To determine if the differences in ocular disease pathogenesis were a result of differences in viral replication early in infection, we measured viral titers in the tear film at 1, 3, and 5 dpi in BTLA−/− LIGHT−/−, CD160−/− LIGHT−/−, and CD160−/− BTLA−/− mice (Fig. 1F). This evidence concerns the gene BTLA and infection.