Mitogenic effects of partially purified interleukin 2 on thymocyte subpopulations and spleen t cells of the mouse.

Partially purified interleukin 2 (IL-2) promotes proliferation of mouse spleen T, but not B cells, and of peanut-agglutinin-negative (PNA-), and cortisone-resistant "mature" thymocytes, but not of PNA+ "immature" thymocytes. Within the cortisone-resistant thymocyte population, IL-2-responsive cells were found in the blast cell fraction. Proliferation was measured by [3H] thymidine incorporation and subsequent increase in viable cells. The mitogenic effect of IL-2 could not be inhibited by 50 mM methyl-alpha-D-mannoside which excludes contaminating concanavalin A (Con A) as a cause of mitogenicity. The relative increase in viable cells in IL-2 vs. control cultures was abrogated by 1.5 mM hydroxyurea. A possible effect of IL-2 on cell survival is thus ruled out. IL-2, when acting as comitogen with Con A, affected only PNA- and cortisone-resistant thymocytes. These cells also showed high intrinsic IL-2 release when stimulated with Con A such that a comitogenic effect of externally added IL-2 was only seen at low cell concentrations. PNA+ thymocytes could neither be induced to release IL-2 nor did these cells become Con A-responsive under the influence of IL-2, thereby excluding an IL-2-mediated maturation.