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Published on: November 21, 2011
Erythrocytes restrict microvesicle-induced production of reactive oxygen species by polymorphonuclear leukocytes
Line Kjaer Winberg1,2, Niclas Stefan Rasmussen1,2, Claus Henrik Nielsen2
1Copenhagen Lupus and Vasculitis Clinic, Copenhagen University Hospital, Center for Rheumatology and Spine Diseases, Rigshospitalet, Copenhagen, Denmark.
Abstract:
Microvesicles (MVs) are extracellular vesicles released by several cell types upon activation or apoptosis. MVs have the potential to activate complement, which has been suggested to mediate their clearance. However, it is not clear how complement-opsonized MVs are prevented from activating circulating polymorphonuclear leukocytes (PMNs) with release of reactive oxygen species (ROS) and potential damage of endothelium and other bystander cells as consequence. We hypothesized that binding of opsonized MVs to erythrocytes (Es) attenuates MV-induced PMN activation. To test this, normal PMNs were exposed to MVs in the presence and absence of Es from allogenic healthy donors. As analyzed by flow cytometry, the presence of Es restricted the PMN binding of MVs by about 85% (p = 0.002) and mediated a 60-70% inhibition of the PMN production of the ROS H2 O2 , induced by MVs, when lipopolysaccharide was used as a primer (p = 0.002). The competitive binding of MVs to Es was partly dependent on complement, since EDTA inhibited MV binding to Es by 75%. These data suggest that Es, through competitive binding, may restrict MV-induced activation of circulating PMNs and thereby serve a role as a regulator of PMN activation.
Insights
Erythrocytes (red blood cells) may prevent microvesicle-induced immune cell activation. Binding of microvesicles to erythrocytes significantly reduces polymorphonuclear leukocyte activation and reactive oxygen species production.
Area of Science:
- Immunology
- Hematology
- Cell Biology
Background:
- Microvesicles (MVs) are released by cells during activation or apoptosis and can activate complement.
- Complement-opsonized MVs may trigger polymorphonuclear leukocytes (PMNs), leading to reactive oxygen species (ROS) release and potential tissue damage.
- The mechanism preventing excessive PMN activation by MVs is not fully understood.
Purpose of the Study:
- To investigate the hypothesis that erythrocyte (Es) binding to complement-opsonized MVs attenuates MV-induced PMN activation.
- To determine the role of erythrocytes in regulating PMN responses to MVs.
Main Methods:
- Normal PMNs were exposed to MVs with and without allogeneic erythrocytes.
- Flow cytometry was used to analyze MV binding to PMNs and ROS (H2O2) production.
- The effect of EDTA on MV binding to erythrocytes was assessed to evaluate complement dependence.
Main Results:
- Erythrocytes significantly restricted MV binding to PMNs by approximately 85% (p=0.002).
- Erythrocytes mediated 60-70% inhibition of MV-induced ROS production in PMNs when lipopolysaccharide was used as a primer (p=0.002).
- EDTA inhibited MV binding to erythrocytes by 75%, indicating partial complement dependence.
Conclusions:
- Erythrocytes, through competitive binding, may limit microvesicle-induced activation of circulating PMNs.
- Erythrocytes potentially play a regulatory role in controlling PMN activation by MVs.
- This interaction could be a protective mechanism against bystander cell damage.
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