Hyporeactivity to interferon induction in newborn piglets

The aim of this study was to produce sustained activation of natural killer (NK) cells in newborn piglets by interferon (IFN) induction with polyinosinic:polycytidylic acid complexed with poly-L-lysine and carboxymethylcellulose [poly(ICLC)]. When a second dose of poly(ICLC) was given 24 or 48 h after the first dose, the piglets were found to be hyporeactive, and the levels of induced IFN were insufficient to activate NK cells in vivo or in vitro. A hyporeactive factor was demonstrated in the serum of piglets 24 and 48 h after they were treated with poly(ICLC), which inhibited IFN induction in vitro with poly(ICLC) but not with Newcastle disease virus. The IFN response of hyporeactive piglets was partially restored by the administration of prostaglandin (PG) F2 alpha at the same time as the second dose of poly(ICLC); piglets treated in this way at 3 days of age showed significantly higher lymphocytic NK activity at 5 days and 7 days than the activity in untreated piglets and in those given one or two doses of poly(ICLC) in the absence of PG F2 alpha. It was concluded that piglets develop hyporeactivity to IFN induction, but the IFN and NK cell activation responses to poly(ICLC) can be restored by treatment with PG.