Binding of murine 125I-labelled natural interferon-gamma to murine cell receptors.

Natural murine interferon-gamma (naMuIFN-gamma) produced by T-lymphoma cells (L12-R4) stimulated with phorbol myristic acetate was purified by use of an anti-MuIFN-gamma immunoadsorbent and was labelled with 125I to study its binding to murine cell receptors. All the cell lines examined bound naMuIFN-gamma, although the binding affinity varied considerably. By adding increasing concentrations of unlabelled naMuIFN-gamma in competition binding assays we determined dissociation constants (KD) of 8.2 X 10(-10) and 7.4 X 10(-10) M for L1210 and TS/A cells, respectively, and of 6.5 X 10(-9)M for L-929 cells. The numbers of receptors present per cell of these lines were 3000, 1000 2000 respectively. Highly purified naMuIFN-gamma as well as recombinant MuIFN-gamma competed for binding sites with 125I-labelled IFN-gamma on L1210 cells, although the latter displayed a KD greater than the former (5.8 X 10(-9) M compared to 8.2 X 10(-10) M). Moreover, protease, but not endoglycosidase, treatment of target cells prevented the subsequent binding of 125I-labelled IFN-gamma, suggesting that a protein moiety is involved in the binding of the ligand. These studies demonstrate that naMuIFN-gamma binds in a specific manner and with high affinity to murine cell receptors.