Central nervous system recruitment of effector memory CD8+ T lymphocytes during neuroinflammation is dependent on  4 integrin

Abstract

Clonally expanded CD8(+) T lymphocytes are present in multiple sclerosis lesions, as well as in the cerebrospinal fluid of patients with multiple sclerosis. In experimental autoimmune encephalomyelitis, CD8(+) T lymphocytes are found in spinal cord and brainstem lesions. However, the exact phenotype of central nervous system-infiltrating CD8(+) T lymphocytes and the mechanism by which these cells cross the blood-brain barrier remain largely unknown. Using cerebrospinal fluid from patients with multiple sclerosis, spinal cord from experimental autoimmune encephalomyelitis and coronavirus-induced encephalitis, we demonstrate that central nervous system-infiltrating CD8(+) T lymphocytes are mostly of the effector memory phenotype (CD62L(-) CCR7(-) granzymeB(hi)). We further show that purified human effector memory CD8(+) T lymphocytes transmigrate more readily across blood-brain barrier-endothelial cells than non-effector memory CD8(+) T lymphocytes, and that blood-brain barrier endothelium promotes the selective recruitment of effector memory CD8(+) T lymphocytes. Furthermore, we provide evidence for the recruitment of interferon-γ- and interleukin-17-secreting CD8(+) T lymphocytes by human and mouse blood-brain barrier endothelium. Finally, we show that in vitro migration of CD8(+) T lymphocytes across blood-brain barrier-endothelial cells is dependent on α4 integrin, but independent of intercellular adhesion molecule-1/leucocyte function-associated antigen-1, activated leucocyte cell adhesion molecule/CD6 and the chemokine monocyte chemotactic protein-1/CCL2. We also demonstrate that in vivo neutralization of very late antigen-4 restricts central nervous system infiltration of CD8(+) T lymphocytes in active immunization and adoptive transfer experimental autoimmune encephalomyelitis, and in coronavirus-induced encephalitis. Our study thus demonstrates an active role of the blood-brain barrier in the recruitment of effector memory CD8(+) T lymphocytes to the CNS compartment and defines α4 integrin as a major contributor of CD8(+) T lymphocyte entry into the brain.

IL-17A secretion by CD8+ T cells supports Th17-mediated autoimmune encephalomyelitis

“…This concept is corroborated by our finding that CCR6 expression by CD8 + T cells was not necessary for their copathogenic function. Consistent with our results, the α4 integrin, a subunit of very late antigen-4 (VLA-4), has been defined as a major contributor of CD8 + T cell entry into CNS (35).…”

Peripheral accumulation of newly produced T and B lymphocytes in natalizumab-treated multiple sclerosis patients

“…Finally, one possible explanation for the lack of differential lymphocyte transmigration through the two different types of endothelium (the only exceptions being CD4 + T central memory cells and memory unswitched B cells) is the similar level of VCAM-1 found on BEC-and LEC-cell surface [31]. These transmigration data only apparently contradict previously published results demonstrating a reduced transmigration of lymphocytes obtained from natalizumab-treated patients [27,28] because these studies were obtained using very different experimental conditions, including the use of purified lymphocyte subsets and of human brain microvascular endothelial cells, activated with different stimuli. Indeed, lymphocyte transmigration is a process that is strictly regulated in conditions of both homeostasis and inflammation [32] and therefore the mechanisms involved in this process can vary substantially as a direct reflection of the involved lymphocyte subsets, the wide range of endothelia encountered in the vasculature, and activation conditions of both.…”

“…In MS patients, this is even more crucial because deficits of immune surveillance, including defects in new T-and B-cell production and in the ability of immune cells to transmigrate across the BBB, may predispose to progressive multifocal leukoencephalopathy (PML) [26,27]. In transmigration assays performed to measure the migratory capacity of lymphocytes, BBB-endothelial cells have been previously used either untreated, activated, or triggered by a gradient of chemoattractants [27][28][29] because, during the MS-associated inflammatory process, activated meningeal or BBB-endothelial cells amplify the migration of immune cells to the CNS parenchyma in a multi-step process that involves selectins, chemokines (and their receptors) and cell adhesion molecules [28]. Because in MS patients, trafficking through non-BBB endothelial cells probably takes place in more physiological conditions, we performed the transmigration assay with non-activated BECs and LECs, thus avoiding the addition of any exogenous cytokine (exception made for the VEGF used for cell growth) that would make results difficult to be interpreted.…”

“…On the contrary, we found that, independently from the treatment, CD4 + and CD8 + cells with phenotypic characteristics of T central memory, T effector memory, and TEMRA + cells have a higher migratory capacity than their naïve counterparts both in MS patients and HDs. Therefore, CD8 + effector memory T lymphocytes transmigrate more readily not only across BBB-endothelial cells than CD8 + non-effector memory counterpart [28], but they also can more efficiently migrate across BECs and LECs than the naïve CD8 + subpopulation. However, again, this feature was observed within CD8 + lymphocytes of both MS patients and HDs.…”

Endothelial Wnt/β-catenin signaling reduces immune cell infiltration in multiple sclerosis

“…Cav-1 levels are known to increase during BBB breakdown following ischemic stroke, when enhanced transcytosis initiates BBB dysfunction (24,25). Finally, healthy BBB vasculature has low levels of leukocyte adhesion molecules, such as vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecules (ICAMs)-1 and -2, which are up-regulated on CNS vessels during EAE/MS to promote T-cell trafficking into the parenchyma (26)(27)(28)(29). Blockade of VCAM-1 interactions with its cognate lymphocyte ligand integrin α4 reduces the clinical severity of EAE (30) and is the basis for MS-modifying therapy with natalizumab (31).…”