Differential response of human thymus cells to CD2 antibodies: fragmentation of DNA of CD45RO+ and proliferation of CD45RO- subsets.

Human thymocytes bearing the CD45RO 'memory' cell phenotype do not proliferate in concanavalin A (Con A)-stimulated cultures and may be destined for intrathymic death. To determine whether this subset would exhibit characteristics of programmed cell death (apoptosis), we examined the integrity of the nuclear DNA by gel electrophoresis. DNA fragmentation was restricted to the CD45RO+ subset of human thymocytes following exposure to stimulating concentrations of anti-CD2 antibodies. Both CD45RO- and CD45RO+ subsets mobilized cytoplasmic Ca2+ following cell-surface CD2 ligation, but entry into the cell cycle and vigorous thymidine uptake were restricted to the CD45RO- subset. Our results provide a mechanism which may account for the failure of thymic CD45RO+ cells to respond to stimuli which elicit proliferation by the reciprocal CD45RA+ subset.