B-cell receptor signaling in lymphoid malignancies and autoimmunity.

The B-cell receptor (BCR) for antigen is a key sensor required for B-cell development, survival, and activation. Rigorous selection checkpoints ensure that the mature B-cell compartment in the periphery is largely purged of self-reactive B cells. However, autoreactive B cells escape selection and persist in the periphery as anergic or clonally ignorant B cells. Under the influence of genetic or environmental factors, which are not completely understood, autoreactive B cells may be activated. Similar activation can also occur at different stages of B-cell maturation in the bone marrow or in peripheral lymphoid organs and give rise to malignant B cells. The pathology that typifies neoplastic lymphocytes and autoreactive B cells differs: malignant B cells proliferate and occupy niches otherwise taken up by healthy leukocytes or erythrocytes, while autoreactive B cells produce pathogenic antibodies or present self-antigen to T cells. However, both malignant and autoreactive B cells share the commonality of deregulated BCR pathways as principal contributors to pathogenicity. We first summarize current views of BCR activation. We then explore how anomalous BCR pathways correlate with malignancies and autoimmunity. We also elaborate on the activation of TLR pathways in abnormal B cells and how they contribute to maintenance of pathology. Finally, we outline the benefits and emergence of mouse models generated by somatic cell nuclear transfer to study B-cell function in manners for which current transgenic models may be less well suited.