The F1 hybrid effect in allogeneic lymphocyte cytotoxicity. Points of similarity between hybrid resistance and ALC.

Allogeneic lymphocyte cytotoxicity (ALC) is characterized by the rapid destruction of intravenously injected allogeneic lymphocytes by unsensitized hosts. While ALC has been reported in several mammalian species, it has been most extensively studied in rats. All the available in vivo and in vitro evidence points to NK cells as the effectors of ALC. The experiments described in this communication show that when donor and host share common ALC determinants, the extent to which allogeneic lymphocytes are killed is greatly reduced, and sometimes even abolished, relative to the killing that would have occurred in the absence of shared determinants. Thus, allogeneic lymphocyte transfers in inbred rat strain combinations having the general pattern A----B are associated with significantly higher levels of ALC than are the corresponding (A x B)F1----B, A----(A x B)F1 or (C x A)F1----(C x B)F1 lymphocyte transfers. The reduced ALC is not due to inability of the F1 hybrid to respond with the full vigor of the parental strains. Nor is it due to an absolute requirement for homozygous presentation of the donor ALC determinants. It is concluded that impaired self-recognition may be an important determinant of killing in ALC, as in some other NK cell-mediated phenomena. Although ostensibly differing immunogenetically from hybrid resistance in mice, ALC includes a range of patterns of reactivity, some of which are similar to those that characterize hybrid resistance. It is suggested that hybrid resistance and ALC may represent quantitative variants of a similar process.