Immunoglobulin A (IgA) is the most abundant antibody isotype in the mucosal immune system. Structurally, IgA in the mucosal surface is a polymeric structure, while serum IgA is monomeric. Most IgAs were generated by the gut and have effects in situ. Besides the function of immune exclusion as a nonspecific immune role, recent studies found it also played an important role in specific immunity and immunoregulation. IgA functions mainly through interaction with multiple receptors. Besides common IgA receptors such as Fc receptor I (FcαRI), transferrin receptor 1 (CD71), asialoglycoprotein receptor (ASGPR), Fcα/μR, FcRL4, and DC-SIGN, whose mechanism and functions are clearly revealed, there are many novel functional IgA receptors have been discovered. As a world-leading company in the field of therapeutic antibody studies, Creative Biolabs pays constant attention to the development of IgA receptors and explores their application potential. Based on our passionate groups and mature platforms, we have gained remarkable achievements and are glad to share our experience with our clients.
Fig.1 IgA isotypes (a) and secretory IgA (SIgA) consist of two IgA molecules (b). (Van Egmond, 2001)
Secretory Component Receptor on Eosinophils
Eosinophils are key mucosal effectors playing roles in protective and pathological reactions in the gut and lung, where most IgA receptors are expressed on. However, there is a receptor specific for secretory IgA and can activate eosinophils. SIgA aggregated by surface immobilization induces respiratory burst and degranulation of eosinophils resulting in target killing, the release of pro-inflammatory cytokines and mediators, and the subsequent apoptosis of the effector cell, which are considered to be related to pathology asthma and allergic rhinitis.
Fcα1/δR Receptor on T Cells
Human T cells have FcδR as IgD receptors, which are up-regulated on mitogen activation and rosette IgD-coated erythrocytes. However, human IgA1 was as effective as soluble IgD at inhibiting T cell rosetting of IgD-coated erythrocytes via IgA receptors, Fcα1/δR. Due to the hinge flexibility of IgD, Fcα1/δR binding to erythrocyte bound IgD but not IgA1. However, the interaction with IgA1 in solution nonetheless makes IgA1 a potential modulator of T-cell activation via this receptor. Fcα1/δR activity may play a role in IgA nephropathy where abnormal glycosylation of the IgA1 hinge occurs.
Other Novel IgA Receptors
Recent studies suggested that a novel IgA receptor was expressed on 75% of isolated human natural killer cells. While interaction analysis suggests that this receptor is not a lectin, the clear mechanism and function are still absent. Moreover, there are some unique IgA receptors expressed in the mouse B cells or T cells.
IgA and IgA receptors occupy key roles in mucosal and systemic immunity, although some IgA receptors are well characterized nonetheless fundamental new functions are still being elucidated. If you are interested in novel IgA receptor research or other fields in therapeutic antibodies, please feel free to contact us.
Reference
- Van Egmond, M.; et al. IgA and the IgA Fc receptor. Trends in immunology. 2001, 22(4), 205-211.
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