Estimation of the relative avidity of 19S IgM rheumatoid factor secreted by rheumatoid synovial cells for human IgG subclasses

Abstract

19S IgM rheumatoid factors (RF) may play an important role in sustaining inflammation in rheumatoid arthritis (RA). As yet, no unique antigenic specificity for RF in RA has been identified. Because the synovium is central to the pathogenic changes in RA, RF produced therein might be pathogenically more important than serum RF. Therefore, we examined the reactivity and relative avidity of 19S IgM‐RF in serum and rheumatoid synovial cells (RSC) from 20 patients with seropositive RA. Reactivities were determined by competitive inhibition of serum RF hemolytic activity and RSC RF‐plaque‐forming cells (PFC) by added soluble antigen, i.e., monomeric human IgG subclasses. Estimation of relative avidities of RSC RF for human IgG subclasses was done by calculation of fractional RF expression in the RSC RF‐PFC assay following inhibition by IgG subclasses. RSC RF had greatest reactivity with IgG3 and IgG1, some reactivity with IgG2, and the least reactivity with IgG4. Serum RF reacted most with IgG1 and IgG2, reacted some with IgG4, but reacted poorly with IgG3. The antigenic determinants with which RSC RF reacted were common to many IgG3 molecules. The highest relative avidity of RSC RF was for IgG3. These observations indicate a selective deficiency of serum RF compared with RSC RF and suggest an important pathogenic role for these qualitatively different RSC RF molecules for in situ RF immune complex‐mediated inflammation in RA synovial tissue.

Differential reactivity of rheumatoid synovial cells and serum rheumatoid factors to human immunoglobulin g subclasses 1 and 3 and their CH3 domains in rheumatoid arthritis

“…No such qualitative differences were apparent in serum R F molecules. These results correspond to those found when inhibition of RSC-RF PFCA volume by 1$G1 and IgG3 was used as a measure of relative R F avidity for antigen (4). Determination of R F reactivity by competitive inhibition measures R F binding to added IgG in the liquid phase, which allows more precise quantitation of binding characteristics.…”

“…Synovial tissue was obtained incidental to clinically indicated surgical procedures (synovectomy, total joint replacement) on seropositive patients, as previously described (3,4). These patients had definite or classic RA, according to the criteria of the American Rheumatism Association (5).…”

“…Myeloma proteins were isolated using ion exchange chromatography, followed by gel permeation chromatography where indicated, as previously described (3,4). All subclass proteins were examined for purity by double immunodiffusion in agar, using antisera to light chains.…”

“…An ELISA inhibition assay was used to assess the amount of contamination of purified human myeloma proteins with other subclasses, using murine monoclonal antihuman IgGl, IgG2, IgG3, and IgG4, as previously described (3,4). The sensitivity of this assay is in the range of 0.5-2 pg/ml for the homologous antigen.…”

Preferential utilization of a novel vλ3 gene in monoclonal rheumatoid factors derived from the synovial cells of rheumatoid arthritis patients

“…Our serologic studies showed that the RFs from rheumatoid synovia have unique fine subclass specificities and affinities that are different from those of serum RFs. For example, RFs from rheumatoid synovia bind well to IgG3, with higher avidity than to IgG1, 2, and 4; in contrast, serum RFs react strongly with IgG1, 2, and 4, but poorly with IgG3 (6). Thus, the molecular characterization of RSC RFs could be of key importance in understanding the etiology and pathogenesis of RA.…”