Elafin is a potent, naturally occurring NE inhibitor (10) with antiinflammatory and antiviral properties that could explain its effect in preventing the adverse impact of HERV-K transferred in neutrophil PAH EVs, but only if the mice recognize the HERV-K envelope as a molecule similar to their own retroviral element, as they did with HERV-K dUTPase. Here, ELANE is linked to pulmonary arterial hypertension.