Studies on mouse mammary tumor virus (MTV) and mouse leukemia virus (MuLV) by immunoelectron microscopy.

Antigenic properties of the mouse mammary tumor virus (MTV or type B) particles and of the murine leukemia virus (MuLV or type C) particles have been studied by immunoelectron microscopy. Mouse mammary tumor cell lines producing either both type B and type C virus particles or only B or C type particles have been used. Mouse reticulum cell sarcoma and rat bone tumor cell lines producing type C particles also have been examined. Three anti-MTV (Verna, Nowinski, Dmochowski) sera and 2 anti-MuLV (Geering, Dmochowski) sera have been used for ferritin labeling. All 3 anti-MTV sera gave ferritin labeling of type B particles present in the different mammary tumor cell lines although the antisera were prepared against MTV from mice of different origin. Thus, the MTV particles share common surface or membrane antigens. Absorption of the anti-MTV sera, either in vivo or in vitro, with material containing antigens of various types confirmed the specificity of ferritin labeling of type B particles. The 3 anti-MTV sera also gave ferritin labeling of intracytoplasmic type A particles wherever present. Absorption with antigenic material of different types demonstrated specificity of the antigenic relationship between intracytoplasmic type A and type B particles. The anti-MuLV sera also gave labeling of the type A particles, which was removed by in vivo absorption of the anti-MuLV sera. These anti-MuLV sera gave labeling of type C particles present in the different cell lines although the antisera were prepared against MuLV from mice of different origin. Thus, the MuLV particles share common surface or membrane antigens, as shown by the ferritin-labeling technique. Absorption of the anti-MuLV sera, either in vivo or in vitro, with material containing antigens of various types confirmed the specificity of labeling of type C particles. No antigenic relationship has been observed between type B and type C virus particles, even when produced by the same cell in the Dmochowski-Williams mammary tumor cell line. Serial titration of 2 anti-MTV (Verna, Dmochowski) sera after in vivo absorption demonstrated a comparatively high titer of ferritin labeling of type B particles by the 2 antisera (1:960 and 1:512, respectively) and of intracytoplasmic type A particles (1:256 and 1:64, respectively). INTRODUCTION