CXCR4 and pulmonary arterial hypertension: However, low levels of antibodies against the chemokine receptors CXCR3 and CXCR4 were also shown to be predictive for deterioration of progressive lung fibrosis (26), whereas high levels of antibodies against the endothelin receptor type-A were predictive for PAH and mortality (27) suggesting that both higher and lower ab levels against G protein coupled receptor could be of diagnostic and prognostic relevance.