The complement-requiring neutralization of equine arteritis virus by late antisera

Abstract

Neutralization of equine arteritis virus (EAV) by late antibody raised in horses, guinea pigs, rabbits, hamsters, and mice was investigated and found to be complement-dependent. The complement-dependent EAV neutralizing antibody activity was found associated with the IgG fraction of late antisera. Early antisera or their IgM and IgG fractions were ineffective. Analysis of virus-antibody interaction at 37° showed that no appreciable loss of EAV infectivity occurred following incubation with heat-inactivated late antiserum for 20 min. However, upon prolonged incubation, partial reduction in EAV infectivity was detected. The sensitization of EAV (as assessed by anti-IgG) was shown to begin following mixing with antiserum and was essentially completed after 20 min of incubation. Neutralization of sensitized EAV by complement or anti-IgG was instantaneous and not temperature dependent. Analysis of EAV infectivity ( in vitro) indicated that specific antibody apparently did not interfere with the early steps of virus-cell interaction. Further studies suggested that following penetration into susceptible cells, sensitized EAV was rendered insensitive to complement inactivation. The present investigation has confirmed the existence of a complement-dependent viral neutralizing antibody in late antisera and, further, has shown that EAV provides a new model for analysis of the complement-dependent neutralization of sensitized virus.