Lymphocyte adhesion to cultured endothelial cells of the blood-retinal barrier

T Cell-Mediated Autoimmunity in Glaucoma Neurodegeneration

Glaucoma as the leading neurodegenerative disease leads to blindness in 3.6 million people aged 50 years and older worldwide. For many decades, glaucoma therapy has primarily focused on controlling intraocular pressure (IOP) and sound evidence supports its role in delaying the progress of retinal ganglial cell (RGC) damage and protecting patients from vision loss. Meanwhile, accumulating data point to the immune-mediated attack of the neural retina as the underlying pathological process behind glaucoma that may come independent of raised IOP. Recently, some scholars have suggested autoimmune aspects in glaucoma, with autoreactive T cells mediating the chief pathogenic process. This autoimmune process, as well as the pathological features of glaucoma, largely overlaps with other neurodegenerative diseases in the central nervous system (CNS), including Alzheimer’s disease, Parkinson’s disease, and multiple sclerosis. In addition, immune modulation therapy, which is regarded as a potential solution for glaucoma, has been boosted in trials in some CNS neurodegenerative diseases. Thus, novel insights into the T cell-mediated immunity and treatment in CNS neurodegenerative diseases may serve as valuable inspirations for ophthalmologists. This review focuses on the role of T cell-mediated immunity in the pathogenesis of glaucoma and discusses potential applications of relevant findings of CNS neurodegenerative diseases in future glaucoma research.

Overexpression of Interleukin-1α Suppresses Liver Metastasis of Lymphoma: Implications for Antitumor Effects of CD8+ T-cells

Interleukin (IL)-1 plays a key role in carcinogenesis, tumor progression, and metastasis. Although IL-1 may enhance the expansion of CD8+ T-cells, the pathological contribution of IL-1-activated CD8+ T-cells to tumor metastasis remains unclear. This study used a liver metastasis model of the EL4 T-cell lymphoma cells transplanted into human IL (hIL)-1α conditional transgenic (hIL-1α cTg) mice. Overproduction of hIL-1α suppressed both macroscopic and histological liver metastasis of EL4 T-cell lymphoma. The hIL-1α-induced inflammatory state increased the number of CD8+ T-cells both within and around metastatic tumors. Moreover, larger numbers of CD8+ T-cells showed greater infiltration of liver blood vessels in hIL-1α cTg mice than in control wild-type mice. Terminal deoxynucleotidyl transferase dUTP nick-end labeling staining of liver tissue from hIL-1α cTg mice indicated increased apoptosis of cells in the tumor. Localization of apoptosis cells resembled that of CD8+ T-cells. In addition, cytotoxicity assay showed that CD8+ T-cell counts from tumor-bearing hIL-1α cTg mice correlated with cytotoxicity against EL4. In summary, IL-1α suppresses lymphoma metastasis, and IL-1α-activated CD8+ T-cells may play important roles in inhibiting both tumor metastasis and metastatic tumor growth.

Correlation of hemorrhage, axonal damage, and blood-tissue barrier disruption in brain and retina of Malawian children with fatal cerebral malaria

Background: The retinal and brain histopathological findings in children who died from cerebral malaria (CM) have been recently described. Similar changes occur in both structures, but the findings have not been directly compared in the same patients. In this study, we compared clinical retinal findings and retinal and cerebral histopathological changes in a series of patients in Blantyre, Malawi, who died of CM.

Methods: The features systematically compared in the same patient were: (1) clinical, gross and microscopic retinal hemorrhages with microscopic cerebral hemorrhages, (2) retinal and cerebral hemorrhage-associated and -unassociated axonal damage, and fibrinogen leakage, and (3) differences in the above features between the pathological categories of CM without microvascular pathology (CM1) and CM with microvascular pathology (CM2) in retina and brain.

Results: Forty-seven patients were included: seven CM1, 28 CM2, and 12 controls. In the 35 malaria cases retinal and cerebral pathology correlated in all features except for non-hemorrhage associated fibrinogen leakage. Regarding CM1 and CM2 cases, the only differences were in the proportion of patients with hemorrhage-associated cerebral pathology, and this was expected, based on the definitions of CM1 and CM2. The retina did not show this difference. Non-hemorrhage associated pathology was similar for the two groups.

