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 stimulati on via the CD40 molecule, the induction of germ-line transcripts of Ig H chain isotypes was analyzed by polymerase chain reaction. The resul ts document that costimulation with mAb to CD40 and IL-4 induces steri le transcription of all Ig H chain isotypes. Of importance, stimulatio n with mAb to CD40 without the addition of IL-4 induced germ-line tran scription of most downstream isotypes, suggesting that this signal is sufficient to initiate the first step in switch recombination.