Detection of disease specific sialoglycoconjugate specific antibodies in bronchoalveolar lavage fluid of non-small cell lung cancer patients

In this study, we report the presence of significantly higher level of GM3 specific IgG antibodies (IgG_TL) in the bronchoalveolar lavage fluid obtained from tumor bearing lung of non-small cell lung cancer (NSCLC) patients as compared to other non-neoplastic controls. The antibodies were isolated using DEAE-cellulose anion exchange chromatography and molecular weight of the subunits of IgG_TL was confirmed in SDS-PAGE. IgG_TL revealed high specificity to GM3 and the IgG distribution was confined to IgG1. Furthermore, IgG_TL showed strong reactivity with NSCLC cell lines as well as the tissue biopsies and cells obtained from fine needle aspirations of NSCLC patients. A 66 kDa membrane glycoprotein of NSCLC cell lines was found to interact specifically with IgG_TL, the intensity of which was drastically reduced in presence of GM3. Further, binding of Maackia amurensis agglutinin [specific for NeuAcα(2→3)Gal unit , the same disaccharide unit also known to be present in GM3] to the 66 kDa band confirmed it to be a sialoglycoprotein in nature. IgG_TL could not show any reactivity to alkaline borohydrate treated or periodate oxidised membrane fractions, suggesting the probable involvement of the carbohydrate moiety of the 66 kDa glycoprotein in the interaction with IgG_TL. Thus, the 66 kDa sialoglycoprotein seems to be the NSCLC specific sialoglycoconjugate. Taken together, IgG_TL antibodies may have the potential to serve as a unique probe for detail investigation of NSCLC specific cell surface sialoglycoconjugate. Further, due to high specificity of IgG_TL to GM3, it may be possible to develop a simple alternative diagnostic approach (GM3-ELISA) for NSCLC.