Hematological assays of inbred specific pathogen-free (SPF) mice of ten different strains inoculated with Friend leukemia virus (FLV) were performed chronologically to assess whether the genetic control of the host may play an important role in viral oncogenicity. Mice strains C57BL/6J, B 10 (H-2b) and B 10D2 (H-2d) were FLV-resistant, BALB/c, DBA/2N (H-2d), RFM (H-2f), AKR and 80% of CBA/JN (H-2k) were FLY-sensitive (polycythemia) and C3H/ He, B10Br and 20% of CBA/JN (H-2k) were FLY-sensitive (anemia). Only the AKR strain mice showed a spontaneous regression of splenomegaly. These results indicate that there is not a strong but a weak correlation between the H-2 haplotype and the reaction to FLV. The main phenomenon in the anemic mice was the monotonous proliferation of the naked blastic cell, whereas that in the polycythemic mice was the enormous increase of the mature erythroblast and the decrease of the naked blastic cell in the later phase. These facts suggest that the naked blastic cell in the mice with polycythemia are reactive and that in the mice with anemia truly neoplastic.
