Role of complement in the pathogenicity of fowlpox virus infection in chickens and chicken embryos.

Abstract

Chickens and chicken embryos were infected with a vaccine or with wild strain of fowlpox virus (FPV), and the effect of complement activation on the pathogenicity of FPV was examined in terms of histological lesions, mortality, virus growth, and host response. In chicken embryos and in chickens, the complement was activated by the vaccine strain but not by the wild strain. The vaccine strain was avirulent in chickens, whereas it was highly virulent in chicken embryos. Carrageenan treatment that inhibited heterophile infiltration of the pock lesions in chicken embryos reduced the virulence of the vaccine strain. Virus-specific antibody response, as well as protective immunity to challenge from another attenuated strain, developed earlier and at highef levels following inoculation by the vaccine strain than by the wild virus. These findings indicate that complement-mediated reactions are involved in the expression of virus pathogenicity as well as in the induction of immune responses.