Extended Data Fig. 4: Effect of Siglec-15 as recombinant protein or cell surface protein on human and mouse T cell functions.

a, The effect of plate-coated hSiglec-15-hIg or control hIg (5 μg ml⁻¹) on human T cell proliferation in the presence of plate-coated anti-human CD3 mAb at the indicated concentrations. Proliferation of T cells was indicated by ³H-thymidine incorporation at 72 h. b, The effect of plate-coated mSiglec-15-mIg or control mIg (5 μg ml⁻¹) on mouse splenic T cell proliferation in the presence of plate-coated anti-mouse CD3 mAb (1 μg ml⁻¹). Proliferation of T cells was indicated by ³H-thymidine incorporation at 72 h. c,d, The effect of soluble mSiglec-15-mIg or control mIg (5 μg ml⁻¹) on mouse splenic CD8⁺ T cells in the presence of coated anti-mouse CD3 mAb (1 μg ml⁻¹). The cell proliferation as indicated by CFSE dilution (c) and IFN-γ in the culture medium (d) at 72 h are shown. e, The 293T-K^bOVA-S15⁺ or S15 negative control cells were placed in a 384-well plate at 1 × 10⁴ per well for 24 h, followed by the addition of OT-I (1 × 10⁴ per well) pre-activated with OVA_257–264. Real-time survival of target cells was monitored by the xCELLigence cellular impedance assay (left panel) and normalized by the value right before adding OT-I cells (normalized cell index). Data at 72 h are shown as a bar in the right panel. All data above are mean ± s.e.m. (n = 3 or 4 cell cultures) and representative of two independent experiments. P values by an two-tailed unpaired t-test.