(A) MHC haplotypes with alleles are illustrated for: the two monkeys with a combination of complete M3 and M4 haplotypes (BM795 and BM796, middle panel), a monkey with M3 but no M4 for MHC I (AM271, left panel), and a monkey with M4 but no M3 (AM260, right panel). (B) Viral loads and CD4 counts of the monkeys in A. In contrast to M3M4 monkeys (white bars), M3 or M4 monkeys (black bars) showed high viral loads and low CD4 counts. Two other monkeys with M3 but not M4, AT789 (M1/M3, M1/M3) and BM280 (M3/M3, M3/M3), had similar disease profiles (not illustrated here).