Immune response in rabbits to virion and nonvirion antigens of the Flavivirus kunjin

Abstract

The nature of the antibodies formed in rabbits in response to the following Kunjin virus antigens was examined: infectious suckling mouse brain (SMB), purified virion or rapidly sedimenting hemagglutinin (RHA), slowly sedimenting hemagglutinin (SHA) and envelope fragments prepared from RHA disrupted by 0.1 or 0.2% sodium deoxycholate (DOC). The hemagglutination inhibiting (HI) and neutralizing antibody responses to SMB, RHA and large envelope fragments (0.1% DOC) were remarkably uniform, antibodies appearing at the same time, attaining similar HI titers (lowest to envelope) and being of similar avidity early and late in the response. The 19S (immunoglobulin M [IgM]) antibodies to all antigens were always relatively type-specific; the 7S (IgG) antibodies were always broadly cross-reactive in HI tests. The envelope antigen is the principal antigen involved in the stimulation of protective neutralizing antibodies and contains type- and group-specific antigenic determinants. There is apparently no significant advantage in using purified RHA or SHA for immunization or as hemagglutinin antigens in attempts to obtain greater specificity in the [diagnostic] HI test. No differences were detected in the antibody responses to infective Kunjin virus, within the range 1400-109 plaque-forming units (PFU). Below 1400 PFU there was no detectable response. Inactivated virus (106 PFU) also stimulated the normal antibody response. Small envelope fragments (derived with 0.2% DOC) and a detergent-solubilized extract of infected cells could not stimulate a detectable antibody response. The small envelope fragments may have induced low dose tolerance in 1 of 2 rabbits.