The Initiation of Th2 Immunity Towards Food Allergens

In contrast with Th1 immune responsesagainst pathogenic viruses and bacteria, the incipient events that generate Th2 responsesremain less understood. One difficulty in the identification of universal operating principles stems from the diversity of entities against which cellular and molecular Th2 responsesare produced. Such responsesare launched against harmful macroscopic parasites and noxious substances, such as venoms, but also against largely innocuous allergens. This suggests that the established understanding about sense and recognition applied to Th1 responsesmay not be translatable to Th2 responses. This review will discuss processes and signals known to occur in Th2 responses, particularly in the context of food allergy. We propose that perturbations of homeostasis at barrier sites induced by external or internal subverters, which can activate or lower the threshold activation of the immune system, are the major requirement for allergic sensitization. Innate signals produced in the tissue under these conditions equipdendritic cells with a program that forms an adaptive Th2 response.