The role of hydroxyl radicals (.OH) damaged immunoglobulin G (IgG) in insulin dependent diabetes mellitus has been investigated. IgG was isolated from normal human serum and modified by hydroxyl radicals, generated by UV irradiation of hydrogen peroxide. .OH-induced modification on IgG has been studied by ultra-violet (UV) absorption spectroscopy, tryptophan/tyrosine fluorescence, circular dichrosim, SDS-PAGE and carbonyl groups estimations. .OH caused extensive damage to IgG. The binding characteristics of circulating antibodies in type 1 diabetes patients against native and modified IgG were assessed. Type 1 diabetes patients (n = 36) were examined by direct binding ELISA and the results were compared with healthy age-matched controls (n = 22). High degree of specific binding of diabetes sera towards .OH modified IgG, in comparison to its native analogue (p < 0.05). Sera from normal human subjects showed negligible binding with either antigen. Our results conclude that .OH-modification of IgG causes structural perturbations, resulting in the generation of neo-epitopes and making it a potential immunogen. IgG modified with .OH may be one of the factors for the induction of circulating type 1 diabetes autoantibodies.
Key words: Autoantibodies, hydroxyl radicals, immunoglobulin G, .OH-IgG, type 1 diabetes mellitus.
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