NCSTN mutations in hidradenitis suppurativa/acne inversa do not influence cytokine production by peripheral blood mononuclear cells

Dear Editor, Hidradenitis suppurativa (HS), also known as acne inverse (AI), is a chronic inflammatory skin disease presenting with deep‐seated nodules, recurrent abscesses and sinus tract formation. Although the exact pathogenesis of HS/AI is poorly clarified, abnormal immune reaction and cytokine secretion play important roles in the development of this disease.1 In recent years, studies have shown that different mutations of nicastrin (NCSTN), a subunit of γ‐secretase, are present in some patients with HS/AI.2 Whether there is a difference in cytokines secreted by the peripheral blood mononuclear cells (PBMCs) of patients with mutations in NCSTN remains unknown. Thus, the present study aimed to compare the cytokine profiles [including tumour necrosis factor (TNF)‐α, interferon (IFN)‐γ, interleukin (IL)‐1β, IL‐6, IL‐10 and IL‐17] of PBMCs of patients with and without mutations in NCSTN. This study was approved by medical ethics committee of the Chinese Academy of Medical Sciences Institute of Dermatology. Eleven Chinese patients with HS/AI with NCSTN mutations were included (Appendix S1; see Supporting Information). All patients met the diagnostic criteria for HS/AI,3 and disease severity was classified according to the Hurley scoring system.4 After written informed consent was obtained from all patients, whole blood was collected from all patients. Overall, 4 mL whole blood was obtained from 11 patients with HS/AI without an NCSTN mutation and from 22 healthy volunteers. All patients had active lesions and received no treatments for at least 2 weeks. The age, disease duration and disease severity of patients with and without NCSTN mutations were comparable. PBMCs were isolated, cultured in vitro and stimulated with 10 ng mL−1 lipopolysaccharide (LPS). Twenty‐four hours after stimulation, TNF‐α, IFN‐γ, IL‐1β, IL‐6, IL‐10 and IL‐17 were detected in the supernatants of the cell culture by enzyme‐linked immunosorbent assay (eBioscience, San Diego, CA, U.S.A.), according to the manufacturer's instructions. The Kruskal–Wallis H test was used to analyse the data, and P < 0·05 was considered statistically significant. The production of TNF‐α, IFN‐γ, IL‐1β, IL‐6, IL‐10 and IL‐17 from the PBMCs of healthy controls and patients with HS/AI are shown in Figure 1. The concentration of cytokines before LPS stimulation was not different among the groups. After the cells were triggered by LPS, the levels of TNF‐α, IL‐1β, IL‐6 and IL‐10 secreted by PBMCs were lower in patients with HS/AI than in the healthy controls; however, there was no difference between patients with and without NCSTN mutations (Fig. 1). Supernatant concentration of cytokines secreted by peripheral blood mononuclear cells from patients with hidradenitis suppurativa/acne inversa (HS/AI) and healthy controls. Concentrations of (a) tumour necrosis factor (TNF)‐α, (b) interferon (IFN)‐γ, (c) interleukin (IL)‐1β, (d) IL‐6, (e) IL‐10 and (f) IL‐17 in different groups. The mean ± SD age of 11 patients with HS/AI with NCSTN mutation was 36·3 ± 15·6 years, and mean ± SD disease duration was 13·5 ±12·1 years. Two, five and four patients were Hurley stage I, II and III, respectively. The mean ± SD age of 11 patients with HS/AI without NCSTN mutation was 38·2 ± 14·7 years, and mean ± SD disease duration was 14·9 ± 12·9 years. Three, four and four patients were Hurley stage I, II and III, respectively. Age, disease duration and severity of familial and sporadic patients were comparable. Twenty‐two healthy volunteers were used as controls (mean ± SD age 36·7 ± 15·7 years). SPSS 17.0 (IBM, Armonk, NY, U.S.A.) was used for the statistical analysis, and P < 0·05 was considered as statistically significant. LPS, lipopolysaccharide. Many cytokines have been detected, and they undergo changes in cases of HS/AI.1 In our study, TNF‐α, IFN‐γ and IL‐1β were secreted by T helper (Th) 1 cells, IL‐6 and IL‐10 were secreted by Th2 cells and IL‐17 was mainly produced by Th17 cells. Giamarellos‐Bourboulis et al. reported that patients with HS/AI have an altered innate and adaptive immune response.5 These patients had decreased numbers of T lymphocytes and natural killer cells, which are the main sources of cytokines, and a lowered monocyte response to bacterial components.5 LPS tolerance can occur in the late phase of some inflammatory diseases,6 and HS/AI may be no exception, as it is a chronic recurrent disorder and the immune response to HS/AI is dynamic. Therefore, in the present study, the PBMCs of patients with HS/AI exhibited a lower cytokine secretion capacity than that of the healthy controls, which is in agreement with the findings of Kanni et al.7 PBMCs, such as T lymphocytes, in the blood vessels of patients with HS/AI were inhibited and activated in skin tissues.7 This may be why the concentrations of TNF‐α, IL‐1β, IL‐6 and IL‐10 in lesions were increased, and the concentrations in supernatants from PBMCs were downregulated. The clinical features of patients with HS/AI with NCSTN mutations were in accordance with the characteristics of the follicular class of HS/AI,8 but the role of NCSTN mutation in the pathogenesis of HS/AI is still largely unknown. Recently, Xiao et al. reported that this gene mutation was involved in HS/AI development, as it affects keratinocyte proliferation and differentiation.9 However, there is a lack of studies of cytokine profiles of PBMCs of patients with HS/AI with NCSTN mutations. We found that there were no differences in the decreased levels of inflammatory factors between patients with and without NCSTN mutations. This result may indicate that NCSTN mutations have no direct effect on inflammatory cells in the process of cytokine production. As many patients with HS/AI had no NCSTN mutation and nicastrin was the only pathogenic factor related to HS/AI,2 10 abnormal cytokines triggered by bacterial infection and other factors may contribute to the pathogenesis of HS/AI with NCSTN mutations. However, owing to two main limitations, the findings of this study should be considered with caution. Firstly, we did not use stimuli other than LPS; secondly, a limited number of patients were enrolled, and different subsets of PBMCs were not analysed. In conclusion, NCSTN mutations alone may be insufficient to detect abnormal cytokine secretion by PBMCs in patients with HS/AI. Further research is mandatory to determine the cytokines present in the lesions of patients with HS/AI, with and without NCSTN mutations. We thank the patients and their family members for their participation in this study. Funding sources: National Nature Science Foundation of China (81101207, 81472905, 81472872), Fundamental Research Funds for the Central Universities and Peking Union Medical College (PUMC) Youth Fund (3332013056), and Young Teachers Training Fund of PUMC. Conflicts of interest: none declared. Appendix S1. Study subjects.