IgA is a secreted antibody at the mucosal membrane such as the gastrointestinal and respiratory tracts and protects from the initial invasion of microbes. However, how this antibody is involved in immunity has been poorly elucidated. Recently a novel Fc receptor for IgA designated as Fcα/μ receptor (Fcα/μR) has been identified and regarded as an important role in the primary stage of immune defense against microbes as well as related to some autoimmune diseases. As a world-leading company in the field of protein engineering, Creative Biolabs has a lot of interest in the research of IgA-Fcα/μR interaction. Based on skilled groups and established platforms in protein expression and analysis, we have gained some achievement in the non-IgG receptors and interactions research, while we are glad to share the experience with our partners all over the world.
Introduction of IgA-Fcα/μR Interaction
As the most primary defense, IgA protects from the initial invasion of microbes which is produced over 2g daily per adult and exists in sera and the mucosal membrane and binds to microbes and toxins present in the lumen and neutralizes them by blocking their entry into the host. A novel Fc receptor for IgA named Fcα/μR may explain the immune response mechanism of IgA. Fcα/μR is a type I transmembrane protein whose extracellular domain has four potential sites for N-linked glycosylation, suggesting that the receptor is a glycoprotein. A pair of cysteine residues in the extracellular domain was flanked by the consensus sequence for Ig-like domains, indicating that Fcα/μR is a member of the Ig supergene family. However, no significant homology of Fcα/μR to other proteins or nucleotide sequences has been detected, which suggests that the Fcα/μR is a single gene-family member.
Fig.1 Molecular characteristics of the Fcα/μR (left) and the location of Fcα/μR gene. (Shibuya, 2006)
Function of IgA-Fcα/μR Interaction
Although it is closely related to poly-Ig receptors, the expression pattern of Fcα/μR is quite different from that of poly-Ig receptors. Mature B lymphocytes expressed significant amounts of the Fcα/μR while immature B lymphocytes did not, suggesting that the Fcα/μR might be involved in B cell development. Moreover, immunohistochemical studies demonstrated that the Fcα/μR is expressed in germinal centers in lymphoid tissues, strongly suggesting that Fcα/μR may play an important role in humoral immune responses.
Fig.2 Structure and function of Fc receptors on hematopoietic cells. (Honda, 2005)
Diseases and IgA-Fcα/μR Interaction
IgA nephropathy is the most common form of glomerulonephritis and is characterized by the deposition of IgA immune complexes in the glomerular mesangium. IgA-Fcα/μR is expressed in a variety of tissues including thymus, spleen, liver, kidney, small and large intestines, and placenta, RT-PCR and Northern blot analyses demonstrated that the Fcα/μR transcripts are abundantly expressed in kidney, small intestine, and lymph node, which suggests a possibility that the Fcα/μR is involved in IgA nephropathy.
Although the mechanism of involvement of the Fcα/μR in the immune response is not clear, it is no doubt that IgA-Fcα/μR interaction shows more importance in nonspecific immunity processes. Creative Biolabs will continue to maintain attention in the field of Fcα/μR research. If you are interested in IgA-Fcα/μR interaction or other fields in protein engineering, please feel free to contact us.
References
- Shibuya, A.; et al. Molecular and functional characteristics of the Fcα/μR, a novel Fc receptor for IgM and IgA. Springer seminars in immunopathology. 2006, 28(4), 377-382.
- Honda, S.; et al. Fcα/μR, a novel Fc receptor for innate antibodies IgM and IgA. International Congress Series. 2005, 1285, 78-83.
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