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Inactivation of staphylococcal phenol soluble modulins by serum lipoprotein particles
Bas G J Surewaard1, Reindert Nijland, András N Spaan
1Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands. b.g.j.surewaard@umcutrecht.nl
Abstract:
Staphylococcus aureus virulence has been associated with the production of phenol soluble modulins (PSM). PSM are known to activate, attract and lyse neutrophils. However, the functional characterizations were generally performed in the absence of human serum. Here, we demonstrate that human serum can inhibit all the previously-described activities of PSM. We observed that serum can fully block both the cell lysis and FPR2 activation of neutrophils. We show a direct interaction between PSM and serum lipoproteins in human serum and whole blood. Subsequent analysis using purified high, low, and very low density lipoproteins (HDL, LDL, and VLDL) revealed that they indeed neutralize PSM. The lipoprotein HDL showed highest binding and antagonizing capacity for PSM. Furthermore, we show potential intracellular production of PSM by S. aureus upon phagocytosis by neutrophils, which opens a new area for exploration of the intracellular lytic capacity of PSM. Collectively, our data show that in a serum environment the function of PSM as important extracellular toxins should be reconsidered.
Insights
Human serum lipoproteins, particularly HDL, neutralize Staphylococcus aureus phenol soluble modulins (PSM), inhibiting their neutrophil-damaging activities. This finding re-evaluates PSM
Area of Science:
- Microbiology
- Immunology
- Biochemistry
Background:
- Staphylococcus aureus virulence is linked to phenol soluble modulins (PSM).
- PSM are known to activate, attract, and lyse neutrophils.
- Previous studies characterized PSM activities without human serum.
Purpose of the Study:
- To investigate the effect of human serum on PSM activities.
- To identify serum components that interact with and neutralize PSM.
- To explore the role of PSM in intracellular environments.
Main Methods:
- Incubation of PSM with human serum and purified lipoproteins (HDL, LDL, VLDL).
- Assessment of neutrophil activation (FPR2) and cell lysis.
- Analysis of PSM-lipoprotein interactions using binding assays.
- Investigation of intracellular PSM production in phagocytosed S. aureus.
Main Results:
- Human serum completely inhibited PSM-induced neutrophil lysis and FPR2 activation.
- Direct interaction between PSM and serum lipoproteins was observed.
- HDL demonstrated the highest capacity to bind and neutralize PSM.
- Evidence suggests intracellular PSM production by S. aureus within neutrophils.
Conclusions:
- Serum lipoproteins, especially HDL, neutralize the extracellular activities of PSM.
- The function of PSM as extracellular toxins requires reconsideration in a serum environment.
- Intracellular PSM production presents a novel avenue for research into S. aureus pathogenesis.
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