IFN-λ Decreases Murid Herpesvirus-4 Infection of the Olfactory Epithelium but Fails to Prevent Virus Reactivation in the Vaginal Mucosa.

Murid herpesvirus-4 (MuHV-4), a natural gammaherpesvirus of rodents, can infect the mouse through the nasal mucosa, where it targets sustentacular cells and olfactory neurons in the olfactory epithelium before it propagates to myeloid cells and then to B cells in lymphoid tissues. After establishment of latency in B cells, viral reactivation occurs in the genital tract in 80% of female mice, which can lead to spontaneous sexual transmission to co-housed males. Interferon-lambda (IFN-λ) is a key player of the innate immune response at mucosal surfaces and is believed to limit the transmission of numerous viruses by acting on epithelial cells. We used in vivo plasmid-mediated IFN-λ expression to assess whether IFN-λ could prophylactically limit MuHV-4 infection in the olfactory and vaginal mucosae. In vitro, IFN-λ decreased MuHV-4 infection in cells that overexpressed IFN-λ receptor 1 (IFNLR1). In vivo, prophylactic IFN-λ expression decreased infection of the olfactory epithelium but did not prevent virus propagation to downstream organs, such as the spleen where the virus establishes latency. In the olfactory epithelium, sustentacular cells readily responded to IFN-λ. In contrast, olfactory neurons did not respond to IFN-λ, thus, likely allowing viral entry. In the female genital tract, columnar epithelial cells strongly responded to IFN-λ, as did most vaginal epithelial cells, although with some variation from mouse to mouse. IFN-λ expression, however, failed to prevent virus reactivation in the vaginal mucosa. In conclusion, IFN-λ decreased MuHV-4 replication in the upper respiratory epithelium, likely by protecting the sustentacular epithelial cells, but it did not protect olfactory neurons and failed to block virus reactivation in the genital mucosa.

Multivalent binding of herpesvirus to living cells is tightly regulated during infection.

Viral infection, initiated by the landing of a virion on a cellular surface, is largely defined by the preliminary interactions established between viral particles and their receptors at the cell surface. While multiple parallel interactions would allow strong virus attachment, a low number of bonds could be preferred to allow lateral diffusion toward specific receptors and to promote efficient release of progeny virions from the cell surface. However, so far, the molecular mechanisms underlying the regulation of the multivalency in virus attachment to receptors are poorly understood. We introduce a new method to force-probe multivalent attachment directly on living cells, and we show, for the first time, direct evidence of a new mechanism by which a herpesvirus surface glycoprotein acts as a key negative regulator in the first step of herpesvirus binding. Using atomic force microscopy, we probe at the single-virion level the number and the strength of the bonds established with heparan sulfate both on model surfaces and on living cells. Our biophysical results, correlated with other techniques, show that the major envelope glycoprotein functions as a regulator of binding valency during both attachment and release steps, determining the binding, diffusion, and release potential of virions at the cellular surface.

Antiviral effect of the nucleoside analogue cidofovir in the context of sexual transmission of a gammaherpesvirus in mice.

Objectives: To investigate the efficacy of cidofovir to block gammaherpesvirus replication in the context of sexual transmission. Methods: A luciferase-expressing strain of murid herpesvirus 4 (MuHV-4) was used to monitor genital virus excretion from infected female BALB/c mice and sexual transmission to naive males. The efficiency of cidofovir to block genital excretion from infected females or replication and host colonization of naive males after sexual contact was tested by treating infected females (either once daily or at a single timepoint), naive males before exposure (either once daily or at a single timepoint) or males 24 h post-exposure. Results: We showed that daily treatment of infected females can reduce MuHV-4 genital shedding by 75%. Similarly, daily preventive treatment of naive males was sufficient to block viral replication and latency establishment in males. In contrast, a single administration of cidofovir to infected females at day 14 post-infection or to naive males 2 to 6 days before contact with MuHV-4-excreting females was not sufficient to significantly reduce viral shedding from females or infection of males, respectively. Interestingly, a single administration of cidofovir to males 24 h after contact with MuHV-4-infected females excreting the virus in the genital tract significantly reduced virus replication in males and seroconversion. Conclusions: Altogether, our results show that cidofovir can significantly reduce gammaherpesvirus replication, excretion and colonization of the naive partner in the context of sexual transmission. Such treatments could therefore be recommended in some specific conditions where gammaherpesvirus infections could be deleterious.

The Major Envelope Glycoprotein of Murid Herpesvirus 4 Promotes Sexual Transmission.

Gammaherpesviruses are important human and animal pathogens. Infection control has proven difficult because the key process of transmission is ill understood. Murid herpesvirus 4 (MuHV-4), a gammaherpesvirus of mice, is transmitted sexually. We show that this depends on the major virion envelope glycoprotein gp150. gp150 is redundant for host entry, and in vitro, it regulates rather than promotes cell binding. We show that gp150-deficient MuHV-4 reaches and replicates normally in the female genital tract after nasal infection but is poorly released from vaginal epithelial cells and fails to pass from the female to the male genital tract during sexual contact. Thus, we show that the regulation of virion binding is a key component of spontaneous gammaherpesvirus transmission.IMPORTANCE Gammaherpesviruses are responsible for many important diseases in both animals and humans. Some important aspects of their life cycle are still poorly understood. Key among these is viral transmission. Here we show that the major envelope glycoprotein of murid herpesvirus 4 functions not in entry or dissemination but in virion release to allow sexual transmission to new hosts.