Activation of the alternative complement pathway by normal and transformed cells in homologous and heterologous sera

A variety of both normal and viral transformed or infected cells have been tested for their ability to activate the alternative pathway of complement in either homologous or heterologous sera. Normal cell lines fail to produce alternative pathway activation in homologous sera but readily activate the alternative pathway in heterologous sera. In contrast, human cells, persistently infected with measles virus or chicken cells transformed with oncogenic avian viruses, produce a marked activation in homologous sera. It is suggested that in certain circumstances, the alternative pathway of complement can discriminate between normal and abnormal "self" cells of foreign cell surfaces.