Requirement for macrophages for interferon to be effective against encephalomyocarditis virus infection of mice.

Suppression of macrophages in mice by treatments with silica or auro-thiomalate (Myocrisin) reduced production of serum interferon by polyriboinosinic acid:polyribocytidylic acid by 85 to 90%, indicating that this double-stranded polynucleotide caused interferon production primarily in macrophages. Suppression of macrophages in mice by silica or Myocrisin treatment did not significantly affect the susceptibility of mice to encephalomyocarditis virus, although at virus doses around 20 times the 50% lethal dose they died about 48 h earlier. Macrophage interferon protected mice from encephalomyocarditis virus infection at much lower doses than fibroblast interferon, and treatment of mice with silica or Myocrisin abolished the protection conferred by macrophage interferon, whereas these treatments had a much smaller effect on the protection afforded by fibroblast interferon. The requirement for macrophages for interferon to be effective in mice can explain why macrophage suppression can cause normally nonlethal viruses to kill adult mice.