The higher levels of MCP-1 in RA-ILD+ may also be caused by the chronic systemic exposure to proinflammatory cytokines characteristic of RA (Hayashida et al., 2001; Rantapää-Dahlqvist et al., 2007; Deshmane et al., 2009; Lin et al., 2014). Here, CCL2 is linked to interstitial lung disease.