Potential Involvement of Platelet-Derived Microparticles and Microparticles Forming Immune Complexes during Monocyte Activation in Patients with Systemic Lupus Erythematosus

Abstract

Microparticles (MPs) are vesicles derived from the plasma membrane of different cells, are considered a source of circulating autoantigens, and can form immune complexes (MPs-ICs). The number of MPs and MPs-ICs increases in patients with systemic lupus erythematosus (SLE). MPs activate myeloid cells by inducing IL-6 and TNF-α in both SLE and other diseases. Therefore, we propose that the recognition of MPs-ICs by monocytes rather that MPs may define their phenotype and contribute to the inflammatory process in patients with SLE. Thus, the aims of this study were to evaluate the association among circulating MPs-ICs from different cell sources, alterations observed in monocyte subsets, and disease activity in patients with SLE and to establish whether monocytes bind and respond to MPs-ICs in vitro. Circulating MPs and monocyte subsets were characterized in 60 patients with SLE and 60 healthy controls (HCs) using multiparametric flow cytometry. Patients had higher MP counts and frequencies of MPs-CD41a + (platelet-derived) compared with HCs, regardless of disease activity. MPs from patients with SLE were C1q + and formed ICs with IgM and IgG. MPs-IgG + were positively correlated with active SLE (aSLE), whereas MPs-IgM + were negatively correlated. Most of the circulating total ICs-IgG + were located on MPs. The proportion and number of non-classical monocytes were significantly decreased in patients with SLE compared with HCs and in patients with aSLE compared with patients with the inactive disease. Non-classical monocytes obtained from patients with SLE exhibited increased levels of CD64 associated with MPs-IgG +, MPs-C1q +, total circulating ICs-IgG +, and disease activity. The direct effects of MPs and MPs-IgG + on monocytes were evaluated in cell culture. Monocytes from both HCs and patients bound to and internalized MPs and MPs-IgG + independent of CD64. These vesicles derived from platelets (PMPs), mainly PMPs-IgG +, activated monocytes in vitro and increased the expression of CD69, CD64, and pro-inflammatory cytokines such as IL-1β, TNF-α, and IFN-α. Therefore, MPs are one of the most representative sources of the total amount of circulating ICs-IgG + in patients with SLE. MPs-IgG + are associated with SLE activity, and PMPs-IgG + stimulate monocytes, changing their phenotype and promoting pro-inflammatory responses related to disease activity.

Different phenotypes of non‐classical monocytes associated with systemic inflammation, endothelial alteration and hepatic compromise in patients with dengue

“…The relative and absolute counts of total monocytes and the classification of monocytes into three subsets (classical: CD14 ++ CD16 − , non‐classical: CD14 + CD16 ++ and intermediate: CD14 ++ CD16 + ) were performed using flow cytometry as previously reported . A total peripheral blood anti‐coagulated with EDTA was stained with anti‐human HLA‐DR‐allophycocyanin (APC) ‐Cy7 (clone L243; BioLegend, San Diego, CA), CD14‐fluorescein isothiocyanate (FITC) MY4 (clone 322A‐1; Beckman Coulter, Hialeah, FL), CD16‐V450 (clone 3G8; Becton Dickinson Biosciences, San Jose, CA) and CD45‐phycoerythrin (PE) ‐Cy7 (clone HI30; BD Bioscience) antibodies for 20 min.…”

“…The characterization of non‐classical monocytes was performed by immunostaining of the peripheral blood mononuclear cells (PBMCs), as per our previous report . These cells were obtained from the venous blood treated with anti‐coagulant EDTA and previously diluted with Dulbecco's phosphate‐buffered saline (DPBS; Gibco‐BRL, Grand Island, NY) at the ratio of 1 : 1, after centrifugation on Histopaque‐1077 (Sigma‐Aldrich, St. Louis, MO) at 900 g for 30 min.…”

“…Microparticles (MPs) were isolated from the venous blood treated with anti‐coagulant citrate and then characterized using flow cytometry, as per our previous report . Briefly, MPs were incubated with anti‐human HLA‐DR and CD105‐APC antibodies (clone 43A3; BioLegend) at the concentration of 350–650 MPs/μl for 25 min at 4° in the dark.…”

Microparticles as autoantigens in systemic lupus erythematosus

“…21 Microparticles in the blood of SLE patients display IgG and IgM on their surface, indicating their role as immune complexes. 57,58 As described by Fortin et al and also Cloutier et al (RA samples), MPs with bound immunoglobulins (microparticle immune complexes or mpICs) could be larger than the usual MPs and display dimensions of 700 nm to approximately 3000 nm. 59,60 In the usual MP assay analysis, these larger particles would not be measured as their size exceeds the usual upper limit of 1000 nm.…”

HMGB1+ microparticles present in urine are hallmarks of nephritis in patients with systemic lupus erythematosus

“…We have reported alterations in the frequency, count, and phenotype of circulating non‐classical monocytes in SLE patients, as well as a significant, negative correlation between the number of these cells and the disease activity index . Circulating microparticles (MPs) are a prominent source of circulating immune complexes (MP‐ICs) and are positively associated with the activation phenotype of non‐classical monocytes in SLE patients .…”