title: First report of elevated monocyte-platelet aggregates in healthy children.
abstract: Platelets are subcellular fragments which circulate in blood and have well established roles in thrombosis and haemostasis in adults. Upon activation, platelets undergo granule exocytosis and express P-Selectin on the cell membrane which binds a ligand on monocytes, leading to monocyte-platelet aggregation. Elevated circulating monocyte-platelet aggregates in adults are linked to atherothrombosis, but have not been investigated in children where thrombosis is less common. This study aimed to measure monocyte-platelet aggregate formation in children using whole blood flow cytometry. Monocyte-platelet aggregates as well as activation and granule exocytosis of platelets were measured in healthy adults (n = 15, median age 28 years) and healthy children (n = 28, median age 7 years). Monocyte-platelet aggregates in healthy children were elevated compared to healthy adults (37.8±4.4% vs 15.5±1.9% respectively, p<0.01). However, this was not accompanied by any difference in platelet activation (PAC-1 binding 6.8±1.5% vs 6.3±2.0% respectively, p = ns) or granule exocytosis (P-selectin expression 4.4±0.5% vs 3.1±0.5% respectively, p = ns). Despite comparable numbers of platelets bound per monocyte (GPIb MFI 117.3±13.7 vs 130.9±28.6 respectively, p = ns), surface P-selectin expression per platelet-bound monocyte was lower in children compared to adults. We therefore provide the first data of elevated monocyte-platelet aggregates in healthy children.
authors.affiliation: School of Medical Sciences, Royal Melbourne Institute of Technology University, Melbourne, Australia.
authors.forename: Christina
authors.initials: C
authors.lastname: Yip
authors.forename: Vera
authors.initials: V
authors.lastname: Ignjatovic
authors.forename: Chantal
authors.initials: C
authors.lastname: Attard
authors.forename: Paul
authors.initials: P
authors.lastname: Monagle
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Linden
mesh_terms: D000328:Adult; D001792:Blood Platelets / Q000166:cytology / Q000502:physiology*; D002648:Child; D005089:Exocytosis; D016650:Fluorescein-5-isothiocyanate / Q000378:metabolism; D005453:Fluorescence; D006262:Health; D006801:Humans; D009000:Monocytes / Q000166:cytology*; D019007:P-Selectin / Q000378:metabolism; D010799:Phycoerythrin / Q000378:metabolism; D010974:Platelet Aggregation / Q000502:physiology*; D055815:Young Adult
chemical_list: D019007:P-Selectin; D010799:Phycoerythrin; D016650:Fluorescein-5-isothiocyanate