Unfractionated human thymocytes have a lower proliferative capacity than CD3-4-8- ones but have a similar capacity for expression of interleukin 2 receptors and production of interleukin 2.

CD3-4-8- and unfractionated thymocytes were compared for their capacity to proliferate, to express interleukin 2 (IL-2) receptor, and to secret IL-2. Phorbol ester and Ca2+ ionophore were used as mitogens. CD3-4-8- thymocytes responded vigorously when stimulated with phorbol ester in the presence of IL-2 or in combination with Ca2+ ionophore. In contrast, unfractionated thymocytes responded weakly when stimulated with either of these mitogens. Surprisingly, however, the stimulation of these populations with either phorbol ester plus IL-2 or phorbol ester plus ionophore induced a high and similar level of IL-2 receptor expression in both thymocyte populations. A similar level of IL-2 secretion in both populations was also obtained when they were stimulated with a combination of phorbol ester plus ionophore. These results suggest that during the maturation process, the majority of thymocytes lose their capacity to be activated by some mitogens, although they maintain their capacity to secrete IL-2 and to express the IL-2 receptor.