Interferon production in BCG-sensitized rabbits challenged with PPD.

Intravenous administration of PPD into BCG-primed rabbits results in the release of IFN into the circulation. Peak interferon titres occur in plasma 1 h after PPD injection, rapidly decline during the following 3 h and depend on the dose of tuberculin administered. Bilateral nephrectomy of BCG-primed rabbits challenged with PPD affects remarkably the disappearance of IFN from the circulation. Characterization of the BCG-PPD-induced IFN shows that it is heat-labile, is almost completely inactivated after dialysis at pH 2 and displays a remarkable cross-species activity, particularly on human cell lines.