Some studies have suggested that allergens may appear in the circulation after ingestion of allergenic food
sources. The reported levels of allergen in serum, however, are low, and conclusions between studies differ.
Here, we investigated factors that determine the detection of allergens in serum after consumption of peanuts.
Ten healthy volunteers ingested 100 g of light-roasted peanuts. Serumsampleswere taken at regular intervals for
six hours. A double monoclonal sandwich ELISAwas used to analyse the presence and quantity of the major peanut
allergen Ara h 6 in serum.
In 4 out of 10 subjects, no Ara h 6 could be detected. Purified Ara h 6 thatwas digested in vitrowas still reactive in
the ELISA, rejecting the possibility that digestion leads to small peptides that could not be detected. Spiking of purified
Ara h 6 in baseline serum showed that the pre-ingestion serum of these four subjects partially prevented
Ara h 6 to react in the ELISA, with a reduction of reactivity of up to 3 orders of magnitude or more. Pre-ingestion
serum of the other six subjects did not show such an effect. The reduction of reactivity of Ara h 6 coincided with
high titres of IgG and IgG4, and removal of IgG from pre-ingestion serum abolished this effect completely, indicating
that IgG and IgG4 inhibited the reactivity of Ara h6 in the ELISA.
Weconclude that some individuals have IgG and IgG4 against food allergens in their blood, which interfereswith
detection of such food allergens in serum. Because this effect does not occur for each individual, the possibility of
such interference should be taken into considerationwhen interpreting immunochemical studies on the absorption
of food allergens in serum.