title: Dendritic cell CNS recruitment correlates with disease severity in EAE via CCL2 chemotaxis at the blood-brain barrier through paracellular transmigration and ERK activation.
abstract: BACKGROUND
  Transmigration of circulating dendritic cells (DCs) into the central nervous system (CNS) across the blood-brain barrier (BBB) has not thus far been investigated. An increase in immune cell infiltration across the BBB, uncontrolled activation and antigen presentation are influenced by chemokines. Chemokine ligand 2 (CCL2) is a potent chemoattractant known to be secreted by the BBB but has not been implicated in the recruitment of DCs specifically at the BBB.
  
  
  METHODS
  Experimental autoimmune encephalomyelitis (EAE) was induced in C57BL/6 mice by injection of MOG35-55 peptide and pertussis toxin intraperitoneally. Animals with increasing degree of EAE score were sacrificed and subjected to near-infrared and fluorescence imaging analysis to detect and localize the accumulation of CD11c+-labeled DCs with respect to CCL2 expression. To further characterize the direct effect of CCL2 in DC trafficking at the BBB, we utilized an in vitro BBB model consisting of human brain microvascular endothelial cells to compare migratory patterns of monocyte-derived dendritic cells, CD4+ and CD8+ T cells. Further, this model was used to image transmigration using fluorescence microcopy and to assess specific molecular signaling pathways involved in transmigration.
  
  
  RESULTS
  Near-infrared imaging of DC transmigration correlated with the severity of inflammation during EAE. Ex vivo histology confirmed the presence of CCL2 in EAE lesions, with DCs emerging from perivascular spaces. DCs exhibited more efficient transmigration than T cells in BBB model studies. These observations correlated with transwell imaging, which indicated a paracellular versus transcellular pattern of migration by DCs and T cells. Moreover, at the molecular level, CCL2 seems to facilitate DC transmigration in an ERK1/2-dependent manner.
  
  
  CONCLUSIONS
  CNS recruitment of DCs correlates with disease severity in EAE via CCL2 chemotaxis and paracellular transmigration across the BBB, which is facilitated by ERK activation. Overall, these comprehensive studies provide a state-of-the-art view of DCs within the CNS, elucidate their path across the BBB, and highlight potential mechanisms involved in CCL2-mediated DC trafficking.
authors.affiliation: Drexel Institute for Biotechnology and Virology Research and Department of Microbiology and Immunology, Drexel University College of Medicine, Philadelphia, PA 19129, USA.
authors.forename: Divya
authors.initials: D
authors.lastname: Sagar
authors.forename: Anne
authors.initials: A
authors.lastname: Lamontagne
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Foss
authors.forename: Zafar K
authors.initials: ZK
authors.lastname: Khan
authors.forename: Martin G
authors.initials: MG
authors.lastname: Pomper
authors.forename: Pooja
authors.initials: P
authors.lastname: Jain
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000378:metabolism; D001812:Blood-Brain Barrier / Q000503:physiopathology*; D002465:Cell Movement / Q000502:physiology*; D002490:Central Nervous System / Q000473:pathology*; D018932:Chemokine CCL2 / Q000378:metabolism*; D003713:Dendritic Cells / Q000473:pathology / Q000502:physiology*; D004195:Disease Models, Animal; D004681:Encephalomyelitis, Autoimmune, Experimental / Q000473:pathology*; D005260:Female; D048748:MAP Kinase Kinase Kinase 3 / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D012720:Severity of Illness Index; D019265:Spectroscopy, Near-Infrared; D013223:Statistics as Topic; D015854:Up-Regulation
chemical_list: D015703:Antigens, CD; D018932:Chemokine CCL2; D048748:MAP Kinase Kinase Kinase 3