Proliferation of circulating T-cells.

Together with B-lymphocytes, T-lymphocytes (or T-cells) comprise the antigen (Ag)-specific arm of the immune response. The Ag receptors of both cell types are generated by recombination of multiple gene segments (1), giving rise to a large repertoire of receptors of differing specificity. When a lymphocyte encounters Ag, cellular activation occurs via aggregation of cell surface Ag receptors (2). The consequences of activation are numerous, but, in the case of the T-cell, include clonal expansion, via proliferation, and also secretion of soluble mediators and growth factors, such as interleukin-2 (for a review of the role of the T-lymphocyte in allergic disease, see ref. 3).