The soluble hemagglutinins of adenoviruses belonging to Rosen's subgroup 3. I. The rapidly sedimenting hemagglutinin

Purification of adenovirus 4 type-specific hemagglutinins for use in diagnostic counterelectrophoresis tests

Three type-specific hemagglutinins of adenovirus (AV) 4 were purified, tested for various activities, and used as immunogens in rabbits. The components were purified by anion exchange and exclusion chromatographies to purification factors of 33, 20, and 37, respectively, and were identified as fiber (polypeptide, mol wt 70,000; incomplete hemagglutinin), penton (mol wt greater than 400,000; incomplete hemagglutinin; possession of cytotoxic activity), and dodecon (mol wt greater than 400,000; complete hemagglutinin; appearance by electron microscopy). Rabbit antisera to these hemagglutinating components possessed type-specific hemagglutination-inhibition and serum neutralization antibodies and were thoroughly evaluated for potency and specificty in immunodiffusion (ID), immunoelectrophoresis, and counterelectrophoresis (CE) tests. The anti-fiber and anti-dodecon sera were highly type-specific in ID and CE tests with a battery of commonly isolated AV serotypes; the anti-penton serum was similarly specific after it was absorbed with AV 2 hexons. These sera were thus proved to be suitable reagents for use in both the routine diagnostic ID test and the more rapid CE test.

Biophysical comparison of two canine adenoviruses

The two canine adenoviruses, infectious canine hepatitis (ICH) virus and infectious canine laryngotracheitis (ICL) virus (also designated as Toronto A26/61 virus), were studied with respect to their morphology and the biological properties of their soluble components. The two viruses were found to be composed of soluble components similar to, and carrying biological activities corresponding to, those of the human adenoviruses after fractionation by rate zonal centrifugation and anion-exchange chromatography. The following soluble components were identified: hexons (carrying a common group-specific complement-fixing antigen), penton oligomers (complete soluble hemagglutinin), and penton and fiber monomers (incomplete soluble hemagglutinins). The latter were indicated by hemagglutination enhancement with selected antisera directed against human adenovirus soluble components. Elution characteristics of corresponding components of the two viruses in anion-exchange chromatography experiments were distinctly different. Electron microscopic examination of purified virions and soluble components revealed the fiber component of ICL virus to be 35 to 37 nm in length, and that of ICH virus to be 25 to 27 nm long.

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.

Immunological and other biological characteristics of pentons of human adenoviruses

Comparative hemagglutination-enhancement (HE) tests demonstrated diversified patterns of antigenic specificities both in the fiber and vertex capsomer part of pentons of human adenovirus types 3, 11 (subgroup I), 9, 15 (II), 1, 2, 4, 5, 6 (III), and 12. All fibers contained a type-specific antigen. Subgroup II and III fibers, in addition, contained specificities both unique for each subgroup and also common to the two subgroups. Fibers of serotypes 4 and 12 displayed a somewhat deviating behavior. All vertex capsomers tested shared a group-specific part. This was the only antigenic specificity demonstrable for serotype 12. Maximal penton HE titers of all sera were reached in tests with incomplete hemagglutinin of type 11. In addition, maximal HE activity of sera against individual serotypes also was recorded against pentons of other members of the same subgroup. Antigen characteristics of vertex capsomers of type 4 indicated a closer relationship to subgroup I than to subgroup III. The toxin activity of pentons was more sensitive to trypsin treatment than their capacity to function as incomplete hemagglutinin. Homotypic antipenton sera, unabsorbed or absorbed with homotypic fibers to remove antibodies against this component, and, to a varying extent, also heterotypic antipenton sera could neutralize toxin activity. Antifiber sera could neutralize toxin activity of pentons carrying short fibers (10 nm, type 3) but not of those carrying long fibers (28 to 31 nm, type 2). It is concluded that toxin activity is carried by a specific part of vertex capsomers and that cell detachment can be brought about via a direct contact between this component and cell membranes. Fiber-mediated attachment does not seem to be necessary for this biological activity to become expressed.