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Short Leucine-Rich Proteoglycans Modulate Complement Activity and Increase Killing of the Respiratory Pathogen

Maisem Laabei1, Guanghui Liu1, David Ermert1

  • 1Division of Medical Protein Chemistry, Lund University, 21428 Malmö, Sweden.

Journal of Immunology (Baltimore, Md. : 1950)
|September 30, 2018
PubMed

Insights

Short leucine-rich proteoglycans (SLRPs) enhance the immune system's ability to kill the pathogen Moraxella catarrhalis. These SLRPs, including fibromodulin, osteoadherin, and biglycan, inhibit immune evasion and promote bacterial clearance.

Area of Science:

  • Microbiology
  • Immunology
  • Biochemistry

Background:

  • Moraxella catarrhalis is a significant respiratory pathogen causing otitis media and COPD exacerbations.
  • The molecular mechanisms of M. catarrhalis pathogenesis and host interactions are not well understood.
  • Developing effective vaccines and immunotherapies against M. catarrhalis is hindered by limited knowledge.

Purpose of the Study:

  • To investigate the novel antibacterial role of short leucine-rich proteoglycans (SLRPs) in host defense against M. catarrhalis.
  • To elucidate the mechanisms by which SLRPs modulate the host immune response to M. catarrhalis.
  • To identify potential therapeutic targets for treating M. catarrhalis infections.

Main Methods:

  • Assessed the ability of fibromodulin (FMOD), osteoadherin (OSAD), biglycan (BGN), and decorin (DCN) to enhance serum killing of M. catarrhalis.
  • Investigated M. catarrhalis binding to SLRPs across various clinical and laboratory strains.
  • Utilized surface protein A2/A2H (UspA2/A2H) to resolve SLRP binding mechanisms.
  • Examined the competitive inhibition of C4b-binding protein (C4BP) by SLRPs.
  • Measured C3b/iC3b deposition and membrane attack complex (MAC) formation.
  • Evaluated neutrophil killing of M. catarrhalis in vitro.

Main Results:

  • FMOD, OSAD, and BGN significantly enhanced serum-mediated killing of M. catarrhalis.
  • M. catarrhalis demonstrated conserved binding to all tested SLRPs, mediated by UspA2/A2H.
  • SLRPs competitively inhibited C4BP binding, leading to increased complement deposition (C3b/iC3b) and MAC formation.
  • OSAD and BGN promoted enhanced neutrophil killing, both complement-dependent and independent.
  • Decorin (DCN) did not enhance M. catarrhalis killing.

Conclusions:

  • SLRPs, specifically FMOD, OSAD, and BGN, possess a novel antibacterial function against M. catarrhalis.
  • These SLRPs enhance bacterial killing by modulating complement activation and inhibiting immune evasion.
  • SLRPs represent a promising target for developing new therapeutic strategies against M. catarrhalis infections.

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