IgG antibodies to food: the pathway in the body

This page shows the biochemical pathway behind the laboratory value IgG antibodies to food: 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

IgG antibodies are immune proteins that B cells form after contact with an antigen. They arise continually against food proteins, often as the IgG4 subclass, and remain in the blood for a long time.

The pathway step by step

1. Dietary protein → Fragments in the gut Digestive enzymes Digestive enzymes break the proteins down. Some fragments remain large enough to be recognised as antigens and pass through the gut wall in small amounts; this happens all the time. Source 3
2. Fragments in the gut → Antigen presentation Dendritic cells in the gut lining pick up fragments and display them on their surface to T helper cells. This happens mainly in the lymph nodes of the gut. Source 3
3. Antigen presentation → B cell · T helper cells A B cell uses its surface antibody to bind exactly the antigen that matches it. Together with signals from T helper cells, this activates the cell. Source 2, 3
4. B cell → Class switching AID · Cytokines The B cell swaps the blueprint for the rear part of the antibody: IgM becomes IgG. Which of the four IgG subclasses forms depends on the messengers from T cells. Source 2
5. Class switching → Plasma cell The mature B cell continuously releases antibodies into the blood. With repeated contact with the same protein, antibodies of the IgG4 subclass often form. Source 1, 4
6. IgG in the blood → Binding to the antigen The arms bind exactly the structure for which the B cell was selected. IgG4 can swap its halves with other IgG4 molecules and then carries two different binding sites. Source 1, 4
7. Binding to the antigen → Immune complex Several antibodies and antigens cluster together into a complex. IgG4 hardly forms such complexes and does not activate the complement system. Source 1, 4
8. Immune complex → Clearance by phagocytes · Fcγ receptors Phagocytes carry Fcγ receptors on their surface. They engulf the complexes and break them down in their digestive vesicles. Source 6
9. IgG in the blood → IgG inside the cell Cells of the vessel wall continuously engulf IgG in vesicles. In their acidic interior the receptor FcRn binds the Fc part and saves the molecule from being broken down. Source 5
10. IgG inside the cell → IgG back in the blood FcRn FcRn releases the IgG back to the outside. This is why IgG stays in the blood longer than the other antibody classes. Source 5

Cofactors in this pathway

• Vitamin A (retinoic acid) — Intestinal dendritic cells form retinoic acid from it, a signal to the T cells to which they present antigens Source 3, 11
• Zinc — Needed for signalling and proliferation of T and B cells; component of many zinc finger proteins Source 7In the ORY catalogue as a laboratory value: Zink
• Vitamin D — Calcitriol acts on dendritic cells, T cells and B cells via the vitamin D receptor Source 8In the ORY catalogue as a laboratory value: Vitamin D
• Selenium — Component of selenoproteins such as the glutathione peroxidases in immune cells Source 9In the ORY catalogue as a laboratory value: Selen
• Iron — Needed for the division of activated lymphocytes, from which plasma cells arise Source 10In the ORY catalogue as a laboratory value: Eisen

Sources

1. Vidarsson G, Dekkers G, Rispens T. IgG subclasses and allotypes: from structure to effector functions. Front Immunol 2014 · PubMed 25368619
2. Stavnezer J, Schrader CE. IgH chain class switch recombination: mechanism and regulation. J Immunol 2014 · PubMed 25411432
3. Pabst O, Mowat AM. Oral tolerance to food protein. Mucosal Immunol 2012 · PubMed 22318493
4. Aalberse RC, Stapel SO, Schuurman J et al. Immunoglobulin G4: an odd antibody. Clin Exp Allergy 2009 · PubMed 19222496
5. Pyzik M, Sand KMK, Hubbard JJ et al. The Neonatal Fc Receptor (FcRn): A Misnomer? Front Immunol 2019 · PubMed 31354709
6. Nimmerjahn F, Ravetch JV. Fcgamma receptors as regulators of immune responses. Nat Rev Immunol 2008 · PubMed 18064051
7. Wessels I, Maywald M, Rink L. Zinc as a Gatekeeper of Immune Function. Nutrients 2017 · PubMed 29186856
8. Aranow C. Vitamin D and the immune system. J Investig Med 2011 · PubMed 21527855
9. Avery JC, Hoffmann PR. Selenium, Selenoproteins, and Immunity. Nutrients 2018 · PubMed 30200430
10. Nairz M, Weiss G. Iron in infection and immunity. Mol Aspects Med 2020 · PubMed 32461004
11. Sirisinha S. The pleiotropic role of vitamin A in regulating mucosal immunity. Asian Pac J Allergy Immunol 2015 · PubMed 26141028

Related pathways

• Branched-chain amino acids — dietary protein
• Borrelia — antigen presentation
• Pancreatic elastase — dietary protein
• Secretory IgA — plasma cell
• Threonine — dietary protein

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
Legal notice Privacy policy All biomarkers