Endogenous ecotropic murine leukemia viral (MuLV) envelope protein as a new autoantigen reactive with non-obese diabetic mice sera.

The identification and characterization of autoantigens associated with autoimmune IDDM (insulin dependent diabetes mellitus) would help to elucidate the pathogenic mechanism of this disease as well as to design antigen-based immunotherapy. Non-obese diabetic (NOD) mice have been used as the best model for studying the pathogenesis of human IDDM. To identify new autoantigens associated with IDDM, the lambda gt11-cDNA library from MIN6N8a, NOD-derived pancreatic beta cell line, was constructed and then candidate autoantigen clones were screened with prediabetic NOD sera. Nine positive clones were selected from 2x10(5)phage plaques. The nucleotide sequencing and homology searching showed that six of the nine positive clones had part of the endogenous ecotropic murine leukemia viral (MuLV) envelope gene. Nested deletion of this envelope gene revealed that the leucine zipper region in the transmembrane domain of MuLV envelope protein was the target epitope(s) reactive with prediabetic NOD mice sera. The prevalence of MuLV envelope protein-positive antibody in NOD mice was around 46%, while the non-NOD mice strains including BALB/c, ICR, C57BL/6, and SJL/J mice did not produce this envelope protein-reactive antibody. The expression of endogenous ecotropic MuLV envelope gene in NOD mouse pancreas was distinct in those with severe insulitis. However, both prediabetic and diabetic NOD mice did not show the MHC class II-restrictive cellular autoimmunity against our purified recombinant envelope protein. In this study, we showed that the endogenous ecotropic MuLV envelope protein was a new autoantigen reactive with the activated NOD humoral immune system.