Human leucocyte interferon: analysis of effect on MLC and effector cell generation.

Mixed lymphocyte cultures (MLC) showed decreased thymidine incorporation when interferon (IF) had been added to the culture medium. The cell-mediated lympholysis (CML) potential generated in mixed lymphocyte cultures grown in the presence of IF was substantially augmented at a certain concentration range. Highly purified leucocyte IF also had this effect, whereas mock preparations did not. The CML-augmenting property was found in the antiviral fraction after separation of semipurified leucocyte IF (by the method of Dahl & Degree). The possibility that the effects were due to a shift in kinetics after culturing in the presence of IF has been excluded. The killer-enhancing properties of IF did not seem to be due to an enhanced expression of histocompatibility antigens, the selective inhibition of CML suppressor cells, or a change in the specificity of recognized target cells. The results of secondary in vitro MLC-CML experiments, in which primary MLC had been carried out in the presence or absence of IF, indicated that the compound acts (in vitro) through preferential selection of cells that are less sensitive to inhibition by IF and more likely to kill.