CD8A and pulmonary arterial hypertension: Nineteen immune traits were nominally (IVW P<0.05) associated with PAH risk; but only 2 of these immune traits: the concentration of CD8+ T cells (IVW, P=0.013, β=0.6), and the concentration of CD3 on double‐negative T cells (IVW, P=0.042, β=0.9), were also significantly associated with serum concentration of serine (Table S3).