International Immunology, Vol. 7, No. 3, pp. 459-469,March 1995
© 1995 Japanese Society for Immunology
Differential sensitivity to transforming growth factor (TGF)-ß 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-ß
Department of Immunology, Arrhénius Laboratories for Natural Sciences, Stockholm University S-10691 Stockholm, Sweden
1 Department of Clinical Immunology, Karolinska Institute Huddinge Hospital, S-14186 Huddinge, Sweden
Correspondence to: Correspondence to: A. Ridderstad
Synovial fluid from patients with rheumatoid arthritis (RA-SF) contains in vivo produced cytokines and inflammatory mediators, including a factor that induces IgG2b production of lipopolysaccharide (LPS) preactivated murine B lymphocytes. In order to determine the mechanism by which RA-SF acts on LPS activated mouse B 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 deficiency in vitro and in vivo, with regard to IgG2b production after LPS stimulation. Since transforming growth factor (TGF)-ß has been suggested to be a switch factor for IgG2b, we aimed at investigating the role of TGF-ß in our experimental system. We found that TGF-ß could not mimic the effect of RA-SF on CBA spleen cells. A small increase of IgG2b secretion was observed with spleen cells from normal CBA mice, whereas Ig secretion of all isotypes was suppressed in CBA/N spleen cells treated with TGF-ß at any concentration. Neutralizing antibodies against TGF-ß suppressed the response of CBA B cells, whereas the response by CBA/N B cells was enhanced by the same antibody preparation. Here we also show that the abnormal B cell responsiveness to TGF-ß, typical of CBA/N, co-segregates with the btk mutation in male (CBA x CBA/N)F2 spleen cells. This was determined by allele specific 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-ß, that is involved in the differentiation of IgG2b expressing cells.
Keywords: btk, CBA/N, rheumatoid arthritis, synovial fluid, transforming growth factor
Received 17 August 1994, accepted 28 November 1994.