Abstract
The lungs of mice infected with the virus of epidemic influenza contain a soluble complement-fixing antigen which is separable from the virus. 1 , 2 The purpose of the work here reported was to investigate the conditions under which this antigen and its corresponding antibody are formed.
Mice were inoculated with the mouse passage strain PR8 of epidemic influenza virus in dilutions from 10-2 to 10-3 of lung. At different intervals of time from 1 to 10 days, 6 to 8 mice receiving each of the dilutions were killed by bleeding from the heart under chloroform anesthesia. The complement-fixing antigen was measured by titration of a saline suspension of the ground lung material against a constant dilution of 1:20 of a pool lof human convalescent serum according to the complement-fixation method previously described. 3
The results are recorded in the accompanying table. One day after inoculation none of the mice showed macroscopically visible lung lesions, but the complement-fixing antigen was already present in relatively high titer except in the group receiving a dilution of 10-6. Between the second and fifth days the appearance of antigen at a maximum titer preceded by 2 to 3 days the maximum development of lung lesions. This suggests that the formation of the antigen is associated with a rapid multiplication of the virus before the appearance of the red pulmonary consolidation. With virus dilutions of 10-3 or above, the maximum titer of antigen seemed to be related to the amount of virus inoculated. In the lungs of mice inoculated with dilutions 10-5 and 10-8 and killed after 4 days, the antigen titered 1 :40 and 1 :20 respectively and no macroscopic lesions were found.
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