Absence of an All-or-None Type of Complement Requirement in Early Neutralizing Antibody against Western Equine Encephalitis Virus

Abstract

Rabbits were immunized by 2 weekly intravenous inoculations of beta-propiolactoneinactivated Western equine encephalitis virus vaccine followed 1 week later by a subcutaneous inoculation of live virus, and complement requirements of early and late neutralizing antibodies were compared. There was no difference between these antibodies, both showing about a 4-fold enhancement of the virus-neutralizing activity in the presence of complement. This was also the case when guinea pigs were given the vaccine by the intraperitoneal route. It is unlikely that previous exposure of the animals to an antigenically related virus caused a booster effect upon the antibody development, because the rabbit antibody could not even neutralize the closely related Sindbis virus either in the presence or in the absence of complement. The reason for the existence of 2 different types of primary responses with respect to the complement requirement of early neutralizing antibody is discussed.