TLR5 influences the development of type 1 diabetes.

In mammalian and human life, it is important that the immune system defends against microorganisms. Although there is a huge overlap, innate cells are good against bacteria, whereas T cells are good against viruses, mainly because of antibody production via T helper and B lymphocytes. Toll-like receptor 5 (TLR5) is a regulator; when it is highly expressed, T cells are inhibited, and innate cells are favored. In glucose-activated pancreatic islets, TLR5 gene expression has been found to be highly upregulated, and the islets may therefore be protected from T cell destruction resulting in autoimmune type 1 diabetes (T1D).

Research design and methods: We investigated mRNA from the islets of Langerhans in patients with newly diagnosed T1D for TLR5 gene expression, as well as Tlr5 and Cd3 expression in the whole pancreatic tissue of female diabetic non-obese diabetic (NOD) mice. Also, we examined for polymorphisms between TLR5, immunological parameters, and T1D.

Results: Islet mRNA for TLR5 was downregulated by one-third of patients with newly diagnosed T1D, compared with controls, and correlated inversely with T cell infiltration in the islets. Moreover, the association between TLR5 and T cells was supported by a corresponding correlation of Tlr5 and Cd3 expression in the pancreatic tissue of diabetic NOD mice. Regarding polymorphisms, two associations were found between TLR5 and monocytes. Also, a significant polymorphism was seen concerning TLR5 and T1D.

Conclusions: In the present study, we find a low expression of mRNA for TLR5 in patients with newly diagnosed T1D associated with enhanced T cell infiltration. T cells are important for autoimmune diseases, including T1D. We hope that the present findings may be influential for the understanding of how T1D develops.