Putrescine and its biosynthetic precursor L-ornithine augment the in vivo immunization against minor histocompatibility antigens and syngeneic tumor cells.

Putrescine was found to augment strongly the in vivo priming for secondary in vitro cytotoxic responses by small numbers of syngeneic ESb-D tumor cells and MHC-compatible allogeneic cells (minor H-antigens). The cytotoxic response against minor H-antigens in putrescine-treated mice showed the typical MHC-restriction that has previously been observed after immunization with higher cell doses without putrescine. The injection of putrescine had practically no effect on the subsequent in vitro primary cytotoxic response against an unrelated set of allogeneic stimulator cells. A similar augmentation of the in vivo immunization for secondary in vitro responses was achieved with L-ornithine, the biosynthetic precursor of putrescine. A substantial secondary in vivo cytotoxic activity against minor H-antigens was also obtained by application of L-ornithine shortly after the primary immunization.