Homologous complement activation on drug-induced apoptotic cells from a human lung adenocarcinoma cell line

Activation of the alternative pathway of homologous complement (C) was observed in a human lung adenocarcinoma cell line, CADO 43, after the cells had become apoptotic following treatment in vitro with vincristine and predonisolone. Deposition of C3b and C3bi on the serum-treated apoptotic cells was revealed by flow cytometry with anti-C3b and -C3bi-specific antibodies and immunoblotting with anti-C3 antibody immunoprecipitates extracted from solubilized fractions of serum-treated apoptotic cells. Two molecular mechanisms were found to be responsible for this post-apoptotic C-activation. Firstly, all C regulators, decay accelerating factor (DAF), membrane cofactor protein (MCP) and C3b/C4b receptor (CR1), were diminished on the cell surface concomitantly with the apoptotic process. Secondly, unidentified molecules which potentially activate homologous C and accept C3b/C3bi fragments became expressed on the cell surface during the apoptotic process. These findings may explain the mechanism whereby tumor cells are efficiently eliminated through chemotherapy.