Interleukin‐1–inhibitory IgG in sera from some patients with rheumatoid arthritis

Inhibition of interleukin‐1°aL (IL‐1°aL) activity was detected in 7 of 41 serum samples from patients with rheumatoid arthritis (RA). These 7 sera inhibited not only IL‐1°aL–induced endothelial cell adherence to neutrophils, but also IL‐1°bT–induced endothelial cell adherence, although to a lesser extent. These sera showed no influence on tumor necrosis factor–induced endothelial cell adherence. No inhibitory activity was found in 40 sera from normal control subjects. Studies to further examine these effects included gel filtration analysis of 2 of the RA sera. The inhibitory activity was eluted near M_r 158 kd and above M_r 250 kd. Analysis by protein A affinity chromatography showed that IL‐1–inhibitory activity was present in protein A–binding fractions. Purified IgG (by DE‐52 column chromatography) from RA patients was found to be as potent an inhibitor as the protein A–binding fractions, which suggests that the major inhibitory activity in RA sera is attributable to IgG molecules. These purified IgG molecules also inhibited IL‐1–induced proliferation of mouse thymocytes but did not influence IL‐2–dependent proliferation of the CTLL‐2 murine T cell line. The 7 patients whose sera showed IL‐1–inhibitory activity had mild RA and low titers of rheumatoid factor. The findings, taken together, suggest a possible regulatory role of IL‐1–inhibitory IgG in RA disease activity.