• Role of Vaccine-Induced IgG in Protection Against Bordetella Pertussis

      Masterson, Mary; Pasetti, Marcela F. (2019)
      Bordetella pertussis is a highly infectious respiratory pathogen that can induce severe bronchopneumonia and respiratory failure in infants (whooping cough). Vaccine formulations consisting of Diphtheria toxoid, Tetanus toxoid, and Acellular Pertussis (aP) components (DTaP and Tdap) protect against disease. It remains unclear how a parenteral vaccine, which primarily elicits systemic IgG, contributes to protection against a respiratory pathogen. The goal of this study was to investigate mechanisms by which vaccine-induced IgG reaches the respiratory mucosa and contributes to protection against B. pertussis infection. We hypothesized that pertussis-specific systemic IgG is transported from circulation into the airways via the neonatal Fc receptor (FcRn). To test this hypothesis, wild type mice and mice lacking FcRn (FcRn-/-) were immunized with DTaP or passively transferred DTaP-immune serum and challenged with B. pertussis. Post-challenge readouts included kinetics of Pertussis Toxin (PT) IgG in serum and bronchoalveolar lavage fluid (BALf), bacterial load quantification, and histopathology of lung tissues. WT vaccinated mice were able to clear the infection, whereas FcRn-/- vaccinated mice had residual bacterial counts and increased lung inflammation. Passive administration of DTaP-immune sera reduced lung colonization in both WT and FcRn-/- mice. However, FcRn-/- recipients exhibited moderate bronchopneumonia (absent in WT mice). The lower bacterial clearance and exacerbated tissue damage observed in actively and passively immunized FcRn-/- mice was not due to the absence of PT-IgG (or differences in IgG isotype) in BALf. Rather, WT and FcRn-/- mice had similar PT-IgG levels in serum and BALf, suggesting that FcRn-independent mechanisms mediate IgG transport across the lung. PT-IgG progressively increased in BALf of passively immunized FcRn-/- mice post-challenge (along with lung inflammation,) suggesting IgG also diffuses through damaged lung epithelium. We observed that neutrophils from FcRn-/- mice had lower B. pertussis opsonophagocytic capacity as compared to WT. This impairment in IgG-mediated antimicrobial function in the absence of FcRn could explain the increased inflammation in FcRn-/- mice. In conclusion, we have shown that pertussis-specific IgG translocation into the airways appears to be FcRn-independent, and that IgG-mediated B. pertussis neutrophil phagocytosis may contribute to bacterial clearance and tissue preservation post-infection through FcRn interactions.
    • Serological Correlates of Protection against Shigellosis in Humans

      Shimanovich, Avital Aviva; Pasetti, Marcela F.; 0000-0001-6516-7221 (2017)
      Shigella infection causes severe diarrheal disease that results in protective immunity. Antibodies, particularly IgG, are believed to play an important role in host defenses against shigellosis. The mechanisms by which antibodies interact with Shigella and prevent infection remain to be understood. The goal of this project was to characterize immune responses against Shigella in humans and define the anti-microbial activity of Shigella-specific antibodies as potential immune correlates of protection (CoP). We established Shigella-specific functional antibody assays and determined serum bactericidal (SBA) and opsonophagocytic killing antibody (OPKA) titers as well as antigen-specific antibody levels pre- and post-challenge in serum from a Phase IIb study. Pre-challenge antibody titers, including SBA, OPKA, IpaB- and VirG(IscA)-specific IgG and IgG1, correlated with reduced severity of shigellosis while IpaC-, IpaD- and LPS-specific IgG levels did not. SBA, OPKA, IpaB-, and VirG-specific IgG antibodies increased after challenge, particularly in volunteers who experienced moderate disease. This is the first demonstration that functional and VirG-specific antibody levels represent CoP in a controlled human challenge study. In a small animal experiment, mice vaccinated intranasally with VirG developed VirG-specific IgG and experienced 60% protection against lethal Shigella pulmonary challenge. Next, we examined the presence of Shigella-specific SBA activity in (1) American volunteers who received oral live-attenuated Shigella vaccine candidates CVD 1204 and 1208S and (2) pregnant women living in an endemic region. We confirmed that live-oral vaccination mimics natural infection by inducing high rates of SBA responses after a single vaccination and that similar activity is present in women naturally exposed to the organism. SBA assays also successfully determined the immunogenicity of a prime-boost vaccination regimen that involved initial dosing of non-human primates with CVD 1208S followed by a boost with CVD 1208S expressing Escherichia coli CFA1 and CS3 antigens. Mechanistic studies to determine the antigenic specificity of SBA indicated that LPS and outer-membrane proteins may be involved, as depletions significantly reduced SBA activity of hyperimmune serum. In conclusion, we demonstrate potential CoP that may determine Shigella-specific immunity. This work provides support for further mechanistic analysis and future studies to determine if functional antibodies can predict protective immunity and vaccine efficacy.