Mouse mammary tumor viruses expressed by RIII/Sa mice with a high incidence of mammary tumors interact with the Vβ-2- and Vβ-8-specific T cells during viral infection

The mouse mammary tumor viruses (MMTVs) that induce mammary adenocarcinomas in mice are transmitted from mother to offspring through milk. MMTV infection results in the deletion of specific T cells as a consequence of interaction between the MMTV-encoded superantigen (Sag) and specific Vβ chains of the T cell receptor. The specificity and kinetics of T cell deletion for a number of highly oncogenic MMTVs, such as C3H- and GR-MMTVs, have been studied in great detail. Some work has also been done with the MMTVs expressed in two substrains of RIII mice, BR6 and RIIIS/J, but the nature of the interaction between T cells and the virus(es) that the parental RIII-strain of mice express has not been investigated. Since RIII mice (designated henceforth as RIII/Sa) have a very high incidence (90-98%) of mammary tumors, and they have been extensively used in studies of the biology of mammary tumor development, we have presently determined the pattern of Vβ-T cell deletion caused by RIII/Sa-MMTV-Sag(s) during viral infection. T cells were isolated from lymph nodes and thymus of young RIII/Sa mice, as well as from BALB/c (BALB/cfRIII/Sa), C57BL (C57BLfRIII/Sa), and RIIIS/J (RIIIS/JfRIII/Sa) mice after they were infected with RIII/Sa-MMTV(s) by foster nursing. The composition of the T cells was analyzed by FACS using a panel of monoclonal antibodies specific to a variety of Vβs. Our results show that milk-borne RIII/Sa-MMTV(s) infection leads to the deletion of CD4⁺ Vβ-2, and to a lesser extent Vβ-8 bearing peripheral and central T cells in RIII/Sa, RIIIS/J, BALB/c, and C57BL mice. Our results are in contrast to the findings that C3H-, GR-, and BR6-MMTVs delete Vβ-14- and/or Vβ-15-specific T cells.