Figure 4. Microbiota-specific memory T cell are functional and can be re-activated by gastrointestinal infection.

(A) 7.5×10⁴ CBir1 Tg (CD45.1) T cells were transferred into congenic (CD45.2) hosts that were subsequently infected orally with 15 cysts of T. gondii. 35 days p.i. with T. gondii mice carrying CBir1 Tg T cells were injected with CBir1 peptide and LPS. Numbers of CBir1 Tg T cells (CD45.1) in the spleen and siLP at day 35 (1° memory) or six days post stimulation with CBir peptide and LPS (2° effector). Shown is a composite of three experiments. (B) Either naïve hosts carrying ~10⁴ naïve CBir1 Tg T cells (open circles) or day 35 (1° memory) T. gondii infected mice (black triangles) were injected with CBir peptide and LPS as in (A). Six days post-injection splenocytes were isolated and stained intracellularly for T-bet. Data shown is representative of three experiments. (C) Naïve hosts carrying ~10⁴ naïve CBir1 Tg or OTII Tg T cells were injected with peptide and LPS. Ten days post-immunization these mice were infected with 15 cysts T. gondii. Percent Ki67+ CBir1 Tg T cells isolated from the spleen and siLP from mice 16 days post-infection (26 days post-immunization). Data shown are representative of 3 separate experiments. CBir1 Tg T cells are gated Live TCRβ⁺ CD4⁺ Foxp3⁻ CD45.1⁺. Graphs show mean +/− SEM **p<0.01, ***p<0.001.