Lysis of RSV-transformed Japanese quail cells by a factor from normal quail serum

Normal sera of Japanese quails caused lysis of tumor cells from a Rous sarcoma virus (RSV)-induced quail tumor (QT cells). Other tumor cell lines, including RSV-transformed quail embryo cells and methylcholanthrene-induced quail tumors, were not lysed. This naturally occurring cytolytic factor (NCLF) was sensitive to heating at 56 degrees C, zymosan, and inulin, and it required magnesium but not calcium for the expression of its activity. These results suggested that NCLF activity was mediated by complement activated through an alternative pathway. This possible complement activation occurred in the absence of specific antibodies to the target cells.