Transplacental priming of the human immune system with environmental allergens can occur early in gestation

Background: Allergen-specific T cells play an important role in the allergi c immune response to various environmental allergens. In vitro studies have shown that T-cell responses to these allergens do occur prenatally. Some a llergens (milk proteins) appear to lead more often to fetal T-cell priming than others (house dust mite allergen, ovalbumin, and birch and grass polle n allergens). Objective: We sought to determine the window of opportunity for prenatal T- cell priming with inhalant and nutritive allergens. Methods: The T-cell reactivity of cord blood cells derived through cordocen tesis from unborn (n = 62) and term babies (n = 114) in response to inhalan t allergens (birch pollen major allergen, recombinant Bet v 1, and timothy grass major allergen, recombinant Phl p 1) was investigated. Results: The results demonstrate that allergen-specific T-cell reactivity i s as common in preterm as in term infants (Bet v 1, 8% and 5%, respectively ; Phl p 1, 20% and 25%, respectively). Conclusions: Our data support the hypothesis that differential handling of the allergenic proteins by the feto-placental barrier and possibly by antig en-presenting cells may directly modulate the ensuing T-cell immune respons e.