Studies on the resistance of the C57B1/6 mouse strain to the polycythemia-inducing strain of the Friend virus (FV-P).

In previous studies it had been found that C57B1/6 marrow cells, normally resistant to infection by the Friend virus (FV-P), became susceptible after their transplantation into lethally irradiated leukemic DBA/2 mice. This loss of FV-P resistance was further analyzed and spleen weight and the number of erythropoietin-(Ep)-independent CFU-E in bone marrow and spleen were measured as the result of successful FV-P infection. C57B1/6 marrow was infected shortly before and in intervals after either isogeneic transplantation or transplantation into lethally irradiated DBA/2 hosts. After isogeneic transplantation there was some susceptibility for FV-P and this seemed to correlate with the regenerative activity of BFU-E at the time of infection. However, there was no difference in the BFU-E kinetics between normal DBA/2 and C57B1/6 mice. C57B1/6 were further pretreated by bleeding, irradiation with 150 R, injection of hydroxyurea and of endotoxin. After hydroxyurea treatment there was an increased proportion of BFU-E in S-phase, but only endotoxin, which did not alter the BFU-E kinetics after 48 h, made C47B1/6 mice susceptible to FV-P infection. These results suggest that the proliferative activity of BFU-E might be important for successful FV-P infection and induction of Ep-independent erythropoiesis but also other conditions regulate the resistance or susceptibility of a mouse strain.