CXCL8 and major depressive disorder: Besides the pro-inflammatory cytokines, studies also prove that chemokines and growth factors participate in the mechanism of linking depression and cognitive impairment, such as interleukin-8 (IL-8) is positively correlated with verbal fluency and eosinophil chemotactic protein 2 (eotaxin-2) is positive with generation ability and letter memory task [23].