Immunological Relationships Between Hexons of Certain Human Adenoviruses

Antisera against hexons of serotypes 2, 4, 5, and 6 (subgroup III), and 15 (subgroup II) were absorbed with purified hexons of various serotypes representing the different subgroups of human adenoviruses. Group, subgroup, and type specificities of hexons could be distinguished. The subgroup specificity of type 4 hexons resembled that of hexons of subgroup I members (types 3, 11, and 16). Antihexon sera gave a type-specific inhibition of virion-associated hemagglutinin. The inhibiting activity of different sera was found to be inversely related to the length of fibers of the serotype concerned. Virions of serotypes carrying fibers shorter than about 20 nm (types 3, 4, 9, 11, and 15) were readily inhibited, whereas those of serotypes with longer fibers (types 2 and 6) were inhibited only by relatively large amounts of antibody measured in terms of homotypic complement fixation activity. The reciprocal cross-neutralization between serotypes 4 and 16 was studied separately. Hexons of both serotypes each carried a type-specific component and, in addition, a unique antigen specificity common to the two types. This common antigen specificity was interpreted to be available to a larger extent at the surface of virions (and probably also isolated hexons) of type 4 than of type 16. These results suggest an explanation for the predominantly one-sided character of the cross-neutralization between types 4 and 16.