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Updated: Jun 16, 2025
Laminar Flow-based Assays to Investigate Leukocyte Recruitment on Cultured Vascular Cells and Adherent Platelets
Published on: April 9, 2018
Biofilm-dispersed pneumococci induce elevated leukocyte and platelet activation
Yashuan Chao1,2, Martina Mørch1,2, Anders P Håkansson3
1Division of Infection Medicine, Department of Clinical Sciences, Lund, Faculty of Medicine, Lund University, Lund, Sweden.
Introduction:
Streptococcus pneumoniae (the pneumococcus) effectively colonizes the human nasopharynx, but can migrate to other host sites, causing infections such as pneumonia and sepsis. Previous studies indicate that pneumococci grown as biofilms have phenotypes of bacteria associated with colonization whereas bacteria released from biofilms in response to changes in the local environment (i.e., dispersed bacteria) represent populations with phenotypes associated with disease. How these niche-adapted populations interact with immune cells upon reaching the vascular compartment has not previously been studied. Here, we investigated neutrophil, monocyte, and platelet activation using ex vivo stimulation of whole blood and platelet-rich plasma with pneumococcal populations representing distinct stages of the infectious process (biofilm bacteria and dispersed bacteria) as well as conventional broth-grown culture (planktonic bacteria).
Methods:
Flow cytometry and ELISA were used to assess surface and soluble activation markers for neutrophil and monocyte activation, platelet-neutrophil complex and platelet-monocyte complex formation, and platelet activation and responsiveness.
Results:
Overall, we found that biofilm-derived bacteria (biofilm bacteria and dispersed bacteria) induced significant activation of neutrophils, monocytes, and platelets. In contrast, little to no activation was induced by planktonic bacteria. Platelets remained functional after stimulation with bacterial populations and the degree of responsiveness was inversely related to initial activation. Bacterial association with immune cells followed a similar pattern as activation.
Discussion:
Differences in activation of and association with immune cells by biofilm-derived populations could be an important consideration for other pathogens that have a biofilm state. Gaining insight into how these bacterial populations interact with the host immune response may reveal immunomodulatory targets to interfere with disease development.
Insights
Biofilm-derived bacteria, but not planktonic bacteria, significantly activate neutrophils, monocytes, and platelets. This interaction is crucial for understanding how Streptococcus pneumoniae causes disease and suggests potential immunomodulatory targets.
Area of Science:
- Microbiology
- Immunology
- Pathogenesis
Background:
- *Streptococcus pneumoniae* colonizes the nasopharynx and can cause invasive diseases like pneumonia and sepsis.
- *Streptococcus pneumoniae* exhibits distinct phenotypes when grown as biofilms versus in planktonic culture.
- The interaction of niche-adapted pneumococcal populations with immune cells in the vascular compartment is poorly understood.
Purpose of the Study:
- To investigate the activation of neutrophils, monocytes, and platelets by different *Streptococcus pneumoniae* populations.
- To compare the immune response to biofilm bacteria, dispersed bacteria, and planktonic bacteria.
- To understand how *Streptococcus pneumoniae* interacts with key immune cells during infection.
Main Methods:
- *Ex vivo* stimulation of whole blood and platelet-rich plasma with *Streptococcus pneumoniae* populations.
- Flow cytometry and ELISA were used to measure immune cell activation markers.
- Assessment of platelet-neutrophil and platelet-monocyte complex formation and platelet responsiveness.
Main Results:
- Biofilm-derived bacteria (biofilm and dispersed) induced significant activation of neutrophils, monocytes, and platelets.
- Planktonic bacteria induced minimal immune cell activation.
- Platelets remained functional post-stimulation, with responsiveness inversely related to initial activation; bacterial association with immune cells mirrored activation patterns.
Conclusions:
- *Streptococcus pneumoniae* populations derived from biofilms elicit a robust immune response involving neutrophils, monocytes, and platelets.
- The distinct immune interactions of biofilm-derived bacteria compared to planktonic bacteria may be critical for disease development.
- Understanding these interactions could identify novel immunomodulatory therapeutic targets for pneumococcal infections.
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