Differentiation of Influenza A and Influenza B by the Complement-Fixation Reaction. ∗

Abstract

A recent report 1 has described the isolation of a new serological type (B) of virus from epidemic influenza. By means of the neutralization test with sera from convalescent animals and human individuals, it was shown that this virus was readily differentiated from virus of the type (A) previously identified. In the process of adaptation of the new virus to mice, attempts were made to ascertain whether serological differentiation could also be obtained with the complement-fixation reaction. While the earlier results were indefinite, these efforts have been renewed since the virus has increased in virulence for mice.

Antigens were prepared from lungs of mice infected with the PR8 strain of the virus of Influenza A 2 and also from mice infected with the Lee strain of Influenza B virus. Two percent suspensions of the infected lungs in physiological salt solution, after clarification by centrifugation, were used in the tests. Two units of complement were employed. Serial two-fold dilutions of serum were made and 0.1 cc of each dilution was mixed with 0.1 cc volumes of complement, antigen and saline. After incubation for 60 minutes at 37°C, 0.2 cc of sensitized cells were added. The tubes were again incubated in the waterbath for 45 minutes when readings were made. A complete set of controls was included in each test.

Acute and convalescent sera obtained from patients infected with Type A virus in 1938-39 and from others shown to have been infected in 1940 with Type B virus were tested for their capacity to fix complement in the presence of each antigen. Representative results are presented in Table I, where the titer of neutralizing antibodies in each serum against 100 M.L.D. of the 2 types of virus is also recorded.