ARE PRIMED CD4(-LYMPHOCYTES DIFFERENT FROM UNPRIMED CELLS() T)

Primed and unprimed lymphocytes are usually classified as separate sub sets of cells, based on phenotypic and functional distinctions. In the case of CD4(+) T lymphocytes, primed cells are thought to proliferate more vigorously, quickly and easily, and to release a different profi le of cytokines, than their naive equivalent. However, most of these d ata were obtained from studies in which populations of lymphocytes wer e compared before and after antigenic stimulation, and therefore did n ot distinguish between the effects resulting from the clonal expansion of specific precursor cells within such populations and those due to cell differentiation per se. We have investigated the contribution of precursor cell frequency to some of the functional changes observed in populations of CD4(+) T cells following antigenic stimulation, using approaches in which antigen-specific precursor frequencies are high in both primary and secondary stimulations: mixed leukocyte reaction res ponses and cells from alpha beta T cell receptor transgenic mice. Our data suggest that when equivalent: numbers of antigen-specific naive a nd previously primed CD4(+) responder T cells are compared, there is n o difference in their potency to proliferate but only the previously a ctivated subset can generate cytokines such as interferon-gamma.