CD4 and infection: Based on our observations that intestinal CD4+ T cells were robustly activated during F1-SSP infection (Figs. 1 and S1) and previous findings (Gopinath et al., 2013; Griffin and McSorley, 2011; Ingram et al., 2017; Srinivasan et al., 2004) that effector CD4+ T cells play crucial roles during Salmonella infection, we reasoned that the absence of Tregs resulted in the hyperactivation of CD4+ T cells, which underlie the pathology.