a1-acid glycoprotein (AGP): a possible carrier of sialyl lewis X (slewis X) antigen in colorectal carcinoma

Abstract

Objectives: 1- to detect a1-acid glycoprotein (AGP) and sialyl Lewis x (sLex) in colorectal malignant, benign and normal samples; 2- to isolate AGP from colorectal cancer and 3- to study its immunoreactivity with an anti-sLex monoclonal antibody (MAb). Materials and methods: tissue and serum samples from 88 patients with colorectal cancer, 22 adenomas and 23 normal were included. Expression of AGP and sLex was studied by immunohistochemistry (IHC); isolation approach: AGP was precipitated with ammonium sulphate and immunoprecipitated with anti-AGP MAb. The immune complex formed was isolated by protein ASepharose CL-4B affinity chromatography and further eluted; fractions were analysed by SDS-PAGE and Western-blot. Statistical analysis was performed by means of Principal Component Analysis. Results: by Western blot employing anti-AGP MAb and sLex MAbs, isolated fractions from malignant samples showed a band at about 45kD. IHC revealed that AGP was expressed in 70% of colorectal carcinoma samples, 50% of benign and 35% of normals. SLex was detected in 31% of malignant samples, 41% of benign and in one normal sample. In malignant samples, AGP reaction comprised the whole specimen with a strong and homogeneous staining while normal and benign samples showed a restricted reaction. In cancer, sLex expression consisted in an intense reactivity in membrane, cellular debris and some cytoplasmic foci while normal and benign samples were occasionally stained. A statistically significant positive correlation was found between AGP and sLex expression. Serum AGP levels were measured by radial immunodiffusion and statistical comparative analysis with tissue expression did not show a correlation between both parameters. Conclusion: AGP may constitute a carrier of sLex in colorectal cancer.