Signaling via 4-1BB inhibits antigen-mediated conversion of CD4⁺CD25⁻ T cells into CD4⁺CD25⁺FoxP3⁺ T cells.

<p>(A) Sorted CD4⁺ CD25⁻ T cells from naïve wild type OT-II transgenic mice were co-cultured with APCs, various doses of OVA_323–339 peptide, and 10 µg/mL of SA-4-1BBL protein for 4 days in the absence of any exogenous cytokines. Untreated cultures (None) and those supplemented with SA protein served as controls. CD25⁺FoxP3⁺ cells were assessed by gating on CD4⁺ population using flow cytometry. Data is representative of at least three independent experiments. (B) as in (A), except CD4⁺ CD25⁻ T cells from naïve OT-II 4-1BB^−/− mice were used. (C) Absolute number of CD4⁺FoxP3⁺ T cells. Data are representative of three independent experiments.