The 88-kDa Eales' protein in serum is a complex of haptoglobin, complement C3, and galectin-1 as identified by liquid chromatography coupled mass spectrometry.

Abstract

Eales' disease (ED), an enigmatic inflammatory disease, affects peripheral retinal veins and thereby vision in males. This study was aimed at identifying and deciphering the role of a novel 88-kDa protein reported in the serum and vitreous of patients with ED. The purified 88-kDa protein was identified by UPLC coupled ESI-QTOF-MS. The identified proteins were quantified in the serum from 20ED patients and controls (age and sex matched), respectively by ELISA. The interaction of these proteins was studied using co-immunoprecipitation, western blot, and MS analyses. N-glycosylation of protein was observed by MS and lectin blot. The 88-kDa protein was identified to be a complex of haptoglobin, complement C3, and galectin-1. ELISA results showed a 1.5-fold increase in levels of haptoglobin (p = 0.008), with level of complement C3 unaltered and 1.2-fold decreased serum galectin-1 levels (p = 0.003) in ED patients compared to controls. Co-immunoprecipitation illustrated the interaction between haptoglobin and complement C3. Reduced sialylation and increased β-1, 6-N-acetyl-glucosamine branched N-glycans were observed in haptoglobin of ED patients. The 88-kDa protein, a complex of haptoglobin, complement C3, and galectin-1, may play a potential role in ED pathogenesis while levels galectin-1 and haptoglobin may serve as potential biomarker of ED.