In vitro and in vivo production of chemotactic inhibitors by tumor cells.

The ascites fluid or peritoneal washings of DBA/2 mice bearing the P815 mastocytoma have been found to contain a chemotactic factor inactivator (CFI) which inactivates the bacterial chemotactic factor as well as the chemotactic activity associated with the C3 and C5 fragments when assayed on rabbit neutrophils. The amount of CFI is proportional to the number of tumor cells in the peritoneal exudate. The inactivator is also found in tumor cell hemogenates as well as in culture fluid from tumor cells growing in vitro. The activity is heat-labile but is not affected by protease inhibitors. Its molecular weight is greater than 50,000 daltons, based on Sephadex chromatography and sucrose density gradient ultracentrifugation studies. In C57BL/6 mice, which reject the mastocytoma, CFI levels decrease in proportion to the decreasing numbers of tumor cells.