IL13 and systemic sclerosis: The numbers of CD4+ and CD8+ T cells represent the predominant T cell subsets in the blood and hardened skin biopsies of SSc patients during the inflammatory phase, as well as the production of pro-fibrotic cytokines such as IL-4 and IL-13 (Fuschiotti, 2016), which play significant roles in activating angiogenesis and promoting collagen production and fibrosis.