Serological behaviour of influenza viruses. I. The effect of different fowl erythrocytes on the results of serological tests.

Two strains of influenza A virus have been identified which show significant variations in their haemagglutination-inhibition titres when tested with different types of fowl cell.The fowl cells studied in relation to these two strains of virus fall into two distinct groups, arbitrarily labelled type I (low titre) and type II (high titre).The type I and type II cells seem related to, but not identical with, the inhibitor-insensitive and inhibitor-sensitive cells described by previous workers.When type I cells are treated with trypsin they behave like type II cells, while the latter are not modified by this treatment.