1. ¹Department of Pathology, Immunology, and Laboratory Medicine, University of Florida College of Medicine, Gainesville, FL, USA
2. ²Division of Rheumatology & Clinical Immunology, Department of Medicine, University of Florida College of Medicine, Gainesville, FL, USA

Correspondence: Dr L-J Yang, MD, PhD, Department of Pathology, Immunology, and Laboratory Medicine, University of Florida College of Medicine, Box 100275 Gainesville, FL 32610-0275, USA. E-mail: yanglj@pathology.ufl.edu

Received 4 June 2009; Revised 27 July 2009; Accepted 12 August 2009; Published online 9 November 2009.

Abstract

Pancreatic duodenal homeobox 1 (Pdx1) protein is a key transcription factor involved in the regulation of insulin gene expression that is expressed at high levels in the -cells of the pancreatic islets. We asked whether Pdx1 is a target of anti-islet autoimmunity in type I diabetes (T1D). Pdx1 autoantibodies (PAAs) were detected in non-obese diabetic (NOD) mice using ELISA, western blotting, and radioimmunoprecipitation of [³⁵S]-labeled insulinoma cell line-derived Pdx1 protein. PAAs were detected as early as at 5 weeks of age, and generally peaked before the onset of clinically overt diabetes in diabetes-prone female NOD mice. Levels declined substantially after the onset of diabetes. PAAs were not detected in the sera of NOD–scid, C57BL/6, or BALB/c mice. The titers of PAAs in NOD mouse sera were as high as 1/93 750 by ELISA. The fine specificity of PAAs was determined by western blotting using a series of truncated recombinant Pdx1 proteins. The immunodominant epitopes were located to the C-terminus of the Pdx1 (p200–283) in NOD mice. PAAs also were detected in sera from human T1D patients, but the major epitopes were localized to amino acids 159–200 as well as the same region (p200–283) recognized by PAAs from NOD mice. Using [³H]thymidine incorporation, the p83 fragment of Pdx1 specifically stimulated proliferation of splenic T cells from recent-onset diabetic NOD mice. The presence of PAAs in prediabetic NOD mice and human T1D patients, and Pdx1-specific T-cell proliferation in NOD mice provide a strong rationale for further investigation of the pathogenic role of immune responses against Pdx1 in T1D.