The influence of genetic resistance on CFU growth kinetics in spleen and femur.

An impaired colony formation of C57BL marrow cells transplanted into F1 (C57BL TIMES CBA) mice was observed. In accordance with the literature this phenomenon has been designated as "genetic resistance". Studies to elucidate the mechanism of the genetic resistance demonstrated that the multiplication phase of the CFU growth curve started in the semi-isogeneic combination about 48 hr later than in the isogeneic combination. In the spleen this resulted in a lower "dip". For the spleen as well as for the femur similar CFU doubling times were found during the multiplication phase when both transplantation combinations were compared. Furthermore the percentage of CFU in S-phase (assessed with the 3-H-TdR suicide technique) during the first days after transplantation were similar in both combinations. When the spleen was removed 5-6 months before irradiation and bone marrow transplantation was performed the growth curve of parental CFU in the femur was identical with the growth curve of isogeneic CFU (no delay was observed). These results are discussed and a few theories explaining the observations are proposed.