Innate Immune Response of the Human Host to Exposure with Herpes Simplex Virus Type 1: In Vitro Control of the Virus Infection by Enhanced Natural Killer Activity via Interleukin-15 Induction

Infections with herpes simplex virus type 1 (HSV-1) in humans and in animal models are accompanied by enhanced natural killer (NK) activity. In vitro, HSV-1 also enhances the NK activity of human peripheral blood mononuclear cells (PBMC). The molecular basis of this enhanced NK activity, however, is not well characterized. We investigated the role of human interleukin-15 (IL-15) in this phenomenon and report here that HSV-1-mediated enhanced NK activity was abrogated by neutralizing antibodies for IL-15 but not for other cytokines (i.e., IL-2, IL-12, gamma interferon [IFN-γ], tumor necrosis factor alpha, or IFN-α). Anti-CD122 antibodies which block signaling through IL-2 receptor β chain, and therefore neutralize the effects of IL-15 (and IL-2), also abrogated this enhancement. Furthermore, HSV-1 increased the levels of IL-15 mRNA and the production of IL-15 in HSV-1-infected PBMC cultures. The neutralization of IL-15 in cocultures of PBMC with HSV-1-infected cells significantly increased HSV-1 production. These results strongly suggest a role for IL-15 in the HSV-1-mediated in vitro enhancement of NK activity and in the PBMC-mediated suppression of HSV-1 replication.