HS-mediated binding of TGF-β1 to SD-4⁺ CTCL cells and PBMCs of patients with SS. (A) CTCL cells were untreated (None) or treated with recombinant TGF-β1 (TGF-β1 added) and stained with anti–TGF-β1 Ab (open histogram) or control IgG (shaded histograms), followed by flow cytometry for surface-bound TGF-β1. The bound amount is expressed as ΔMFI. (B) MJ or HuT-78 cells were pretreated with control Ig, anti–SD-4 Ab, anti–TGF-β type II receptor or anti–HS Ab before addition of TGF-β1. Binding of TGF-β1 was examined and expressed as ΔMFI. (C) MJ cells were loaded with TGF-β1 and incubated for the indicated time periods. Cell surface–bound TGF-β1 was assayed by flow cytometry and expressed as a percentage relative to MJ cells just before incubation. Similarly, PBMCs from 3 different patients were assayed for cell surface binding of TGF-β1 (D), blocking of the binding by Ab pretreatment (E), or retention of cell-bound TGF-β1 (F).