Ii, HLA-DM, HLA-DR) determined that not only the levels of mature MHC-II on the cell surface are reduced in the presence of Nef, but also that the expression of an immature MHC-II molecule, containing the invariant chain Ii, is increased and this function appears to be specific for the Nef protein, since it is not observed during infection with Nef-deleted viruses. The gene discussed is S100B; the disease is infection.