Autoantibodies to glutamate decarboxylase detected in diabetes-prone BB/OK rats do not distinguish onset of diabetes

Abstract

The diabetes syndrome of the BB rat resembles human Type 1 (insulin-dependent) diabetes including the prevalence of autoantibodies to the 64 kDa Beta-cell autoantigen, which has been identified as glutamate decarboxylase. This study aimed at detecting the prevalence and level of glutamate decarboxylase autoantibodies in 120-day-old diabetic and non-diabetic diabetes-prone BB/OK rats compared to those of sex- and age-matched diabetes-resistant LEW.1A rats. The antibodies were detected using semipurified glutamate decarboxylase from rat brain in two immunoassays, a direct and a sandwich enzyme-linked immunosorbent assay. For the last assay autoantibody-containing immunoglobulins of a serum from a patient with the stiff-man syndrome were used to bind specifically the enzyme as autoantigen in plastic wells. The antibody levels measured as optical density at 490 nm (x +/- SD)/prevalence of the diabetic group (120 +/- 29 days of age) of BB/OK rats 0.57 +/- 0.29 (n = 51)/88% as well as those of the nondiabetic group (121 +/- 26 days of age) with 0.51 +/- 0.29 (n = 32)/97% was significantly increased (p < 0.01) compared to those of the diabetes-resistant control group 0.15 +/- 0.06 (n = 29)/0%. Furthermore in a 209 +/- 27-day-old group (n = 21) of non-diabetic but diabetes-prone BB/OK rats the autoantibody levels of 1.21 +/- 0.39 vs 0.51 +/- 0.26 were further significantly enhanced (p < 0.01). These results were confirmed by a sandwich assay.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain-reactive autoantibodies in BB/d rats do not recognize glutamic acid decarboxylase

“…It is unclear why our results contrast with those of others [29] who detected antibodies to GAD in BB/OK rats with a mean age of 120 days. However, the lack of anti-GAD antibodies in our rats is consistant with the lack of ICA in BB rats [12,13] and NOD mice [39].…”

“…Indeed, the ELISAs employed in the study of Ziegler et at. [29] do not definitively prove the occurrence of antibodies to GAD. They delected autoantibodies using semi-purified GAD from rat brain in a direct and sandwich ELISA.…”

“…Antibodies to 64-t(D istet cell protein/GAD may precede other antibody markers [4]. Antibodies to 64-kD antigen have been reported in BB rats [17.18] and NOD mice [38], as well as antibodies to GAD in BB/OK rats [29], although these do not show an association with disease onset. Using a direct ELISA we were abte to detect antibodies in BB/d rats which bound to a GAD-enriched brain preparation.…”

“…Immunoprecipitation of in vitro translated, radiolabelled rat GAD-65 failed to detect autoantibodies to 64-kD/GAD in our BB rats (M. Christie, personal communication). Indeed, the ELISAs employed in the study of Ziegler et al [29] do not definitively prove the occurrence of antibodies to GAD. They detected autoantibodies using semi-purified GAD from rat brain in a direct and sandwich ELISA.…”

“…It is therefore interesting to look for the presence of these antibodies in BB rats. Antibodies to GAD have been reported in BB/OK rats [29], although these studies only looked for the presence of antibodies at one or two time points. In this study we examined the humoral autoimmune response in BB/d rats from age 28 to 113 days and looked for the possible presence of anti-GAD antibodies in relation to disease onset.…”