Natural Killer Cells Exhibit a Peculiar Phenotypic Profile in Systemic Sclerosis and Are Potent Inducers of Endothelial Microparticles Release

Abstract

The pathophysiology of systemic sclerosis (SSc) involves early endothelial and immune activation, both preceding the onset of fibrosis. We previously identified soluble fractalkine and circulating endothelial microparticles (EMPs) as biomarkers of endothelial inflammatory activation in SSc. Fractalkine plays a dual role as a membrane-bound adhesion molecule expressed in inflamed endothelial cells (ECs) and as a chemokine involved in the recruitment, transmigration, and cytotoxic activation of immune cells that express CX3CR1, the receptor of fractalkine, namely CD8 and γδ T cells and natural killer (NK) cells. We aimed to quantify circulating cytotoxic immune cells and their expression of CX3CR1. We further investigated the expression profile of NK cells chemokine receptors and activation markers and the potential of NK cells to induce EC activation in SSc. We performed a monocentric study (NCT 02636127) enrolling 15 SSc patients [15 females, median age of 55 years (39–63), 11 limited cutaneous form and 4 diffuse] and 15 healthy controls. Serum fractalkine levels were significantly increased in SSc patients. Circulating CD8 T cells numbers were decreased in SSc patients with no difference in their CX3CR1 expression. Circulating γδ T cells and NK cells numbers were preserved. CX3CR1 expression in CD8 and γδ T cells did not differ between SSc patients and controls. The percentage and level of CX3CR1 expression in NK cells were significantly lowered in SSc patients. Percentages of CXCR4, NKG2D, CD69-expressing NK cells, and their expression levels were decreased in NK cells. Conversely, CD16 level expression and percentages of CD16+ NK cells were preserved. The exposure of human microvascular dermic EC line (HMVEC-d) to peripheral blood mononuclear cells resulted in similar NK cells degranulation activity in SSc patients and controls. We further showed that NK cells purified from the blood of SSc patients induced enhanced release of EMPs than NK cells from controls. This study evidenced a peculiar NK cells phenotype in SSc characterized by decreased chemokine and activation receptors expression, that might reflect NK cells involvement in the pathogenic process. It also highlighted the role of NK cells as a potent mechanism inducing endothelial activation through enhanced EMPs release.

The immunopathogenesis of fibrosis in systemic sclerosis

“…An inhibitor of HMGB1 attenuated neutrophil activation [131] Natural killer A peculiar natural killer cell phenotype in SSc patients was identified characterized by decreased chemokine and activation receptors expression. These SSc-derived natural killer cells were potent inducers of endothelial microparticle release suggesting that there may be a role for natural killer cells in the activation of endothelial cells in SSc [133] Innate lymphoid Type 2 innate lymphoid (ILC2) cells are elevated in patients with SSc. ILC2 counts correlated with skin fibrosis.…”

“…This complex network of signalling between different immune cells is only now beginning to become unravelled, with new evidence emerging regularly to provide new players in SSc immunopathogenesis. For example, only a few studies have highlighted the potential for platelets , neutrophils , natural killer cells and innate lymphoid cells to be dysregulated and contribute to the pathogenesis of SSc. Type 2 innate lymphoid cells are found in higher numbers in SSc and correlate strongly with the Rodnan skin score and also the presence of lung fibrosis.…”

GWAS for systemic sclerosis identifies multiple risk loci and highlights fibrotic and vasculopathy pathways

“…Our results are consistent with previous reports linking NK cells to SSc 41 . In a very recent publication, Benyamine et al 42 reported a particular expression profile of NK cells in SSc and showed that this cell type induced endothelial activation 42 . These findings may provide a link between vascular damage and the immune imbalance in SSc.…”

Elevated Circulatory Levels of Microparticles Are Associated to Lung Fibrosis and Vasculopathy During Systemic Sclerosis

“…MPs can originate from every type of cells, particularly under stress conditions. Endothelial cell (EC) damage is one major hallmark of SSc and lead to the shedding of endothelial MPs [EMPs; (12,13)]. Batteux et al showed in a murine model of SSc, that inhibiting MPs shedding either chemically or genetically diminishes the hallmarks of oxidative and endothelial stress but also skin and lung fibrosis (14).…”