title: Differences in avidity of IgG antibodies to pertussis toxin after acellular pertussis booster vaccination and natural infection.
abstract: BACKGROUND
  Pertussis toxin (PT) is a specific virulence factor of Bordetella pertussis and it is included in all acellular pertussis vaccines (aP). Although immunity after infection seems to persist longer than that after vaccination, the exact mechanism(s) is not known. Primary aim of this study was to develop an ELISA method for measuring avidity index (AI) of IgG-anti-PT antibodies and to compare antibody responses after booster vaccination and infection. Secondary aim was to evaluate if the AI-ELISA has potential in the serodiagnosis of pertussis.
  
  
  METHODS
  Serum samples from a total of 409 subjects were included in the study. Paired sera were taken from 97 adolescents who received booster vaccine ten years ago (dTpa-004) and from 80 young adults who received a second booster dose ten years after the previous booster vaccine (dTpa-040). Thirty-two paired sera from culture-confirmed pertussis patients, 161 single sera from serologically diagnosed patients and 39 single sera from healthy controls were included. AI of IgG-anti-PT antibodies were determined with newly developed ELISA using diethylamine (DEA) as a bond breaking agent. The IgG-anti-PT antibodies were measured by standardized ELISA.
  
  
  RESULTS
  A significant increase was found in antibody concentrations and AI between PRE and one month POST vaccination ten years ago [GMC for antibody: 7.9 IU/ml vs. 98.3 IU/ml (p=0.0001); for AI: 40.4% vs. 56.1% (p=0.0001)]. Similar result was observed after the second booster dose [GMC for antibody: 9.2 IU/ml vs. 92.4 IU/ml (p=0.0001); for AI: 36.1% vs. 59.5% (p=0.0001)] and between the first and second sera of culture-confirmed patients [GMC for antibody: 6.9 IU/ml vs. 285.1 IU/ml (p=0.0001); for AI: 40.5% vs. 68.4% (p=0.0001)]. Healthy controls showed lower levels of both antibodies and AI.
  
  
  CONCLUSIONS
  Our results suggest that there may be difference in quality and quantity of antibodies to PT after vaccination and after infection. Furthermore, AI could be a help for vaccine studies.
authors.affiliation: Department of Infectious Disease Surveillance and Control, National Institute for Health and Welfare, Turku, Finland.
authors.forename: Alex-Mikael
authors.initials: AM
authors.lastname: Barkoff
authors.forename: Kirsi
authors.initials: K
authors.lastname: Gröndahl-Yli-Hannuksela
authors.forename: Juho
authors.initials: J
authors.lastname: Vuononvirta
authors.forename: Jussi
authors.initials: J
authors.lastname: Mertsola
authors.forename: Teemu
authors.initials: T
authors.lastname: Kallonen
authors.forename: Qiushui
authors.initials: Q
authors.lastname: He
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000907:Antibodies, Bacterial / Q000276:immunology*; D000915:Antibody Affinity; D000992:Antitoxins / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D005260:Female; D006801:Humans; D007117:Immunization, Secondary / Q000379:methods*; D007074:Immunoglobulin G / Q000276:immunology; D007223:Infant; D008297:Male; D008875:Middle Aged; D037342:Pertussis Toxin / Q000276:immunology*; D010567:Pertussis Vaccine / Q000008:administration & dosage / Q000276:immunology*; D022282:Vaccines, Acellular / Q000008:administration & dosage / Q000276:immunology; D014917:Whooping Cough / Q000276:immunology* / Q000517:prevention & control*; D055815:Young Adult
chemical_list: D000907:Antibodies, Bacterial; D000992:Antitoxins; D007074:Immunoglobulin G; D010567:Pertussis Vaccine; D022282:Vaccines, Acellular; D037342:Pertussis Toxin