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We studied the effect of the different types of interferons on the production of cytotoxin by human peripheral blood mononuclear cells (PBMCs) stimulated with the mitogen phytohemagglutinin (PHA). Maximum secreted levels of cytotoxin were observed at day 3 in culture and consisted of both tumor necrosis factor alpha (TNF-alpha) and lymphotoxin as determined by specific antibodies. Type I interferons (IFN-alpha and IFN-beta) consistently suppressed cytotoxin production. Both TNF-alpha and lymphotoxin were significantly suppressed. Mean suppression by IFN-alpha and IFN-beta (1000 U/ml) was 56 and 66%, respectively, in PBMCs from 18 different donors. The suppressive effects of IFN-alpha and IFN-beta on cytotoxin production were dose responsive over a range of 10 to 1000 U/ml. Type II interferon (IFN-gamma) did not have consistent significant effects. Pretreatment with IFN-alpha or IFN-beta for 24 or 48 h prior to PHA stimulation also resulted in significant suppression. Supplementation with interleukin-2 (10 U/ml) or IFN-gamma (1000 U/ml) did not overcome cytotoxin suppression by IFN-alpha or IFN-beta. Cytotoxin suppression by IFN-alpha and IFN-beta together appeared to be noninteractive. Suppression appeared not to be due to blockade of the cytotoxin release, since both cell-associated cytotoxin and secreted cytotoxin were suppressed to the same level. These results demonstrated that cytotoxin and lymphotoxin production by PHA-stimulated PBMCs could be down-regulated by type I interferons and that there is a substantial difference between the action of type I interferons and type II interferons (IFN-gamma) in modulating the biosynthesis of cytotoxins.

A mathematical model based on the median effect principle was used to demonstrate its usefulness in studying cytokine interactions. The inhibition of cytopathological effects due to encephalomyocarditis virus (EMCV) by interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF) in WISH cells using a microtiter assay was employed. The model was used to analyze the characteristics of the dose-effect relationships of IFN-gamma, TNF, and their combination. The method also was used to define synergism as opposed to additive interaction. This application of the median-effect model proved to be easy and accurate and could be useful in the study of interactions in cytokine research.