Objective. To quantify immunoglobulin and C1q on circulating cell-derived microparticles (MPs) in patients with systemic lupus erythematosus (SLE) and to determine whether immunoglobulin and C1q levels are correlated with clinical and serologic parameters.Methods. Sixty-eight clinically well-characterized SLE patients, 38 healthy controls, 6 patients with systemic sclerosis (SSc), and 6 patients with rheumatoid arthritis (RA) were included. The numbers of annexin V-binding MPs displaying IgG, IgM, or C1q were enumerated by flow cytometry. MP protein levels were determined by mass spectrometry in clinically defined subsets of SLE patients and controls. The MP IgG load was determined by flow cytometric analysis of all samples from SLE patients and healthy controls.Results. SLE patients had significantly increased total and relative numbers of IgG-positive MPs (P ‫؍‬ 0.0004), with a much higher average IgG load per MP (P < 0.0001) than healthy controls. Quantitative mass spectrometry of purified MPs verified significantly increased IgG, IgM, and C1q levels in SLE patients. In RA and SSc patients, the average IgG load per MP was significantly lower than in SLE patients (P ‫؍‬ 0.006 and P ‫؍‬ 0.05, respectively). Also, the IgM load and C1q load per MP were significantly higher in SLE patients than in the control groups (P < 0.05), except for IgM in the RA group. IgG-positive MPs were significantly associated with the presence of anti-double-stranded DNA, anti-extractable nuclear antigen, and antihistone antibodies, with total IgG, and with decreased leukocyte counts. Average IgG load per MP was associated with lower concentrations of MPs, the presence of anti-C1q antibodies, and complement consumption. Systemic lupus erythematosus (SLE) is an autoimmune disease with a wide range of clinical manifestations (1). One of the serologic hallmarks of SLE is the presence of circulating, high-affinity autoantibodies against nuclear constituents (2). These autoantibodies may form circulating proinflammatory immune complexes (ICs) that directly trigger plasmacytoid dendritic cells (PDCs) and the complement system, e.g., in the kidneys (3). Also, IC and autoantibody activation of SLE neutrophils prone to NETosis, i.e., specialized neutrophil cell death, contributes to the sustained PDC activation that is typical of SLE (4,5). The etiology of antinuclear autoimmunity in SLE remains unclear, but persistent, poorly cleared circulating cellular remnants, including microparticles (MPs) and neutrophil extracellular traps, are likely sources of immunogenic autoantigens (6-9). Conclusion. Our findings indicate that circulating cell-derived MPs in SLE patients

Objective. To characterize the unique qualities of proteins associated with circulating subcellular material in systemic lupus erythematosus (SLE) patients compared with healthy controls and patients with other chronic autoimmune diseases.Methods. Using differential centrifugation and high-sensitivity nano-liquid chromatography tandem mass spectrometry, we systematically profiled proteins of microparticles (MPs) from SLE patients (n ‫؍‬ 12), systemic sclerosis (SSc) patients (n ‫؍‬ 6), and rheumatoid arthritis (RA) patients (n ‫؍‬ 6), as well as healthy controls (n ‫؍‬ 12).Results. We identified 531 unique proteins and showed that the differences between healthy controls and patients with SLE with regard to the abundance of 248 proteins were highly statistically significant. Almost half of the proteins that were increased by >2-fold were complement proteins and Ig (increased by 100-4,000 times). MP Ig and complement loads also distinguished SLE from RA and SSc and correlated strongly with clinical SLE severity. Subsets of microtubule proteins, fibronectin, 14-3-3, and desmosomal proteins as well as ficolin 2 and galectin 3 binding protein were also highly increased. In SLE MPs, levels of cytoskeletal, mitochondrial, and organelle proteins, including lysosome-associated membrane protein 1 and transforming growth factor ␤1, were decreased.Conclusion. The data show that SLE patients have increased numbers of MPs that are heavily tagged for removal and fewer MPs with normal protein composition. SLE MPs are unique and specific proteins that represent novel leads for our understanding of SLE and for the development of new treatments of the disease.

Although more common in women, SSc appears as strikingly more severe in men. Our results obtained through the largest worldwide database demonstrate a higher risk of severe cardiovascular involvement in men. These results raise the point of including sex in the management and the decision-making process.

Circulating microparticles (MPs) are produced as part of normal physiology. Their numbers, origin, and composition change in pathology. Despite this, the normal MP proteome has not yet been characterized with standardized high-resolution methods. We here quantitatively profile the normal MP proteome using nano-LC-MS/MS on an LTQ-Orbitrap with optimized sample collection, preparation, and analysis of 12 different normal samples. Analytical and procedural variation were estimated in triply processed samples analyzed in triplicate from two different donors. Label-free quantitation was validated by the correlation of cytoskeletal protein intensities with MP numbers obtained by flow cytometry. Finally, the validity of using pooled samples was evaluated using overlap protein identification numbers and multivariate data analysis. Using conservative parameters, 536 different unique proteins were quantitated. Of these, 334 (63%) were present in all samples and represent an MP core proteome. Technical triplicates showed <10% variation in intensity within a dynamic range of almost 5 decades. Differences due to variable MP numbers and losses during preparative steps could be normalized using cytoskeletal MP protein intensities. Our results establish a reproducible LC-MS/MS procedure, provide a simple and robust MP preparation method, and yield a baseline MP proteome for future studies of MPs in health and disease.