An investigation of some factors affecting cross-reactivation between influenza A viruses.

Some parameters of the reactivation of ultravioletor chemically inactivated fowl plague virus by live A 2 viruses were examined. Clones of reactivated virus were obtained by two different techniques, either by isolation from plaques on chick embryo fibroblast cells or by terminal dilution in pieces of allantois-on-shell. Recombinants isolated from plaques were of one type, namely they contained only the neuraminidase antigen of the live A2 virus. In contrast, recombinants isolated in pieces of allantois-on-shell possessed a variety of A2 characteristics, and only a small proportion of these were of the type isolated by the plaque technique. Studies in which fowl plague virus was exposed to ultraviolet or ethylene iminoquinone for various time periods enabled comparisons to be made of the rate of loss of infectivity and the rate of loss of ability to be reactivated. The results of these studies were interpreted as indicating that approximately 7o ~ of the genome of fowl plague virus could be reactivated by A2 virus, and that this portion of the genome contained the genetic information for the haemagglutinin and neuraminidase antigens, the heat stability of the haemagglutinin, lethality for the chick embryo and efficient plaque production.