Comment: As postulated, histopathological features of hemorrhages, axonal damage and non-hemorrhage associated fibrinogen leakage correlated in the retina and brain of individual patients, although the difference in hemorrhages between the CM1 and CM2 groups was not consistently observed in the retina. These results help to underpin the utility of ophthalmoscopic examination and fundus findings to help in diagnosis and assessment of cerebral malaria patients, but may not help in distinguishing between CM1 and CM2 patients during life.

IL-1 enhances expansion, effector function, tissue localization, and memory response of antigen-specific CD8 T cells

Here, we show that interleukin-1 (IL-1) enhances antigen-driven CD8 T cell responses. When administered to recipients of OT-I T cell receptor transgenic CD8 T cells specific for an ovalbumin (OVA) peptide, IL-1 results in an increase in the numbers of wild-type but not IL1R1^−/− OT-I cells, particularly in spleen, liver, and lung, upon immunization with OVA and lipopolysaccharide. IL-1 administration also results in an enhancement in the frequency of antigen-specific cells that are granzyme B⁺, have cytotoxic activity, and/ or produce interferon γ (IFN-γ). Cells primed in the presence of IL-1 display enhanced expression of granzyme B and increased capacity to produce IFN-γ when rechallenged 2 mo after priming. In three in vivo models, IL-1 enhances the protective value of weak immunogens. Thus, IL-1 has a marked enhancing effect on antigen-specific CD8 T cell expansion, differentiation, migration to the periphery, and memory.

Lymphocyte trafficking through the blood-brain barrier is dependent on endothelial cell heterotrimeric G-protein signaling

We have previously shown that the engagement of ICAM-1 on brain endothelial cells (EC) results in the propagation of EC signaling pathways that are necessary for efficient lymphocyte migration across the tight vascular barriers of the brain. Signaling via this receptor alone, however, is unlikely to explain the differential recruitment of leukocytes at different vascular beds. In this study, we investigated the role of EC heterotrimeric G-protein-mediated signaling in supporting transendothelial migration of T lymphocytes. Treatment of brain EC monolayers with pertussis toxin (PTX) resulted in ADP-ribosylation of G-protein alpha subunits and inhibition (>80%) of lymphocyte migration without affecting lymphocyte adhesion. Aortic and high endothelial venule EC treated identically resulted in only partial inhibition of lymphocyte migration (<40%). Expression of ribosylation-resistant (PTX-insensitive) G-protein alpha subunits in brain EC restored their ability to support lymphocyte migration after pretreatment with PTX. Treatment of brain EC with PTX did not inhibit ICAM-1-stimulated tyrosine phosphorylation of focal adhesion kinase, suggesting the effects of PTX in inhibiting EC facilitation of lymphocyte migration are distinct from activation of EC through ICAM-1. We conclude that a heterotrimeric G-protein-mediated signaling pathway in brain EC is essential for efficient transendothelial migration of T lymphocytes into the brain.

Kinetics and polarization of the membrane expression of cytokine-induced ICAM-1 on rat brain endothelial cells

ICAM-1 is a major cellular adhesion molecule by which lymphocytes attach to vascular endothelial cells. Rat brain endothelial cells (RBEC) in culture show very low levels of ICAM-1. However, after exposure to IL-1beta and IFN-gamma, the ICAM-1 expression increases up to 20-fold (as judged by FACS analysis). We used immunogold electron microscopy to examine the kinetics in distribution of cytokine-induced ICAM-1 on the surfaces of tight-junction RBEC (grown on matrigel-coated transwells) when exposed to cytokines from either the luminal (upper well) or the abluminal (lower well) surface. Luminal stimulation produced an early upregulation of ICAM-1 not only on the luminal surface of the endothelial cells but also on the lateral surface below the tight junctions and on the abluminal surface. Peak expression on the abluminal surface of the monolayer occurred at the time of maximal "trapping" of lymphocytes seen during an in vitro migration assay. This suggests that the in vitro trapping, as well as the in vivo trapping described by others, may have its basis in a receptor-ligand interaction. We also demonstrate that when the monolayer is stimulated with cytokine from the abluminal surface there is a delayed but preferential upregulation of ICAM-1 on the luminal surface.

