Cell-associated infectivity in the blood of C57Bl mice bearing a radiation-induced leukemia (RadLV/D)

The leukemogenic activity of the blood constituents was studied in C57Bl mice bearing a reticulosarcoma of the spleen and lymph nodes induced by a Radiation Leukemia Virus (RadLV/D). In the blood plasma, viral C-particles could hardly be detected and the infectious titer (ED 50 at 45 days) remained at a very low level up to 63 days after inoculation. Attempts to purify and concentrate a viral fraction, the infectivity of which should be higher than that of crude plasma, were unsuccessful. From 14 to 63 days after inoculation, the infectious titers of whole blood, lymphocyte and erythrocyte fractions were of the same order of magnitude as that of an acellular extract of lymphoid tissues: 10²-10³. The erythrocyte cell line being not involved in the evolution of the disease, particular care was taken to eliminate possible contaminants (lymphocytes or adsorbed C-particles) from the erythrocyte suspensions; the activity of the erythrocytes remained unaltered after differential centrifugation on Ficoll/Urografine, SE-Cellulose/Sephadex chromatography and trypsinization. Lysis by osmotic shock or immune hemolysis always resulted in a partial or total loss of biological activity, indicating that to be infectious the structure of the erythrocytes must be preserved. As it has been described for different other types of oncornavirus-induced tumors it appears that blood cells, including erythrocytes or/and erythrocyte-precursors may play a role in the transmission of the RadLV/D induced leukemia.