Detection of "alpha-type" inhibitors in the presence of low levels of specific influenza antibodies.

In native, heated or otherwise treated egg white and in sera of men and guinea pigs, haemagglutination inhibition titres were determined against three inhibitor-sensitive (IS) strains and one inhibitor-resistant (IR) variant on influenza A virus. A few human sera with no detectable antibody revealed high inhibition titres even against the IR variant. Human sera after treatment with trypsin and periodate revealed mostly a reduction or no change, and exceptionally an increase of their inhibition titre. The extent of these changes varied with different influenza virus strains and showed a positive correlation with the inhibitor content and no correlation with the antibody levels of the sera. The so-called "nonspecific" thermostable inhibitors possess a certain degree of specificity for different influenza virus strains.