Compatibility Factors Influencing the Acceptance of Rat Bone Marrow Graft by the Irradiated Mouse **

Heavily irradiated mice have been protected from otherwise lethal bone marrow damage by intravenous injection of rat bone marrow."'S5'14 It has been amply demonstrated that the radio-protection offered by the rat bone marrow is actually due to myelopoietic repopulation of the mouse marrow cavity by rat marrow precursor cells."",'8 13 l Mice given supralethal irradiation plus rat bone marrow have been demonstrated to produce rat erythrocytes,4"5"8' rat granulocytes,7"8 and rat platelets.9 This rather bland acceptance of rat bone marrow by the irradiated mouse naturally led to experiments designed to test the possibility that bone marrow from other heterologous species would "take" and grow in the irradiated mouse. In our laboratory we have found that marrow from humans, guinea pigs, rabbits, and hamsters all failed to prevent lethal marrow damage in the irradiated mouse, and these same negative results have been reported by others.' It seemed quite evident, then, that rat bone marrow is the only "heterologous" marrow that has been found acceptable to the irradiated mouse. The studies reported in this communication deal with the compatibility factors between rat and mouse that allow this inter-species marrow graft acceptance.