B Cell–Associated Surface Molecules and B Cell Responses

The B cell is the central element of humoral immunity. The main function of B cells is to generate antibody-secreting plasma cells and memory cells in response to specific antigens. B cells are also involved in a broad spectrum of immune responses, including antigen presentation to T cells and cytokine production. Immunoglobulins (Ig) anchored to the cell membrane constitute the antigen-specific receptor of B cells (BCR). Although the BCR is essential for the function of B cells, a number of B cell–associated surface molecules have been identified that also regulate B cell function. Signals delivered by these molecules positively and negatively regulate BCR responses to antigen, and are key for their development, activation, proliferation, differentiation, and effector functions. These molecules are differentially expressed during lymphocyte development and activation, and can also be used to identify and isolate several B cell subsets. The determination of the expression patterns of these molecules is essential for the diagnosis of B cell malignancies and immunodeficiencies. Moreover, some of these molecules have proven to be therapeutic targets for the treatment of B cell–related diseases, such as B cell malignancies and autoimmune diseases.