However, Vβ TCR chain usage was comparable in splenic CD8 T cells from IDO1-KO and B6 mice during primary infection with X31 (Fig. S2), indicating that altered TCR Vβ repertoires were not a consequence of developmental differences in T cell repertoires in IDO1-KO and B6 mice and arose due to adaptive responses to X31/PR8 infection. Here, IDO1 is linked to infection.