Immunological Relationships of Strains of Filtrable Virus Recovered from Cases of Human Influenza

Abstract

Smith, Andrewes and Laidlaw 1 isolated a filtrable virus from the nasopharyngeal washings of influenza patients following the inoculation of these materials into ferrets. Two strains of virus isolated by them in England during successive winters were found to be immunologically identical. 2 These same workers reported that the virus of swine influenza isolated by Shope 3 was antigenically related to the human strains.

During the Autumn of 1934, at the Hospital of the Rockefeller Institute, we were successful in infecting ferrets and mice with strains of a filtrable virus obtained from the sputum of cases of epidemic influenza in Puerto Rico. 4 These 2 strains have been called P. R. 5 and P. R. 8. Additional strains of virus have been isolated from cases of influenza in New York and Philadelphia. During the course of these experiments, Andrewes, Laidlaw and Smith 2 reported independently that they had successfully infected mice with the viruses of both swine and human influenza. They also reported that the serum of a hyperimmune horse, or of hyperimmune ferrets, neutralized the infectivity of the respective strains of virus.

The infection in mice, following the intranasal inoculation of the virus is characterized by the development of pulmonary lesions, but death of the animals is somewhat irregular. The serum of ferrets recovered from infection, when mixed with suspensions of the homologous strain of virus and instilled into the nasal passages of mice, has been found to prevent the development of these pulmonary lesions. The serum of normal ferrets, however, has no neutralizing effect. It is possible, therefore, to measure in mice the neutralizing capacity of the serum of a recovered ferret against homologous and heterologous strains of virus.