Increased severity of HSV-1 keratitis and mortality in mice larking the 2-5A-dependent RNase L gene

PURPOSE. The 2',5'-oligoadenylate-dependent RNase L gene functions in the i nterferon-inducible RNA decay pathway known as the 2-5A system. The purpose of this study was to determine whether the absence of this gene affects th e pathogenesis of herpes simplex virus type-1 (HSV-1) ocular infection in t he mouse. METHODS. HSV-1 (strain McKrae) was applied bilaterally to unscarified corne as of RNase L-null mice and congenic controls. To evaluate the severity of herpetic keratitis, slit lamp examinations (SLE) were performed every other day for 14 days. To study corneal histology and apoptosis, HSV-1-inoculate d RNase-L-null and congenic control mice, as well as mockinoculated mice (a poptosis negative control), were killed at 6 and 18 hours postinoculation ( PI). Uninoculated mite that underwent corneal scarification (apoptosis posi tive control) were killed 2 hours after scarification. Eyes were dissected and the corneas processed for light and transmission electron microscopy an d the TUNEL assay. RESULTS. In comparison with the congenic control mice, RNase L-null mice sh owed significantly more severe herpetic keratitis (PI day 8, SLE score, mea n +/- SEM: 3.27 +/- 0.10 vs. 2.34 +/- 0.06; P < 0.001) and significantly hi gher mortality (PI day 14, 70% vs. 20%; P < 0.001). Few apoptotic cells wer e seen in HSV-1-infected RNase L-null mice, although DNA fragmentation cons istent with apoptosis was detected in the corneas of congenic control mice 6 and 18 hours after HSV-1 inoculation and in uninfected mice with scarifie d corneas. Signs of apoptosis were not present in the mock-infected corneas . Electron microscopic evidence of keratocytic apoptosis was detected only in the uninfected scarified corneas and the HSV-1-infected congenic control corneas. CONCLUSIONS. The increased severity of ocular disease and increased mortali ty in the RNase L-null mice provides evidence, for the first time, that the 2-5A system contributes to protection during ocular herpetic infection. Th e reduced frequency of apoptosis in these mice suggests that one possible m echanism for this protective effect could be the induction of apoptosis in corneal cells as a means of reducing the spread of infectious virus.