Interleukins and immunosuppressive factors: a regulatory system?

On exogenous stimulus immunocompetent leucocytes produce antigen-specific factors, which essentially determine the magnitude and duration of T-lymphocyte dependent immunoreactions. Interleukin 1 (IL-1, monokin) and interleukin 2 (IL-2, lymphokine) form a bimodal amplification system which may operate in vivo at the level of peripheral lymphoid organs, which interleukin 3 (IL 3, lymphokine) may function as a positive feed-back signal at the level of multipotential stem cells. The physiological IL-2 has wider importance, since the permanent expression of Il-2 gene due to the insertion of the viral promoter sequence (HTLV in human) led to uncontrolled proliferation of T-cells and to the development of lymphomas and leukemias of mature T-cell phenotype. On the afferent arc of immunoreactions endogenous factors mediate T-cell proliferation inhibitory effect probably via interaction with the interleukin system. Some practical aspects of these two antagonistic group of factors are presented and discussed.