High Frequency of IFN-γ-Producing PLZFloRORγtlo iNKT1 Cells Infiltrating HSV-1 Infected Cornea is Associated with Asymptomatic Ocular Herpes Infection

The invariant natural killer (iNKT) cells are among the first innate immune cells to elicit early protective immunity that control invading viral pathogens. The role of iNKT cell subsets, iNKT1, iNKT2, and iNKT17, in herpes immunity remains to be fully elucidated. In this study, we examined the protective role of corneal-resident iNKT cell subsets, using the mouse model of ocular herpes infection and disease. Wild type (WT) C57BL/6 mice and CD1d knockout (KO) mice were infected ocularly with HSV-1 (strain McKrae). Cornea, spleen and liver were harvested at 0, 2, 5, 8 and 14-days post-infection (p.i.) and the frequency and function of the three major iNKT cell subsets were analyzed and correlated with symptomatic and asymptomatic corneal herpes infections. The profile of sixteen major pro- and anti-inflammatory cytokines was analyzed in corneal lysates using western blot and Luminex assays. Early during ocular herpes infection (i.e. day 2), IFN-gamma-producing PLZF(lo)RORgammat(lo) iNKT1 cell subset, was the predominate iNKT cell subset in the infected asymptomatic corneas. Moreover, compared to asymptomatic corneas of HSV-1 infected WT mice, the symptomatic corneas CD1d KO mice, with iNKT cells deficiency, had increased level inflammatory IL-6 and decreased levels of IL-12, IFN-gamma, the JAK1, STAT1, NFkappaB and ERK1/2 pathways. Our findings suggest that the IFN-gamma-producing PLZF(lo)RORgammat(lo) iNKT1 cells play a protective innate immune response against symptomatic ocular herpes.IMPORTANCE We investigated the protective role of iNKT cell subsets in asymptomatic ocular herpes infection. We found that early during ocular herpes infection (i.e. on day 2 post-infection), IFN-gamma-producing PLZF(lo)RORgammat(lo) iNKT1 cells were the predominate iNKT cell subset in the infected corneas of asymptomatic B6 mice (with low to no corneal herpetic disease), compared to corneas of symptomatic mice (with severe corneal herpetic disease). Moreover, compared to asymptomatic corneas of wild type (WT) B6 mice, the symptomatic corneas of CD1d KO mice, that lack iNKT cells, showed: (i) a decrease in the level of IFN-gamma and IL-12; (ii) an increase in the level of inflammatory IL-6; and (iii) a down-regulation of JAK1, STAT1, NFkappaB and ERK1/2 ERK1/2 pathways. The findings suggest that, early during ocular herpes infection, cornea-resident IFN-gamma-producing PLZF(lo)RORgammat(lo) iNKT1 cells protect from symptomatic ocular herpes.