In the present study we investigated how mice with a constitutive (CD28 –/–; further named CD28KO) or conditional deletion of CD28 (CD28-/flox Cre+/-; further named Cre) are able to deal with a TMEV-infection in comparison to controls without Cre-expression (CD28-/flox Cre-/-; further named B6) and to controls without tamoxifen administration. This evidence concerns the gene CD28 and infection.