CD4 and infection: Further, our observations of minimal damage to the BBB in both TAP1-null and MHCII-null mice day 12 post-infection seem to suggest that the presence of α/β TCR bearing T cells may indeed be providing protection from a breach in BBB, either via help provided by CD4 T cells to produce high titer neutralizing antibodies, or via CD8 T cells to lyse infected target cells, or both.