RESUMO
Using the indirect immunofluorescence technique and radioimmunoprecipitation test (RIP test) according to ABELEV and ELGORT (1970) immunological investigations intracytoplasmic A particles isolated from mouse mammary tumors were performed. In order to purify the virus particles sucrose gradients were employed according to TANAKA et al. (1972) and in some details according to SMITH and WIVEL (1973). In immunofluorescence studies on mammary tumor slices a complete cross-reaction between antisera against A particles from mammary tumors and MTV-B particles from mouse milk was observed. Both kinds of antisera reacted in identical fluorescence pattern types with intracytoplasmic A particle clusters and with extracellular accumulations of B type virions, respectively, in tumors of different histological structures. RIP test studies suggest that these cross-reactions are attributed to three common antigens in A and B type viruses. Thus, there does not remain any doubt that intracytoplasmic A particles in murine mammary tumors are MTV-related. All these A particles antigens were identically detected using an antiserum against A particles isolated from mouse leukemia cells (serum kindly provided by Dr. TANAKA). The biological role of intracytoplasmic A particles in mouse tissues is discussed. In contrast to the precursor theory, it is believed that they could represent something like a nonsense way of particle maturation in MTV-infected cells.
