SUMMARY Seasonal changes in disease activity have been observed in multiple sclerosis, an autoimmune disorder that affects the central nervous system. These epidemiological observations suggest that environmental factors influence the disease course. Here we report that melatonin levels, whose production is modulated by seasonal variations in night length, negatively correlate with multiple sclerosis activity in humans. Treatment with melatonin ameliorates disease in an experimental model of multiple sclerosis and directly interferes with the differentiation of human and mouse T cells. Melatonin induces the expression of the repressor transcription factor Nfil3, blocking the differentiation of pathogenic Th17 cells as well as boosts the generation of protective Tr1 cells via Erk1/2 and the transactivation of the IL-10 promoter by ROR-α. These results suggest that melatonin is another example of how environmental-driven cues can impact on T cell differentiation and have implications for autoimmune disorders such as multiple sclerosis.

Objective To investigate the effects of leptin on different T‐cell populations, in order to gain more insight into the link between leptin and obesity. Methods Three hundred and nine RRMS patients and 322 controls participated in a cross‐sectional survey, to confirm whether excess weight/obesity in adolescence or early adulthood increased the risk of MS. Serum leptin levels were determined by ELISA. MBP83–102, and MOG63–87 peptide‐specific T cells lines were expanded from peripheral blood mononuclear cells. Leptin receptor expression was measured by RT‐PCR and flow cytometry. Bcl‐2, p‐STAT3, pERK1/2, and p27kip1 expression were assayed using ELISA, and apoptosis induction was determined by Annexin V detection. Cytokines were assessed by ELISPOT and ELISA, and regulatory T cells (Tregs) by flow cytometry. Results Logistic regression analysis, showed excess weight at age 15, and obesity at 20 years of age increased MS risk (OR = 2.16, P = 0.01 and OR = 3.9, P = 0.01). Leptin levels correlated with BMI in both groups. The addition of Leptin increased autoreactive T‐cell proliferation, reduced apoptosis induction, and promoted proinflammatory cytokine secretion. Obese patients produced more proinflammatory cytokines compared to overweight/normal/underweight subjects. Inverse correlation was found between leptin levels and circulating Treg cells (r = −0.97, P < 0.0001). Leptin inhibited Treg proliferation. Effects of leptin on CD4+CD25− effector T cells were mediated by increased STAT3 and ERK1/2 phosphorylation, and down modulation of the cell cycle inhibitor P27kip1. In contrast, leptin effects on Tregs resulted from decreased phosphorylation of ERK1/2 and upregulation of p27kip1. Interpretation Leptin promotes autoreactive T‐cell proliferation and proinflammatory cytokine secretion, but inhibits Treg‐cell proliferation.

Background. Comorbid autoimmune diseases in MS patients have been studied extensively with controversial results. Moreover, no such data exists for Latin-American MS patients. Methods. We conducted a case-control study aimed to establish the prevalence of autoimmune disorders in a cohort of Argentinean MS patients. Results. There were no significant differences in autoimmune disease prevalence in MS patients with respect to controls. The presence of one or more autoimmune disorders did not increase risk of MS (OR 0.85, 95% CI 0.6–1.3). Discussion. Our results indicate absence of increased comorbid autoimmune disease prevalence in MS patients, as well as of increased risk of MS in patients suffering from other autoimmune disorders.

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