text: 2944474  Effect of recombinant human fibroblast interferon and mezerein on growth, differentiation, immune interferon binding and tumor associated antigen expression in human melanoma cells.  The combination of recombinant human fibroblast interferon (INF-delta) and the antileukemic compound mezerein (MEZ) results in a synergistic suppression in the growth of human melanoma cells and a concomitant increase in melanin synthesis. In the present study we have further analyzed this synergistic interaction and have also evaluated the effect of IFN-delta and MEZ, alone and in combination, on recombinant human gamma interferon (IFN-gamma) binding and Class I HLA and melanoma associated antigen (MAA) expression in the HO-1 human melanoma cell line. Single cell clones isolated from the HO-1 cell line varied in their sensitivity to the antiproliferative effects of IFN-delta and MEZ. With all twelve clones, however, the combination of IFN-delta plus MEZ was more growth inhibitory than either agent used alone, even in HO-1 subclones displaying relative resistance to IFN-delta. By continuous growth in gradually increasing concentrations of IFN-delta, a variant population of HO-1 cells, HO-1 delta R-D, was generated which was more resistant to the antigrowth effects of IFN-delta than the original HO-1 parental cell line. In the IFN delta R-D cell line the combination of IFN-delta plus MEZ synergistically suppressed growth. Exposure of HO-1 cells to      units/ml IFN-delta or    ng/ml MEZ for 96 hr resulted in no change or an increase in the binding of labelled IFN-gamma to surface receptors, whereas the combination of IFN-delta plus MEZ increased IFN-gamma binding 2-to-4-fold in HO-1 cells. This increase was the result of an increase in the number of receptors on treated cells coupled with a protection against a decrease in receptors observed for confluent untreated cells. Changes in IFN-gamma binding resulting from treatment with IFN-delta plus MEZ were not associated with alterations in the binding affinity of INF-gamma to its receptor. Changes were also observed in the expression of HLA Class I antigens and MAAs following treatment of HO-1 cells with IFN-delta, MEZ or IFN-delta plus MEZ. IFN-delta and MEZincreased  the expression of HLA Class I antigens a 96 kd MAA defined by MoAb CL203, a     kd MAA defined by MoAb 376.96 and a 115 kd MAA defined by MoAb 345.134 but decreased the expression of a high molecular weight-melanoma associated antigen (HMW-MAA) defined by MoAb 325.28S.(ABSTRACT TRUNCATED AT     WORDS)