Tetanus toxin as a marker for small-cell lung cancer cell lines

Tetanus toxin labeling of human lung cancer cell lines was investigated using direct and indirect immunofluorescence and immunohistochemical staining. Cells of characterized permanent cell lines, eight small-cell lung cancer (SCLC) cell lines of classic subtype, six SCLC cell lines of variant subtype and seven non-small-cell lung cancer (NSCLC) cell lines, were incubated with a saturating concentration of tetanus toxin. For staining, fluorescein-isothiocyanate-(FITC)-conjugated anti-(tetanus toxin) antibodies were used or a mouse monoclonal anti-(fragment C) antibody with subsequent binding of FITC-conjugated anti-(mouse Ig) antibody or peroxidase-anti-peroxidase complex. Only SCLC showed an intense fluorescence/immunoreactivity restricted to the cell membrane. Quantitative analysis of tetanus toxin labeling by flow cytometry revealed the percentage of positive cells to be between 35% and 95% in SCLC without obvious differences between the classic and variant subtypes of SCLC. In NSCLC the percentage of positive cells was lower than 10%. These results demonstrate that SCLC in contrast to NSCLC can be labeled with tetanus toxin, emphasizing the neuroendocrine properties of this tumor, and that tetanus toxin labeling may become a useful diagnostic marker for SCLC cells in cytology.