Antigenic relationships between avian paramyxoviruses. III. A mathematical model of antigenic drift and a computer-assisted approach for construction of a phylogenetic tree.

The suggested model of antigenic kinship between related paramyxoviruses is based on another concept of antigenic determinant, as compared to the previously suggested combinatorial mathematical model by the authors. According to it, antigenic changes of any determinant do not proceed by "leaps" but can be changed gradually. Such changed determinant can induce a correspondingly changed type of antibodies which still preserve a certain kinship to the original type of the determinant (before its changing) revealed by cross reaction serological tests. Accordingly, there can be "families" of the determinants differing by degree of relatedness to (or, reversely, by antigenic distance from) the "original" ("ancestor") determinant. In addition to another interpretation of the antigenic kinship, the new mathematical model was used as an approach for revealing phylogenetic relationships between antigenically related viruses.