Neutrophil Extracellular Traps contribute to the pathogenesis of leprosy type 2 reactions

Abstract

25Up to 50% of patients with the multibacillary form of leprosy is expected to 26 develop acute systemic inflammatory episodes known as type 2 reactions (T2R), 27 thus aggravating their clinical status. Thalidomide rapidly improves T2R 28 symptoms. But, due to its restricted use worldwide, novel alternative therapies 29 are urgently needed. A hallmark of T2R lesions is the presence of a neutrophil-30 rich inflammatory infiltrate. In this study, the potential involvement of neutrophil 31 extracellular traps (NETs) production in T2R pathogenesis was investigated. 32Abundant NETs were found in T2R skin lesions, and increased spontaneous 33NETs formation was observed in T2R peripheral neutrophils. Both the M. leprae 34 whole-cell sonicate and the CpG-Hlp complex, mimicking a mycobacterial TLR9 35 ligand, were able to induce NETs production in vitro. Moreover, TLR9 expression 36 was shown to be higher in T2R neutrophils, suggesting that DNA recognition via 37 TLR9 may be one of the pathways triggering this process during T2R. Finally, 38 treatment of T2R patients with thalidomide for 7 consecutive days resulted in 39 decreasing all of the evaluated in vivo and ex vivo NETosis parameters. 40Altogether, our findings shed light on the pathogenesis of T2R, which, it is hoped, 41 will contribute to the emergence of novel alternative therapies in the near future. 42 43 44 45 46 3 Author summary 47 48Leprosy is caused by a mycobacterium that has a predilection for skin and nerve 49 cells. The chronic course of the disease may be interrupted by acute 50 inflammatory episodes known as reactions, despite effective bacterial killing with 51 antibiotics. Reactions aggravate patient's clinical status and may become a 52 medical emergency. Type 2 reactions (T2R) only occur in patients with high 53 bacterial burden and is treated with thalidomide and/or corticosteroids. We are 54 interested in understanding how inflammation is triggered and amplified during 55 T2R. In this study we investigated the potential role of extracellular DNA released 56 by neutrophils (known as NETs) in T2R, since they have been shown to cause 57 inflammation. Abundant NETs were found in T2R skin lesions, and increased 58 spontaneous NETs formation was observed in neutrophils present in the blood of 59 T2R patients. Moreover, bacterial constituents were able to induce NETs 60 production. Finally, treatment of T2R patients with thalidomide resulted in 61 decreased NET formation. Altogether, our findings shed light on the 62 pathogenesis of T2R, which, it is hoped, will contribute to the identification of 63 biomarkers for early diagnosis and emergence of novel alternative therapies in 64 the near future. 65 66 67 68 69

A real‐world study of low‐dose thalidomide in severe erythema nodosum leprosum highlighting its mechanistic rationale in a resource‐constrained target population

“…15,19,20 Recent studies have focused on the role of neutrophil DNA extracellular traps (NET), and there is good data to show that thalidomide has an inhibitory action on NET. 21 In addition thalidomide effectively decreases the activated low-density neutrophils, increases the level of TGF-b, an inhibitor of neutrophilic degranulation, and also decreases MMP-9 serum levels. 22 The dramatic reduction in neutrophilic infiltrate within 7 days of thalidomide induction lends further support to this view 23 (Fig.…”

“…Thalidomide treatment reduces CD64 expression and neutrophil infiltration and suppresses IL‐1β as well as IL‐10R1, which stimulates neutrophils 15,19,20 . Recent studies have focused on the role of neutrophil DNA extracellular traps (NET), and there is good data to show that thalidomide has an inhibitory action on NET 21 . In addition thalidomide effectively decreases the activated low‐density neutrophils, increases the level of TGF‐β, an inhibitor of neutrophilic degranulation, and also decreases MMP‐9 serum levels 22 .…”

Case Report: Rapid Response to Low-Dose Thalidomide in a Case of Severe Steroid Recalcitrant Erythema Nodosum Leprosum

“…It has been shown that dead Mycobacterium leprae have a superior capacity to induce CCL-4 and IL-8 in primary neutrophils, which elegantly explains the fact that dead M. leprae mediate ENL. 13 A recent study has also found that neutrophil DNA extracellular traps also play a role in ENL, 14 and there are data to show that thalidomide has a inhibitory action on neutrophils, thus making it an effective drug in ENL. The dramatic reduction in neutrophilic infiltrate within 7 days of thalidomide induction lends further support to this view.…”

Analysis of COVID-19 Leprosy patients: Double Trouble?

“…The commonality among the patients with ENL and COVID-19 is the presence of neutrophilia and high NLR (22). One study showed the presence of circulating and skin-lesion neutrophil releasing NET along with higher DNA-histone serum levels upon comparison with non-reactive multibacillary controls (23). From a clinical perspective, COVID-19 and ENL differ, however, their transcriptome profiling and neutrophil activation are similar.…”