Christmann et al. investigated the monocyte–macrophage activation in patients with SSc-PAH by combining transcriptomics, proteomics, and cytomics; the results revealed the upregulation of MRC1 (c-type mannose receptor 1, a marker of alternative activation of monocyte–macrophage) expression in CD14+ cells, and this was greatly increased upon stimulation with IL-13, the concentration of which was most increased in patients with lcSSc-PAH [141,142]. This evidence concerns the gene IL13 and pulmonary arterial hypertension.