Figure 1626

Diagram of immunoglobulin A (IgA) secretion and transport. Immunoglobulin A (IgA) is secreted by plasma cells into the lamina propria. Here, it dimerizes and then binds to a transmembrane Fc receptor on the membrane of the enterocyte. The extracellular portion of the membrane receptor will remain with the IgA dimer and will later become the secretory component of the IgA. The IgA-receptor complex enters the cell by endocytosis and is carried to the apical surface within the endocytotic vesicles (a process called transcytosis). The vesicle fuses with the apical plasma membrane, releasing the IgA-receptor complex as secretory IgA (slgA). The IgA monomers and dimers, the Fc receptors, and the endocytotic vesicles are greatly exaggerated in size for clarity. The actual sizes of the vesicles involved approximate those shown in the adjacent enterocytes.

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