Hyporeactivity factor produced after induction of immune interferon in mice sensitized with BCG

Sera from BCG-sensitized ICR and C57BL/10J mice challenged with BCG were examined. Two types of hyporeactive factor (HF), which produced refractoriness to induction of interferon (IF) by Newcastle disease virus in mouse embryo fibroblasts, were produced in addition to type II immune IF. One was destroyed at pH 2, and the other was not. The acid-labile HF, together with immune IF, appeared 2 h after challenge with BCG. Acid-labile HF and immune IF were not neutralized by antiserum against L-cell IF and may be one substance. On the other hand, acid-stable HF appeared later and was neutralized by antiserum against L-cell IF. Furthermore, acid-stable HF was more stable at 56 degrees C than were immune IF and pH-labile HF. Induction of IF by Newcastle disease virus was also reduced in mice 6 h after receiving one injection of BCG, irrespective of whether the animals were previously sensitized to BCG.