Further Observations on Red Cell Agglutinating Agent Present in Lungs of Virus-Infected Mice

The red cell agglutinating agent present in the lungs of mice infected with pneumonitis virus has been subjected to further study. Maximum agglutination develops after heating the fresh lung extract at 75°C for 5 minutes. The agent is absorbed from active extracts by preparations of mouse red cells and of fresh normal mouse lungs. Mice injected with the heated agent develop active immunity against the living virus and their sera have the capacity of inhibiting red cell agglutination. The sera of rabbits immunized against living pneumonitis virus or against active heated mouse lung extract inhibit red cell agglutination. Hamsters appear to be susceptible to infection with the pneumonitis virus but attempts at continued serial passage were unsuccessful. The agglutinating agent has been purified by precipitation with ammonium sulfate. The purified agent retains its agglutinating and immunizing capacity.