Exposure to Allergens during Development

The development of allergic sensitization can occur as early as fetal life. In fact, the fetal immune system is set up to produce a T helper type 2 cytokine response to foreign antigens, as the alternative T helper type 1 cytokines would facilitate rejection of the fetus by the mother, whose major histocompatibility antigens differ from those of the fetus. Herein we describe human and animal studies that demonstrate how exposure to allergens during fetal and neonatal life can instruct the developing immune system to produce IgE antibodies that will subsequently elicit type 1 hypersensitivity responses to inhaled allergens. The roles of environmental pollutants and the genetics of the individual are closely involved in shaping development of allergic reactivity in the lung.