ERVW-1 and HIV-1 infection: As previously reported in studies of natural HIV-1 infection (34), conformational and linear gp41 responses represented the dominant IgA Env antigen specificity, followed by gp140 and gp120 responses (gp41 binding in milk: 100% positive, median SA of 43.9; gp41 principal immunodominant domain [gp41 PID] in milk: 100% positive, median SA of 8.41; gp140 binding in milk: 86% positive, median SA of 4.83; gp120 binding in milk: 75% positive, median SA of 2.55) (Fig. 1A).