Identification by in situ hybridization of IFN-beta-producing murine macrophages obtained from high and low interferon producers.

Resident peritoneal macrophages obtained from If-1h and If-1l mice were induced in vitro with Newcastle disease virus. Then, 3, 5 and 7 h after induction, the cells were fixed and analysed for the presence of Mu IFN-beta mRNA by in situ hybridization, using a 35S-labelled Mu IFN-beta cDNA as a probe. The number of cells that were scored positive was the same in cultures derived from high responder If-1h and from low responder If-1l mice, and reached 100% of the cells present in the cultures. This result highly suggests that low responder mice have the same number of IFN-producing cells as high responders, and that the difference in production is not due to an increased number of producer cells in high responders.