The strongest susceptibility to progression from human immunodeficiency virus type 1 (HIV-1) infection to the acquired immunodeficiency syndrome (AIDS) is conferred by the major-histocompatibility-complex (MHC) class I type HLA-B*35,Cw*04 allele. In May 31 New England Journal of Medicine, Xiaojiang Gao and colleagues from Johns Hopkins School of Medicine, Baltimore shows that a single amino acid change in HLA molecules has a substantial effect on the rate of progression to AIDS.

Gao et al genotyped HLA class I loci for 850 patients who seroconverted and had known dates of HIV-1 infection. HLA-B*35 subtypes were divided into two groups according to peptide-binding specificity: the HLA-B*35-PY group, which consists primarily of HLA-B*3501 and binds epitopes with proline in position 2 and tyrosine in position 9; and the more broadly reactive HLA-B*35-Px group, which also binds epitopes with proline in position 2 but can bind several different amino acids (excluding tyrosine) in...