Proteomic profiling of serum is a powerful technique to identify differentially expressed
proteins that can serve as
biomarkers predictive of disease onset. In this study, we utilized two-dimensional (2D) gel analysis followed by matrix-assisted-
laser desorption/ionization time-of-flight mass spectrometry analysis to identify putative serum
biomarkers for autoimmune
type 1 diabetes (T1D) in biobreeding diabetes resistant (BBDR) rats induced to express the disease. Treatment with
toll-like receptor 3 ligand, polyinosinic:polycytidilic
acid (pIC), plus
infection with Kilham rat virus (KRV), a rat parvovirus, results in nearly 100% of young BBDR rats becoming diabetic within 11-21 d. Sera collected from prediabetic rats at early time points following treatment with pIC + KRV were analyzed by 2D gel electrophoresis and compared with sera from control rats treated with
phosphate-buffered saline, pIC alone or pIC + H1, a non-diabetogenic parvovirus. None of the latter three control treatments precipitates T1D. 2D gel analysis revealed that
haptoglobin, an acute phase and
hemoglobin scavenger
protein, was differentially expressed in the sera of rats treated with pIC + KRV relative to control groups. These results were confirmed by Western blot and
enzyme-linked
immunosorbent assay studies, which further validated
haptoglobin levels as being differentially increased in the sera of pIC + KRV-treated rats relative to controls during the first week following
infection. Early elevations in serum
haptoglobin were also observed in LEW1.WR1 rats that became diabetic following
infection with rat cytomegalovirus. The identification and validation of
haptoglobin as a putative serum
biomarker for autoimmune T1D in rats now affords us the opportunity to test the validity of this
protein as a
biomarker for human T1D, particularly in those situations where
viral infection is believed to precede the onset of disease.