Objective: To study the role of HLA class II genes in conferring susceptibility to seronegative vs seropositive rheumatoid arthritis (RA).
Methods: The distribution of DRB1 and DPB1 alleles in 33 seronegative, 20 weakly seropositive, 79 distinctly seropositive patients with RA, and in 181 healthy controls was determined by genomic typing: IgM rheumatoid factor (RF) seronegativity was ascertained in Waalers' latex, and ELISA tests.
Results: DRB1*0101/2 (encoding variants of DR1) was associated with weakly seropositive RA (and possibly seronegative RA) but not the clearly seropositive disease. In contrast DRB1*0401 and DRB1*0408 (encoding the Dw4 and Dw14.2 variants of DR4, respectively) were associated with clearly seropositive RA but were not increased among patients having weakly seropositive or seronegative RA. DRB1*0404 (encoding the Dw14.1 variant of DR4) was increased to some extent in all examined RA subsets. The distribution of DPB1 alleles in the patients was as in the controls.
Conclusion: Seronegative and weakly seropositive RA differ from clearly seropositive RA in HLA class II associations.