title: Potency under pressure: the impact of hydrostatic pressure on antigenic properties of influenza virus hemagglutinin.
abstract: BACKGROUND
  Influenza vaccines are effective in protecting against illness and death caused by this seasonal pathogen. The potency of influenza vaccines is measured by single radial immunodiffusion (SRID) assay that quantifies antigenic forms of hemagglutinin (HA). Hydrostatic pressure results in loss of binding of influenza virus to red blood cells, but it is not known whether this infers loss of potency.
  
  
  OBJECTIVE
  Our goal was to determine the impact of pressure on HA antigenic structure.
  
  
  METHODS
  Viruses included in the 2010-2011 trivalent influenza vaccine were subjected to increasing number of cycles at 35,000 psi in a barocycler, and the impact of this treatment measured by determining hemagglutination units (HAU) and potency. Potency was assessed by SRID and immunogenicity in mice.
  
  
  RESULTS
  After 25 cycles of pressure, the potency measured by SRID assay was below the limit of quantification for the H1N1 and B viruses used in our study, while the H3N2 component retained some potency that was lost after 50 pressure cycles. Pressure treatment also resulted in loss of HAU, but this did not strictly correlate with the potency value. Curiously, loss of potency was abrogated when influenza A, but not B, antigens were exposed to pressure in chicken egg allantoic fluid. Protection against pressure appeared to be mediated by specific interactions because addition of bovine serum albumin did not have the same effect.
  
  
  CONCLUSIONS
  Our results show that pressure-induced loss of potency is strain dependent and suggests that pressure treatment may be useful for identifying vaccine formulations that improve HA stability.
authors.affiliation: Division of Cellular and Gene Therapies, Office of Cell, Tissue and Gene Therapy, Bethesda, MD, USA.
authors.forename: Schafer L
authors.initials: SL
authors.lastname: Eichelberger
authors.forename: Ishrat
authors.initials: I
authors.lastname: Sultana
authors.forename: Jin
authors.initials: J
authors.lastname: Gao
authors.forename: Melkamu
authors.initials: M
authors.lastname: Getie-Kebtie
authors.forename: Michail
authors.initials: M
authors.lastname: Alterman
authors.forename: Maryna C
authors.initials: MC
authors.lastname: Eichelberger
mesh_terms: D000818:Animals; D000956:Antigens, Viral / Q000276:immunology*; D002645:Chickens; D005260:Female; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000276:immunology*; D006874:Hydrostatic Pressure; D005779:Immunodiffusion; D007252:Influenza Vaccines / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D009975:Orthomyxoviridae / Q000276:immunology*; D064166:Vaccine Potency
chemical_list: D000956:Antigens, Viral; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D007252:Influenza Vaccines
keywords: Hemagglutinin; hydrostatic pressure; immunogenicity; influenza; potency