Haemophilus influenzae survival during complement-mediated attacks is promoted by Moraxella catarrhalis outer membrane vesicles

Abstract number: 1733_313

Tan T.T., Mörgelin M., Forsgren A., Riesbeck K.

Objectives:Moraxella catarrhalis causes respiratory tract infections in children and adults with COPD. It is often isolated as a co-pathogen with Haemophilus influenzae. The underlying mechanism for this cohabitation is unclear. The aim of this study was to investigate if M. catarrhalis is able to contribute to the survival of H. influenzae in human serum.

Methods: The M. catarrhalis ubiquitous surface proteins (Usp) A1 and A2 are known to contribute to M. catarrhalis serum resistance by interactions with various complement proteins. M. catarrhalis also secretes outer membrane vesicles (blebs) in vitro. Hence, we examined nasopharyngeal samples of a 9-year old child who had grown pure cultures of M. catarrhalis during an episode of sinusitis. Both electron microscopy and gold labeled anti-UspA1 and A2 antibodies were used to analyse the samples. The effect of M. catarrhalis blebs on the bacteriolytic activity of human serum against H. influenzae was examined by incubating blebs with serum before performing bactericidal assays. The interaction of these blebs with the complement system was further documented by dot-blot assays.

Results: Blebs carrying Usp A1/A2 are secreted both in vivo and in vitro. These blebs do carry UspA1 and A2 and they absorb the third component of complement system (C3), counteracting the complement cascade directed against H. influenzae. An improved survival was evident in all clinical strains (n = 5) of H. influenzae tested. In contrast, UspA1/2 deficient blebs are much weaker inhibitors of the complement-dependent killing of H. influenzae.

Conclusion: Our results suggest a novel strategy in which pathogens collaborate to conquer innate immunity and that the M. catarrhalis vaccine candidates, UspA1/A2 play a major role in this interaction.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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