The physiological interferon response. II. Interferon is present in lymph but not in plasma of healthy rabbits.

If interferon is produced by the gut-associated lymphoid tissue of healthy rabbits under normal conditions and is not all bound in situ, it may spill over and be detectable in lymph. We therefore measured antiviral activity in lymph and plasma simultaneously. We found that antiviral activity was consistently measurable in abdominal and thoracic lymph but not in plasma or in the lymph collected from the hind leg duct. The antiviral activity was neither due to lipoproteins, nor immunoglobulins, nor to cell-produced viral inhibitors other than interferons. Extensive characterization of the antiviral activity indicated that the inhibitor is either rabbit interferon gamma or an acid-labile interferon alpha or a mixture; appropriate antisera will be necessary to resolve this uncertainty. The results support the view of the existence of a physiological interferon response.