cells in response to the mimotope peptide. (A and B) Splenocytes from BDC2.5 transgenic NOD mice were cultured with the mimotope peptide in the presence or absence of 2H6 cells. The ratio of BDC2.5 cells to 2H6 cells was 2:1. The same culture was also performed with 2H6 cells in Transwells (0.4 μm) to prevent the cell contact between 2H6 and BDC2.5 cells without preventing the flow of soluble factor(s). Splenocytes from 2H6 transgene-negative NOD mice were used as controls in the coculture system at the same ratio. A represents 1 of 3 experiments. To confirm that suppression was indeed mediated by 2H6 cells, the experiments were also repeated using 2H6 cells from 2H6.scid mice and purified CD4⁺ T cells from NOD mice as controls at the same ratio as in A. B shows 1 of the 2 such experiments. Results are illustrated as Δ cpm = proliferation with mimotope peptide – proliferation with medium for each of the conditions. (C) The suppression by 2H6 cells is completely abolished if 2H6 cells express a dominant-negative TGF-β receptor (TGF-βDNRII) (designated 2H6 DNR T cells). The abolition was seen in both coculture and Transwell culture conditions. C represents 1 of 2 experiments, and the ratio of BDC2.5 T cells to 2H6 DNR cells was also 2:1 as for the experiment shown in A and B.