Eosinophils In Allergy And Asthma

Asthma and allergic disease occur when the immune system improperly responds to harmless environmental substances such as pollen or mold. Common allergic reactions include eczema, hives, hay fever, asthma, food allergies, and reactions to the venom of stinging insects such as wasps and bees.

Immune responses can be classified as Th1 or Th2 based on the type of inflammation and molecules secreted after stimulation. Th1 immune responses traditionally fight intracellular infections such as bacterial and viral infections, whereas Th2 responses are specialized for large parasites such as worms. Asthma and allergic disease result from an improper Th2 immune response.

Although eosinophils, a type of immune cell, have long been considered to mediate allergic and asthmatic Th2 immune responses, they may also play a role in determining the switch between Th1 and Th2 immune responses. Tulic et al therefore examined the development of eosinophils in human children. They observed an age-dependent decrease in the number of eosinophils in the thymus, an organ where early Th1/Th2 differentiation may occur, suggesting an early role of eosinophils in Th2 bias.

Dr. Moqbel's group suggests that "functional thymic IDO+ eosinophils during human infant life may have an immunomodulatory role in Th2 immune responses."