Passage of undegraded dietary antigen into the blood of healthy adults. Further characterization of the kinetics of uptake and the size distribution of the antigen.

The molecular weight distribution of ovalbumin (OA) absorbed into the blood in eight healthy adults after a test meal was analysed by high pressure liquid gel permeation chromatography (HPLC) followed by ELISA for OA. OA was found either as free OA or as aggregates of a size mainly below 700 kD. The addition of OA in vitro to an antibody-containing serum resulted in OA-containing immune complexes (OA-IC) of similar size. The size distribution of serum OA-IC was more heterogeneous late than early in the 7-h observation period. Free OA disappeared at an equal or higher rate than OA-IC when both entities were present in the same individual. The presence of OA-IC was related to the serum IgG antibody levels. IgG, but not IgA or IgM, could be detected in OA-IC (in three individuals) by ELISA. The kinetics of OA appearance was followed for 48 h after a test meal in three individuals. In one person, serum OA reached peak values at 24 h and detectable amounts persisted for 48 h after the test meal. In the other test persons the OA levels peaked earlier. The present study indicates that in healthy adults dietary antigens are absorbed and circulate regularly in minute amounts apparently as native protein and/or as small immune complexes, mostly containing IgG antibodies.