CD34 and systemic sclerosis: The participation of CD34+SCs/TCs in the organization of the extracellular matrix explains the important role of these cells in fibrosing/sclerosing diseases—as the Italian school has demonstrated in systemic sclerosis (scleroderma) [38,47,48,56,57,58,59,60,61]—as well as in the basophilic degeneration of collagen and mucinosis.