ABSTRACT
Influenza virus neuraminidase (NA) has been shown to induce protective but infection-permissive immunity in experimental animals. Challenge infection following such immunization is attended by decreased viral replication and disease manifestations but is sufficient to provide antigenic stimulation and definitive immunity to the virus. The present report describes the preparation and characterization of a purified NA vaccine (NAV) used in Phase 1 (immunogenicity and toxicity) trials in humans. In essence, virion NA was isolated from detergent-disrupted virus by affinity chromatography on oxamic acid-agarose, treated with formalin and tested for its enzymatic activity and for its immunogenicity in Balb/c mice and New Zealand rabbits. The preparation was essentially free of viral hemagglutinin but contained residual NP and M1 proteins. Both dispersed and aggregated NA tetrameric heads were seen in electron micrographs. Enzymatic activity was preserved, and minimal immunogenic doses in mice and rabbits, respectively, were 3.7 and 0.027 micrograms per kg.
Subject(s)
Antigens, Viral/immunology , Influenza Vaccines/immunology , Neuraminidase/immunology , Animals , Female , Influenza Vaccines/isolation & purification , Mice , Mice, Inbred BALB C , Microscopy, ElectronABSTRACT
The immunogenicity and toxicity of a purified influenza virus (N2) neuraminidase vaccine (NAV) were investigated in 88 human subjects aged 18-40, and compared to response to a conventional trivalent influenza vaccine, Fluogen (Parke-Davis). NAV doses ranged from 2.6 to 69.9 micrograms and were given intramuscularly. Serologic neuraminidase-inhibiting (NI) and neuraminidase-specific ELISA responses in this N2-primed population were roughly proportional to the dose administered. Maximal response was seen in 14-21 days and NI antibody titers persisted unabated for the 6-month post-vaccination follow-up period. All doses were well tolerated with respect to local and systemic reactions. NI tests performed with the putative (1975) priming N2 antigen demonstrated anamnestic response but did not reveal responses not already shown with the homologous (1992) antigen. Response to this purified, non-adjuvanted preparation encourages continuing investigation of the induction of infection-permissive immunity with influenza virus neuraminidase.
Subject(s)
Influenza A virus/immunology , Influenza Vaccines/immunology , Neuraminidase/immunology , Adolescent , Adult , Antibody Formation , Antibody Specificity , Chromatography, Affinity , Humans , Influenza Vaccines/adverse effectsABSTRACT
In studies of infection of young Balb/c mice with a mouse virulent strain of X-31 (H3N2) influenza A virus we have shown a profound virus dose-related effect of infection on body weight. Most of this effect is prevented by prior administration of either inactivated whole virus vaccine, which prevents infection, or purified influenza virus neuraminidase, which is infection-permissive, but reduces pulmonary virus replication by 1.5 to 3 orders of magnitude. These studies support the concept of infection-permissive immunization and suggest that levels of virus replication previously shown to be antigenic can be sustained without significant systemic effects.
Subject(s)
Influenza A virus/immunology , Influenza Vaccines/immunology , Neuraminidase/immunology , Orthomyxoviridae Infections/physiopathology , Weight Loss , Animals , Female , Immunization , Mice , Mice, Inbred BALB CABSTRACT
The hemagglutinin (HA) and neuraminidase (NA) external glycoprotein antigens of H1N1 and H3N2 subtypes of epidemiologically important influenza A viruses prevalent during recent decades were subjected to intensive antigenic analysis by four different methods. Prior to serological analysis with polyclonal rabbit antisera, HA and NA antigens of four viruses of each subtype were segregated by genetic reassortment to forestall nonspecific steric hindrance during antigen-antibody combination. This analysis has demonstrated that with respect to antigenic phenotype, HA and NA proteins have evolved at different rates. With H1N1 viruses, an arrest of significant evolution of the NA discordant with the continuing antigenic drift of HA was found in the 1980-1983 period. It is probable that the different and independent rates of evolution of HA and NA reflect the greater selective pressure of HA antibodies, which forces the more rapid emergence of HA escape mutants. The slower antigenic change found for NA further supports the potential for NA-specific infection-permissive immunization as a useful stratagem against influenza.
