In COPD, leukocyte activation by cigarette smoke extract (CSE) occurs in a RhoA-dependent manner, increasing endothelial CXCL16-leukocyte CXCR6 adhesion via NADPH oxidase (Nox)5 expression and RhoA/p38 mitogen-activated protein kinase (MAPK) /NF-κB activation [45]. The gene discussed is RHOA; the disease is chronic obstructive pulmonary disease.