The following results were obtained in a study of hemagglutination reactions with influenza virus which occur only in the cold:

  1. Allantoic fluid suspensions of PR8 or Lee influenza viruses agglutinate sheep and rabbit red cells in high titer at 4 C but not at room temperature or 37 C.

  2. The cold hemagglutination is apparently due to the influenza virus particle, as indicated by specific inhibition of the reaction with antiserum and sedimentation of the hemagglutinin by centrifugation at 12,000 rpm for 30 minutes.

  3. Influenza virus heated to 56 C for 30 minutes agglutinates sheep cells at room temperature.

  4. The receptors of sheep cells can be removed by the action of influenza virus at 37 C, even though agglutination of the cells is not manifest at this temperature. Sodium periodate is also effective in removing the receptors.

  5. Human and chicken red cells, which have been treated with influenza virus so as partially to remove the receptors and the cells then stabilized with formalin, also show the cold hemagglutination reaction. Heated influenza virus, however, does not agglutinate the cells at room temperature.

  6. The receptors of human red cells involved in the hemagglutination reaction with isoagglutinins or bean extract, and the receptors of sheep cells which react with amboceptor or bean extract, are not affected by treatment of the cells with sodium periodate. Furthermore, Group A or B human red cells, which had been treated with influenza virus to remove the virus receptors, showed no alteration in their capacity to adsorb isoagglutinins.

The implications of these findings are considered in the discussion.

1

Research Fellow, U. S. Public Health Service.

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