Lymphocyte Migration Through Brain Endothelial Cell Monolayers Involves Signaling Through Endothelial ICAM-1 Via a Rho-Dependent Pathway

Lymphocyte extravasation into the brain is mediated largely by the Ig superfamily molecule ICAM-1. Several lines of evidence indicate that at the tight vascular barriers of the central nervous system (CNS), endothelial cell (EC) ICAM-1 not only acts as a docking molecule for circulating lymphocytes, but is also involved in transducing signals to the EC. In this paper, we examine the signaling pathways in brain EC following Ab ligation of endothelial ICAM-1, which mimics adhesion of lymphocytes to CNS endothelia. ICAM-1 cross-linking results in a reorganization of the endothelial actin cytoskeleton to form stress fibers and activation of the small guanosine triphosphate (GTP)-binding protein Rho. ICAM-1-stimulated tyrosine phosphorylation of the actin-associated molecule cortactin and ICAM-1-mediated, Ag/IL-2-stimulated T lymphocyte migration through EC monolayers were inhibited following pretreatment of EC with cytochalasin D. Pretreatment of EC with C3 transferase, a specific inhibitor of Rho proteins, significantly inhibited the transmonolayer migration of T lymphocytes, endothelial Rho-GTP loading, and endothelial actin reorganization, without affecting either lymphocyte adhesion to EC or cortactin phosphorylation. These data show that brain vascular EC are actively involved in facilitating T lymphocyte migration through the tight blood-brain barrier of the CNS and that this process involves ICAM-1-stimulated rearrangement of the endothelial actin cytoskeleton and functional EC Rho proteins.

Immune regulation within the central nervous system

The brain constitutes an environment that is specifically designed to accommodate, regulate and shape immune responses. On one hand, the central nervous system (CNS) has traditionally been regarded as an immunologically privileged organ, owing to local tissue barrier and immunosuppressive microenvironment. On the other hand, activated microglia and astrocytes express MHC and adhesion/costimulatory molecules, release reactive oxygen intermediates and cytokines, and participate in local immune regulation. Bidirectional interactions between immune and neuroglial components occur in response to infectious and traumatic lesions. Glial cells may facilitate and amplify immune effector mechanisms within the CNS. Cytokines and chemokines within the CNS constitute a specialized CNS-cytokine network, and regulate the development and recovery from autoimmune diseases within the CNS. The interactions between glial cells and lymphoid cells are constituents of a complex immune regulatory system within the CNS. New data on the cross-talk between the CNS and the immune systems are envisaged, and followed by an attempt to create a synthesis of current knowledge.

Factors controlling T-cell migration across rat cerebral endothelium in vitro

The migration of lymphocytes through primary cultures of rat brain microvascular endothelial cell monolayers was examined in vitro by time-lapse videomicroscopy. Antigen-specific T cell line migration was dependent on the duration of culture (post-antigen stimulation) with exogenous interleukin-2 (IL-2). Peak migration (approximately 50% of T-cells during the 4 h migration assay) occurred after 4 days of culture with IL-2 but did not coincide with maximal expression of LFA-1, VLA-4 or the IL-2 receptor. On unstimulated endothelia antibody blockade of LFA-1 or ICAM-1 inhibited T-cell line migration to 8.0% and 6.8% of control values, respectively, whereas blocking VLA-4 and VCAM-1 had no effect. On IL-beta activated endothelium blocking LFA-1 and ICAM-1 was less effective (24.9% and 27.3% of control values, respectively) and blockade of VLA-4 and VCAM-1 brought about a reduction to 63.0% and 68.3% of controls respectively. Inhibition of IL-2-dependent proliferation with an IL-2 receptor blocking antibody also significantly inhibited T-cell migration to 22.2% of controls. Peripheral lymph node (PLN) lymphocytes could also be induced to migrate through untreated cerebral endothelial cell monolayers by cross-linking CD3 which was also time and IL-2-dependent with maximal migration (22.7%) occurring after three days in the presence of exogenous IL-2. Blocking LFA-or ICAM-1 resulted in a significant reduction in migration across IL-1 beta-activated endothelial cells to 17.4% and 20.9% of control values respectively although blocking the VLA-4/VCAM-1 interaction had no significant effect. Activation of PLN lymphocytes with concanavalin A for up to 5 days did not induce migration but when left in contact with the endothelial monolayer for 24 h migration reached 31.0%. These studies indicate that T-cells require a combination of signals to trigger the migratory phenotype which is necessary to enable them to penetrate the blood-brain barrier.

