Sulphur balneotherapy and patient’s immunity: H2S effects on human CD4+ T cell polarization to Th17 and Treg phenotype

Abstract

H2S - known for decades as a toxic gas - is endogenously generated from cysteine and belongs to the family of gasotransmitters, such as nitric oxide (NO) and carbon monoxide (CO) (Szabo C, 2007). H2S-donors, sulfur balneotherapy and sulfur spa waters might be beneficial in the treatment of colitis, asthma, psoriasis and systemic lupus erythematosus (Fiorucci S, 2007; Zhang G, 2013; Han Y, 2013). However, the role of H2S in inflammation is still under debate and the molecular mechanisms of H2S in immune regulation remain largely unknown. H2S has been reported to exert both pro-inflammatory and anti-inflammatory effects. The inhibition of endogenous H2S production suppresses inflammatory response (Miller et al., 2012). On the other hand, administration of exogenous H2S has been shown to possess anti-inflammatory effects (Zanardo et al., 2006) i.e. down-regulation of pro-inflammatory cytokine expression (IL-1, TNF, IFN IL-12, IL-23) and increased expression of IL-10, a classical anti-inflammatory cytokine. We have previously demonstrated both in vitro and in vivo on primary psoriatic lesions that hydrogen sulfide not only reduce the basal expression and secretion of IL-8, but also interfere with IL-17- and IL-22-induced IL-8 production. Moreover, we showed that hydrogen sulfide dramatically decreased CD4 T cell proliferation in response to mitogens and reduced IL-2 production (Mirandola P et al., 2007). A fine balance between IL-17 producing CD4+ T cells (Th17) and Treg has recently emerged as a crucial point in inflammation associated with various autoimmune and immune-mediated diseases. The Th17 and Treg developmental pathways are reciprocally interconnected. Th17 cells represent a pro-inflammatory subset, that contributes to autoimmunity and tissue damage (Burkett PR, 2015). On the contrary, Treg cells have a suppressor activity important in the establishment and maintenance of self-tolerance. Recently, H2S has been suggested to be involved in T cells lineage polarization and T cell-associated immune homeostasis. Yang et al. demonstrated that H2S is required for FoxP3 stable expression and Treg differentiation in mouse models. Reduced levels of H2S were responsible for the impairment of CD4+Foxp3+ Treg cell differentiation and function and the onset of systemic autoimmune disease in mice (Yang R, 2015). Given the pivotal role of Th17/Treg cell ratio in the onset and clinical evolution of immune-mediated pathologies, we investigated the effects of exogenous H2S on human resting CD4 T cell polarization to Th17 and/or Treg phenotype. We differentiated ex-vivo human resting CD4+ (Th0) T cells to Th17 or Treg lineages treating cell cultures with the H2S-releasing donor NaHS. By RT-PCR, we observed that NaHS treatment increased Foxp3 mRNA levels in CD4+ T cells cultured under Treg-polarizing conditions. However, NaHS was also able to increase RORγT mRNA levels in CD4+ T cells under Th17 polarizing conditions, suggesting a role of sulfurs in the activation of both polarization pathways.