To exclude the possibility that the phenotypes we observed in MHC Class I6b2M-/-and MHC Class II-/-mice were due to abnormal immune ontogeny in knockout mice, we determined the requirement for CD4 and CD8 T cells in the clearance of primary MNV infection in WT mice depleted of CD4 and CD8 T cells. Depletion of CD4 and CD8 T cells was at least 90% effective as assessed by flow cytometry of isolated splenocytes ( Figure 5A ) and this depletion protocol is effective at depleting T cells in secondary lymphoid organs and the intestine [47, 48] . In comparison to control antibody, depletion of CD4 T cells, led to a significant increase in MNV titers in the distal ileum (p = 0.0053, Figure 5B ), but not the MLN ( Figure 5C ). In contrast, depletion of CD8 T cells led to an increase in MNV titers in both the distal ileum (p = 0.004, Figure 5B ), and the MLN (p = 0.0025, Figure 5C ).