Sandwich assay using labeled lectin and kit therefor
The present invention provides a sandwich assay for quantifying a glycoprotein, which is a substance to be detected, in a sample using a labeled lectin, wherein the effect attributed to a contaminant, namely noise on the quantified value of the substance to be detected, is suppressed by introduction of a simple treatment. The sandwich assay includes a treatment for inhibiting the binding of the labeled lectin to a sugar chain carried by the contaminant non-specifically adsorbed to the measurement region, which contaminant is contained in the sample and which sugar chain is the same as that of the substance to be detected.
1. A sandwich assay for quantifying a glycoprotein as a substance to be detected, using a labeled lectin and a capturing substance immobilized on a measurement region,
said sandwich assay comprising a treatment for inhibiting the binding of said labeled lectin to a sugar chain that is carried by a contaminant non-specifically adsorbed to said measurement region and is the same as that of said substance to be detected,
wherein said treatment for inhibiting the binding of said labeled lectin to said sugar chain is a treatment of bringing a substance showing an action of cleaving disulfide bonds into contact with said contaminant and thereby dissociating a domain comprising said same sugar chain as that of said substance to be detected,
said substance showing an action of cleaving disulfide bonds is brought into contact with said contaminant before said contaminant is brought into contact with said capturing substance,
said substance to be detected is a glycoprotein comprising an N-acetyl-D-galactosamine β1-4 N-acetylglucosamine residue-containing sugar chain, and
said substance showing an action of cleaving disulfide bonds is at least one selected from the group consisting of sodium metabisulfite and sodium toluenethiosulfinate.
2. The sandwich assay according to claim 1 , wherein
said contaminant non-specifically adsorbed to said measurement region is a glycoprotein comprising the same sugar chain as said substance to be detected.
3. The sandwich assay according to claim 2 , wherein said substance to be detected is a glycoprotein which comprises: the same sugar chain as that of said glycoprotein as said contaminant; and a binding site for said capturing substance, within the same domain.
4. The sandwich assay according to claim 2 , wherein
said contaminant comprises an N-acetyl-D-galactosamine β1-4 N-acetylglucosamine residue-containing sugar chain, and
said labeled lectin is Wisteria floribunda lectin (WFA), soybean lectin (SBA), Trichosanthes japonica lectin-II (TJA-II) or Vicia sativa lectin (VVL) that is labeled.
5. The sandwich assay according to claim 2 , wherein said contaminant is at least one selected from the group consisting of immunoglobulin M (IgM), inter-α-trypsin inhibitor (IαI), α2-macroglobulin (α2M), haptoglobin (HP) and immunoglobulin G (IgG).