Secretory IgA: the pathway in the body

This page shows the biochemical pathway behind the laboratory value Secretory IgA (sIgA): which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

Secretory IgA is an antibody made of two IgA molecules, a J chain and the secretory component. It lies in the mucus layer of the gut and binds bacteria, viruses and food components there.

The pathway step by step

1. Peyer's patches → B cell with IgA Class switching · TGF-β, APRIL, BAFF Signalling molecules such as TGF-β, APRIL and BAFF direct class switching: the B cell changes the type of its antibody from IgM to IgA. Source 1
2. B cell with IgA → Plasma cell The B cell matures into a plasma cell and migrates into the layer beneath the gut epithelium. There it continuously releases IgA. Source 1
3. Plasma cell → Dimeric IgA · J chain The plasma cell links two IgA molecules via a small protein, the J chain. Only this double form fits the transport receptor of the gut cell. Source 2
4. IgA at the pIgR → Route through the cell The cell ferries the complex in small vesicles from one side to the other. This route through the cell is called transcytosis. Source 2
5. Route through the cell → Secretory IgA Proteases At the gut surface, the receptor is cleaved. A piece of it stays attached to the IgA: the secretory component. It makes the molecule resistant to digestive enzymes. Source 2, 3
6. Secretory IgA → sIgA in the mucus The finished sIgA lies in the mucus layer covering the gut cells. The sugar chains of the secretory component hold it there. Source 3
7. sIgA in the mucus → Binding of microbes sIgA attaches to bacteria, viruses and food components. Clumped together, they stay in the mucus and reach the gut cells less often; this process is called immune exclusion. Source 3
8. Binding of microbes → sIgA in the stool Part of the sIgA leaves the gut with the stool, where it can be measured. Source 3

Cofactors in this pathway

• Vitamin A — Retinoic acid is formed from it and steers the class switch of the B cell to IgA Source 4
• Acetate — Binds the GPR43 receptor of the B cell, a route involved in the class switch to IgA Source 6
• Acetyl-CoA — Formed in the B cell from short-chain fatty acids and supplies building blocks for antibodies Source 7
• Vitamin D — The active form makes maturing B cells express the homing receptor CCR10 Source 5In the ORY catalogue as a laboratory value: Vitamin D

Sources

1. Gutzeit C, Magri G, Cerutti A. Intestinal IgA production and its role in host-microbe interaction. Immunol Rev 2014 · PubMed 24942683
2. Johansen FE, Kaetzel CS. Regulation of the polymeric immunoglobulin receptor and IgA transport: new advances in environmental factors that stimulate pIgR expression and its role in mucosal immunity. Mucosal Immunol 2011 · PubMed 21956244
3. Mantis NJ, Rol N, Corthésy B. Secretory IgA's complex roles in immunity and mucosal homeostasis in the gut. Mucosal Immunol 2011 · PubMed 21975936
4. Mora JR, von Andrian UH. Role of retinoic acid in the imprinting of gut-homing IgA-secreting cells. Semin Immunol 2009 · PubMed 18804386
5. Shirakawa AK, Nagakubo D, Hieshima K et al. 1,25-dihydroxyvitamin D3 induces CCR10 expression in terminally differentiating human B cells. J Immunol 2008 · PubMed 18292499
6. Wu W, Sun M, Chen F et al. Microbiota metabolite short-chain fatty acid acetate promotes intestinal IgA response to microbiota which is mediated by GPR43. Mucosal Immunol 2017 · PubMed 27966553
7. Kim M, Qie Y, Park J et al. Gut Microbial Metabolites Fuel Host Antibody Responses. Cell Host Microbe 2016 · PubMed 27476413

Related pathways

• IgG antibodies to food — plasma cell

As of 2026-09-16. Draft, written by Claude to schema v2; sources checked in PubMed; expert approval pending
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