Monoclonal antibodies defining the cluster-5A small cell lung carcinoma antigen

The cluster-5A antigen on small cell lung cancer has been previously identified by the murine IgG2a monoclonal antibody SWA20. We now describe four new murine monoclonal antibodies. SEN3 (IgG1), SEN11 (IgG3), SEN12 (IgG2b) and SEN31 (IgG1) which recognise the same antigen. The antibodies have similar binding characteristics as antibody SWA20 on cell lines and on a limited number of frozen sections of human tissues when examined by immunofluorescence and immunohistochemistry. Radioimmunoassays on fixed cells showed competitive binding of all antibodies with radiolabelled antibody SWA20. Solid phase radioimmunoassays with the new antibodies on biochemically treated target cells showed similar characteristics to antibody SWA20, including sensitivity to treatment with periodate and neuraminidase. Immunoblotting experiments with all antibodies revealed similar bands at molecular weights of 180, 100 and 50 kD. Binding studies after incubation of cells with inhibitors of glycoprotein synthesis suggest the cluster-5A antigen to be a N-linked sialoglycoprotein.