Anatomic lesions produced by the Molonev and Harvey strains o f Murirre Sarcoma Virus ( M S V -M and M S V -H ) in mice have becn compared. Erythroblastic splenomc~galy is a distinctive feature of disease produced by MSV-H. Solid tumors induced by both viruses were quite similar in morphology, although sonic consistent difliwnces were noted. The tumors appear to arise by niassive recruitment of primitive mesenchynial cells rather than by clonal proliferatioti. The morphological fiaturcs of these lesions would suggest that, although MSV-M and MSV-H are similar entities, they arc not quite iden tical. Four transplant lines have been established from the mouse tumors; three MSV-H and one MSV-M. The MSV-M line ( C B A strain) was initiated with difficulty and did not release sarcoma virus. The MSV-H lines (two CBA and one BALBIc)
MATERIAL AND METHODS
VirusThe Moloney strain of MSV (MSV-M) obtained from Dr. J. B. Moloney and Dr. R. Bassin (Nat. Cancer Tnst., NIH, Bethesda, Md., USA), was passaged by intramuscular inoculation in newborn mice, and viral stocks consisted of either crude aqueous 10% tumor extracts clarified by low-speed centrifugation, or semi-purified extracts prepared by a procedure similar to that described by Moloney (1956).The Harvey strain of MSV (MSV-H), obtained from Dr. J. J. Harvey (MRC Clinical Res. Centre, Mill Hill, London, N.W.7, UK) was passaged by intraperitoneal inoculation in newborn mice, and viral stocks consisted of pooled plasma and crude or semi-purified 10% aqueous extracts of spleens and tumors from diseased animals. Some stocks were also prepared from filtered supernatant fluids from tumors established in tissue culture.
AnimalsThese included inbred CBA, IC and BALB/c mice of the colonies of the National Institute for Medical Research, and the Centre National de la Recherche Scientifique, and outbred SwissWebster mice obtained from the Charles River Breeding Laboratories and from Dr. R. Siegler (Boston University School of Medicine, Boston, Mass., USA).
InoculationsNewborn or older animals were inoculated by the intramuscular, intraperitoneal, or subcutaneous routes with 0.05-0.1 ml of virus. Tumors and organs were fixed in 5 % corrosive aqueous trichloracetic acid and stained with hematoxylin and eosin, or phosphotungstic acid hematoxylin (PTAH). All inoculated legs were cut and stained at three levels. Serial sections of some enlarged spleens were also examined, and splenic imprints were stained with May-GriinwaldGiemsa.
Transplantation and tissue culturing techniquesMinced tumor fragments were implanted subcutaneously by trocar. Titrations of tumor cells were performed by subcutaneous inoculation of single-cell suspensions obtained by trypsinization. Tumors were grown in tissue culture by trypsinization, or explantation in growth medium. Lightly trypsinized tissueculture-grown cells were also reinoculated to isologous host animals.
MediaCells were cultured in a 50% mixture of modified Eagle's Minimal Essential Medium (8 X vitamins; 2 xamino acids), and Medium 199, with 10% c...
