CD4 and infection: Moreover, F52/70 infection caused more immunosuppression in younger birds than older birds, and more immunosuppression than 228E in younger birds, however, the kinetics of CD4+CD25+ TGFβ+ cell infiltration was the same between younger and older birds infected with F52/70, and the kinetics of CD4+TGFβ+ and CD4+CD25+ TGFβ+ cell infiltration was the same between F52/70 and 228E infection in younger birds, suggesting the infiltration of these cells into the BF is unlikely to be contributing to immunosuppression.