To discriminate cellular interactions mediated by antigen-dependent and -independent mechanisms, we transferred congenic, LCMV-specific CD4 and CD8 T cells recognizing epitopes of the LCMV glycoprotein into mice 5 days before infection (Fig. 5a) and included congenic markers (SMARTA:CD90.1; P14:CD45.1) in our cytometry panel (Methods). The gene discussed is CD4; the disease is infection.