The role of actin and myosin in antigen extraction by B lymphocytes.

B cells must extract antigens attached to the surface of antigen presenting cells to generate high-affinity antibodies. Antigen extraction requires force, and recent studies have implicated actomyosin-dependent pulling forces generated within the B cell as the major driver of antigen extraction. These actomyosin-dependent pulling forces also serve to test the affinity of the B cell antigen receptor for antigen prior to antigen extraction. Such affinity discrimination is central to the process of antibody affinity maturation. Here we review the evidence that actomyosin-dependent pulling forces generated within the B cell promote affinity discrimination and power antigen extraction. Our take on these critical B cell functions is influenced significantly by the recent identification of formin-generated, myosin-rich, concentric actin arcs in the medial portion of the T cell immune synapse, as B cells appear to contain a similar contractile actomyosin structure. Published by Elsevier Ltd.