Interleukin-10 treatment can suppress stromal keratitis induced by herpes simplex virus type 1

Herpes simplex virus type 1 (HSV-1) infection of the murine cornea induces an intense inflammatory response that can lead to permanent blindness. We tested whether IL-10, a cytokine that has anti-inflammatory properties, could suppress the development of stromal disease. Murine rIL-10 was inoculated intracorneally 4 h before and again on days +2 and +5 relative to the time of topical HSV-1 corneal infection. Additionally, the mice received IL-10 i.p. at the time of virus administration and again 3 days post-infection. Four weeks post-infection, the incidence of blinding disease was 95% in the saline-treated controls but only 36% in the IL-10-treated animals. Histologic studies showed extensive cellular infiltrates in control corneas but not in those of the IL-10-treated eyes. Examination of the proinflammatory cytokine levels in the cornea 10 days after infection revealed that the presence of IL-2 was 10-fold lower and IL-6 some 50-fold lower than that found in the controls. IL-1α levels were not reduced. The IL-10 treatment protocol employed did not suppress the systemic cellular or humoral immune responses to viral Ag, nor was the rate of HSV-1 clearance from the eye different from that seen in the controls. In vitro studies revealed that spontaneous production of IL-6 by excised normal corneas was inhibited by >95% with low dose IL-10. IL-1α synthesis was not inhibited. Collectively, these results indicate that IL-10 treatment can 1) suppress the production of certain cytokines produced by corneal cells, and 2) minimize ocular inflammation without compromising clearance of the infecting virus from the eye.