LAUSR

AIM Luciferase immunoprecipitation (LIPS) assays show good sensitivity and specificity in testing islet specific autoantibodies for diagnosis of type 1 diabetes (T1D). However, there are currently no LIPS assays available for detecting proinsulin/insulin autoantibody (IAA) previously. We here developed a LIPS assay to measure IAA using nano luciferase (NanoLuc)-proinsulin fusion protein. METHODS The NanoLuc-proinsulin fusion protein expression plasmid was constructed and transfected to COS1 cells. Expression and binding specificity to IAA of the fusion protein were validated. A LIPS assay using the NL-proinsulin fusion protein was developed and compared to radioimmunoassay (RIPA) in testing sera from 50 healthy controls and 34 T1D patients. RESULTS The fusion protein was correctly expressed in transfected COS1 cells. Both NANOLUC activity and proinsulin were detected in the medium of transfected COS1 cells. Fusion protein bound to monoclonal anti insulin antibody and sera from T1D patients or NOD mice, these bindings were inhibited by recombinant human insulin. The LIPS assay using the fusion protein showed sensitivity of 47.1% and specificity of 98.0%. Further analysis supported correlation between the IAA indexes of all the T1D samples detected by LIPS assay and radioimmunoassay (RIPA, R2 = 0.6132, p < 0.0001). CONCLUSIONS The NanoLuc-proinsulin fusion protein based LIPS has the potential to detect IAA for diagnosis of T1D.