Human cerebrospinal fluid central memory CD4⁺T cells: Evidence for trafficking through choroid plexus and meninges via P-selectin

Abstract

Cerebrospinal fluid (CSF) from healthy individuals contains between 1,000 and 3,000 leukocytes per ml. Little is known about trafficking patterns of leukocytes between the systemic circulation and the noninflamed CNS. In the current study, we characterized the surface phenotype of CSF cells and defined the expression of selected adhesion molecules on vasculature in the choroid plexus, the subarachnoid space surrounding the cerebral cortex, and the cerebral parenchyma. Using multicolor flow cytometry, we found that CSF cells predominantly consisted of CD4 ؉ ͞CD45RA ؊ ͞CD27 ؉ ͞ CD69 ؉ -activated central memory T cells expressing high levels of CCR7 and L-selectin. CD3 ؉ T cells were present in the choroid plexus stroma in autopsy CNS tissue sections from individuals who died without known neurological disorders. P-and E-selectin immunoreactivity was detected in large venules in the choroid plexus and subarachnoid space, but not in parenchymal microvessels. CD4 ؉ T cells in the CSF expressed high levels of P-selectin glycoprotein ligand 1, and a subpopulation of circulating CD4 ؉ T cells displayed P-selectin binding activity. Intercellular adhesion molecule 1, but not vascular cell adhesion molecule 1 or mucosal addressin cell adhesion molecule 1, was expressed in choroid plexus and subarachnoid space vessels. Based on these findings, we propose that T cells are recruited to the CSF through interactions between P-selectin͞P-selectin ligands and intercellular adhesion molecule 1͞lymphocyte function-associated antigen 1 in choroid plexus and subarachnoid space venules. These results support the overall hypothesis that activated memory T cells enter CSF directly from the systemic circulation and monitor the subarachnoid space, retaining the capacity to either initiate local immune reactions or return to secondary lymphoid organs. B etween 175,000 and 500,000 cells are present in the cerebrospinal fluid (CSF) of healthy individuals. Their functions and trafficking patterns are obscure, although it is believed that they participate in the immune defense of the CNS. Leukocytes traffic rapidly between blood and subarachnoid space (SAS), as indicated by studies in patients treated with anti-CD2 Abs, which demonstrated Ab-labeled cells in the CSF 18 h after infusion (1). The cellular composition of CSF, characterized by a predominance of lymphocytes but few erythrocytes, mononuclear phagocytes, or polymorphonuclear neutrophils, is not a simple reflection of peripheral blood (PB), suggesting a stringently regulated control over cell migration into the SAS.Despite an extensive literature delineating the formation of the fluid component of CSF, the sites of entry and exit of leukocytes to the CSF are not well characterized. Based on results of studies conducted in rodents, it has been proposed that lymphocytes migrate into the brain and spinal cord through the blood-brain barrier surrounding deep parenchymal vessels and subsequently drain into the CSF (2). This concept was challenged by a recent study using intravital microsco...

Molecular anatomy and functions of the choroidal blood-cerebrospinal fluid barrier in health and disease

“…T cell mediated CNS immune surveillance is rather strictly limited to the CSF-filled ventricles and subarachnoid spaces. This is supported by the observation that in healthy individuals 150,000-750,000 immune cells are present in the CSF [68] and they are equally distributed between the ventricular and lumbar CSF [110]. Other sterile bodily fluids, e.g.…”

“…Accumulation of innate and adaptive immune cells in the choroid plexus stroma in multiple sclerosis patients is associated with the appearance of increased numbers of memory/ effector T cells (Fig. 6) [51,68], B cells, and antibodyproducing cells in the CSF of these patients [26], suggesting that immune cells that invade the ventricles have to eventually pass the choroid plexus epithelium. Indeed, mimicking the increase of CNS danger signals by intracerebroventricular injection of TNF-α, besides eliciting an inflammatory response throughout the brain, leads to T cell accumulation in the choroid plexus stroma [169].…”

CNS-specific immunity at the choroid plexus shifts toward destructive Th2 inflammation in brain aging

“…1 C and D). Thus, unlike the CSF, which is dominated by CD4 + T CM cells (16,17), the CP specifically retains CD4 + T EM cells throughout life. T cells in the CP were colocalized with the epithelium (Fig.…”

Th1 Polarization of T Cells Injected into the Cerebrospinal Fluid Induces Brain Immunosurveillance

“…These leukocytes, which are primarily CD4 + CD45RA 2 CD27 + CD69 + activated central memory T (T CM ) cells (1,2), migrate from the periphery into the CSF by one of two known mechanisms: 1) crossing the fenestrated endothelium to the choroid plexus stroma and then crossing the choroid plexus epithelium (which is tightly regulated by the blood-CSF barrier) into the CSF; or 2) crossing meningeal vessels before draining into the CSF through the subarachnoid space (2)(3)(4).…”

“…Consecutively, secondary inflammatory stages in this model involve T cell infiltration via activated venules of the CNS parenchyma (4,5). Adhesion molecules such as P-selectin, VCAM-1, or ICAM-1 (interacting with P-selectin glycoprotein ligand-1, VLA-4, and LFA-1, respectively, on the T cells) play a key role in mediating the extravasation of the T cells through the bloodbrain barrier or the blood-CSF barrier after the T cells are attracted to the CNS (2,(6)(7)(8). Such infiltration of T cells into the CSF and perivascular space of the CNS parenchyma may physiologically underlie a routine immune surveillance of the CNS in search for pathogens (9).…”