The role of B lymphocytes as antigen-presenting cells
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B lymphocytes are regarded as professional antigen-presenting cells (APCs) despite their primary role in humoral immunity. Over the last two decades, studies designed to define the role of the B cells as APCs have generated discrepant results, showing that B cells are either unnecessary or required for T cell priming and either immunogenic or tolerogenic to T cells. The reasons for these discrepancies are not clear. Here we review mechanisms regulating B cell antigen presentation and the data derived from the major studies conducted by different groups representing each school of thought. In general it is clear that B cells process and present specific and nonspecific antigens differently. The presentation of specific antigen through the B cell antigen receptor occurs with very high efficiency and is associated with B cell activation, resulting in the activation of cognate T cells. In contrast, the presentation of nonspecific antigen by B cells is minimized and dissociated from B cell activation. As a result, B cells inactivate T cells that recognize nonspecific antigenic epitopes presented by B cells, or they induce regulatory T cell differentiation or expansion. These mechanisms serve to ensure effective production of high-affinity antigen-specific antibodies but minimize the production of nonspecific antibodies and autoantibodies.
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Peter E. Jensen, M.D., ARUP Professor and Chair, Department of Pathology, University of Utah, Emma Eccles Jones, Medical Research Building, 15 North Medical Drive East, Ste 1100, Salt Lake City, Utah 84112-5650, USA