THU267 A Novel In Vitro Assay Correlates Insulin Receptor Autoantibodies To Fasting Insulin In Type B Insulin Resistance
Authors: Abel Brent , Minich Waldemar , Schwiebert Christian , Welsink Tim , Seemann Petra , Schomburg Lutz , Brown Rebecca J 
Published: October 2023

Abstract
Disclosure: B. Abel: None. W. Minich: Stock Owner; Self; ImmunometriX GmbH. C. Schwiebert: Employee; Self; Bruker Corporation. T. Welsink: Employee; Self; Bruker Corporation. P. Seemann: Stock Owner; Self; ImmunometriX GmbH, selenOmed GmbH. L. Schomburg: Stock Owner; Self; selenOmed GmbH. R.J. Brown: None.
Severe insulin resistance (IR) in the presence of insulin receptor autoantibodies (InsR-aAb) is known as type B IR (TBIR). TBIR has a spectrum of phenotypes, including severe IR with uncontrolled diabetes (DM), milder IR without uncontrolled DM, hypoglycemia, and remission states. Considerable progress in therapy has been achieved, but diagnosis and monitoring of InsR-aAb remains a challenge. We aimed to develop a robust in vitro method for InsR-Ab quantification and correlate it with clinical outcomes. 28 longitudinal serum samples from 9 patients with TBIR were collected before, during, and after immunosuppression. Samples included 11 in states of remission, 4 in hypoglycemia, 6 in mild IR, and 7 in severe IR. Samples from 8 patients with IR not due to TBIR (type 1 DM, N=1; type 2 DM, N=4; lipodystrophy, N=2; and INSR mutation, N=1) were used as controls. A bridge-assay for InsR-aAb detection was established using recombinant human insulin receptor as bait and detector and validated using monoclonal antibodies as positive controls. The assay consists of an immobilized recombinant InsR at a plastic surface and an InsR-Luc fusion protein for detection of InsR-aAb. There was dose-dependent increase in intensity over &gt;2 orders of magnitude with InsR-specific commercial mAb, but not with control mAb. In the presence of insulin, strong InsR phosphorylation was observed in cells incubated with Ig from control sera, but not those incubated with Ig from TBIR patient sera.
Fasting insulin was highest in severe TBIR (median 1000 [IQR 273-1000] mcU/mL), followed by mild (71[32-230]), and lower in hypoglycemia (6 [3,103]) and remission (14[6,35]), P=0.0014, and was moderately elevated in insulin resistant controls (55[11,120]). A1c was elevated in severe TBIR & controls (9.9±3.0 & 9.1±3.8%) and near-normal in mild, hypoglycemic, and remission states of TBIR (5.7±1.3, 6.0±0.7, 5.7±1.1). InsR-aAb titers changed in parallel to changes in TBIR state and severity: highest in severe TBIR (median 700 [IQR 365-977]), followed by mild (176[98-254]), and lower in hypoglycemia (14[1.3-189]) and remission (17[3-28]). All TBIR samples showed clearly elevated signal intensities versus controls (0.9[0.7-1.1], Bonferroni corrected P&lt;0.05 for all TBIR states vs controls). During treatment, InsR-aAb for each subject declined with amelioration of disease symptoms. Fasting insulin strongly correlated with InsR-aAb titers (r=0.825, p&lt;0.001). The assay correctly identified all samples from patients with TBIR vs controls with non-autoimmune IR, and thus is an easy to interpret diagnostic tool. InsR-aAb titers correlated with fasting insulin, supporting direct relevance of InsR-aAb as causal for disease severity and as therapeutic targets for Ab depletion. By easing diagnosis and monitoring of TBIR, the new assay for InsR-aAb quantification should enhance access to timely and effective treatment for TBIR.
Presentation: Thursday, June 15, 2023