CD4 and infection: Moreover, efficient suppression of FV-induced bone marrow pathology by Treg cells did not necessitate direct viral-antigen recognition by Treg cells because the TCR repertoire of Treg cells in virus-naive and FV-infected mice was lacking virus-specific clones and no conversion of FV-specific pathogenic CD4+ T cells into FoxP3-expressing Treg cells occurred during infection.