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Platelet-platelet and platelet-leukocyte interactions induced by outer membrane vesicles from N. meningitidis
Mohammad Reza Mirlashari1, Inger Anne Hagberg, Torstein Lyberg
1Research Forum, Ullevaal University Hospital, Oslo, Norway. m.r.mirlashari@ioks.uio.no
Unlabelled:
A large part of native meningococcal lipopolysaccharide (LPS), i.e., LPS integrated in the outer cell membrane, is released in the form of 'blebs' from surplus outer membrane material. In the present study we investigated the effects of purified outer membrane vesicles (OMVs) on blood platelet-platelet and platelet-leukocyte interactions. Citrated whole blood was stimulated in vitro with equal amounts (on a weight basis) of OMV-integrated LPS, purified LPS (P-LPS) from the same meningococcal strain and purified E. coli-LPS. The samples were analyzed by flow cytometry. Upon OMV stimulation platelet aggregation increased 2.1-fold, platelet degranulation 1.8-fold, (measured as CD62P expression), platelet binding to monocytes 2.6-fold, whereas platelet binding to granulocytes increased 2.8-fold. Also, the fraction of large heteroconjugates, i.e., large CD45-positive cell aggregates increased 15.7-fold compared to control. P-LPS and E. coli-LPS also significantly increased platelet aggregation and heteroconjugate formation but did not influence platelet degranulation and binding of platelets to leukocytes in whole blood. When using platelet-rich plasma (PRP), OMVs increased platelet aggregation 2.1-fold and CD62P expression 1.9-fold. P-LPS and E. coli-LPS also significantly increased platelet aggregation in PRP but did not influence platelet degranulation. None of the LPS preparations induced platelet microvesiculation, either in whole blood or in PRP.
Conclusion:
Meningococcal-derived OMVs as well as purified meningococcal LPS, contribute to increased platelet-platelet and platelet-leukocyte aggregation and may thus be of great importance in the development of microthrombosis and organ dysfunction related to fulminant meningococcal septicemia.
Insights
Outer membrane vesicles (OMVs) from meningococcus significantly increase platelet aggregation and binding to leukocytes. Purified lipopolysaccharide (LPS) also promotes aggregation, highlighting their role in sepsis-related microthrombosis.
Area of Science:
- Immunology
- Microbiology
- Hematology
Background:
- Meningococcal lipopolysaccharide (LPS) is released via outer membrane vesicles (OMVs).
- OMVs and LPS are key components in bacterial outer membranes and can interact with host cells.
Purpose of the Study:
- To investigate the effects of meningococcal outer membrane vesicles (OMVs) and purified lipopolysaccharide (LPS) on blood platelet interactions.
- To compare the effects of OMV-integrated LPS, purified LPS (P-LPS), and E. coli LPS on platelet aggregation and leukocyte binding.
Main Methods:
- In vitro stimulation of human whole blood and platelet-rich plasma (PRP) with OMVs, P-LPS, and E. coli LPS.
- Analysis of platelet aggregation, degranulation (CD62P expression), and platelet-leukocyte heteroconjugate formation using flow cytometry.
Main Results:
- OMVs significantly increased platelet aggregation (2.1-fold), degranulation (1.8-fold), and binding to monocytes (2.6-fold) and granulocytes (2.8-fold).
- OMVs also markedly increased large CD45-positive cell aggregates (15.7-fold).
- Purified LPS (meningococcal and E. coli) increased platelet aggregation and heteroconjugate formation but did not affect degranulation or platelet-leukocyte binding in whole blood.
Conclusions:
- Meningococcal OMVs and purified LPS promote platelet-platelet and platelet-leukocyte aggregation.
- These interactions are significant in the pathogenesis of microthrombosis and organ dysfunction in meningococcal septicemia.