Hyporeactivity to interferon induction: characterization of a hyporeactive factor in the serum of encephalomyocarditis virus-infected mice

Mice infected with encephalomyocarditis virus develop a severe state of hyporeactivity to interferon induction. One mechanisms possibly responsibile for development of hyporesponsiveness in these animals is a circulating factor which can be detected in their serum 96 h after encephalomyocarditis virus infection (at the time of peak hyporeactivity in vivo). This report describes some of the physiocochemical characteristics of this serum hyporeactive factor (SHF). SHF is a protein with a molecular weight between 20,000 and 40,000 that was extremely labile at 56 C, losing greater than 90% of its biological activity in 8 min, but stable at 37 c for at least 4 h. Hyporeactive factor was also stable over a pH range of 2 to 11 for 48 h at 4 C. These results suggest that SHF is physicochemically similar to interferon. However, no interferon could be detected in the SHF preparation, and no loss in biological activity was observed when the serum factor was incubated with anti-interferon antibody, suggesting that they are separate substances.