[Interleukin 2 inhibitor activity in blood serum]

Abstract

Normal murine, horse and human sera inhibit the proliferation of thymocytes, T blast cells and cloned cytotoxic T lymphocytes in vitro dose dependently. This effect is specific to IL 2-dependent cell proliferations. The inhibitory activity does not decrease the binding of IL 2 to its receptor, but inhibits the IL 2 receptor expression dose dependently. An excess of purified IL 2 can overcome the inhibition of IL 2-dependent cell proliferation. Using gel filtration, we have found the inhibitory activity in the region of 80,000 MW. This inhibitory activity is precipitated by 50% saturated ammonium sulfate. The species-specificity of this inhibitor in serum is very low. The IL 2-inhibitor is discussed as a part of natural immunoregulation and as a hint for activation of the immune system.