CCL21 and pulmonary arterial hypertension: Exosomes transport, through the blood stream, RNAs that codify membrane receptors related to the interaction of microbiota with LC, GC, CC, PAH, CD, and UC cells, mainly SLC proteins, integrins, syndecans, and glycoproteins, as core communication signals, which are key deregulated genes in cancer and inflammatory diseases of the gut and the lung transported by exosomes.