Microparticles in the blood of patients with SLE [Lupus]: Size, content of mitochondria and role in circulating immune complexes, 2019, Mobarrez et al

[Andy]

Highlights

Blood in SLE shows increased levels of microparticles containing nucleic acids.

Microparticles in SLE display IgG as well as nucleic acids.

A sub-population of microparticles in SLE is larger in size than 0.7 μm.

The majority of the large microparticles contain mitochondrial molecules.

The level of microparticles with mitochondria is associated with features of SLE.

Abstract
Objective
Microparticles (MPs) are small extracellular vesicles released from apoptotic or activated cells through a blebbing process. MPs express surface molecules from their parental cells and they bind IgG to form circulating immune complexes (MP-ICs) in patients with systemic lupus erythematosus (SLE). Through investigation of MP size, IgG expression, content of nucleic acids and mitochondrial molecules, we hypothesized that unrecognized particle populations can be identified in SLE.

Methods
We investigated 327 well-characterized SLE patients and 304 controls divided into two sets (280/280 and 47/24). We measured MPs by flow cytometry using a gating strategy to encompass small (0.2–0.7 μm) and large (0.7–3.0 μm) MPs. Nucleic acids were labeled with SYTO 13 and mitochondria with MitoTracker. Expression of mitochondria markers TOM-20 and Hexokinase 1 and the presence of IgG was investigated.

Results
MPs staining with SYTO 13 were more frequent in 280 SLE patients compared to 280 controls. In 47 SLE patients, levels of large MPs were elevated compared to 24 controls. The majority of large MPs contained mitochondria (mitoMPs). The number of mitoMPs associated positively with high disease activity, anti-dsDNA antibodies and pro-inflammatory cytokines. Patients with active lupus nephritis had higher levels of mitoMPs and IgG-positive mitoMPs.

Conclusion
Blood of patients with SLE contain a previously unrecognized population of circulating large MPs with bound IgG and mitochondrial proteins. Levels of these particles are related to several measures of active SLE, suggesting that these structures may have a role in disease pathogenesis.

Paywall, https://www.sciencedirect.com/science/article/pii/S089684111930099X
Sci hub, https://sci-hub.se/10.1016/j.jaut.2019.05.003

 

[Jonathan Edwards]

The methodology in terms of numbers studied is peculiar. It looks as if they did two different studies. The abstract gives no hard figures which it should.

We would expect SLE patients to have more microparticles than controls and probably including bits of mitochondria because a central feature of lupus is failure to clear debris from circulation by complement. The resulting immune complexes are generally thought to be the cause of nephritis and some other features.