PROGRAMMING FOR RESPONSIVENESS TO ENVIRONMENTAL ANTIGENS THAT TRIGGERALLERGIC RESPIRATORY-DISEASE IN ADULTHOOD IS INITIATED DURING THE PERINATAL-PERIOD

Allergy to airborne environmental antigens (allergens) is a major caus e of asthma in children and adults. This review argues that the develo pment of allergen-specific immunologic memory of the type that predisp oses to allergy development is the end result of a T-cell selection pr ocess operative during infancy, which is triggered via encounters betw een the immature immune system and incoming airborne allergens from th e environment. In normal individuals this process leads to the develop ment of allergen-specific T-memory cells that secure the T helper (Th) -1 pattern of cytokines, which actively suppress the growth of their a llergy-inducing Th-2 cytokine-secreting counterparts. However, these p rotective allergen-reactive Th-1 memory cells fail to develop in some individuals, permitting the subsequent proliferation of allergen-speci fic Th-2 cells that can trigger allergic reactions. Recent evidence su ggests that genetic predisposition to allergy may be due in part to hy peractivity of control mechanisms operative in utero and which normall y protect the fetoplacental unit against the toxic effect of Th-1 cyto kines.