MMP9 and Stroke: Ren et al. significantly improved stroke in mice using blood replacement and found that the total number of leukocytes and neutrophils in the blood of stroke mice was significantly reduced during and 1 h after BR treatment, and that BR treatment significantly reduced plasma levels of the pro-inflammatory cytokines IL-1β, IL-6, and TNF-α, as well as the chemokines CXCL1 and MMP-9 in stroke mice (Ren et al., 2020) (Figure 1).