IL-13 was also elevated to higher levels in sera of patients with lcSSc with PAH, and MCR1 was induced on CD14+ monocytes suggesting monocytes are activated in lcSSc patients with PAH of an alternative (i.e., IL-4/IL-13) rather than classical [i.e., IFNγ/lipopolysaccharides (LPS)] pathway (123). This evidence concerns the gene IL4 and pulmonary arterial hypertension.