The role of sensitizing antibody in the neutralization of equine arteritis virus by complement or anti-IgG serum

Abstract

The dissociability of the infectious equine arteritis virus (EAV)-antibody complexes was investigated before and after neutralization with complement or anti-IgG to determine the possible role of the sensitizing antibody in the multicomponent virus neutralization system. The binding between EAV and sensitizing antibody was irreversible as tested by rapid dilution and sonic vibration. Following digestion of antiserum with trypsin, the antibody retained its capacity to bind to EAV and render it sensitive only to inactivation by anti-IgG. When sensitized EAV was treated with trypsin, about 80% of viral infectivity was no longer sensitive to complement inactivation but remained sensitive to inactivation by anti-IgG. A kinetic study revealed that, when complement-neutralized EAV was treated with trypsin, the maximal recovery of viral infectivity was obtained at 5 min and remained relatively steady for about 150 min. Further analysis indicated that trypsin-mediated reactivation of the complement or anti-IgG-neutralized EAV was accomplished, as expected, by the cleavage of the sensitizing antibody into Fc portion and Fab fragments. The Fab fragments, apparently remained attached to the virion as determined by the sensitivity of the digested neutralized complex to anti-IgG reinactivation and its resistance to complement reinactivation. The present investigation suggests that neutralization of sensitized EAV by complement is dependent on the presence of the complement determinants of the sensitizing antibody, while neutralization by anti-IgG is only dependent on the presence of the antibody determinants. It appears that the role of the sensitizing antibody in the multicomponent EAV-neutralization system is that of providing the specific attachment sites for complement and anti-IgG, the effectors of such viral neutralization.