The antiproliferative effects of human recombinant interferon-alpha (rIFN-alpha A) and interferon-beta (rIFN-beta ser) were assessed in vitro against seven human glioma cell lines. Further analysis of one of these lines (EFC-2) in response to rIFN-alpha A demonstrated a minimum growth inhibition by day 6 of treatment, whereas a 50% inhibition of cell growth was observed with a dose of 50 U/ml of IFN-beta ser. No significant growth inhibition was seen by rIFN-alpha A at doses up to 500 U/ml. Addition of rIFN-alpha A to rIFN-beta ser-treated EFC-2 cells neither suppressed nor augmented the antiproliferative response to IFN-beta ser. The binding of 125I-labeled rIFN-alpha A or 125I-labeled rIFN-beta ser to EFC-2 cells was inhibited competitively by increasing concentrations of either unlabeled rIFN-alpha A or rIFN-beta ser. This suggests that the cellular receptors for both rIFN-alpha A and rIFN-beta ser appear to be intact and appear to bind both agents equally. Furthermore, incubation of EFC-2 cells for 72 h with either rIFN-alpha A or rIFN-beta ser resulted in an increase in 2',5'-oligoadenylate (2-5A) synthetase activity 5-fold with rIFN-alpha A and 50-fold with rIFN-beta ser. Similarly, the 68-kD IFN-induced protein kinase was induced substantially with rIFN-beta ser but only slightly induced with rIFN-alpha A treatment. These results suggest that EFC-2 human glioma cells demonstrate a differential sensitivity in terms of growth inhibition to rIFN-beta ser and to rIFN-alpha A which appears to correlate with a differential induction of both intracellular 2-5A synthetase and protein kinase activity. These results cannot be explained solely on the basis of surface receptor binding of rIFN-alpha A and rIFN-beta ser. These data do suggest that, for human glioma cells in culture, type I IFN receptors may display a subtle architectural variation that allows equivalent binding of both IFN-alpha and IFN-beta ser, but allows an enhanced signal transduction and biological effect only after binding a specific IFN subtype.
A component of Mycobacterium bovis BCG referred to as BCG-a was isolated through the combined use of monoclonal antibody directed to BCG and affinity chromatography. Analysis of BCG-a by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a single prominent band with a molecular weight of ca. 10,000. Structural characterization of BCG-a consisting of amino acid composition and amino-terminal sequence determination was carried out. The intact BCG-a antigen was bound by neither the lectin from common lentils nor concanavalin A, implying that BCG-a does not carry any asparagine-linked oligosaccharides. Immunoprecipitation of '251-labeled BCG-a with polyclonal and monoclonal antibodies directed against BCG resulted in bands having the same mobility on sodium dodecyl sulfate-polyacrvlamide gel electrophoresis as did free '251-BCG-a. In radioimmunoassays 12I-BCG-a was bound by the monoclonal antibody and by
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