IL-1R1 expression by colonic CD4⁺ T cells is dependent on IL-23 stimulation. (A) C57BL/6 Rag1^−/− mice were transferred with 4 × 10⁵ CD4⁺ CD25⁻ CD45RB^Hi T cells from C57BL/6 WT or Il1r1^−/− mice. Mice were sacrificed when recipient of WT naive CD4⁺ T cells developed clinical signs of colitis. CD4⁺ T cells were FACS sorted from cLPL preparations and Il23r expression was evaluated by qRT-PCR (n = 5 mice/group, 1 out of 2 representative experiments shown). (B) C57BL/6 mice were transferred with 1:1 mixtures of CD45.1⁺ (WT) and CD45.2⁺ (Il23r^−/−) CD4⁺CD45RB^hi T cells. Mice were sacrificed upon development of clinical signs of inflammation (∼6 wk) and WT or Il23r^−/− populations of T cells were FACS sorted based on the expression of CD45.2. Il1r1 and Rorc expression levels were evaluated by qRT-PCR (data are shown as mean ± SEM; n = 6 from 2 independent experiments). (C) CD62L^Hi CD44^low CD25⁻ naive CD4⁺ T cells isolated from WT or Il23r^−/− mice were cultured under Th17-polarizing conditions. At the indicated time points, Il1r1 expression was evaluated by qRT-PCR (data are shown as mean ± SD; n = 2 from 2 pooled independent experiments). *, P < 0.05; **, P < 0.01.