Specificity of 5l Cr-Release Cytotoxicity of Lymphocytes Immune to Murine Sarcoma Virus 2

Abstract

Cellular immune reactivity of C57BL/6 mice after inoculation with murine sarcoma was studied by the ¹⁵Cr-release cytotoxicity assay. The specificity of the reactions against a tumor target cell induced by Rauscher leukemia virus was examined with an inhibition test. Unlabeled target cells sharing antigens with the labeled target cells could competitively inhibit release of the radioisotope. The results obtained with this inhibition assay correlated well with those obtained with direct cytotoxicity tests against various target cells. C57BL/6 leukemia cells, induced by Friend, Moloney, or Rauscher viruses, could inhibit, and a Gross virus-induced leukemia was negative. However, further results revealed a pattern of specificity different from that seen with serologic reactions. Transplantable BALB/c leukemias, induced by Moloney or Rauscher viruses, gave consistently negative results. Most vlrus-Induced tumors in other species were also negative. Several mouse cell lines spontaneously infected with endogenous C-type viruses were positive, whereas uninfected parental cells were negative. In addition, treatment of a negative cell line with bromodeoxyuridine, an agent causing expression of endogenous viral activity, induced the transient appearance of antigen. This study indicated that the antigens detected by the ⁵¹Cr-release cytotoxicity assay ot cell-mediated immunity may be related to expression of an endogenous C-type virus, rather than to the murine sarcoma virus. This antigen has been tentatively designated MEV-SA-1. The study distinguished between antigenic specificities detected by humoral antibody and those detected by an assay of cell-mediated immunity.