DIFFERENTIAL SENSITIVITY TO TRANSFORMING GROWTH-FACTOR (TGF)-BETA OF CBA AND OF CBA N B-CELLS DEMONSTRATES THAT THE IGG2B INDUCING FACTOR IN SYNOVIAL-FLUID FROM RHEUMATOID-ARTHRITIS PATIENTS IS NOT IDENTICAL TO TGF-BETA/

Synovial fluid from patients with rheumatoid arthritis (RA-SF) contain s in vivo produced cytokines and inflammatory mediators, including a f actor that induces lgG2b production of lipopolysaccharide (LPS) preact ivated murine B lymphocytes, In order to determine the mechanism by wh ich RA-SF acts on LPS activated mouse a cells, CBA/N mice were used as an experimental model, The X-linked immunodeficiency of these mice is caused by a point mutation in the Bruton's tyrosine kinase (btk) gene , We have earlier shown that RA-SF can reconstitute the CBA/N B cell d eficiency in vitro and in vivo, with regard to IgG2b production after LPS stimulation, Since transforming growth factor (TGF)-beta has been suggested to be a switch factor for lgG2b, we aimed at investigating t he role of TGF-beta in our experimental system, We found that TGF-beta could not mimic the effect of RA-SF on CBA spleen cells, A small incr ease of IgG2b secretion was observed with spleen cells from normal CBA mice, whereas Ig secretion of all isotypes was suppressed in CBA/N sp leen cells treated with TGF-beta at any concentration, Neutralizing an tibodies against TGF-beta suppressed the response of CBA a cells, wher eas the response by CBA/N a cells was enhanced by the same antibody pr eparation, Here we also show that the abnormal a cell responsiveness t o TGF-beta, typical of CBA/N, co-segregates with the btk mutation in m ale (CBA X CBA/N)F-2 spleen cells, This was determined by allele speci fic PCR recognizing the identified base substitutions of the btk gene, typical of the two strains, We propose that RA-SF contains a factor, separate from TGF-beta, that is involved in the differentiation of IgG 2b expressing cells.