Differences in HLA frequencies between HIV-positive and HIV-negative Mexicans. Allelic frequencies were calculated for HLA-A and B genes, in the cohort of 292 HIV-positive individuals from this study (dark grey) and compared to those previously reported for a cohort of 381 individuals of 191 Mexican families by Barquera et al  (light grey). HLA typing in both cases was carried out by SSP-PCR as described in the Methods. For comparability, HLA nomenclature for histocompatibility used by Barquera et al. was substituted with its genetic equivalent, i.e. B65 and B64 were included as B*14 alleles; B62, B63, B70, B71, B72, and B75 were included as B*15 alleles; and B61, and B60 were included as B*40 alleles, according to the equivalents accepted by the WHO Nomenclature Committee for Factors of the HLA System http://www.ebi.ac.uk/imgt/hla/dictionary.html.