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-α and murine IFN-β labeled by nick-translation to high specific activity (2-4 × 108dpm/μ g) with α -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-α and -β probes. Differential hybridization with either the IFN-α or -β 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-α mRNA, whereas in the majority of the positive cells IFN-β mRNA was present.