Human natural immunoglobulin M antibodies induce apoptosis of human neuroblastoma cells by binding to a M-r 260,000 antigen

Sera of healthy humans contain natural cytotoxic IgM antibodies that specif ically recognize a M-r 260,000 antigen (NB-p260) on the surface of human ne uroblastoma (NB) cells. Here we demonstrate that anti-NB IgM antibodies pre pared from different healthy individuals induce, in all human NB cell lines analyzed thus far, typical morphological and biochemical features of apopt osis including nuclear fragmentation, chromatin condensation, and DNA fragm entation. Both the binding of human anti-NE IgM to NB cells and the inducti on of apoptosis could be inhibited by preincubation of NB cells with murine IgG raised against purified NB-p260, Furthermore, preincubation of human a nti-NB IgM with purified NB-p260 immobilized onto a solid support abolished its ability to induce apoptosis in NB cells. Natural human anti-NE IgM fai led to bind to and induce apoptosis in control tumor cell lines that lack e xpression of NB-p260, The anti-NB IgM-induced apoptotic response was also o bserved in vivo in xenografted human NB tumors. After a single i.v. injecti on of anti-NB IgM into nude rats bearing solid NB xenografts, many areas of pyknotic cells with fragmented nuclei were observed that stained positive using the terminal dUTP nick end labeling method. In conclusion, the data d emonstrate that natural anti-NB IgM antibodies in the sera of healthy indiv iduals are potent mediators of apoptotic cell death of NB cells both in vit ro and in vivo. The NB-p260 antigen was identified as the apoptosis-inducin g receptor for anti-NB IgM. Whereas natural anti-NB IgM and NB-p260 may be useful tools for immunotherapy of NB, their biological significance remains to be determined.