ALK-5 and TGF-βRII are required for GDF-15–induced inhibition of chemokine-triggered neutrophil arrest in cremaster venules. IVM of chemokine-induced leukocyte arrest in postcapillary venules of the cremaster muscle of ALK-5^lox/lox (A) or TGF-βRII^lox/lox (B) control mice, and of ALK-5^LysMKO (C) and TGF-βRII^LysMKO (D) mice. Fifteen-second movies were taken before and 1 minute after intra-arterial injection of CXCL1 (600 ng) every minute for 10 minutes. GDF-15 (4 μg) or vehicle was intra-arterially injected 15 minutes before the experiment. Number of analyzed mice were 6 (A-B,D) and 5 (C). Data are shown as mean ± SEM. *P < .05; **P < .01; ***P < .001.