Printed in U.S.A. Production by Mixed Lymphocyte Cultures of a Type II Interferon Able to Protect Macrophages Against Virus Infections

In supernatants of mixed mouse spleen cell cultures established for 4 days, a species-specific inhibitor of virus replication with a broad antiviral spectrum was found. The inhibitor was destroyed by trypsin, was nondialyzable and acid labile, and was not neutralized by antibody to mouse L cell interferon. This indicates that in mixed lymphocyte cultures a type II interferon is made that has no immunological relationship with "fibroblast " interferon. This leukocyte prod-uct was shown to protect mouse peritoneal macrophages against the cytopathic effects of influenza and mouse hepatitis viruses. It is suggested that lymphocyte interferon may collaborate with macrophages in host defense against viruses, as a mediator of cellular immunity. Evidence has accumulated that the inter-feron (IF) produced by leukocytes is distinct from that produced by other cells. Based princi-pally on antigenic differences, three different types of IF can now be distinguished in mic