A monoclonal mouse antiallotype antibody reacts with certain human and other vertebrate immunoglobulins: genetic and phylogenetic findings.

A new mouse monoclonal antibody, 18.1, recognizes an allotypic determinant on mouse IgG1 of the "a" allotype. We found that this alloantibody reacts with immunoglobulins of evolutionarily distant vertebrate species including man, and with only certain isotypes or allotypes in some of these species. Most mammalian sera are reactive, except those from lagomorphs, marsupials, and monostremes. Avian and reptilian sera are also positive, while the amphibian and fish sera tested were negative. In human sera, 18.1 detects the isotypic marker on IgG2 and an allotypic marker on IgG3. This reactivity parallels the distribution of the Gm non-g determinant. These findings are discussed in relation to the phylogeny of IgG and its subclasses.