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Serum amyloid A is an innate immune opsonin for Gram-negative bacteria

Chandrabala Shah1, Ranjeeta Hari-Dass, John G Raynes

  • 1Immunology Unit, Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel St, London WCIE 7HT, United Kingdom.

Blood
|June 1, 2006
PubMed

Insights

Serum amyloid A (SAA) enhances the innate immune system's ability to recognize and clear Gram-negative bacteria. SAA opsonization significantly boosts neutrophil and macrophage responses to bacteria like E. coli and P. aeruginosa.

Area of Science:

  • Immunology
  • Microbiology
  • Biochemistry

Background:

  • Serum amyloid A (SAA) is a major acute-phase protein in mammals.
  • Previous research showed SAA binds to Gram-negative bacteria via outer membrane protein A (OmpA).

Purpose of the Study:

  • To investigate if SAA influences the response of innate phagocytic cells to bacteria.
  • To determine SAA's role in innate immune recognition of bacterial pathogens.

Main Methods:

  • Assessing neutrophil phagocytosis and reactive oxygen intermediate production with SAA-opsonized bacteria.
  • Evaluating macrophage phagocytosis and cytokine (TNF-alpha, IL-10) production.
  • Comparing responses to SAA-binding (E. coli, P. aeruginosa) versus non-binding (S. pneumoniae) bacteria.

Main Results:

  • SAA opsonization significantly increased neutrophil phagocytosis of E. coli, comparable to serum opsonization.
  • SAA enhanced neutrophil reactive oxygen intermediate production.
  • SAA opsonization increased macrophage phagocytosis of E. coli and boosted TNF-alpha and IL-10 production in response to SAA-opsonized Gram-negative bacteria.
  • No enhancement was observed with S. pneumoniae, which does not bind SAA.

Conclusions:

  • SAA acts as a novel innate recognition protein for Gram-negative bacteria.
  • SAA significantly enhances the phagocytic cell response to Gram-negative bacteria at physiological concentrations.
  • SAA plays a crucial role in the innate immune system's defense against Gram-negative infections.

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