A TH2-like cytokine profile maintains the pregnant state. In fact, atopic compared to nonatopic mothers are more likely to have several children. The newborn destined to become atopic has low levels of interferon gamma and this continues to occur over the first two years of life. The cause of this defect remains to be discovered. In addition, the foetus is capable of mounting allergen–specific responses from 23 weeks of gestation. Why we all do not become atopic is probably due to deletion of allergen–reactive T-cells from the host by anergy or apoptosis as a consequence of high-dose antigen exposure in the gut and the development of oral tolerance. 

For antigens/allergens to trigger an immunological event they are required to be presented to T lymphocytes [Image: wayhomestudio/Freepik].

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