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Anergy, a condition in which cells persist in the periphery but are unresponsive to antigen, is responsible for silencing many self-reactive B cells. Loss of anergy is known to contribute to the development of autoimmune diseases, including systemic lupus erythematosus and type 1 diabetes. Multiple transgenic mouse models have enabled the dissection of mechanisms that underlie anergy, and recently, anergic B cells have been identified in the periphery of wild-type mice. Heterogeneity of mechanistic concepts developed using model systems has complicated our understanding of anergy and its biological features. In this Review, we compare and contrast the salient features of anergic B cells with a view to developing unifying mechanistic hypotheses that explain their lifestyles.The generation of B cells occurs throughout life and proceeds through several distinct stages and checkpoints (FIG. 1). After birth, B-cell generation occurs in the bone marrow, where cells progress through pro-B-cell and pre-B-cell stages of development. At the next stage (as immature B cells), they acquire antigen specificity by virtue of expression of a functional Bcell receptor (BCR); this is also the first key specificity checkpoint in B-cell development. Cells that successfully traverse this phase enter the periphery as transitional B cells.The ability of the adaptive immune system to provide protection against pathogens requires a diverse BCR repertoire that can recognize a broad range of foreign proteins. Diversity is generated early in development by random rearrangement of immunoglobulin genes. This inevitably results in the genesis of receptors that recognize self antigens. It is estimated that 75% of human early immature B cells are self-reactive 1 . About a third of these self-reactive immature B cells are purged from the repertoire by receptor editing, wherein renewed immunoglobulin gene rearrangement generates a new light chain to pair with the existing immunoglobulin heavy chain in an anthropomorphic effort to generate a non-self-reactive © 2007 Nature Publishing Group Correspondence to J.C.C. cambierj@njc.org. Competing interests statementThe authors declare no competing financial interests. DATABASES NIH Public Access Author ManuscriptNat Rev Immunol. Author manuscript; available in PMC 2013 July 17. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript BCR 2,3 . Failing this, these B cells are deleted by apoptosis 4 . Despite these mechanisms of central tolerance, many self-reactive B cells escape to the periphery where they are silenced by an induced state of unresponsiveness known as anergy (BOX 1). Anergy can be viewed as nothing more than the state of lethargy that ensues when B cells mount a normal initial response to antigen but fail to receive secondary signals that sustain their activation. Paradoxically, the maintenance of anergy requires chronic binding of antigen and signal transduction, yet the stimulation of unoccupied receptors fails to trigger signal transduction pathways that are...

The contribution of anergy to silencing of autoreactive B cells in physiologic settings is unknown. By comparing anergic and nonanergic immunoglobulin-transgenic mouse strains, we defined a set of surface markers that were used for presumptive identification of an anergic B cell cohort within a normal repertoire. Like anergic transgenic B cells, these physiologic anergic cells exhibited high basal intracellular free calcium and did not mobilize calcium, initiate tyrosine phosphorylation, proliferate, upregulate activation markers, or mount an immune response upon antigen-receptor stimulation. Autoreactive B cells were overrepresented in this cohort. On the basis of the frequency and lifespan of these cells, it appears that as many as 50% of newly produced B cells are destined to become anergic. In conclusion, our findings indicate that anergy is probably the primary mechanism by which autoreactive B cells are silenced. Thus maintenance of the unresponsiveness of anergic cells is critical for prevention of autoimmunity.