Absolute quantification of microparticles by flow cytometry in ascites of patients with decompensated cirrhosis: a cohort study

Background: Microparticles (MPs) are small (<1 mu m) cell membrane-derived vesicles that are formed in response to cellular activation or early stages of apoptosis. Increased plasma MP levels have been associated with liver disease severity. Here we investigated the clinical impact of ascites MPs in patients with decompensated liver cirrhosis. Methods: Ascites and blood samples of 163 patients with cirrhosis (ascites n = 163, blood n = 31) were collected between February 2011 and December 2012. MPs were obtained from ascites and from blood by two-step ultracentrifugation and quantified by flow cytometry. Quantitative absolute MP levels were correlated with clinical and laboratory baseline parameters as well as patient outcomes. Ascites microparticles were stained with antibodies against CD66b (neutrophils) and CD3 (lymphocytes) in a subgroup of 60 matched patients. Results: MPs were detected in all ascites and blood samples. Absolute ascites MP levels correlated with blood levels (r = 0.444, p = 0.011). Low ascites MP levels (<488.4 MP/mu L) were associated with a poor 30-day survival probability (<488.4 MP/mu L 71.1% vs. >488.4 MP/mu L 94.7%, log rank p = 0.001) and such patients had a higher relative amount of ascites microparticles derived from neutrophils and lymphocytes. Low levels of ascites MPs, high MELD score and antibiotic treatment were independent risk factors for death within 30 days. Conclusions: Ascites MP levels predict short-term survival along with the liver function in patients with decompensated cirrhosis. Further studies which evaluate ascites MPs as disease specific biomarker with a validation cohort and which investigate its underlying mechanisms are needed. Neutrophils and lymphocytes contributed more frequently to the release of microparticles in patients with low ascites levels, possibly indicating an immune activation in this cohort.