Study of aspartate at residue 9 of HLA-C molecules in Japanese patients with psoriasis vulgaris.

The frequency of aspartate at residue 9 (Asp-9) of HLA-C molecules was investigated among 75 Japanese patients with psoriasis vulgaris and 50 healthy controls. We developed a technique of polymerase chain reaction sequence-specific primer (PCR-SSP) amplification of genomic DNA for HLA-C alleles with a codon for Asp-9. The specificity of amplification was confirmed by direct sequencing of the amplified products and amplification from total RNA (RT-PCR). Asp-9 was positive in all individuals with Cw6 and/or Cw7, but negative in the others, indicating that Asp-9 was specific to Cw6 and Cw7 antigens in our subjects. The frequency of Asp-9 was significantly increased in the patient group (48% vs. 20%; P < 0.002). The frequency of alanine at residue 73 (Ala-73), which was positive for Cw4, Cw6, Cw7, and some C blanks, was also increased in our previous study (81% vs. 48%; P < 0.0001). Asp-9 is located on a beta sheet of alpha 1 domain of HLA-C molecule and influences the peptide binding of the C pocket of the groove together with Ala-73. Both Asp-9 and Ala-73 could contribute to the disease susceptibility to psoriasis vulgaris in the immune responses.