Action spectrum of antiviral factor from chicken sera

Rous sarcoma virus infections of regressor line chickens stimulate the transient production of antiviral factors in the serum. Earlier the present authors reported that a viral neutralization factor (VNF) inactivated Rous sarcoma virus during a 3-h incubation. The VNF is likely to have a broad antiviral and antimicrobial spectrum because it is active against several unrelated pathogenic poultry viruses. The present study measured the activity of VNF against Newcastle disease virus, infectious bursal disease virus, and infectious bronchitis virus. The VNF is active in immunologically incompetent systems and must be preincubated with the virus in order to inhibit it. Based upon the current experiments, it is proposed that VNF is not an immunomodulator but directly inactivates the virus. The VNF agent appears to be one of a newly identified class of nonspecific antiviral agents produced in vivo in chickens in response to a viral infection.