Chronic Obstructive Pulmonary Disease (COPD) is a progressive, life threatening disease that manifests with difficulty in breathing for which there is no cure. Dr. Raul Torres and Dr. John Hartney have identified a previously uncharacterized signaling pathway used by murine and human macrophages to promote pulmonary inflammation that relies on autocrine thromboxane receptor signaling and its inhibition by the intracellular signaling molecule ARHGEF1. Researchers discovered that leukocytes from individuals with COPD display significantly reduced levels of ARHGEF1 compared to healthy individuals and have demonstrated that ARHGEF1 expression is a predictor of responsiveness to thromboxane receptor antagonist therapy. Thus, ARHGEF1 expression can be utilized as a companion diagnostic for COPD, allowing clinicians to identify and selectively treat a subpopulation of patients who will be most responsive to thromboxane receptor inhibitors.