CD4 and infection: Indeed, whereas wild type C57BL/6 miceinfected with CPE85B survived significantly longer than those infected withH37Rv (median survival >300 and 239 days, respectively;p = 0.0062), MHCIIKO mice, which lack CD4+T cells, exhibited indistinguishable susceptibility to infection with the CPE85Band H37Rv strains (median survival 79 and 81 days, respectively;p = 0.425), (Figure 5A), clearly establishing that in vivo attenuation of theCPE85B strain depends on MHC II antigen presentation and CD4+ Tcell responses.