The microbial product lipopolysaccharide confers diabetogenic potential on the T cell repertoire of BDC2.5/NOD mice: implications for the etiology of autoimmune diabetes

Both genetic predisposition and environmental factors participate in the etiology of Type-1 diabetes. To test the role of the microbial product lipopolysaccharide (LPS) as an environmental trigger of autoimmune diabetes, we employed transgenic (tg) BDC2.5/NOD mice that bear an islet-specific CD4(+) T cell repertoire (>95%), but do not develop the spontaneous diabetes that typifies the NOD (nonobese diabetic) strain. LPS administration provoked diabetes in BDC2.5/NOD mice by their 16th week of age. However, LPS administration in NOD mice did not accelerate their diabetes. This finding indicates that the frequency of islet-specific T cells influences LPS-mediated diabetes. Furthermore, in vitro LPS-cultured splenocytes from BDC2. 5/NOD and BDC2.5-microMT (B-cell-deficient) mice effectively transferred diabetes into immunodeficient NOD-scid/scid mice but not immunosufficient NOD mice. Therefore, B lymphocytes are not required for LPS-provoked autoimmune diabetes. Flow cytometric analysis then revealed that LPS-stimulation in vitro induced the expression of an IL-2 receptor (CD25) on CD4 T cells; this indicates that the activation of islet-specific T cells is a prerequisite to eliciting diabetes in this situation. Overall, these results point to microbial LPS as an etiopathogenic agent of autoimmune diabetes.