the formyl peptide receptor. The gG-2p20-induced activation of phagocytes had a profound impact on NK cell functions. The reactive oxygen species produced by gG-2p20-activated phagocytes both inhibited NK cell cytotoxicity and accelerated the apoptotic cell death in NK cell-enriched lymphocyte populations. Hence, we have for the first time been able to identify a potential function of the secreted portion of HSV-2 glycoprotein G. We propose that the proinflammatory gG-2p20 peptide identified could contribute to a reduced function and viability of NK cells during HSV-2 infection due to its ability to recruit and activate phagocytic cells.

Role of polymorphonuclear leukocytes in resolution of HSV-2 infection of the mouse vagina

A naturally occurring population of polymorphonuclear leukocytes (PMNs) was detected in the vaginal lumen of uninoculated mice. A large population of these cells also infiltrated the vaginal mucosa following intravaginal HSV-2 inoculation. We examined the role of PMNs in preventing infection of the vaginal mucosa, virus clearance, and limiting virus spread to the lumbosacral ganglia. Depletion of PMNs prior to HSV-2 inoculation did not increase the incidence of infection suggesting that the small population of resident PMNs was ineffective in preventing infection by a viral pathogen. Depletion of PMNs impacted virus clearance from the vagina over a range of HSV-2 doses resulting in significantly higher virus titers on days 4 through 6 after inoculation. Virus clearance was delayed in PMN-depleted immune mu MT mice suggesting that PMN involvement in HSV-2 clearance did not require specific antibody. PMN-depletion of non-immune mice increased virus spread to the sensory ganglia only in mice inoculated with high virus doses. Immunization of mice with an attenuated strain of HSV-2 protected the sensory ganglia against acute infection with a challenge strain. Although PMN depletion of immune mice significantly increased virus titers in the vagina, the incidence of acute virus replication in the sensory ganglia was not different than in control-treated immune mice suggesting that PMNs were not required for protection of the sensory ganglia in immune animals. Taken together, these results suggest that PMNs were involved in resolving genital HSV-2 infections, but played only a limited role in preventing HSV-2 spread to the sensory ganglia.

Neutrophils aid in protection of the vaginal mucosae of immune mice against challenge with herpes simplex virus type 2

Large numbers of polymorphonuclear leukocytes (PMNs) infiltrated the murine vaginal mucosa within 24 h after intravaginal inoculation with an attenuated strain of herpes simplex virus type 2 (HSV-2). The role of these cells in resolution of a primary genital infection and in protection of HSV-immune animals against challenge with a fully virulent HSV-2 strain was investigated. Depletion of greater than 95% of the PMNs at the vaginal mucosal surface prior to intravaginal inoculation with an attenuated HSV-2 strain resulted in significantly higher virus titers on days 3 to 7 but only slightly delayed resolution of the primary genital infection. These results suggest that neutrophils helped control the infection but that other immune mechanisms ultimately cleared the virus. Interestingly, depletion of PMNs from HSV-immune mice prior to challenge with a fully virulent HSV-2 strain resulted in a rise in virus titers to levels comparable to those of nonimmune mice and a more pronounced diminution of virus clearance from the vaginal mucosa despite the presence of HSV-specific B and T cells. Levels of gamma interferon (IFN-gamma) and HSV-specific antibody were comparable in neutrophil-depleted and control-treated immune mice following HSV-2 challenge, suggesting that RB6-8C5 treatment did not impair T- and B-cell function. Therefore, these results suggest that neutrophils play a role in limiting and clearing HSV-2 vaginal infections and that they are, in association with HSV-specific B and T cells, an important component in immune protection of the vaginal mucosa.

Herpes simplex virus-1 entry into cells mediated by a novel member of the TNF/NGF receptor family

We identified and cloned a cellular mediator of herpes simplex virus (HSV) entry. Hamster and swine cells resistant to viral entry became susceptible upon expression of a human cDNA encoding this protein, designated HVEM (for herpesvirus entry mediator). HVEM was shown to mediate the entry of several wild-type HSV strains of both serotypes. Anti-HVEM antibodies and a soluble hybrid protein containing the HVEM ectodomain inhibited HVEM-dependent infection but not virus binding to cells. Mutations in the HSV envelope glycoprotein gD significantly reduced HVEM-mediated entry. The contribution of HVEM to HSV entry into human cells was demonstrable in activated T cells. HVEM, the first identified mediator of HSV entry, is a new member of the TNF/NGF receptor family.

Differentiation of the U937 macrophage cell line removes an early block of HSV-1 infection

In the human macrophage-like cell line U937, which is resistant to infection with herpes simplex virus type 1 (HSV-1), it was previously shown that resistance can be overcome by inducing differentiation of the cells by treatment with phorbol 12-myristate 13-acetate (PMA). The present data show that differentiation, and not PMA treatment alone, enabled HSV-1 replication, because vitamin D3 and mezerein were also able to cause U937 cells to differentiate to a state permissive for HSV-1 infection. Additionally, a portion of the undifferentiated cells underwent a productive infection when treated with PMA 2 days after infection, suggesting persistence of HSV-1 in these cells. The nonpermissiveness of the undifferentiated cells was further defined. Resistance did not involve differences in virus uptake, because the amounts of viral DNA in the infected cells and nuclei of differentiated and undifferentiated U937 cells were not significantly different early after infection. However, only very low levels of RNA for HSV-1 immediate-early, early, and late genes could be detected in the undifferentiated U937 cells by Northern blot analysis compared with the differentiated U937 cells. These data suggest that the primary block in HSV-1 replication in undifferentiated U937 cells occurred after transport of the viral DNA to the cell nucleus but prior to steady-state accumulation of viral RNA for immediate-early genes.