CTSG and rheumatoid arthritis: However, in distinct circumstances, it was found that CatG is not regulated properly, for instance, CatG is increased in photoaged human skin (Zheng et al., 2011), chronic inflammatory pain (Liu et al., 2015), and rheumatoid arthritis tissue (Adkison et al., 2002; Hu and Pham, 2005; Miyata et al., 2007) as well as in peripheral blood mononuclear cells (PBMCs) from type 1 diabetes mellitus (T1D) (Zou et al., 2011).