Background Microparticles (MPs) are circulating cellular blebs released by activated and apoptotic cells. MPs have been associated with autoimmune diseases (1) and with vascular events in the general population (2).

Objectives We investigated the number and phenotype of MPs in patients with systemic lupus erythematosus (SLE) and population based controls. We hypothesised that the MP profile could identify SLE subgroups with previous vascular events and/or antiphospholipid syndrome (APS).

Methods 290 consecutive SLE patients and 290 controls, individually matched to the patients were included. Previous vascular events, clinical characteristics and presence of antiphospholipid antibodies (aPL) were tabulated. MPs positive for phosphatidylserine (PS) were identified with lactadherin and measured by flow cytometry. They were phenotyped according to cellular origin (platelet, endothelial or leukocyte) and protein expression (CD40 ligand=CD40L, tissue factor=TF, vascular cell adhesion molecule 1=VCAM-1 or high-mobility group protein B1=HMGB1). C4d expression was measured on endothelial and platelet MPs, regardless of PS expression.

Results There was a highly significant difference between SLE patients and controls for all MPs, regardless of origin, p<1x 10^-40 for all. Moreover, MPs exposing inflammation and/or activation markers CD40L, TF, VCAM-1, HMGB1 or C4d were also significantly increased in the SLE patients, p<1 x 10^-15 for all. Associations with borderline p-values (p=0.044 and p=0.047) between endothelial MPs and previous vascular events were noted.

Conclusions Patients with SLE had 2-10 times elevated levels of MPs of various cellular origins in blood. Associations with borderline p-values between MPs of endothelial origin and previous vascular events were found but the subgroup with APS could not be identified by MP profile. Though, analytical challenges remain; the remarkably high levels of MPs in SLE patients may provide new insights into the pathogenesis of SLE, and MPs merit further evaluation as candidate diagnostic biomarkers for SLE.

References

1. Pisetsky DS, Ullal AJ, Gauley J, Ning TC. Microparticles as mediators and biomarkers of rheumatic disease. Rheumatology (Oxford). 2012;51(10):1737-46.

2. Lacroix R, Dubois C, Leroyer AS, Sabatier F, Dignat-George F. Revisited role of microparticles in arterial and venous thrombosis. J Thromb Haemost. 2013;11 Suppl 1:24-35.

Acknowledgements The work in this abstract will be part of Dr Vikerfors thesis, defended 24 Feb and distributed both electronically and in paper format 30 Jan.

Disclosure of Interest None declared