Characterizing Pathogenic B Cells that Cause Autoimmune Diabetes

Type 1 Diabetes Mellitus (T1D) is caused by a permanent destruction of insulin-producing β-cells of the pancreas by autoreactive T cells. Despite advances in insulin therapy, patients often face serious cardiovascular and neurological complications. Since most patients are children and young adults it is imperative to identify therapeutic targets to prevent the disease without causing generalized immunosuppression. Using autoimmune prone non-obese diabetic (NOD) mice, the widely used model of T1D with spontaneous gene mutations in either Fas (lpr) or FasL (gld), we hypothesize the involvement of a specific population of B cells in the disease process. These B cells express Fas ligand (FasL), which is part of the pathway involved with T cell homeostasis. FasL expressed in these cells break immune tolerance in autoimmune prone NOD mice. Using flow cytometry B cell populations were characterized in spleen, pancreatic and inguinal lymph nodes, and in peritoneal cavity of NOD mice as well as in C57BL/6 and Balb/c mice.  We detected FasL expressing B cells in spleen of all three mouse strains tested (NOD, C57BL/6, and Balb/c), but higher levels were detected in NOD mice. In addition, gld/gld mice B cells did not up-regulate FasL, CD23, or CD86 like the NOD Wt mice which was illustrated by activation with LPS and anti-IgM. We looked for apoptosis among FasL+ B cells in the spleen of NOD, B6 and Balb/c and found higher annexin V levels in B6 and Balb/c than NOD, supporting the hypothesis that B cells in NOD mice, are pathogenic.