Comparison of immunoreactivity between two different monoclonal antibodies recognizing peptide and polysialic acid chain epitopes on the neural cell adhesion molecule in normal tissues and lung tumors.

A comparative immunohistochemical study of two different monoclonal antibodies against different epitopes on the neural cell adhesion molecule (N-CAM) was performed. Various normal tissues and lung tumors were examined for reactivity with NCC-LU-243, a monoclonal antibody which recognizes a peptide epitope on N-CAM, and monoclonal antibody 735 (MoAb 735), which reacts with a polysialic acid chain epitope on N-CAM. When acetone-fixed normal tissues were used, the immunoreactivities of MoAb 735 and NCC-LU-243 were not identical. In lung tumors, almost all small cell cancers (SCLC) and carcinoid tumors, and some non-SCLC were stained by both monoclonal antibodies. NCC-LU-243 stained the cell membrane only of almost all SCLC cells and clusters of non-SCLC cells. MoAb 735 stained the cell membrane of SCLC in a patchy manner and not only the cell membrane but also the cytoplasm of some non-SCLC. However cytoplasmic staining was evaluated as 'not positive'. The number of positive cases and the size of the positive tumor cell population determined by cell membrane staining with MoAb 735 were smaller than those determined with NCC-LU-243 in both SCLC and non-SCLC cases. In routinely formalin-fixed materials, the immunoreactivity of both monoclonal antibodies, especially of NCC-LU-243, decreased after prolonged fixation as in surgically resected and autopsy materials. However, both monoclonal antibodies were found to be useful when materials were fixed for a short period of time as in biopsy specimens.