Some biological activities of rabbit anti-interferon serum.

After prolonged immunization of rabbits with a semipurified mouse interferon preparation in Freund's incomplete or Al-Span-Oil adjuvant, a specific interferon-neutralizing immunoglobulin was obtained from antiserum with a capacity of neutralizing about 49000 mouse interferon units per ml. The specific activity of the antiserum and immunoglobulin was confirmed in tests in which the interaction of antibodies with the cell surface was ruled out. The antiserum (and the immunoglobulin) neutralized both the antiviral and the cell-growth inhibitory activities of interferon. The "slow" and the "fast" fractions of purified interferon preparations were equally sensitive to the neutralizing effect of antibodies. On the other hand, the reaction of heat-inactivated interferon with the antiserum did not diminish the neutralizing activity of the latter, suggesting a destruction of interferon antigenic sites.