Nicotinamide Reduces High Secretion of IFN- γ in High-Risk Relatives Even Though It Does Not Prevent Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disease suggested to be of a T helper (Th)1-like origin. This study aimed to investigate the Th1-like and Th2-like profile in high-risk individuals during the prediabetic phase and the immunologic effect of treatment with nicotinamide. High-risk first-degree relatives of T1D patients participating in the European Nicotinamide Diabetes Intervention Trial (ENDIT) were treated with either nicotinamide or placebo. Peripheral blood mononuclear cells (PBMC) were obtained during the prediabetic phase and close to the onset of manifest T1D and from nondiabetic high-risk individuals. Using the sensitive enzyme-linked immunospot (ELISPOT) technique to distinguish Th1-like from Th2-like lymphocytes, secretion of interferon-γ (IFN-γ) and interleukin-4 (IL-4) was analyzed from PBMCs spontaneously and after in vitro stimulation with the diabetes-associated autoantigens, glutamic acid decarboxylase 65 (GAD₆₅, protein and peptide, aa 247–279), recombinant tyrosine phosphatase (IA-2), and heat shock protein (HSP, aa 437–460). High-risk individuals showed high spontaneous as well as autoantigen-induced IFN-γ secretion. Secretion of IFN-γ and the IFN-γ/IL-4 ratio, induced by autoantigens, decreased in individuals developing T1D (p < 0.05), whereas nondiabetic individuals showed an increased IL-4 response (p < 0.05). Thus, a Th1-dominated cytokine profile observed in high-risk individuals inclined toward a diagnosis of diabetes. Nicotinamide caused decreased spontaneous (p = 0.05) and in vitro autoantigen-induced IFN-γ secretion (p < 0.05) and may play a role in immune regulation, even though it has not been shown to prevent T1D.