The significance of natural killer activity in the resistance of allogeneic hosts to the embryonal carcinoma cell line F9.

A number of mouse strains of known F9 resistance phenotype have been tested for their in vitro natural killer activity against both F9 and YAC target cells. The pattern of in vitro natural killer activity observed does not correlate with the pattern of in vivo F9 resistance. The relative efficiencies of in vitro lysis of the F9 and YAC targets by endogenous natural killer effectors from the 129/Sv, SJL/J, C57Bl/6J, and BALB/cJ strains do, however, parallel each other, even though overall levels of F9 target lysis are very low. Since cold competition experiments indicate that the embryonal carcinoma cell lines tested, F9, PCC4/Aza, and PCC3/A/1, can compete efficiently with YAC as target, this low lysis of embryonal carcinoma cells may be due to an intrinsic lysis resistance. The finding that the parietal endoderm cell line PYS-2 and the trophoectodermal cell line TDM1 also compete with YAC targets in cold competition experiments is discussed in relation to previous reports suggesting that such differentiated derivatives lack natural killer target structures.