Significance of antibodies to streptococcal M protein in psoriatic arthritis and their association with HLA-A*0207

Psoriatic arthritis (PA) is an immune disease associated with HLA-A2 in the Japanese population. To investigate mechanisms the association between HLA-A2 and PA, we examined in vivo immune responsiveness to Streptococcus pyogenes. Recombinant M proteins for the subtype specific N-terminal half (AB region) and conserved C-terminal half (C region) were produced separately. IgG antibody level against each region was measured by ELISA in 31 PA patients, 88 patients with psoriasis vulgaris, 6 patients with rheumatoid arthritis and 77 healthy controls. We found that IgG antibody levels against the C region were markedly higher in the PA patient group than in the other disease groups or controls. Further, IgG antibody levels were higher in PA patients with spondylitis and polyarticular arthritis than in PA patients with rheumatoid-like arthritis and arthritis mutilans. In contrast, no significant difference in the IgG antibody levels against the AB region was observed among the tested groups. HLA-A2 DNA typing showed that HLA-A*0207 was associated with PA (RR = 17.6; p(corr) < 0.01) and the IgG antibody responses to the C region correlated well with the presence of HLA-A*0207. These results suggest that streptococcal infection may be involved in the pathogenesis of PA by participating in the HLA-linked immune responsiveness.