Interestingly, functional studies have shown that while agonistic anti-PDGFR antibodies (i.e., antibodies able to activate PDGFR-downstream molecular signalling pathways) are highly specific for SSc, only non-agonistic anti-PDGFR antibodies have been found in other conditions (including other CTDs) and in healthy controls [135]. Here, PDGFRB is linked to systemic sclerosis.