Correlation between molecular size and interferon- inducing activity of poly I:C.

: Electron microscopy showed that commerical poly I: C consisted of molecules varying in length from less than 0.05 nm to more than 5 nm and also in morphology . To clarify the relationship between its molecular size and interferon-inducing activity, poly I: C was sonicated or fractionated by sucrose density gradient centrifugation, and the molecular length distribution and interferon-inducing activity of each preparation was determined in vivo and in vitro. The results showed that (1) poly I : C molecules 0.1-0.3 nm long were the most effective for interferon induction; (2) sonication of poly I : C reduced its molecular length and also the interferon-inducing activity, the degree of reduction varying in different fractions; and (3) the interferon-inducing activity of poly I: C of 0.1-0.3 nm obtained by sucrose density gradient centrifugation was higher than that poly I: C of corresponding length prepared by sonication.