Here the poly-Ig receptor is proteolytically cleaved, its transmembrane and cytoplasmic domains are left attached to the epithelial cell, and the extracellular domain of the receptor, which carries the IgA molecule, is released into the intestinal lumen.
It is an integral membrane glycoprotein with five extracellular domains homologous to Ig domains and is thus a member of the Ig superfamily. This receptor is synthesized by mucosal epithelial cells and expressed on their basal and lateral surfaces. The IgA produced by plasma cells in the lamina propria is in the form of a dimer that is held together by the coordinately produced J chain, which is covalently bound by disulfide bonds to the Fc regions of the a heavy chains of two IgA molecules. The complex is transported across the epithelial cell, and the bound IgA is released into the lumen by proteolytic cleavage.
The molecular mechanisms of class switching are described in Chapter Some of the IgA that is transported across the intestinal epithelium may be produced by plasma cells that differentiated and remained within underlying GALT follicles.Īs we discussed earlier, activated B cells that undergo isotype switching into IgA-producing cells in the GALT and mes-enteric lymph nodes may enter into the systemic circulation and then selectively home back to the intestinal lamina propria, where they may reside as plasma cells.
This T cell-dependent pathway yields high-affinity IgA antibodies that preferentially target pathogens and toxins. IgA class switching in the gut occurs by both T-dependent and T-independent mechanisms. These cells then pass to the mesenteric lymph nodes where the immune response is amplified. We apologize for the inconvenience, and intend to launch our services in EU soon.
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