Delayed-type hypersensitivity: activation of mast cells by antigen-specific T-cell factors initiates the cascade of cellular interactions.

In delayed-type hypersensitivity reactions sensitized T cells orchestrate a cascade of cellular interactions. Initiation of these responses depends on a newly recognized event, namely the release of vasoactive mediators fiom mast cells that are activated by antigen-specific T-cell-derivedfactors. Here Philip Askenase and Henk Van Loveren discuss how this event initiates a sequence of steps that lead to T-cell recruitment of effector cells; and how this event differs from activation of mast cells by IgE antibody. They also suggest that the conventional time-based separation of immediate and delayed hypersensitivity should be replaced by a classcation based on the type of antigen-specific lymphocyte - B or T-responsible for the effects of hypersensitivity.