[Sensitivity to influenza infection of X-ray-irradiated animals and the protective effect of a thymus extract].

The A 2/Romania 1/73 (H3N2) strain of influenza virus at the 15th passage on chick embryos was compared to the mouse adapted A0/PR8/34 (H0N1) strain, as regards pathogenicity for X-ray irradiated mice. Irradiated mice showed a greater sensitivity to influenza infection than nonirradiated controls, irrespective of the strain used: hemagglutinating (HA) titers were constantly higher in the first group of animals. Administration of a polypeptidic thymus extract to irradiated mice inoculated with the A0/PR8 strain had a protective effect and was followed by a decrease in mean HA titer from 1/3077 to 1/164. The authors discuss the possible mechanisms of the viral multiplication rate increase in irradiated animals and of the higher resistance against influenza infection noted in thymus-extract treated animals.