CD4 and Sepsis: In the study of sepsis‐associated encephalopathy, Luo found that the precursor form of BDNF is proBDNF, which is upregulated in the immune system by downregulating circulating CD4 + T cells, limiting their infiltration into the meninges and disrupting meningeal pro/anti‐inflammatory homeostasis, promotes the pathogenesis of sepsis‐associated encephalopathy.38