Antiviral and interferon-inducing activities of a new peptidomannan, KS-2, extracted from culture mycelia of Lentinus edodes.

Oral (PO) administration of KS-2 to adult DDI mice resulted in a peak serum interferon (IF) titer of 800 units (U)/ml 20 hours after administration with detectable levels persisting until 30 hours. After intraperitoneal (IP) injection, a peak serum IF titer of 1,600 U/ml was detected and it followed the same time course as that of oral administration. The IF induced by KS-2 shared certain physico-chemical properties with the standard preparation of immune IF and was not neutralized by an antiserum against type I IF. In mice infected intranasally (IN) with influenza A2 (H2N2) virus, KS-2 was found to possess significant protective activities. Efficacy of the agent was evidenced by an increase in survivor number, a prolongation of mean survival time, an inhibition of the development of lung consolidation induced by the viral infection and a decrease in virus titer in lung tissues. Both PO and IP administrations of KS-2 protected mice against infection and significant antiviral activities were achieved not only by prophylactic but also chemotherapeutic administration. The protective activities of KS-2 against influenza virus infection in mice are discussed in view of the immunopotentiation of the host animals.