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Quantitation of Viral Antigens Released into Plasma and Culture Fluids by Murine Mammary Tumor Cells¹

University of Tennessee Center for the Health Sciences, Memphis, Tennessee 38163 [E. M. R., B. A. S.], and The Catholic Medical Center of Brooklyn and Queens, Woodhaven, New York 11421 [D. S. M., R. L. S.]

Radioimmunoassays capable of measuring mouse mammary tumor virus (MMTV) 52,000 M.W. envelope glycoprotein (gp52) and 27,000 M.W. protein (p27) have been used to quantitatively compare plasma concentrations of these viral antigens in mice bearing spontaneous mammary tumors. Although gp52 was detected in the plasma of all tumor-bearing mice tested, p27 was detected in only a portion of tumor-bearing animals. In p27-positive animals, gp52 was detected in higher concentrations than p27. These findings demonstrate that gp52 has preferential utility as a plasma marker for the presence of mammary tumors in MMTV-infected hybrid (BALB/c x DBA/8 F₁), Paris RIII, and C3H/HeJ mice. In addition, cultures of MMTV-producing cells [GR-MMTV and MMTV(C3H)Fel I] were used as models to study the release of viral antigens in the absence of serum antibody or additional host factors. Comparisons of extracellular soluble and particulate antigen concentrations demonstrated that gp52 and p27 were present in substantially higher concentrations as soluble than virion-associated antigens. The mean ratio of non-virion-associated gp52 to viron-associated gp52 was 12.5:1 for GR-MMTV cells and 37.3:1 for MMTV(C3H)Fel I cells. The marked stability of MMTV in culture fluids suggested that virion breakdown was not responsible for the accumulation of soluble viral antigens in culture. The information obtained suggests that abundant virus-free antigens may be of greater use than virion-associated anitgens as a source of viral antigen to evaluate mammary tumor status.

¹ This work was supported by the Willie Mae Darwin Memorial Grant for Cancer Research (American Cancer Society Grant VC-283), USPHS Grant CA-28305-01, and USPHS Grant 1Pol CA-25842.

² To whom requests for reprints should be addressed.

Received 3/27/81. Accepted 7/ 9/81.