CCR8 and colitis: In the same model, M2b-sEV treatment improve colonic length in mice with colitis, which was more effective than M2a-sEVs and M2c-sEVs, and played a protective role by mediating the increase in Treg cell population and upregulation of IL-4 through the CC chemokine 1 (CCL1)/CC chemokine receptor 8 (CCR8) axis and reducing the production of pro-inflammatory cytokines (IL-1β, IL-6, and IL17a) (Yang et al., 2019).