Conceptual model of effects of maternal and infant geohelminth infections on allergen skin test reactivity. The effects of both exposures are presumed to occur via the development of a modified Th2 (mTh2) response during chronic geohelminth infection. A modified Th2 response may affect allergen skin test reactivity through 2 distinct mechanisms: 1) a direct effect on mast cell function independent of aeroallergen-specific IgE resulting in an increased threshold for activation through enhanced production of spontaneous or geohelminth-induced IL-10. Such effects would be predicted to effect wheal sizes non-specifically including the histamine positive control. 2) An indirect effect on mast cell function by attenuation of the association between specific IgE and skin test reactivity. This effect would be predicted to be aeroallergen-specific, affect only those wheals for which an individual has significant levels of specific IgE (at > 0.35 kU/L) but not the positive control, and be mediated by aeroallergen-induced IL-10. The effect could also be mediated by geohelminth-induced IL-10 for aeroallergens where the IL-10-stimulating allergens share significant immunological cross-reactivity with helminth allergens.