CD4 and infection: In a previous work we reported that the MHC class IB M1 haplotype correlated with a high viral load (P = 0.0280) and CD4 loss (P = 0.0343), whereas the MHC class IB M2 and M6 haplotypes correlated with increased susceptibility (P = 0.0199) and resistance (P = 0.0087) to infection, respectively [38].