Granulocytes in Ocular HSV-1 Infection: Opposing Roles of Mast Cells and Neutrophils

PURPOSE. The contributions of mast cells (MCs) to immunologic defense against pathogens in the eye are unknown. We have characterized pericorneal MCs as tissue-resident innate sentinels and determined their impact on the immune response to herpes simplex virus type-1 (HSV-1), a common ocular pathogen. METHODS. The impact of mast cells on the immune response to HSV-1 infection was investigated using MC-deficient KitW-sh mice. Virus titers, inflammatory cytokine production, eicosanoid profiles, cellular immune responses, and ocular pathology were evaluated and compared with C57BL/6J mice during an acute corneal HSV-1 infection. RESULTS. Corneas of KitW-sh mice have higher viral titers, increased edema, and greater leukocyte infiltration following HSV-1 infection. Following infection, cytokine profiles were slightly elevated overall in KitW-sh mice. Eicosanoid profiles were remarkably different only when comparing uninfected corneas from both groups. Neutrophils within infected corneas expressed HSV-1 antigen, lytic genes, and served as a disease-causing vector when adoptively transferred into immunocompromised animals. Myeloid-derived suppressor cells did not infiltrate into the cornea or suppress the expansion, recruitment, or cytokine production by CD8(+) T cells following acute HSV-1 infection. CONCLUSIONS. Collectively, these findings provide new insight into host defense in the cornea and the pathogenesis of HSV-1 infection by identifying previously unacknowledged MCs as protective innate sentinels for infection of the ocular surface and reinforcing that neutrophils are detrimental to corneal infection.