Ligand-independent tonic signaling in B-cell receptor function.

The random and inherently imprecise process of V(D)J recombination is the foundation for generation of the B-cell receptor (BCR). Signals must be generated to trigger selective processes that retain cells expressing a functional BCR, and these signals must be antigen-independent to insure an unbiased and diverse pool of newly formed B cells. Moreover, BCR expression, and presumably signaling, is essential for the continued survival of the B cell. Although BCR signaling is generally thought to depend upon ligand-induced aggregation, recent studies argue that some aspects of BCR signaling occur independently of antigen, and, furthermore, these non-induced or 'tonic' signals are linked to specific cellular processes operating at multiple stages of B-cell development. The potential co-existence of tonic and induced signaling suggests a unique aspect of BCR complexes, or at least an aspect of receptors that has previously been under-appreciated.