Role of IgA and IgA Receptors in Immunity
IgA and IgA receptors are closely related to mucosal and systemic immunity. IgA-related diseases are usually accompanied by elevated serum IgA levels and IgA tissue deposition. These diseases include IgA nephropathy, ankylosing spondylitis, HIV infection, alcoholic cirrhosis, and herpetiform dermatitis. On the other hand, IgA receptor deficiencies have a serious impact on immune hemostasis and may cause various adverse reactions such as allergies, intestinal autoimmunity, and vasculitis.
Functions of Common IgA Receptors
IgA can interact with receptors on a variety of cells, including polymeric immunoglobulin receptor (pIgR), Fc receptor-like 4 (FcRL4), asialoglycoprotein receptor (ASGPR) and FcaRI. PIgR can mediate the transport of dimeric IgA to the mucosal cavity, where it is released in the form of SIgA. What's more, B cells display inhibitory IgA receptor FcRL4, which is thought to help modulate mucosal IgA responses. ASGPR is expressed in the liver, which is involved in the clearance of IgA. Finally, it is worth noting that the IgA Fc receptor FcαRI is expressed by bone marrow cells. It has been shown that the interaction between monomeric serum IgA and FcαRI induces inhibitory signals. In contrast, the close combination of IgA immune complex and FcαRI induces an inflammatory response, which provides new possibilities for solving infections. However, studies have shown that excessive IgA immune complexes can activate immune cells, leading to autoimmune diseases. In summary, the number of different IgA receptors, their differential expression on cells, and the effector functions induced by different IgA are involved in maintaining homeostasis.
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