Abstract
Equine abortion virus (EAV), a herpesvirus, agglutinates horse red blood cells (RBC). The hemagglutinin appears to be an integral part of the viral envelope and is not “soluble” as was formerly anticipated. The hemagglutination proved to be stable at 4 °, 20 °, and 37 °, and could not be reversed by Vibrio cholerae neuraminidase. Trypsin could not be used for reversion since RBC treated with trypsin proved to be nonagglutinable by EAV. The hemagglutinating (HA) activity was destroyed by dithiothreitol indicating the role of disulfide groups in hemagglutinin. The HA activity was also destroyed by proteolytic enzymes (trypsin, α-chymotrypsin, or Pronase), but proved to be resistant to the action of lipid solvents (chloroform or ether) or phospholipase C. The EAV hemagglutinin is thus a protein, the activity of which is not dependent on lipids. In fresh virus harvests the HA titers were directly proportional to infectivity titers, 1 HA unit being equal to about 10 7.0 plaque-forming units in PK-15 cells. In virus preparations, purified from such harvests, 1 HA unit was found to be equal to approximately 0.65 μg protein. These figures might explain why the antibody response to hemagglutinin was poor following immunization by natural infection or vaccination.
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