Several cell populations have been reported to produce IL-10 after LCMV infection: LCMV specific CD4+ T cells secrete IL-10 on day 5 post infection [22], IL-10 mRNA is upregulated in dendritic cells (DCs), B cells, macrophages, CD4+ and CD8+ T cells on day 9 post infection [2] and purified CD4+ T cells and DCs produce IL-10 upon LCMV infection of splenocytes in vitro[3]. Here, CD4 is linked to infection.