CD4 and listeriosis: Since the frequency of Lm-specific IFN-γ+ and IL-2+ CD4+ T cells were not affected by A20-deficiency in primary and secondary listeriosis, and, additionally, CD25 expression of CD8+ T cells was upregulated normally in CD8+ T cells, a diminished CD4+ T cell response is unlikely to cause the A20-dependent effects in CD8+ T cells.