Fig. 6.

Acquisition of Tr-like suppressive activity by conventional CD4⁺ T cells. We tested suppression in a conventional Tr assay, where CD4⁺CD25^– T cells (the Te cells) are activated by soluble CD3 mAb. Putative Ts cells were added to Te cells, and decreased proliferation is used as an indicator of suppression. (A) Nrp1-Fc-treated CD4⁺CD25^– T cells and Fc-treated cells did not suppress proliferation (data represent 1:1 Ts:Te ratio). LAP-TGF-β1-treated T cells were weakly suppressive. However, Nrp1-Fc/LAP-TGF-β1 double-treated T cells were strongly suppressive (1:1 Ts:Te ratio; see B for other ratios; P<0.0001 vs. all single-treated T cells). The suppressive effect was not seen when Nrp1-Fc was replaced by Fc. (B) Nrp1-Fc and LAP-TGF-β1 double-coated CD4⁺CD25^– T cell-mediated suppression was TGF-β-dependent. The suppression was almost completely reversed by 1D11 anti-TGF-β mAb (50 μg/ml). Naturally occurring CD4⁺Nrp1⁺ T cells (sorted ex vivo) produced a comparable degree of suppression. The data are representative of three independent experiments.