CD4 expression is important but not essential for infection with exogenous mouse mammary tumor virus

We studied local events in the popliteal lymph nodes of CD4-deficient mice following foot pad injection with an MMTV strain which carries the gene for a Vβ14-specific superantigen. Injection of the Vβ14-specific MMTV induced vigorous expansion of Vβ14⁺ CD4⁺ T cells and B cells in their lymph nodes of CD4+/- heterozygous control mice. On the other hand, CD4-/- mice injected with the MMTV showed a proliferation of Vβ14⁺ T cells among the population of TCRαβ⁺ CD4^-CD8^- T cells, although to a lesser extent. This phenomenon was not accompanied by vigorous B cell expansion. A PCR assay revelated that the MMTV definitely infected the lymph nodes cells of the CD4-/- mouse. However, the infectivity of the MMTV in CD4-/- mice was approximately 20 times lower than that in CD4+/- mice. These findings indicate that, in MMTV infection of CD4-deficient mice, the superantigen-reactive T cells among the population of TCRαβ⁺ CD4(z)CD8(x) T cells substitute for the superantigen-reactive CD4⁺ T cells of normal mice, and that the absence of CD4 molecules decreased the infectivity of MMTV because of insufficient expansion of the superantigen-reactive T cells.