# Host Immune Response Mechanisms Against Herpes Simplex Virus Type 2 Infection

## TL;DR

This paper reviews how the human immune system fights HSV-2, a virus causing genital herpes, and highlights gaps in understanding that hinder vaccine and treatment development.

## Contribution

The paper synthesizes recent findings on innate and adaptive immune responses to HSV-2, emphasizing their roles in controlling infection and latency.

## Key findings

- Innate immunity, including TLRs and interferons, limits early HSV-2 replication but is countered by viral immune evasion proteins.
- Tissue-resident memory T cells are critical for suppressing HSV-2 reactivation in nerve ganglia.
- Neutralizing antibodies and CD4+ T cells are key components of adaptive immunity against HSV-2.

## Abstract

Herpes simplex virus type 2 (HSV-2) is the primary pathogen responsible for genital herpes. Predominantly transmitted via sexual contact, HSV-2 not only poses significant physical and psychological burdens on infected individuals but also substantially elevates the risk of HIV acquisition and represents a potentially fatal threat to newborns. Following primary infection, HSV-2 establishes lifelong latent infection within the sacral ganglia. Currently, there are no vaccines or therapeutics capable of eradicating this latent virus reservoir or effectively preventing initial infection. The core impediment to developing such interventions lies in the incomplete elucidation of the protective immune mechanisms against HSV-2 and its precise molecular pathogenesis. The host immune response against HSV-2 hinges critically on the coordinated interplay between innate and adaptive immunity. The innate immune system, serving as the first line of defense, acts to curtail early viral replication and initiate adaptive responses. This is achieved through mechanisms, including the genital mucosal barrier, activation of Toll-like receptors (TLRs), the cGAS-STING signaling pathway, interferon (IFN)-mediated antiviral effector functions, and activation of innate immune cells such as natural killer (NK) cells and dendritic cells (DCs). Crucially, however, HSV-2 counteracts these host defenses by expressing immune modulatory proteins (e.g., ICP0, ICP27, ICP35) that target key host antiviral signaling pathways, thereby affecting immune evasion. Within the adaptive immune response, neutralizing antibodies generated by the humoral immunity can provide localized protection at mucosal sites, but their protective efficacy is limited due to sophisticated viral immune evasion mechanisms. Cellular immunity, particularly mediated by CD4+ T cells, constitutes the core mechanism for viral clearance and suppression of recurrent outbreaks. Notably, tissue-resident memory T cells (TRMs) play a pivotal role in controlling the reactivation of latent HSV-2 within the ganglia. This review integrates current research advances to delineate the innate and adaptive immune mechanisms engaged during HSV-2 infection from the perspective of the dynamic host–virus interplay, with an ultimate aim to provide a theoretical foundation informing the rational development of preventive vaccines and therapeutic agents against HSV-2.