Resolvins Modulate Netosis and Autoimmunity in Sickle Cell Disease

Sickle cell disease (SCD) is a genetically determined hematological disease which is characterized by anemia, chronic hemolysis, and multi-organ chronic inflammatory vasculopathy with acute vaso-occlusive painful crises and chronic organ damage. The pathophysiology of SCD is complex and involves several other cell types and metabolic pathways than erythrocytes, including neutrophils and soluble factors such as cytokines or alternative complement pathway which affect the function of vascular endothelium. An inflammatory vasculopathy with chronically activated neutrophils releasing Neutrophil Extracellular Traps (NETs) is a key component of the pathophysiology of sickle cell disease (SCD). Chiang et al. have recently shown that resolvins (Rv) reduce NETS and improve NETs clearance in a model of sepsis by Staphylococus aureus, a known trigger of NETosis (Chiang N et al. Blood 139 (8): 1222, 2022). We previously reported that targeting pro-resolution mechanisms with Rv improves SCD vasculopathy and organ damage in humanized sickle mice. Here, we studied 23 adult patients with SCD, followed by the Comprehensive center for hemoglobinopathies and rare anemias, University of Verona and AOUI Verona from January 2019 to December 2021. For each patient the presence/absence of concomitant rheumatological condition such as rheumatoid arthritis, other inflammatory arthropathies, immune-mediated dermatological conditions, Sicca syndrome and Raynaud's phenomenon, were assessed. Eight age, and ethnicity matched healthy controls were analyzed. Blood was collected for hematological and biochemical assay as part of the standard clinical care for these patients. Additional blood was collected for research studies on whole blood and on plasma cytokines. SCD patients display significant increase in tumor- necrosis-factor (TNF)- α (p = 0.011) and interleukin (IL)-10, suggesting both active inflammatory state and an upregulated counterregulatory mechanism to limit inflammation. We observed that antinuclear antibodies (ANA), but not extractable nuclear antibodies (ENA), were significantly increased in SCD patients (provide specific data here). Previous reports have reported the presence of this type of autoantibodies in the absence of autoimmune clinical manifestations in patients with SCD (Toly-Ndour C et al J Rheumatol 38: 302, 2011). ANA⁺ SCDsubjects (defined by a cell nuclei homogenous pattern, and positive dilution in the 1:80 to 1: 160 range) had a higher inflammatory and hemolytic status, as demonstrated by increased WBC and neutrophil counts and LDH values compared to ANA^- subjects. NETosis plays a key role in modification and externalization of autoantigens involved in production of autoantibodies such as ANA. Here, we found basal NETosis was higher, though not significant, in ANA⁺ SCD subjects compared to ANA^-SCD patients. This was associated with lower expression of receptors for RvD1 and D2, namely ALX, GPR32/DRV1, and GPR18/DRV2 on PMN, monocytes, and lymphocytes from ANA⁺ SCD patients when compared to ANA^- SCD subjects, who were also characterized by relatively low LDH compared to ANA+ SCD patients. Exogenous treatment of SCD neutrophils with RvD1 and D4 significantly dampened NETs release and enhanced NETs clearance by macrophages. RvD4 along with other pro-resolving mediators also stimulated ex vivo clearance of P. aeruginosa and S. aureus by SCD neutrophils. Our findings provide a novel link between autoimmunity and neutrophil-mediated vasculopathy in SCD and highlight the importance of Rv and their immune-pro-resolution effects in limiting disease progression in SCD but also to modulate the host response to infections and sepsis, which is altered in SCD.

No relevant conflicts of interest to declare.