Mechanisms of T cell peptide epitope-dependent late asthmatic reactions.

Short peptide sequences corresponding to T cell epitopes have been identified in the major cat allergen Fel d 1. In order to directly activate allergen-specific T cells in cat-allergic asthmatic individuals, peptides were administered by intradermal injection. Subsequently, a proportion of subjects experienced a delayed reduction of airway calibre manifested as a decrease in FEV(1). Changes in lung function occurred approximately 3 h after peptide injection, peaked at 6 h and resembled an isolated late asthmatic reaction (LAR). Using molecular tissue typing techniques, it was determined that many of the individuals experiencing isolated LAR expressed particular HLA-DR molecules. These molecules were shown in subsequent experiments to bind individual peptides within the preparation and thus to activate T cells in a major histocompatibility complex (MHC)-restricted fashion. The precise mechanisms whereby MHC-restricted activation of allergen-specific T cells gives rise to bronchoconstriction are currently under investigation.