Antibody-mediated protection against genital herpes simplex virus type 2 disease in mice by Fc gamma receptor-dependent and -independent mechanisms

Abstract

The ability of antibody (Ab) to modulate HSV pathogenesis is well recognized but the mechanisms by which HSV-specific IgG antibodies protect against genital HSV-2 disease are not well understood. The requirement for Ab interactions with Fcgamma receptors (FcgammaR) in protection was examined using a murine model of genital HSV-2 infection. IgG antibodies isolated from the serum of HSV-immune mice protected normal mice against HSV-2 disease when administered prior to genital HSV-2 inoculation. However, protection was significantly diminished in recipient mice lacking the gamma chain subunit utilized in FcgammaRI, FcgammaRIII, FcgammaRIV and FcepsilonRI receptors and in normal mice depleted of Gr-1(+) immune cell populations known to express FcgammaR, suggesting protection was largely mediated by an FcgammaR-dependent mechanism. To test whether neutralizing Ab might provide superior protection, a highly neutralizing HSV glycoprotein D (gD)-specific monoclonal antibody (mAb) was utilized. Similar to results with HSV-specific polyclonal IgG, administration of the gD-specific mAb did not prevent initial infection of the genital tract but resulted in lower virus loads in the vaginal epithelium and provided significant protection against disease and acute infection of the sensory ganglia; however, this protection was independent of host FcgammaR expression and was manifest in mice depleted of Gr-1(+) immune cells. Together, these data demonstrate that substantial Ab-mediated protection against genital HSV-2 disease could be achieved by either FcgammaR-dependent or -independent mechanisms. These studies suggest that HSV vaccines might need to elicit multiple, diverse antibody effector mechanisms to achieve optimal protection.

Fig. 1

Protection afforded by HSV-specific polyclonal Ab requires host cell expression of FcγR. A, Survival curves of B6 or FcγR^−/− polyclonal Ab recipients (n=13–16) following ivag challenge with 5×10³ PFU HSV-2 strain 186. Results shown were pooled from 2 experiments. Survival curves are marked to denote statistical significance as follows: ^*p< 0.0001, ^**p < 0.006 compared to PBS-treated B6 mice, and ^ψp < 0.008 compared to FcγR ^−/− Ab recipients by Logrank test. B, HSV-2 titers in the vaginae of Ab-treated or control-treated mice (n=8) on day 1 and 2 post ivag HSV-2 inoculation. Day 2 titers for B6 Ab recipients are significantly different compared to PBS-treated B6 mice (p < 0.0001, Logrank test) and FcγR^−/− Ab recipients (p < 0.05, Logrank test). C, Quantification of IFN-γ-producing cells from the iliac lymph nodes of B6 or FcγR^−/− mice challenged 6 days previously with 5×10³ PFU HSV-2 strain 186. Results shown represent the mean response of 6 mice to UV-killed HSV-2 or the CD8 epitope from HSV glycoprotein B (gB_498–505). Less than 10 IFN-γ-secreting cells/LN were detected in naïve mice.

Fig. 2

Survival of mice following passive transfer of gD-specific mAb. A, Groups of 10–20 mice received PBS, or either 50µg or 1.0µg 10E4.2G2a, prior to ivag inoculation with 5×10³ PFU HSV-2. Survival curves are marked to denote statistical significance as follows: ^**p< 0.0001 compared to PBS-treated B6; ^ψp < 0.016 compared to FcγR^−/− Ab recipients; and ^*p < 0.04 compared to PBS-treated B6 mice by Logrank test. Groups of 15µMT and Rag 1 ^−/− mice (B) or B6 and FcγR^−/− mice (C) were given 50µg 10E4.2G2a or PBS 2 days before ivag inoculation with 5×10³ PFU HSV-2. Results shown are from representative experiments of two performed. Survival curves significantly different than PBS controls are marked with an asterisk (p<0.001, Logrank test). D, HSV-2 titers in the genital tracts from groups of 15 B6 mAb recipients, FcγR^−/− mAb recipients or B6 PBS-treated controls were quantified on the indicated days after HSV-2 inoculation. Marked values are significantly different compared to PBS-treated controls (^*p < 0.001; ^**p < 0.01, ANOVA).

Fig. 3

Presence of Gr-1⁺ cells in the vagina, sensory ganglia and spinal cords of HSV-2 inoculated mice. Vaginal lavages, sensory ganglia and spinal cords were harvested and pooled from 5 uninfected or HSV-2 inoculated mice on day 2 post-inoculation. Leukocytes were isolated and stained for expression of Gr-1 or F4/80, as described in Materials and Methods. A, Vaginal lavage cells from uninfected mice. B, Vaginal lavage cells from mice inoculated 2 days previously with 5×10³ PFU HSV-2. C, Spinal cord cells from uninfected mice. D, Spinal cord cells obtained on day 2 post-HSV-2 inoculation. Results are representative of at least two experiments performed.

Fig. 4

Mechanisms of antibody-mediated protection against HSV-2. A, Virus neutralization. B, Complement-dependent lysis of HSV-infected cells. C, ADCC.