Identification of individual interferon-producing cells by in situ hybridization

Individual interferon (IFN)-producing cells were identified by hybridization in situ followed by autoradiography. cDNAs corresponding to murine IFN-alpha and murine IFN-beta labeled by nick-translation to high specific activity (2-4 X 10(8) dpm/micrograms) with alpha-35S-labeled dATP were used as probes for hybridization with IFN mRNA in mouse C-243 cells induced with Newcastle disease virus. Control experiments with non-induced cells or with non-IFN-related labeled DNA monitored the specificity of the autoradiographic signal. Under optimal conditions of IFN induction, between 15% and 40% of the cells gave a hybridization signal with a mixture of IFN-alpha and -beta probes. Differential hybridization with either the IFN-alpha or -beta probe or a mixture of both, at three different time intervals after induction, revealed that only a small fraction of cells had detectable amounts of IFN-alpha mRNA, whereas in the majority of the positive cells IFN-beta mRNA was present.