Analysis of rabbit and guinea pig complement efficiency in cytotoxicity tests against fibrosarcoma and lymphosarcoma cells.

In a complement-dependent 51Cr cytotoxicity assay, using as target murine fibrosarcoma or lymphosarcoma cells, the rabbit complement (RC) was more efficient than guinea pig complement (GPC) when tested either with strong antisera, such as antihistocompatibility sera, or with weak sera, such as wera from normal mice shown previously to posses a natural antitumor response. The high efficiency of RC was not due to activation by antibodies of a different class or specificity than those activating GPC. In fact, both 2-mercaptoethanol (2-Me)-sensitive or-resistant immunoglobulins could activate both RC and GPC, and the results of absorption tests indicated that the antibodies detected using either of the 2 complements were directed against the same specificities. In addition, the results of tests searching for cooperative antibodies excluded that a cooperative effect might be responsible for the high efficiency of RC. With weak antisera, sera of different rabbits were found to have different complement activity.