Functionality of cross-reactive antibodies against Moraxella catarrhalis

Abstract

Event Abstract Back to Event Functionality of cross-reactive antibodies against Moraxella catarrhalis Daria Augustyniak1*, Monika Piekut1 and Grażyna Majkowska-Skrobek1 1 University of Wroclaw, Department of Pathogen Biology and Immunology, Institute of Genetics and Microbiology, Poland Introduction: Antibody-dependent immune response against human respiratory tract pathogen Moraxella catarrhalis is critical for its effective elimination [1-5]. Outer membrane proteins (OMPs) and lipooligosaccharide are the major surface-exposed immune targets in this bacterium [1-3,6].The goal of the study was to characterize the broad-spectrum effectiveness of cross-reacting antibodies produced in response to whole cells (Mc) or purified outer membrane proteins (OMPs) of this pathogen. Methods: Antisera were obtained from mice immunized with whole bacteria (anti-Mc sera) or Zwittergent-isolated OMPs (anti-OMPMc sera) [3]. The titers of cross-reactive antibodies were measured by whole-cell ELISA whereas their avidities by ELISA elution assay with sodium thiocyanate. The following functional methods were used: (1) the antibody-dependent bactericidal assay, (2) the opsonophagocytic assay with human THP-1 cell line, and (3) the blocking adhesion assay with human A549 epithelial cell line. Results: There were high titers of cross-reactive antibodies both in anti-Mc and anti-OMPMc sera. The titers of anti-OMPMc sera were higher than that of anti-Mc sera. The cross-reactive IgG produced exclusively to OMPs had stronger avidity comparing to those elicited against whole M. catarrhalis cells. Additionally, these antibodies played a pivotal role in complement-mediated killing of heterologous M. catarrhalis isolates. The positive relationship between total titer of complement-fixing subclasses IgG2a and IgG2b and bactericidal titer was found for both anti-Mc and anti-OMPMc sera. The opsonophagocytic potency as well as reduction of bacterial attachment to human epithelium was much stronger for cross-reactive anti-OMPMc than cross-reactive anti-Mc antibodies. Conclusion: The presence of cross-reactive antibodies with bactericidal, opsonophagocytic and bacterial adhesion blocking potency may be additional source to control host-Moraxella catarrhalis interaction especially when the host immune status is prone to a new infection.