Absorption of food protein antigen in infants with food protein-induced enterocolitis.

Increased gastrointestinal absorption of intact antigen with systemic immunization has been considered a major etiologic factor in the development of food sensitivity. We attempted to test this hypothesis in infants with suspected food protein-induced entercolitis by measuring serum ovalbumin (OVA) concentrations after ingestion of egg white (prior to the performance of good challenges to establish this diagnosis). We first noted significant underestimation of serum OVA concentrations in the presence of even low serum anti-OVA antibody concentrations (greater than 1:12). Next, using selected noninhibitory sera, we found that all infants studied absorbed some OVA, there was no correlation between serum OVA levels and age (3-11 months), and there was no significant difference between serum OVA concentrations in infants who subsequently had positive oral food challenge responses (120 +/- 67 ng/ml) and a matched group with negative challenges (102 +/- 80). These data do not support the hypothesis that "intestinal closure" (antigen exclusion) occurs in the neonatal period or the role of antigen absorption as the major etiological factor in the development of food sensitivity. Better methods of quantitating macromolecular absorption must be developed before the role of antigen absorption in food sensitivity can be assessed. Of note, urinary excretion of intact OVA also occurred. This varied greatly from one voiding to the next and continuing for at least 13 hr after ingestion.

Milk- and soy protein-induced enterocolitis: evidence for lymphocyte sensitization to specific food proteins.

Stimulation ( [3H]thymidine incorporation) of blood lymphocytes cultured with food proteins was evaluated in infants with food protein-induced enterocolitis and correlated with the results of oral diagnostic challenges with the same foods (soy, cow's milk, and egg white). The geometric mean stimulation index for lymphocytes from patients with positive oral soy protein challenge that were cultured with soy protein was 8.5, and for patients with positive cow's milk challenge the stimulation index was 6.0 when casein was used in the cultures. Both values are significantly different from the values obtained from patients with negative oral challenges (p less than 0.01). The enhanced lymphocyte responses were specific for the food proteins responsible for clinical symptoms. It is not clear whether these lymphocyte responses are due to systemic immunization secondary to macromolecular absorption, or to an abnormality in immune regulation such as a delay in the development of oral tolerance mechanisms. They suggest, however, that circulating lymphocytes sensitive to the food antigens that produce the clinical symptoms are frequent in infants with this discrete form of food protein hypersensitivity.

Food protein-induced enterocolitis: altered antibody response to ingested antigen.

To evaluate the role of immunologic mechanisms in one specific syndrome of food intolerance in infants, food protein-induced enterocolitis, we measured class-specific serum antibodies to three food proteins, ovalbumin, soy, and cow milk, prior to diagnostic food challenges in 18 infants suspected to have this syndrome. Infants with positive challenge reactions to egg, soy, or cow milk had 5-10 times higher levels of IgA antibody directed against that food than did the infants with negative challenges. Levels of IgG antibody to soy and egg were also significantly higher (greater than 10-fold) in infants with positive challenge responses. There was no significant difference in levels of IgM food antibodies between the two groups. IgA anti-soy antibody levels rose in all 12 infants tested 2-10 weeks after a single soy feeding (challenge). However, IgM anti-soy antibody increased in the five infants who had a negative response to the challenge feeding and decreased in those seven with a positive response. The difference between the two groups was statistically significant (P less than 0.01). Some correlation existed (r = -0.68) between the increase in IgA anti-soy antibody and the decrease in IgM anti-soy antibody for infants with positive soy challenges. Although a pathogenic role for these antibodies is not proven, the findings suggest an altered immunologic response to ingestion of food antigens in infants with food protein-induced enterocolitis.