Studies of Germfree Animals I. Response of Mice to Infection With Influenza A Virus. ∗

Summary

Germfree mice were found to be more susceptible than conventional mice to mouse-adapted influenza A strain PR8, although the difference in susceptibility is small. Work with more precise dosage methods is indicated to ascertain the nature of the difference. At 21 days after infection, the predominant leukocytic response in GF lungs was lymphocytic infiltration, while conventional mice responded with lymphocytes, polymorphonuclear leukocytes, and macro-phages. Gamma₂ globulin was not detected by IE prior to infection either in GF mice or in 20 of 23 GF mice at 3 weeks after infection. HI antibody was not detected in GF mice before and after infection, but was detected in conventional mice after infection. Addendum. Since the submission of this paper, we have been able to elicit HI antibody production in germfree mice after intra-peritoneal inoculation of five LD₅₀ of live PR8 virus.