title: Significance of rheumatoid factor isotypes in seronegative rheumatoid arthritis.
abstract: In a cross-sectional study of 124 patients with definite or classical rheumatoid arthritis (RA) and negative agglutination assays, rheumatoid factor (RF) isotypes were measured using an ELISA technique. Elevated levels of IgA-RF were found in 55 patients (44%), IgG-RF in 99 (80%), and IgM-RF in 20 (16%). The levels of IgA- and IgM-RF correlated with each other (P less than 0.001). Elevated levels of IgM-RF were associated with a more severe disease course. Elevated levels of IgA-RF correlated with the occurrence of bone erosions. The results of this study suggest that in patients with RA and negative agglutination assays, both IgM- and IgA-RF are markers of disease severity.
authors.affiliation: Department of Rheumatology, University Hospital Leiden, The Netherlands.
authors.forename: F
authors.initials: F
authors.lastname: Eggelmeijer
authors.forename: H G
authors.initials: HG
authors.lastname: Otten
authors.forename: H H
authors.initials: HH
authors.lastname: de Rooy
authors.forename: M R
authors.initials: MR
authors.lastname: Daha
authors.forename: F C
authors.initials: FC
authors.lastname: Breedveld
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001172:Arthritis, Rheumatoid / Q000097:blood / Q000276:immunology* / Q000473:pathology; D001842:Bone and Bones / Q000473:pathology; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007070:Immunoglobulin A / Q000032:analysis; D007132:Immunoglobulin Isotypes / Q000032:analysis*; D007075:Immunoglobulin M / Q000032:analysis; D007841:Latex Fixation Tests; D008297:Male; D008875:Middle Aged; D012217:Rheumatoid Factor / Q000032:analysis / Q000145:classification*
chemical_list: D007070:Immunoglobulin A; D007132:Immunoglobulin Isotypes; D007075:Immunoglobulin M; D012217:Rheumatoid Factor