Characterization of CD40-dependent immunoglobulin class switching

Previous studies have shown that signalling via CD40 together with cytokine s stimulates immunoglobulin (Ig) class switching in B cells. This process i ncludes induction of germline (GL) transcripts and switch recombination. Us ing an agonistic rat anti-mouse CD40 monoclonal antibody (MoAb), we investi gated the role of CD30 signalling in these molecular events. We found that stimulation of murine B cells induced high steady-state levels of germline gamma 1, gamma 2b and low levels of epsilon transcripts. No detectable gamm a 2a or alpha RNA were found and the level of gamma 3 transcripts was high both in stimulated and unstimulated cells. Although cells treated with anti -CD40 MoAb had high levels of GL gamma 1 and gamma 3 transcripts, we failed to detect switching to IgG1 or IgG3. However, anti-CD40 MoAb-stimulated ce lls increased expression of IgG2b. Interestingly, anti-CD40 plus interleuki n (IL)-5 induced switching to IgG1. Previous work has demonstrated that CD4 0 signalling, but not lipopolysaccharide (LPS), induces the gamma 1 promote r and that NF-kappa B motifs are important. We show here that both LPS and anti-CD40 activated NF-kappa B proteins binding to the gamma 1 promoter. Th e bound NF-kappa B complexes were different with regard to total concentrat ion and subunit composition. In the light of our data, the mechanism of CD4 0-mediated Ig class switching is discussed.