Li et al. (2021) found that rhREG4 attenuated the severity of rat osteoarthritis by facilitating the proliferation of articular chondrocytes. In a rat model of acutely-injured liver, treatment with recombinant interleukin 22 (IL-22) lentivirus reduced serum total bilirubin, alanine and aspartate transaminases, and enhanced REG4 expression, suggesting that REG4 might be involved in the protective effects of IL-22 on hepatic injury (Zhang et al., 2015). Here, REG4 is linked to osteoarthritis.