The specificity and regulation of T-cell responsiveness to allergens.

CD4+ T lymphocytes initiate and regulate both the specific and nonspecific effector mechanisms of allergic immune responses. The definition of immunogenic components within allergens has allowed the specificity of the T-cell repertoire to be examined, and the refinement of their molecular structure is now facilitating the mapping of functional epitopes. Nevertheless, the immunological mechanisms that distinguish between atopic and nonatopic states remain unclear; as knowledge of the complex network of cytokines in the regulation of immune responses unfolds, this problem may be resolved. Population genetics indicates that susceptibility to allergic disease is partly determined by products of the major histocompatibility gene complex. The use of molecular genetic probes and monoclonal T cells demonstrates the functional importance of both the HLA-DRAB1 and -DRAB3 gene products in T-cell recognition of allergen. Collectively, this information has made it possible to develop in vitro models examining the modulation of responsiveness to allergens.