Quantitative Detection of Class-Specific Rheumatoid Factors and IgA Rheumatoid Factor Subclasses

Abstract

An Enzyme-Linked-Immuno-Sorbent-Assay (ELISA) for the quantitative detection of rheumatoid factors (RF) and an ELISA for measurement of IgA-RF subclasses was developed. In sera from 108 patients with rheumatoid arthritis (RA) of whom 47 had a positive latex agglutination assay, 100 healthy controls and 119 diseased controls (49 systemic lupus erythematosis (SLE), 20 osteoarthritis and 50 bronchial asthma) the levels of IgG-, IgA-, IgM-, IgA1- and IgA2-RF were evaluated by ELISA. In serum samples from RA patients with a positive latex test, elevated levels of IgG-, IgA-, and IgM-RF could be demonstrated in 94%, 91% and 98% respectively. In serum samples from RA patients with a negative latex test, elevated levels of IgG-, IgA-, and IgM-RF could be demonstrated in 72%, 69% and 8% respectively. In the latter patient group increased levels of one or more RF-isotypes could be detected in 82% of the patients. In the diseased controls less than 8% of the sera were positive for the three RF-isotypes investigated except that from the SLE patients 25% and 64% were positive for IgG-and IgA-RF respectively. Highly significant correlations were found between serum IgM-RF levels as detected by ELISA and those of the latex and the Rose-Waaler agglutination assays. Positive correlations were also found between the serum levels of the three RF-isotypes investigated. In serum samples from RA patients with a positive latex test, elevated levels of IgA1- and IgA2-RF could be detected in 94% and 62% respectively. In serum samples from RA patients with a negative latex test, elevated levels of IgA1- and IgA2-RF could be detected in 36% and 52% respectively. In serum samples from patients with SLE, elevated levels of IgA1- and IgA2-RF could be detected in 41% and 37% respectively. A significant correlation was found between levels of IgA1- and IgA2-RF in sera from RA patients but not in sera from SLE patients