We concluded that the different patterns of Ig isotype expression in DR1 and B10 mice after NC infection fit closely with the contrasting patterns of cytokine production by virus-specific CD4 T cells, since IL-4 and IFN-γ act reciprocally in promoting expression of IgG1 and IgG2b/IgG2c, respectively [12]. This evidence concerns the gene CD4 and infection.