ABSTRACT
Natural killer (NK) cells have been recognized primarily for their cytotoxic reactivity against malignant cells. However, concurrently with the revelation of NK cell antitumor potential, it became evident that these cells are also involved in the regulation of the growth of semisyngeneic, allogeneic, and xenogeneic bone marrow transplants. The immunogenetics of murine bone marrow transplantation portrayed an enigma for transplantation immunologists for almost 2 decades. One of the most perplexing observations in this area was the failure of irradiated F1 hybrid mice to support the growth of parental bone marrow transplants, the phenomenon designated hybrid resistance. Interpretation of hemopoietic resistance as a host antigraft reaction led to a multitude of controversial discussions among immunologists. It was quite trying to acknowledge the existence of the cell-mediated mechanism with features deviating so sharply from classical concepts of transplantation immunology.
