B Cell Development in Mucosa-Associated Lymphoid Tissues

Abstract

A defining function of the mucosal immune system is B cell differentiation to immunoglobulin A (IgA)-secreting plasma cells and the transport of polymeric IgA to mucosal surfaces. Mucosa-associated lymphoid tissues (MALTs) efficiently sample external antigens and provide a unique environment for antigen-specific IgA B cell differentiation. T cell–dependent immunoglobulin class switch from IgM to IgA is controlled by B cell interactions with follicular T cells and cytokines, such as transforming growth factor-β1. IgA B cells generated in MALTs express specific homing and chemokine receptors that then regulate their preferential homing back to effector sites within mucosal tissues. Trafficking of IgA-secreting plasma cells to the lamina propria throughout mucosal tissues contributes to a regional mucosal immune system and facilitates IgA transport across the mucosal epithelial barrier. In some mammalian species, gut-associated lymphoid tissues in young animals also provide a specialized environment for antigen- and T cell–independent development of the preimmune B cell repertoire. MALTs in the terminal small intestine of these mammalian species play an important role in primary B cell repertoire development, contributing to the development of both systemic and mucosal immunity.