B cells activated via CD40 and IL-4 undergo a division burst but require continued stimulation to maintain division, survival and differentiation

T cell stimulation of B cell proliferation during T-B collaboration require s membrane-bound stimulatory ligands, such as CD40 ligand and the secretion of soluble cytokines, such as IL-4. Nevertheless, it remains unclear wheth er T cell contact is required to provoke each consecutive B cell division, or whether B cells divide in a T cell-free burst following the initial stim ulation. To test this, naive B cells were cultured with anti-CD40 monoclona l antibody (mAb) and IL-4 and, after various times, these stimuli were remo ved and the cells re-cultured with or without further stimulation. Followin g stimulus removal, B cells were able to continue proliferating, with the s ize of the B cell burst dependent on the strength of the initial anti-CD40 mAb stimulus. Furthermore, in the absence of activating signals from anti-C D40 and/or IL-4, re-cultured B cells died rapidly. In addition, B cells und ergoing a stimulus-free division burst could switch to IgG1. Thus, maximal B cell proliferation, differentiation and survival may require continued, a lthough not necessarily consecutive, cognate interactions with T cells. The se results suggest that antigen persistence and T cell help are necessary t o sustain B cell proliferation and differentiation in vivo.