CD4 and infection: Although the relatively small number (∼1–2 cells per mouse) of FliC431–439-specific Foxp3+ Tregs in naïve mice precluded further analysis beyond these absolute cell numbers, the expansion of FliC431–439-specific Tregs and non-Treg effector CD4+ T cells at early and late time points after infection allowed the relative expression of likely determinants of Treg suppression to be characterized.