Microparticles as novel biomarkers/effectors in severe sepsis

Microparticles (MP) are submicron structures produced by all cells upon activation or apoptosis that act as a non-soluble means of communication between cells. They ferry proteins, bioactive lipids, RNA and receptors, as well as ridding cells of redundant organelles and toxins. They have been recently investigated for their pathophysiological role and as potential biomarkers/effectors in many diseases. In severe sepsis, studies of MP so far have produced inconsistent and even conflicting results. In this project, it was demonstrated that cell derived MP subsets vary according to the cause of severe sepsis (community acquired pneumonia (CAP) or faecal peritonitis (FP)), where CAP patients had higher levels of circulating MP. Surprisingly, FP patients MP levels were comparable to healthy volunteers. Further stratification of MP subsets according to their expression of the protein alpha-2-macroglobulin (A2M) has yielded better differentiation between the two diseases. The A2M expressing MP were significantly higher in survivors of community acquired pneumonia sepsis, but there was no similar association in patient with FP. Granulocyte macrophage colony-stimulating factor (GM-CSF) and interferon γ (IFN- γ) are being studied as possible adjuvant therapies in sepsis. They seem to reverse the immune-paresis that ensues after the initial insult. MP produced from whole blood stimulated with GM-CSF and IFN- γ were studied in this project. Both GM-CSF and IFN- γ increased MP expressing A2M over control. These MP elicited a pro-inflammatory phenotype when incubated with neutrophils or endothelial cells which may contribute to the potential benefits of GM-CSF and IFN- γ in severe sepsis.HCA internationa

Microparticle alpha-2-macroglobulin enhances pro-resolving responses and promotes survival in sepsis

Incorporation of locally produced signaling molecules into cell-derived vesicles may serve as an endogenous mediator delivery system. We recently reported that levels alpha-2-macroglobulin (A2MG)-containing microparticles are elevated in plasma from patients with sepsis. Herein, we investigated the immunomodulatory actions of A2MG containing microparticles during sepsis. Administration of A2MG-enriched (A2MG-E)-microparticles to mice with microbial sepsis protected against hypothermia, reduced bacterial titers, elevated immunoresolvent lipid mediator levels in inflammatory exudates and reduced systemic inflammation. A2MG-E microparticles also enhanced survival in murine sepsis, an action lost in mice transfected with siRNA for LRP1, a putative A2MG receptor. In vitro, A2MG was functionally transferred onto endothelial cell plasma membranes from microparticles, augmenting neutrophil–endothelial adhesion. A2MG also modulated human leukocyte responses: enhanced bacterial phagocytosis, reactive oxygen species production, cathelicidin release, prevented endotoxin induced CXCR2 downregulation and preserved neutrophil chemotaxis in the presence of LPS. A significant association was also found between elevated plasma levels of A2MG-containing microparticles and survival in human sepsis patients. Taken together, these results identify A2MG enrichment in microparticles as an important host protective mechanism in sepsis

Microparticle alpha-2-macroglobulin enhances pro-resolving responses and promotes survival in sepsis

These studies were supported by The Wellcome Trust (program 086867/Z/08) and the William Harvey Research Foundation to MP, the United Kingdom Intensive Care Society to CJH and the National Institutes of Health GM Grant P01GM095967 (awarded to Charles N. Serhan). LVN is supported by an Arthritis Research UK Career Development Fellowship (19909). EPSRC Seed Funding Cross disciplinary Grant (QMUL) awarded to GBS and MP. This work forms part of the research themes contributing to the translational research portfolio of Barts and The London NIHR Cardiovascular BRU

Identification of an activated neutrophil phenotype in polymyalgia rheumatica during steroid treatment: a potential involvement of immune cell cross-talk.

We have reported the existence of a distinct neutrophil phenotype in giant cell arteritis (GCA) patients arising at week 24 of steroid treatment. In the present study, we investigated whether longitudinal analysis of neutrophil phenotype in patients with polymyalgia rheumatica (PMR) could reveal a novel association with disease status and immune cell cross-talk. Thus, we monitored PMR patient neutrophil phenotype and plasma microvesicle (MV) profiles in blood aliquots collected pre-steroid, and then at weeks 1, 4, 12 and 24 post-steroid treatment.Using flow cytometric and flow chamber analyses, we identified 12-week post-steroid as a pivotal time-point for a marked degree of neutrophil activation, correlating with disease activity. Analyses of plasma MVs indicated elevated AnxA1+ neutrophil-derived vesicles which, in vitro, modulated T-cell reactivity, suggesting distinct neutrophil phenotypic and cross-talk changes at 24 weeks, but not at 12-week post-steroid.Together, these data indicate a clear distinction from GCA patient neutrophil and MV signatures, and provide an opportunity for further investigations on how to 'stratify' PMR patients and monitor their clinical responses through novel use of blood biomarkers