IRF1 and infection: To define the relationship between MHV68 orf36 and B cell-intrinsic IRF-1 expression during chronic infection, parameters of chronic MHV68 infection were measured in Cd19Cre/wtIrf1fl/fl (Cre-positive) and Cd19wt/wtIrf1fl/fl (Cre-negative) mice 16 days after intranasal inoculation with 10,000 PFU of WT or orf36-deficient MHV68 mutant (N36S) (24).