Primary sensitization to inhalant allergens.

The neonatal T-cell system is capable of responding to allergens at birth, indicating the occurrence of prenatal sensitization, and the cytokine profile of these responses is skewed towards the Th-2 type. This response is further modified by postnatal exposure to different types of allergens. In relation to inhalant allergen (employed by HDM) the low level fetal Th-2 responses in non-atopics appear to be down-regulated rapidly after birth, parallel to an increase in allergen-specific IFN-gamma production. In contrast, atopics appear to consolidate their initial Th-2 responses, and around the age of 6 exhibit a cytokine response profile similar to the adult pattern. A pre-existing deficiency in IFN-gamma production may be one of the key factors determining the postnatal persistence of Th-2 responses in atopics.