Biological characterization of a tumour-growth-promoting factor from ascitic fluid of tumour-bearing mice.

Tumour-growth-promoting activity has been observed in ascitic fluids of mice with progressively growing SV40- and chemically induced tumours. Administration of ascitic fluid to animals together with a normally non-tumorigenic dose of SV40- transformed tissue culture cells (TU-5) will cause these cells to grow progressively and eventually kill the animals. Also, the mKSA-specfic, immunologically non-responsive state (the eclipse phase) of mice bearing large mKSA tumours can be maintained by administration of ascitic fluid or serum from tumour-bearing animals after the tumours have been surgically removed. Normally, complete immunity to a secondary tumour cell challenge is re-established approximately 10 days after removal of the primary tumour, but daily injections of ascitic fluid or serum will maintain sclipse so that a secondary challenge of tumour cells will grow progressively. The active component apparently acts non-specifically, since ascitic fluid from an unrelated tumour also is able to maintain the mKSA-specific eclipse phase. Thascitic fluid has no apparent immunosuppressive activity in vivo.