Children with or without cow's milk protein intolerance were investigated for serum antibodies to native cow's milk proteins, processed cow's milk proteins and native- and pepsin-digested β-lactoglobulin. Antibodies of IgG and IgA isotypes were determined with ELISA and those of IgE isotype with RAST.
Children who exhibited slowly appearing untoward reactions to cow's milk feeding had significantly higher titres of IgG antibodies against both native and digested β-lactoglobulin than children with an immediate type of reaction or no intolerance. The IgG antibodies to pepsin-digested β-lactoglobulin were efficiently inhibited by native β-lactoglobulin even at low concentrations, which suggests that there were no antibodies specific for the degraded proteins. The children with slow reactions to cow's milk also tended to have higher antibody levels of the IgG and IgA isotypes to both native and processed cow's milk. Antibodies to this mix of antigens discriminated less well, however, than the antibodies to isolated β-lactoglobulin between the groups of children with slowly appearing reactions, with immediate reactions and the controls. Seven out of nine children with an immediate type of reaction to cow's milk protein had IgE antibodies against cow's milk protein determined with the RAST, while this type of antibodies could not be demonstrated in any child in the two other groups. Using processed or digested protein as antigen did not increase the sensitivity of the antibody determinations.