CD4-specific conditional TREM-2 KO mice exhibited lower levels of activation markers CD69 and CD134, as well as TH1 cytokines IFN-γ and TNF, together with higher viral load and lung destruction after MHV-A59 infection compared with WT mice, suggesting that TREM-2 is required in T cell–mediated immune defense and inflammation. This evidence concerns the gene TNFRSF4 and infection.