Meningeal and perivascular macrophages of the central nervous system play a protective role during bacterial meningitis.
Meningeal (MM) and perivascular macrophages (PVM) constitute major populations of resident macrophages in the CNS that can be distinguished from microglial cells. So far, there is no direct evidence that demonstrates a possible role of MM and PVM in the CNS during normal or pathologic conditions. To elucidate the role of the MM and PVM during CNS inflammation, we have developed a strategy using a single intraventricular injection of mannosylated clodronate liposomes, which results in a complete and selective depletion of the PVM and MM from the CNS. Depletion of the MM and PVM during experimental pneumococcal meningitis resulted in increased illness, which correlated with higher bacteria counts in the cerebrospinal fluid and blood. This was associated with a decreased influx of leukocytes into the cerebrospinal fluid, which occurred despite an elevated production of relevant chemokines (e.g., macrophage-inflammatory protein-2) and a higher expression of vascular adhesion molecules (e.g., VCAM-1). In contrast, the higher bacterial counts correlated with elevated production of local and systemic inflammatory mediators (e.g., IL-6) indicating enhanced local leukocyte and systemic immune activation, and this may explain the worsening of the clinical signs. These findings show that the PVM and MM play a protective role during bacterial meningitis and suggest that a primary action of these macrophages is to facilitate the influx of leukocytes at the blood-brain barrier. More in general, we demonstrate for the first time that the PVM and MM play a crucial role during inflammation in the CNS.
Polfliet
M M
MM
Department of Molecular Cell Biology and Pediatrics, Vrije Universiteit Medical Centre, Amsterdam, The Netherlands. M.Polfliet.cell@med.vu.nl
Zwijnenburg
P J
PJ
van Furth
A M
AM
van der Poll
T
T
Döpp
E A
EA
Renardel de Lavalette
C
C
van Kesteren-Hendrikx
E M
EM
van Rooijen
N
N
Dijkstra
C D
CD
van den Berg
T K
TK
D000818:Animals; D001812:Blood-Brain Barrier / Q000276:immunology*; D002555:Cerebrospinal Fluid / Q000166:cytology; D054426:Chemokine CXCL2; D018925:Chemokines / Q000134:cerebrospinal fluid; D002634:Chemotaxis, Leukocyte; D004002:Clodronic Acid / Q000008:administration & dosage; D007276:Injections, Intraventricular; D008264:Macrophages / Q000276:immunology*; D008586:Meningitis, Pneumococcal / Q000276:immunology*; D051381:Rats; D017208:Rats, Wistar; D019010:Vascular Cell Adhesion Molecule-1 / Q000096:biosynthesis
D054426:Chemokine CXCL2; D018925:Chemokines; C404915:Cxcl2 protein, mouse; D019010:Vascular Cell Adhesion Molecule-1; D004002:Clodronic Acid