Comparison of dose-dependent inhibitory activity of natural TGF-β1 and recombinant TGF-β1 on FMLP-induced neutrophil locomotion. In response to 10 nM FMLP, the locomotory activity of neutrophils incubated in the upper compartment of the chemotaxis chamber in the absence or presence of natural TGF-β1 (nTGF-β1)–containing RBC supernatant (panel A) was compared with the locomotory activity of neutrophils incubated in the upper compartment of the chemotaxis chamber in the absence or presence of various doses of recombinant TGF-β1 (rTGF-β1) (panel B). Results in panel A are from data reported in Figure 1 and are expressed on a molar basis, with the concentration of natural TGF-β1 in RBC supernatant used in the assay (4.26 ng/mL) being taken into account. Ctrl indicates control.