RADIOSENSITIVITY AND GROWTH OF FRIEND LEUKEMIA VIRUS STUDIED WITH SPLEEN FOCUS ASSAY METHOD

Radiobiological and growth properties of a spleen focus‐forming strain of Friend Leukemia Virus (FV) have been investigated with the spleen focus assay method. The sensitivity of FV to ultraviolet light (2537 Å) and to 60Co γ‐rays was determined by irradiation of virus preparations in vitro to different doses and, at each radiation dose, measurement of the surviving fraction of spleen focus‐forming activity of the virus in SIM mice. Bacteriophage T4 mixed with the virus preparations served as internal dosimeter. It was found that for UV irradiation, the D10 of FV was 4.8 × 103 ergs/mm2. For ionizing radiation, the D10 of FV was 5.6 × 104 rads. The multiplication of FV in vivo was investigated by measurement of virus titers in the spleen at various times following the intravenous injection of FV into SIM mice. Immediately after injection of a high dose of FV, 2–3% of the input virus reached the spleen. Its concentration then fell rapidly to a minimum at around 16 hours. Then the virus concentration in the spleen increased exponentially with a doubling time of 4–6 hours until the 5th day, when it reached a plateau lasting at least 18 days. The concentration of FV recoverable from the spleen at various times after infection was found to be related to the input dose of virus. Accumulation of virus in plasma paralleled the increase in virus content of the spleen. Supralethal irradiation of SIM mice prior to or soon after infection by FV drastically reduced the amount of virus that could be recovered from the spleen at all times thereafter. Copyright © 1969 Wiley‐Liss, Inc., A Wiley Company