H2AX and infection: To investigate whether Ddb1 deletion in activated CD4+ T cells resulted in genomic stress with DNA damage accumulation, we sacrificed WT and Ddb1-TaKO mice after LCMV Armstrong infection and then stained CD4+ T-cell with antibodies against histone H2AX phosphorylated at serine 139 (γH2Ax) to assess DNA damage.