IgG4 antibodies to foods

IgG4 is one of four subclasses of IgG antibodies and the smallest of them in the blood. IgG4 antibodies to foods are measured in serum – in the test catalogue in “Vorscreen B” together with IgE antibodies and DAO, and as a separate IgG4 food screen. The blood sample is taken in a practice. The IgG food test, by contrast, captures IgG antibodies as a whole without reporting the IgG4 subclass separately; it is explained on its own page.

What IgG4 antibodies do in the body

IgG4 is formed when the immune system encounters a protein repeatedly and over a longer period without any threat. Regulatory messengers such as interleukin-10 then steer the B cells towards producing this subclass. IgG4 has special properties: it can swap its two arms with other IgG4 molecules, therefore usually binds a protein only once, hardly forms large immune complexes and practically does not activate the complement system. It can also intercept food proteins before they bind to IgE on mast cells. IgG4 is therefore regarded as an antibody of tolerance, not of inflammation.

Low IgG4 to foods – what does it mean?

A low or undetectable IgG4 value to a food usually shows that it is eaten rarely or not at all and that the immune system has had little contact with it. Tolerance of a food can also arise via other routes, for example via regulatory T cells, without much IgG4 being formed. A low value says nothing about an IgE-mediated allergy or about intolerances such as to lactose, fructose or histamine.

Raised IgG4 to foods – what happens in the body?

High IgG4 values to a food mainly reflect frequent and plentiful consumption: the immune system has dealt intensively with the protein and built up a tolerance response. A rise in IgG4 has been observed in children growing out of a cow's milk or hen's egg allergy and during allergen immunotherapy. It is being discussed whether a more permeable gut lining encourages more contact and thus higher values. Whether raised IgG4 values to foods cause symptoms is disputed: allergy societies regard them as a sign of contact and tolerance, while individual studies in irritable bowel syndrome observed improvements after leaving out IgG-positive foods. The value is not to be confused with total IgG4 in IgG4-related disease.

The interpretation is given in your report.