Cytochalasans and PMA induce IL-2 receptors on CD8+ lymphocytes.

The cytochalasans, fungal metabolites that interact with actin, can affect lymphocyte proliferation; high concentrations inhibit lectin-induced proliferation and low concentrations augment it. The phorbol ester tumor promoter, PMA, alone is not mitogenic for primary lymphocytes but enhances the activity of mitogenic lectins. Because the cytochalasans have been reported to increase intracellular Ca2+ and because PMA activates protein kinase C, lymphocytes were treated with PMA and cytochalasin B (CyB) to determine if this combination would induce DNA synthesis. While this treatment by itself did not cause proliferation, lymphocytes cultured with PMA and CyB overnight, washed, and recultured with IL-2 proliferated to the same degree as lymphocytes stimulated with Con A. Three different cytochalasans, cytochalasin B, cytochalasin D, and chaetoglobosin C, all of which bind to cellular actin with different affinities and only one of which affects glucose transport, induced IL-2 receptors in combination with PMA. Flow cytometric analysis with an antibody to the IL-2 receptor alpha subunit confirmed the induction of receptors on CD8+ cells. However, no IL-2 was produced after the exposure of lymphocytes to the combination of cytochalasans and PMA. Therefore, there was sufficient signal to induce IL-2 receptor expression but not to induce IL-2.

Prolactin-induced mitogenesis of lymphocytes from ovariectomized rats.

PRL can induce interleukin-2 (IL-2) receptor expression in splenocytes from ovariectomized (OVX) female rats. In this further study of the effects of PRL on lymphocytes in vitro we found that PRL induced IL-2 receptor expression, IL-2 production, and proliferation of splenocytes and thymocytes from OVX rats. Cells from male rats were not affected. The proliferative response, as measured by [3H]thymidine incorporation, depended on the concentration of PRL and the presence of adherent cells in the culture. After a 48-h incubation with PRL (1 microgram/ml), splenocytes from OVX rats incorporated essentially the same amount of [3H]thymidine as cells incubated with the polyclonal T-cell mitogen Concanavalin-A (ConA). As determined by autoradiography, approximately 40% of the splenocytes responded to PRL or to ConA. After incubation of splenocytes and thymocytes with PRL, bioactive IL-2 was detected in culture medium only from cells of OVX female rats, while incubation with ConA caused IL-2 production by lymphocytes from both male and OVX rats. However, ConA induced IL-2 activity sooner than PRL. Immunofluorescent-flow cytometric analysis revealed time-dependent increases in percentages of IL-2 receptor-positive splenocytes as well as increases in percentages of total T-cells and cells of the CD8 and, to a lesser extent, the CD4 subclass after PRL stimulation.