Human fibroblasts ubiquitously express glutamic acid decarboxylase 65 (GAD65): Possible effects of connective tissue inflammation on GAD antibody titer

Background: Type 1 diabetes is caused by a destruction of pancreatic beta c ells due to autoimmunity. Autoantibody against glutamic acid decarboxylase (GAD) 65 expressed in pancreatic beta cells is widely used as a predictive marker for pancreatic destruction. In this study, we hypothesized that if c ertain cells in periodontal tissues could express GAD, then it may influenc e GAD antibody titer. Methods: We used: 1) reverse transcription-polymerase chain reaction (PCR) analysis to detect GAD 65 mRNA in various cells; 2) nucleotide sequencing a nalysis to confirm that amplified PCR product is the gene encoding GAD; and 3) Western blotting to determine the expression of GAD 65 protein in human gingival fibroblasts. Immunohistochemical staining of GAD 65 protein in no rmal and inflamed gingiva was performed to examine the potential influence of periodontal inflammation on GAD 65 expression. GAD antibody titer in ser a of periodontal patients as well as healthy subjects was measured to deter mine if periodontal patients could develop autoantibody against GAD 65. Results: Cultured human gingival, periodontal, and dermal fibroblasts and m esangial cells expressed GAD mRNA. Nucleotide sequencing analyses confirmed the amplified PCR product as GAD 65. Western immunoblotting analyses and i mmunohistochemical staining revealed that the GAD 65 protein was expressed in vitro and in vivo. The expression of GAD 65 in inflamed tissue was highe r than that in normal tissues. Two of 62 periodontal patients without diabe tes showed an increased antibody titer against GAD 65, while none of the sy stemically healthy subjects showed an increased antibody titer against this antigen. Conclusions: We concluded that periodontal inflammation may result in highe r levels of GAD and influence GAD antibody titer, and, hence, affect diabet ic diagnosis based upon GAD antibody production.