LIGATION OF CD40 INDUCES STERILE TRANSCRIPTS OF MULTIPLE IG H-CHAIN ISOTYPES IN HUMAN B-CELLS

Stimulation of human B cells with mAb to CD40 in the presence of IL-4 induces proliferation and differentiation into Ig-secreting cells. To delineate the molecular events leading to Ig secretion after stimulation via the CD40 molecule, the induction of germ-line transcripts of Ig H chain isotypes was analyzed by polymerase chain reaction. The results document that costimulation with mAb to CD40 and IL-4 induces sterile transcription of all Ig H chain isotypes. Of importance, stimulation with mAb to CD40 without the addition of IL-4 induced germ-line transcription of most downstream isotypes, suggesting that this signal is sufficient to initiate the first step in switch recombination.