Sensitization Does Not Develop In Utero

Abstract

Bønnelykke K, Pipper CB, Bisgaard H. J Allergy Clin Immunol. 2008;121(3):646–651 PURPOSE OF THE STUDY. To investigate the relationship of allergen-specific immunoglobulin E (IgE) in cord blood to sensitization in early infancy and the origin of such IgE. STUDY POPULATION. There were 243 children followed from birth. The patients were part of the Copenhagen Prospective Study on Asthma in Childhood (COPSAC) and, thus, were considered to be at risk for atopy because of a maternal history of asthma. METHODS. Cord blood IgE was determined at the time of birth and again at 6 months of age. Total IgE, specific IgE to milk and egg, and a cumulative level of specific IgE to a panel of common aeroallergens were analyzed and compared with maternal IgE. Cord blood IgA was also assessed as a marker of maternal contamination of fetal blood, because IgA is not thought to cross the placental barrier during pregnancy. RESULTS. Specific IgE against mixed allergens was detected in 34 (14%) of the cord blood samples, and specific IgE against single allergens was detected in 22 samples. IgA was detected in 98% of the samples. None of the specific IgE found in cord blood was detected at 6 months of age. Cord blood IgE was not detected in any infants whose mothers were not sensitized, and the infants who did have cord blood IgE detected displayed a “fingerprint match” to maternal IgE. In every case, the IgE for a specific allergen detected in cord blood was the same as that detected in maternal blood, and it was present in a relatively similar concentration to that found in maternal blood. The cord blood IgA level also showed a linear relationship to the IgE level, suggesting that more maternal contamination resulted in higher IgE levels in cord blood. CONCLUSIONS. IgE in cord blood does not reflect in utero sensitization but seems to reflect maternofetal transfer of IgE. REVIEWER COMMENTS. The questions rarely change, but our answers often do. In recent years, the American Academy of Pediatrics recommended that some parents avoid certain foods during pregnancy to reduce the chance of their child developing atopic disease. These recommendations were based on studies that showed that the human fetus is capable of producing IgE as early as the 20th week of gestation and that cord blood IgE seemed to be a predictor of future atopy. Now the evidence seems to suggest that although sensitization could theoretically occur in utero, it simply does not. This study provides convincing evidence that the IgE in cord blood does not come from the infant but, rather, from the mixing of maternofetal blood, probably at the time of delivery. This study, along with other evidence that has come to light recently, raises questions about whether maternal dietary restriction of allergens during pregnancy impacts allergy outcomes to the avoided food/foods.