Background/Purpose: Apoptotic microparticles (MPs) in the circulation of systemic lupus erythematosus (SLE) patients are enriched for nucleic acids and complexed with IgG (MP-IC), as compared with those from healthy controls (HC).  These MPs have been shown to activate monocytes, suggesting that they are an important stimulus for production of pro-inflammatory factors in SLE. We previously presented data showing that nucleic acid-enriched IgG-complexed MPs are also increased in asymptomatic anti-nuclear antibody (ANA) positive individuals (ANA⁺NS), in the absence of elevated levels of pro-inflammatory factors. Although platelets represent the main source of MPs in healthy individuals, endothelial- and neutrophil-derived MPs are also found in SLE. In this study, we examined the origin of MPs in ANA⁺NS.

Methods: Flow cytometry was used to examine the number, origin, nucleic acid content, and IgG binding of peripheral blood Annexin V⁺MPs in ANA^–HC (n=18), ANA⁺NS (≥1:160 by IF, n=48), and SLE patients (n=33). MP nucleic acid content was determined by staining with Syto13 and the MP cell source by staining with antibodies against CD41a (Platelets), CD105 (endothelium), CD45 (hematopoietic cells), CD14 (monocytes), CD66b (neutrophils), CD19 (B cells), CD3 (T cells), and CD235a (erythrocytes).

Results: Consistent with published work and with our previous data, SLE patients had increased levels of MPs and MP-ICs that contained higher levels of nucleic acids, as compared to ANA^– HC. A subset of ANA⁺NS had similar elevations in the amount of IgG coating their MPs and nucleic acid content to those seen in SLE. As expected, the majority of the MPs obtained from HC exhibited platelet markers (Figure A). Notably, in ANA⁺NS individuals and SLE patients the proportion of Annexin V⁺ platelet-MPs was reduced compared to HC (Figure A) and there were increased proportions of Annexin V⁺ CD66b⁺MPs (apoptotic neutrophils-MPs) and CD45⁺MPs (hematopoietic) (Figure B and C). However, the proportion of neutrophil-MPs was significantly higher in SLE than in ANA⁺NS (Figure B). There were non-statistically significant trends to higher CD14⁺MPs (monocytes-MPs) and endothelial MPs in ANA⁺ NS. There were no CD19, CD3, or CD235a positive MPs detected.  

Conclusion: Apoptotic and/or activated neutrophils and hematopoietic cells are a significant source of auto-antigenic MPs in both ANA⁺NS individuals and SLE patients.  However, neutrophil apoptosis/activation appears to be more prominent in SLE patients, raising the possibility that it contributes to the pro-inflammatory process that discriminates symptomatic and asymptomatic ANA⁺individuals.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/neutrophils-are-an-important-source-of-microparticles-in-lupus-and-asymptomatic-ana-individuals/