CONCOMITANT INFECTION WITH EXOGENOUS MOUSE MAMMARY-TUMOR VIRUS ENCODING I-E-DEPENDENT SUPERANTIGEN IN I-E-NEGATIVE MOUSE STRAIN

We found that milk from II TES mice contained two species of exogenous mouse mammary tumor viruses MMTV). Sequence analysis of the open read ing frame (ORF) in the MMTV 3' long terminal repeat indicated that the two MMTV, MMTV (II TES2) and MMTV (II TES14), encode superantigens sp ecific for V beta 2(+) T cells and V beta 14(+) T cells, respectively. In an experiment of subcutaneous injection of II TES milk, both T cel ls bearing TCR V beta 2 and V beta 14 proliferated vigorously in the d raining lymph node from BALB/c mice (H-2(d)I-E(+)), whereas only V bet a 14(+) T cells showed significant proliferation in C57BL/6 mouse (B6H -2(b)I-E(-)) lymph nodes. These findings indicated that the superantig en encoded by MMTV (II TES2) required MHC class II I-E molecules exclu sively for Ag presentation, but MMTV (II TES14) stimulated V beta 14() T cells even in the absence of I-E molecules. Semiquantitative analy sis of MMTV proviruses using PCR revealed that B6 mice were not infect ed with MMTV (II TES2) by injection of this MMTV alone. However, injec tion of II TES milk containing both MMTV (II TES14) and MMTV (II TES2) induced infection of B6 mice with MMTV (II TES2) besides MMTV (II TES 14), in spite of no expansion of V beta 2(+) T cells in this mouse str ain. These results suggested that I-E-negative mice were concomitantly infected with MMTV (II TES2) with the help of I-E independent T cell activation mediated by MMTV (II TES14).