Conceptual model for the effects of maternal and infant geohelminth infections on asthma in children. The effects of these exposures on asthma are considered to occur via effects on bronchial hyperreactivity. The protective effects of chronic helminth exposures (maternal and infant infections within the first 2 years of life) are presumed to occur via the development of a modified Th2 (mTh2) response that may affect bronchial hyperreactivity through: 1) Immune regulation/suppression-suppression of airways inflammation via enhanced production of geohelminth or aeroallergen-induced IL-10. 2) Homeostasis-enhanced production of spontaneous IL-10 will suppress airways inflammation non-specifically. Alternatively children without early geohelminth exposures and that are first exposed to infection after 2 years of age (> 24 m) may respond to A. lumbricoides infection with strong inflammatory responses in the airways that up-regulate pro-inflammatory pathways including Th1, Th2, and Th17. The modified Th2 response will be defined by the presence of specific IgG4 antibodies to geohelminths. RTIs- respiratory tract infections. ETS-environmental tobacco smoke.