Humoral immunity to dietary antigens in healthy adults. Occurrence, isotype and IgG subclass distribution of serum antibodies to protein antigens.

The occurrence of antibodies to five dietary protein antigens in the sera from 21 healthy adults was investigated by a modified Farr assay. Antibody to ovalbumin (OA) occurred most frequently (90%) whereas only 24% had antibodies to alpha-lactalbumin (ALA). No correlation was noted between the titer of antibodies against bovine serum albumin (BSA) and OA in the single individual. The avidity constants (10(8)-10(9) l/mol) and cross-reactivities against other albumins of anti-BSA antibodies in two human sera were comparable to that of the antibodies in pooled hyperimmune rabbit antiserum. Crossed radioimmunoelectrophoresis showed serum anti-BSA and anti-OA antibodies to be predominantly of the IgG class (13/13, 10/10), occasionally of the IgA- (6/13, 1/10) and rarely of the IgM class (1/13, 0/10). Analysis by radioelectroimmunoassay (rocket immunoelectrophoresis) of the IgG subclass distribution of anti-BSA and anti-OA antibodies showed total absence of IgG3. In contrast, antibodies of the IgG4 subclass were frequently present even in sera with very low levels of total IgG4.