Explain how the poly-Ig receptor transports dimeric IgA antibodies across cellular barriers, and specify the type of cell barrier involved
What will be an ideal response?
Dimeric IgA is made in mucosa-associated lymphoid tissue (MALT) and is transported across the barrier of the mucosal epithelium. First, dimeric IgA binds to the poly-Ig receptor on the basolateral surface of an epithelial cell, followed by uptake through receptor-mediated endocytosis into an endocytic vesicle. On reaching the opposite face of the cell, the apical surface, the vesicle fuses with the membrane. Here the poly-Ig receptor is cleaved proteolytically between the membrane-anchoring and the IgA-binding regions, thus releasing IgA into the mucous layer on the surface of the epithelium. Dimeric IgA remains attached to a small piece of the poly-Ig receptor, called the secretory component, which holds the IgA at the epithelial surface through interactions with molecules in the mucus. The rest of the poly-Ig receptor is degraded and serves no further purpose.
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