Characterization of inhibitor(s) of lymphocyte activation in serum from rats with adjuvant arthritis

Serum from adjuvant arthritic rats inhibits the concanavalin A- (Con A) and lipopolysaccharide-induced stimulation of lymph node cells, leaving the basal and phytohemagglutinin-stimulated 3H-thymidine incorporation unaffected. Con A-stimulated 3H-thymidine uptake is also inhibited in rat spleen and peripheral blood lymphocytes and in dog peripheral blood lymphocytes. The intensity of the inhibitory activity in serum is positively correlated with the intensity of the secondary lesions of adjuvant arthritis. Inhibitory activity was not found in serum from rats bearing nystatin-induced inflammation. Serum fractionation studies indicated that the inhibitory activity cannot be attributed to low molecular weight alpha2-glycoproteins or to gamma-globulins and alpha2-macroglobulins, but it is present in a fraction migrating with beta-globulins. The inhibitory activity in arthritic rat serum is reduced by treatment with non-steroidal anti-inflammatory drugs, but is unaltered by D-penicillamine. It is suggested that this inhibitory activity is part of the systemic response to an immunologically mediated inflammation.