Studies of the rat immune response to plasmacytoma 5563 in C3H mice

Washed lymphocytes from immunized rats showed no reaction against mouse plasmacytoma 5563 in vivo or in vitro.Cell-free lymph from immunized rats was shown to be cytotoxic to the tumour cells in vitro. This effect we have shown to be solely in the 19s fraction after Sephadex G-200 separation.This 19s fraction conferred partial protection to tumour bearing mice when given shortly after transplantation, but had negligible effect against late well established tumour.