Islet autoantibodies, including autoantibodies directed against the 65kDa isoform of glutamate decarboxylase (GAD65Ab), are present in the majority of patients with newly diagnosed type 1 diabetes (T1D). Whereas these autoantibodies are historically viewed as an epiphenomenon of the autoimmune response with no significant pathogenic function, we consider in this study the possibility that they impact the major islet function, namely glucose-stimulated insulin secretion. Two human monoclonal GAD65Ab (GAD65 mAb) (b78 and b96.11) were investigated for uptake by live rat beta cells, subcellular localization and their effect on glucose-stimulated insulin secretion. The GAD65 mAbs were internalized by live pancreatic beta cells, where they localized to subcellular structures in an epitope-specific manner. Importantly, GAD65 mAb b78 inhibited, while GAD65 mAb b96.11 enhanced, glucose-stimulated insulin secretion (GSIS). These opposite effects on GSIS rule out non-specific effects of the antibodies and suggest that internalization of the antibody leads to epitope-specific interaction with intracellular machinery regulating insulin granule release. The most likely explanation for the alteration of GSIS by GAD65 Abs is via changes in GABA release due to inhibition or change in GAD65 enzyme activity. This is the first report indicating an active role of GAD65Ab in the pathogenesis of T1D.

中文翻译：

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针对谷氨酸脱羧酶的自身抗体干扰分散的大鼠胰岛中葡萄糖刺激的胰岛素分泌

大多数新诊断的 1 型糖尿病 (T1D) 患者体内都存在胰岛自身抗体，包括针对 65kDa 谷氨酸脱羧酶同工型 (GAD65Ab) 的自身抗体。尽管这些自身抗体历来被视为自身免疫反应的副现象，没有显着的致病功能，但我们在本研究中考虑了它们影响主要胰岛功能（即葡萄糖刺激的胰岛素分泌）的可能性。研究了两种人单克隆 GAD65Ab (GAD65 mAb)（b78 和 b96.11）的活体大鼠 β 细胞摄取、亚细胞定位及其对葡萄糖刺激的胰岛素分泌的影响。GAD65 mAb 被活胰腺 β 细胞内化，并以表位特异性方式定位于亚细胞结构。重要的是，GAD65 mAb b78 抑制葡萄糖刺激的胰岛素分泌 (GSIS)，而 GAD65 mAb b96.11 增强葡萄糖刺激的胰岛素分泌 (GSIS)。这些对 GSIS 的相反作用排除了抗体的非特异性作用，并表明抗体的内化导致与调节胰岛素颗粒释放的细胞内机制发生表位特异性相互作用。GAD65 Abs 改变 GSIS 的最可能的解释是由于 GAD65 酶活性的抑制或变化导致 GABA 释放的变化。这是第一份表明 GAD65Ab 在 T1D 发病机制中发挥积极作用的报告。