A Flocculation Phenomenon with Human Sera and Suspensions of the Virus of Epidemic Influenza

Abstract

Neutralization and complement-fixation tests with the virus of epidemic influenza have been described and studied rather extensively but no agglutination, precipitation, or flocculation reaction has as yet been reported. Theoretically such reactions should be demonstrable, provided a sufficient quantity of virus is contained in the antigen. 1 Attempts to purify and concentrate the virus by ultracentrifugation in this laboratory have not in general yielded suitably reactive antigens. During the course of investigation it was observed, however, that a flocculative phenomenon could be obtained consistently with certain human sera and crude suspensions of lungs of mice infected with influenza virus, the reaction being especially marked with sera of patients convalescent from epidemic influenza. It is the purpose of this report to describe the conditions under which the reaction occurs and to discuss briefly some of the results.

Methods. Mice of the Swiss strain are inoculated intranasally with 1 to 2% suspensions of lungs of mice infected with PRS strain of influenza virus. At the time of appearance of visible areas of pulmonary consolidation—approximately 40 to 50 hours after inoculation—the mice are sacrificed and the lungs ground with alundum in meat-infusion broth (pH 7.8) to form a 10% suspension by weight. After light centrifugation equal volumes of supernatant fluid and serum are mixed in small tubes and incubated at 37°C. After 1 hour's incubation the tubes are shaken lightly and the degree of flocculation is recorded in the usual manner. Frequently flocculation does not occur until the tubes are shaken but once the reaction takes place a precipitate settles to the bottom of the tubes in large coarse floccules. Meat-infusion broth is not essential in the preparation of the antigen and can be replaced by M/150 phosphate buffer pH 7.2 or 0.4% NaCl solutions.