Estradiol enhances B cell humoral immune responses against genital herpes simplex virus type 2 (HSV-2) in mice in an IL-17 dependant pathway

M FIROZ MIANRamtin GhasemiPuja BagriJoshua JC McGrathDanya ThayaparanDanis P SniderCharu Kaushic^*

• McMaster University, Hamilton, Canada

Abstract Introduction: Estradiol is known to enhance anti-viral immunity and protect against HSV-2 infection. Previously, we reported that intranasal immunization with attenuated HSV-2 (TK-) with estradiol (E2) showed enhanced Th17 responses leading to increased anti-viral Th1 immunity in HSV-2 post-challenge. Whether enhanced Th17 cells also lead to improved B cell antibody responses against HSV-2 challenge in E2 treated immunized mice was not examined and is the focus of the current study. Methods: Ovariectomized (OVX) C57BL/6 or IL-17 knockout mice were implanted with 17β-estradiol (E2) or placebo pellets subcutaneously. Two weeks later, mice were immunized intranasally (i.n.) with 10^4 pfu of TK-HSV-2 and 4-or 6-weeks later, blood sera and vaginal washes were collected to measure IgGs by ELISA. Mice were challenged intravaginally with 10^4 pfu WT HSV-2 4-6 weeks post-immunization, and vaginal washes were collected daily day 5 post-challenge to determine viral titers. Mononuclear cells isolated from vaginal tract, spleen, NALT, cLN and iLN tissues were analyzed by flow-cytometry for plasma and memory B cell phenotypes. Results: E2-treated WT OVX immunized mice after HSV-2 challenge showed significantly increased HSV-2-specific IgG2b and IgG2c antibodies in serum and vaginal secretions compared to placebo mice and enhanced B220-CD138+ IgG2c+ plasma cells within the nasal mucosa and vaginal tract 6-weeks post-immunization. Furthermore, E2 treatment enhanced the subsets of CD19+ IgD-memory B cells 4-weeks post-immunization within the iLN and spleen. Notably, E2-enhanced B cell antibody responses conferred greater protection from HSV-2 challenge compared to placebo mice displaying 2-3 logs decreased viral titers and reduced genital pathology (20%) compared to placebo group (85%). Importantly, E2-enhanced plasma and B cell antibody responses observed in WT mice were abrogated in IL-17-/- mice with 2-3 logs higher viral titers as equivalent to WT placebo-and IL-17-/- mice. Conclusion: This study provides novel evidence that E2-enhanced antiviral response is partly mediated by increased B cell antibody responses that requires IL-17. Thus, E2 could be exploited in developing an effective mucosal vaccine driving B cells through intranasal immunization to elicit stronger HSV-2-specific antibody responses in the female genital tract.