Search

The correlates for protection against influenza infection are incompletely characterized. We have applied an ELISA strategy that distinguishes antibodies against native viral surface antigens (potentially neutralizing) from antibodies directed against internal and denatured viral proteins (not neutralizing) to three groups of vaccinated subjects: (1) participants in a study of repeated annual vaccination, (2) elderly subjects and (3) patients with Systemic Lupus Erythematosus compared to control subjects. Antibody increase after vaccination was inversely related to the level of pre-existing antibodies in all groups; most subjects had significant initial antibody levels and showed little increase in amount of antibody after vaccination, but the avidity of their serum antibodies tended to increase. Antibodies against denatured virus proteins varied with vaccine formulation; vaccines that are more recent have less total protein for the same amount of native hemagglutinin. We propose an index consisting of rank order of antibody level plus antibody avidity, both measured against native virus, plus hemagglutination-inhibition antibody titer, as a useful measure of immunity against influenza.

Objective: Our studies aimed to measure the quality of antibody response to influenza vaccines in the elderly. The frequency of significant rise in hemagglutination inhibition (HAI) titer in the elderly is low and although annual vaccination reduces morbidity and mortality, better correlates of vaccine efficacy in the elderly are needed., Methods: We measured the amount and avidity of serum antibodies against native H3N2 influenza glycoproteins or denatured virus (unfoldons) in pre- and post-vaccinated sera of 36 elderly subjects., Results: Eighty percent of subjects had high pre-immunization antibody levels and only 13% showed >or=2fold increase after vaccination, but 33% showed >or=2fold increase in avidity. With increasing dosage there was a significant increase in avidity against unfoldons with 50% of subjects showing >or=2fold increase at the highest dose. Elderly subjects given subunit vaccine showed higher reactivity with unfoldons (78% of native) than younger subjects studied earlier who were given inactivated whole virus vaccine (19% of native)., Conclusion: The clear inverse relationship between pre-immunization antibody levels and antibody increase after vaccination implies that a major reason for the low frequency of antibody responses in elderly subjects is simply because they have high pre-immunization antibody levels. Only low reactivity was observed with earlier viruses. The increased proportion and avidity of antibodies against unfoldons is of concern, as these are not protective, and vaccine developers need to be aware of the role of age or vaccine formulation in inducing anti-unfoldon antibodies.

The crystal structure of the complex between neuraminidase (NA) of influenza virus A/Memphis/31/98 (H3N2) and Fab of monoclonal antibody Mem5 has been determined at 2.1A resolution and shows a novel pattern of interactions compared to other NA-Fab structures. The interface buries a large area of 2400 A2 and the surfaces have high complementarity. However, the interface is also highly hydrated. There are 33 water molecules in the interface>or=95% buried from bulk solvent, but only 13 of these are isolated from other water molecules. The rest are involved in an intricate network of water-mediated hydrogen bonds throughout the interface, stabilizing the complex. Glu199 on NA, the most critical side-chain to the interaction as previously determined by escape mutant analysis and site-directed mutation, is located in a non-aqueous island. Glu199 and three other residues that contribute the major part of the antigen buried surface of the complex have mutated in human influenza viruses isolated after 1998, confirming that Mem5 identifies an epidemiologically important antigenic site. We conclude that antibody selection of NA variants is a significant component of recent antigenic drift in human H3N2 influenza viruses, supporting the idea that influenza vaccines should contain NA in addition to hemagglutinin.