ANALYSIS OF SUPPRESSION MECHANISM OF T-CELL ACTIVATION THROUGH HISTIDINE-RICH GLYCOPROTEIN RECEPTOR

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In order to analyze the down-modulating mechanism of T-cell activation by histidine-rich glycoprotein (HRG), I tried to isolate the HRG receptor from the bovine white blood cells. At the initial stage, the detection of HRG binding proteins was performed by the dot blot analysis in which the sample solution was spotted on a PVDF membrane and the binding of biotinylated HRG was assessed with streptoavidin and biotinylated alkaline phosphatase. Since this method is not quantitative, the biosensor technique was introduced to detect the interaction between HRG and specific binding proteins. After solubilization of membrane proteins from white blood cells with 2% Triton X-100, the extracts was applied to an HRG-immobilized agarose column. HRG binding proteins were eluted from the column by raising the ionic strength and then lowering the pH of the solution to 2.5. The HRG specific binding proteins were obtained by the latter elution condition and further purified by a DEAE-Sephacel column. In the binding assay, the interaction between these binding proteins and HRG immobilized to the aminosilane cell was suppressed in the presence of free HRG.This suppression effect was more evident in the presence of HRG previously treated with plasmin. This may indicate that the receptor was for the plasmin-modified HRG.SDS-PAGE showed that this preparation contained mainly two kinds of polypeptide with a molecular weight of 45,000 and 25,000. The amino terminal sequences of these polypeptides were the same and these polypeptides were considered to be derived from the single polypeptide. The sequence and mass fingerprinting failed to identify this polypeptide against database and this polypeptide was thought to be novel. The structural analysis of this protein is underway.