DISTINCT ACTIVITIES OF INTERFERON-GAMMA, LYMPHOKINE AND CYTOKINE DIFFERENTIATION-INDUCING FACTORS ACTING ON THE HUMAN MONOBLASTIC LEUKEMIA-CELL LINE U937

Abstract

The human monoblast leukemia line U937 is growth inhibited and induced to express various characteristics of mature monocytes by lymphokines (LK) and other cytokines. Previous experiments have shown that interferon-.gamma. (IFN-.gamma.) is responsible for some but not all of the differentiation-inducing effects on U937. To determine the variety and specificity of activity, the following factors were studied: phytohemagglutinin-induced LK that contained IFN-.gamma. (100 units/ml); purified IFN-.gamma.; human colony-stimulating factor 1 (CSF-1); and conditioned medium (a) (CM) from the human bladder carcinoma cell line 5637 and the hepatoma cell line SK-HEP. LK preparations contained no colony-stimulating activity, whereas CM from 5637 and SK-HEP both contained granulocyte-macrophage CSF (3000-4000 units/ml) but no IFN activity. IFN-.gamma. is the major Ig Fc receptor-inducing species within lymphokine, since anti-interferon-.gamma. antibody inhibited most of this activity. Other sources of Fc receptor-inducing activity were CM from SK-HEP and 5637 cell lines. Human CSF-1 when tested up to 800 units/ml was inactive for Fc receptor induction. LK induced the chemotactic peptide receptor, but this induction was due to factors other than IFN-.gamma. as anti-IFN-.gamma. antibody did not inhibit the induction and purified IFN-.gamma. at a dose equivalent to that found in LK (100 units/ml) had no activity in the assay. SK-HEP and 5637 CM had strong chemotactic peptide receptor-inducing activity, but human CSF-1 was inactive up to 800 units/ml. Peroxide production after stimulation with phorbol myristic acid could be induced by LK, LK with anti-IFN-.gamma. antibody, 5637 and SK-HEP treatment. IFN-.gamma. (100 units/ml) and CSF-1 (800 units/ml) were ineffective. Peroxide production was induced by IFN-.gamma. at concentrations > 1000 units/ml. The inducibility of several enzymatic activities was determined as additional measures of maturation. N-Acetylglucuronidase was induced, for example, by LK, IFN-.gamma., 5637 CM and phorbol myristic acid. Alkaline phosphatase was induced by LK, IFN-.gamma., dexamethasone and phorbol myristic acid. 1, 25-Dihydroxycholecalciferol was also examined and could induce most of the maturational markers examined. Non-IFN cytokines from several sources evidently have profound differentiation-inducing effects on monoblast leukemia cells in a pattern different from that of IFN-.gamma.. The inducing factors in LK and nonlymphoid cytokines have similar biological activity on U937 cells and the LK factor is not associated with CSF-1. [Implications with respect to differentiation therapy and immunomodulation were presented.].