Binding of 125I-labeled human interferon to cell lines with low sensitivity to interferon

Iodinated human interferon alpha A (HuIFN-alpha A) was found to bind specifically to IFN-sensitive RSa cells: the dissociation constant was 8.7 X 10(-10)M and the estimated number of receptor sites per cell was 1110. Seven cell lines that were either insensitive or of low sensitivity to the antiproliferative effect of IFN were found to contain a much smaller (3- to 4-fold) number of receptor sites, but the dissociation constants of these binding sites were of the same order of magnitude as those of receptors on RSa cells. Under the present experimental conditions, cell resistance to the antiproliferative effect of IFN is closely associated with the number of receptor sites.