In vivo infectivity of the fibrotropic C-type viral isolates from C57BL/Ka mice.

Of the three fibrotropic C-type viral isolates from C57BL/Ka mice, only the BL/Ka(B) virus is capable of infecting normal hematopoietic and lymphoid cell populations of C57BL/Ka mice in vivo, and none are tumorigenic. Inoculation of this virus alone into neonates resulted in transient replication in the bone marrow, spleen, and occasionally the thymus. Thymocytes could, however, be permanently infected in such animals if BL/Ka(B) were coinoculated with the xenotropic BL/Ka(X) virus. Neonatal injection of BL/Ka(B) prior to fractionated wholebody irradiation yielded an increase in the percentage of virus-productive radiogenic lymphomas and a decrease in incidence of such tumors. Injection of BL/Ka(B) into normal adult C57BL/Ka mice did not yield overt expression of virus replication in any of the tissues tested; latent infection could, however, be detected in the marrow and in the reticuloepithelium of the thymus. Whole-body X-irradiation of adults with 400 rads partially restored the neonatal susceptibility of bone marrow cells to infection by the isolate. BL/Ka(B) injection after fractionated whole-body irradiation of weanling C57BL/Ka mice increased the percentage of virus-positive lymphomas and revealed that a bone marrow cell subpopulation permissive for infection by the virus increases greatly in abundance soon after irradiation.