Objective: Increasing attention has been paid to the significance of antifilaggrin antibodies (AFA) in rheumatoid arthritis (RA). We studied the prediction of RA by AFA in serum specimens from the period prior to the onset of clinical RA.
Methods: A case-control study was nested within a Finnish cohort of 19.072 adults who had neither arthritis nor a history of it at the baseline examination during 1973-77. Pre-illness serum specimens for the assay of AFA by ELISA, using filaggrin purified from human skin as the antigen, were available from 124 of the 126 patients who had developed RA by late 1989. Of the incident cases 89 were positive for rheumatoid factor (RF). Three controls per each incident case were individually matched for sex, age, and municipality.
Results: Pre-illness serum AFA level was found to be directly proportional to the risk of RF positive RA. The odds ratio (95% confidence interval) in the highest quintile compared to the lowest quintile was 5.4 (2.2-13.6). In the subgroup of subjects positive for RF at baseline the figure was 24 (4.0-140). AFA did not predict the development of RF negative RA. A close association of the same order of magnitude between RF and AFA was noted in the pre-illness sera and in the control sera.
Conclusion: AFA still within the "normal" range predicts RA in a linear fashion. AFA and RF are associated markers of the rheumatoid immunological process.