EFFECT OF MACROPHAGES ON THE G0-G1 AND G1-S TRANSITION OF THYMOCYTES

Mouse thymocytes freed of adherent cells and stimulated by mitogens yield only a poor proliferative response ([3H]-thymidine uptake). The activation process assessed fluorocytometrically (RNA synthesis) is not reduced to the same extent. Addition of adherent cells causes full restoration of both activation and proliferation; 2-mercaptoethanol (2-ME) restores activation completely, but proliferation only partially. Cell viability is not influenced by the absence or presence of adherent cells or of 2-ME during the first 24 h of incubation, which is the time period used to assess cell activation. Macrophages can be replaced completely by the addition of 2-ME and interleukin 1 (IL-1) or IL-2 containing supernatants. The addition of these substances even appears to be superior, suggesting that macrophages can suppress and enhance the thymocyte response to mitogens. Thus, the current concept of the multifunctional role of macrophages is further supported. Depending on the selected mitogen, it appears that only the IL-1 production is an absolute, but indirect requirement for mitogen-stimulated thymocytes in order to proceed through the cell cycle.