Polyriboinosinic-Polyribocytidylic Acid-Induced Interferons in Calves

SUMMARY The synthetic double-stranded complex of polyriboinosinic and polyribocytidylic acids (poly i:c) was tested as an inducer of interferon in young calves. After calves were given intravenous injections of poly i:c, serums were examined for interferon by the plaque-reduction method in bovine embryonic kidney cell cultures, using vesicular stomatitis (vs) virus for challenge inoculum. Peak titers of circulating interferon occurred 2 hours after calves were injected. Serum interferon either was not detected or was reduced in titer by postinjection hour 6. Diethylaminoethyl-dextran (deae-dx) did not by itself induce circulating interferon nor did it increase the titer or prolong the concentrations of circulating interferon when it was given simultaneously with poly i:c. Calves developed a resistance or tolerance to the interferon-inducing effects of poly i:c. Two of 4 calves injected intravenously every 24 hours with poly i:c for 3 injections did not produce circulating interferon after the last injection, and in the other 2 calves the titers of serum interferon detected after the 3rd injection were lower than those found after the 1st injection. Toxicity characterized by increased respiratory rate, dyspnea, central nervous system depression, and increased rectal temperatures was evident in most calves injected with poly i:c. Properties of the induced inhibitors were those of interferon.