Interacting Chemokine Signals Regulate Dendritic Cells in Acute Brain Injury

Brain trauma is known to activate inflammatory cells via various chemokine signals although their interactions remain to be characterized. Mice deficient in Ccl3, Ccr2 or Cxcl10 were compared with wildtype mice after controlled cortical impact injury. Expression of Ccl3 in wildtypes was rapidly upregulated in resident, regularly spaced reactive microglia. Ccl3-deficiency enhanced endothelial expression of platelet selectin and invasion of peripheral inflammatory cells. Appearance of Ccr2 transcripts, encoding the Ccl2 receptor, reflected invasion of lysozyme 2-expressing phagocytes and classical antigen-presenting dendritic cells expressing major histocompatibility complex class II. Ccr2 also directed clustered plasmacytoid dendritic cells positive for the T-cell attracting chemokine Cxcl10. A reduction in Ccr2 and dendritic cells was found in injured wildtype cortex after cyclophosphamide treatment resembling effects of Ccr2-deficiency. The findings demonstrate the feasibility to control inflammation in the injured brain by regulating chemokine-dependent pathways.