IL4 and Urethral stricture: Another possibility is that the fibrosis related signaling [e.g., TGF-beta, connective tissue growth factor (CTGF/CCN2), platelet-derived growth factor (PDGF), interleukin 4 (IL-4), etc.] pathways are activated during the urethral reconstruction process, which promotes fibrosis and recurrence of urethral stricture (Sangkum et al., 2015).