Mechanisms of human glutamic acid decarboxylase 65 DNA vaccine preventing diabetes in non-obese diabetic mice

Abstract

To investigate the mechanisms of human GAD65 DNA vaccine preventing insulitis and diabetes in NOD mice. Female NOD mice at 4 weeks of age were randomly divided into PBS (n = 21), pcDNA (n = 20), and hGAD65 (n = 21) groups. Mice in each group received two intramuscular injections of 0.05 ml PBS alone, 50 microg pcDNA3.1 and 50 microg DNA vaccine emulsified in 0.05 ml PBS 7 days apart respectively. The accumulative diabetes incidence was followed-up to 30 weeks of age in each group of NOD mice. Pancreas was removed from NOD mice at 12 weeks of age in each group (n = 10) to score insulitis severity by routine H-E staining. The apoptotic beta cells in islets were observed with double-labeling technique of TUNEL in situ combined standard sensitive avdin-biotin complex (sABC) immunohistochemical method. Their spleens were for cell culture and total RNA extraction. Spleen IL-4, IFN-gamma, NF-ATc and NF-ATp mRNA levels were tested by RT-PCR. IL-4 and IFN-gamma levels in sera and supernatants of spleen cells were measured by ELISA. (1) At 30 weeks of age, the diabetes incidence was 95.2%, 80.0% and 61.9% in PBS, pcDNA and hGAD65 group respectively. The diabetes incidence in the PBS group was higher than that in hGAD65 group (P = 0.008). (2) At 12 weeks of age, the insulitis scores in hGAD65 group was lower than that in PBS group (P = 0.001) and pcDNA group (P = 0.027) respectively. (3) The apoptotic beta cell rates in hGAD65 group was lower than that in PBS group (P = 0.014) and pcDNA group (P = 0.023). (4) IL-4 levels in sera, spleen IL-4 and NF-ATc mRNA level in hGAD65 group were higher than those in PBS group (all P < 0.05) and pcDNA group (all P < 0.05) respectively, NF-ATp mRNA level in hGAD65 group was lower than that in PBS group (P < 0.05). Human GAD65 DNA vaccine via downregulating NF-ATp and upregulating NF-ATc and IL-4, makes Th cells deviate to Th2, and sequently prevents insulitis, beta-cell apoptosis and diabetes onset in NOD mice.