Background Although the immunological hallmark of rheumatoid arthritis (RA) – rheumatoid factor (RF), has modest disease specificity the determination of its subclasses could show individual characteristics of the pathogenic process with possible correlation with the clinical phenotype and treatment respond.
Objectives To analyse the serum (S) and synovial fluid (SF) concentration of RF subclassesin RA patients (pts) and to compare them and clinical data and structural damages in regard to their use as markers for the disease activity (DA), progression and possible treatment decisions.
Methods 151 RA pts according to the 1987 ACR criteria were included in the study. Levels of RF IgG, IgM and IgA in S and SF samples were measuredby ELISA and analysed in regard to the laboratory data for DA, radiological and functional stage.
Results There was a correlation between the S and SF concentration of RF IgG (r = 0.778, p < 0.001), RF IgA (r = 0.631, p < 0.001) and RF IgM (r = 0.577, p < 0.001). Double positivity for RF subclasses was found as follows: RF IgM+/IgA+ in 62% of the pts, RF IgM+/IgG+ in 25% of the pts, RF IgG+/IgA+ in 17% of the pts, and the simultaneously presence of the three subclasses RF IgM+/IgA+/IgG+ in 11% of the pts. S and SF concentrations of RF IgG were lower in pts with diseases duration more than 10 years and lower functional status, the opposite was found for RF IgA concentrations. There was no correlation between the systemic and local concentration of RF IgA with the DA. The latter was found to correlate with higher S concentration of both RF IgA+/IgM+.
Conclusions RF accounts for the inflammatory process in RA. Systemic and local concentrations of RF subclasses characterise the pathogenic process where RF IgG is involved in the early and IgA in the latter stages of the autoimmune inflammatory reaction. RF subclass determination in the clinical practice could be used for pts follow-ups and in the process of making treatment decisions with personalising the disease modifying therapy.