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Evaluation of Irradiation-Plus-Urethan-induced Murine Leukemia Virus "Release" Using a New Method for Quantitation of Oncornaviruses in Tissues¹

Department of Pathology, University of North Carolina School of Medicine, Chapel Hill, North Carolina 27514 [R. C. B., J. A. K.], and Department of Pathology, Rutherford Hospital, Inc., Rutherfordton, North Carolina 28139 [R. C. B., A. K.]

The quantity of C-type RNA tumor viruses in homogenate-sonicates of thymus-bone marrow tissues of C57BL/6J and RFM/Un mice 10 days after irradiation (X-rays or -rays)-plus-urethan treatments is no greater than that in thymus-bone marrow homogenates from nontreated control mice. These results indicate that the leukemogenic activity, shown to be present in such thymus-bone marrow homogenates at this time after irradiation-plus-urethan treatment, is not due to change in quantity of C-type viruses as has been proposed.

Virus quantity in tissues was evaluated by a new procedure that includes use of a microchamber with the sides situated on rotor radii so as to produce a uniform virus-containing sediment of tissue homogenate-sonicate that is evaluated by electron microscopic examination of thin sections cut perpendicular to the membrane surface. Samples containing as little as 10⁵ to 10⁶ viruses can be relatively easily counted. Semipurified or purified viruses can also be counted after mixing with a tissue homogenate-bovine serum albumin diluent.

¹ Supported by NIH Grant CA 12222, U. S. Atomic Energy Commission under contract with the Union Carbide Corporation, Western Carolina Pathology-Associates Medical Laboratories, Professional Association and Rutherford Hospital, Inc. Abstract of a part of this research was presented at the 65th Annual Meeting of the American Association for Cancer Research, March 27 to 30, 1974, in Houston, Texas.

² To whom requests for reprints should be addressed, at Department of Pathology, Rutherford Hospital, Rutherfordton, N. C. 28139.

Received 9/16/74. Accepted 1/ 9/75.