T-cell responses in allergy and asthma.

T-helper-2-type cytokines and some chemokines play an essential role in the pathogenesis of both allergy and asthma. A change in the T-helper 1/T-helper 2 balance, caused by the dramatic change in the microbial environment of children, may account for the increasing prevalence of these conditions, but can also provide a conceptual basis for the development of new therapeutic strategies.