Studies on the Effect of Bacterial Endotoxin on Primary Herpetic Keratitis

¹ Virus Laboratory at Wills Eye Research Institute, Wills Eye Hospital Philadelphia, Pa. 19130.

The effect of intraocular injection of endotoxin derived from S. marcescens was investigated in herpes simplex virus-infected rabbit eye. The findings demonstrated that a 20 µg dose of endotoxin injected intravitreously or intracorneally 3 or 18 hours before virus infection produced a severe uveitis, but significantly reduced herpetic keratitis and growth of virus in the cornea. Inhibition of herpetic keratitis was not related to a virucidal effect of endotoxin but to the dose employed. Time course studies revealed that ocular injection with endotoxin at 3 or 18 hours before infection appeared to be critical, whereas injection at other times before virus challenge failed to demonstrate a sparing effect. However, a marginal but significant therapeutic effect was achieved when endotoxin was injected intravitreously at 72 hours postinfection. Assay of various structures of the eye for content of virus inhibitor revealed that interferon-like activity was detected in the iris and ciliary body only at 3 and 18 hours after injection of endotoxin, whereas the presence of the inhibitor was not demonstrated at any time in the aqueous humor, conjunctiva, or cornea. Histopathologic studies of the cornea from an endotoxin-treated, infected eye disclosed that the cell layers of the cornea were easily distinguishable and ulcers in the corneal epithelium were generally not observed.