The inhibitory effect of GDF-15 on PMN adhesion, and transendothelial migration is abolished in ALK-5 and TGF-βRII null PMNs. (A-D) PMNs of ALK-5^LysMKO or TGF-βRII^LysMKO mice or littermate controls without the Cre transgene (ALK-5^lox/lox or TGF-βRII^lox/lox) were preincubated with GDF-15 (100 ng/mL) for 20 minutes followed by stimulation with CXCL1 (100 ng/mL) for 1 minute (where indicated), before adhesion to hIgG1 or ICAM-1-Fc coated support was determined (A-B); or binding to soluble ICAM-1-Fc (1.5 μg/1 × 10⁶ cells) and α-human IgG-APC antibody (0.75 μg/1 × 10⁶ cells) was determined by flow cytometry (C-D). (E-F) Transendothelial migration of PMNs from ALK-5^lox/lox, TGF-βRII^lox/lox, ALK-5^LysMKO, or TGF-βRII^LysMKO mice (as indicated) through a TNF-α–stimulated bEnd.5 cell monolayer in transwell filters along a CXCL1 chemotactic gradient was analyzed. Where indicated, PMNs were incubated with GDF-15 (100 ng/mL) for 20 minutes before transmigration. Data are pooled from 4 (A,C,F), 3 (B,D), and 5 (E) independent experiments with 6 replicates in each adhesion experiment and with at least 3 replicates in each transendothelial migration assay. Data are shown as mean ± SEM. *P < .05; **P < .01; ***P < .001. n.s., not significant; TEM, transendothelial migration.