SV40 large T immortalised cell lines of the rat blood-brain and blood-retinal barriers retain their phenotypic and immunological characteristics

In the central nervous system the blood-brain and blood-retinal barriers (BBB and BRB respectively) are instrumental in maintaining homeostasis of the neural parenchyma and controlling leucocyte traffic. These cellular barriers are formed primarily by the vascular endothelium of the brain and retina although in the latter the pigmented epithelial cells also form part of the barrier. From primary cultures of rat brain endothelium, retinal endothelium and retinal pigment epithelium (RPE) we have generated temperature sensitive SV40 large T immortalised cell lines. Clones of brain (GP8.3) and retinal (JG2.1) endothelia and RPE (LD7.4) have been derived from parent lines that express the large T antigen at the permissive temperature. The endothelial cell (EC) lines expressed P-glycoprotein, GLUT-1, the transferrin receptor, von Willebrand factor and the RECA-1 antigen and exhibited high affinity uptake of acetylated LDL and stained positive with the lectin Griffonia simplicifolia. The RPE cell line was positive for cytokeratins and for the rat RPE antigen RET-PE2. All the cell lines expressed major histocompatibility complex (MHC) class 1 and intercellular adhesion molecule (ICAM)-1 constitutively and could be induced to express MHC class II and vascular cell adhesion molecule (VCAM)-1 following cytokine activation. The EC also expressed platelet endothelial cell adhesion molecule (PECAM)-1. Monolayers of these cells could support the migration of antigen-specific T cell lines. The generation of immortalised cell lines derived from the rat BBB and BRB should prove to be useful tools for the study of these specialised cellular barriers.

Vesicular stomatitis virus infection of the central nervous system activates both innate and acquired immunity

Vesicular stomatitis virus (VSV) causes acute infection of the central nervous system (CNS) when intranasally applied. We have examined cellular inflammatory changes in the CNS following VSV infection. As early as 1 day postinfection (p.i.), astrocytes were activated in the olfactory bulb (OB). This was followed by activation of microglia, first observed in the OB at day 3 p.i. Expression of inducible nitric oxide synthase was observed in activated microglia in the OB at day 3 p.i., and increased inducible nitric oxide synthase expression coincided with decreased virus titers in tissue homogenates. Expression of major histocompatibility complex (MHC) class I molecules on astrocytes and microglial, endothelial, and ependymal cells was also rapidly induced and followed by induced expression of MHC class II molecules on astrocytes and microglial and endothelial cells. Consistent with the pattern of viral dissemination, MHC molecules were expressed temporally from the rostral-to-caudal direction. Infiltration of CD8+ cells was observed as early as 1 day p.i. in the OB. CD4+ cells were detected in the OB at day 4 p.i. Increasing T-cell infiltration coincided with decreased virus titers. In contrast, B-cell infiltration of the CNS was not detected until day 14 p.i., after the virus was cleared and mice were showing behavioral signs of recovery. Breakdown of the blood-brain barrier was detected beginning at day 6 p.i., was most severe at day 8 p.i., and was followed by full recovery. Collectively, these data show that both innate immunity (production of nitric oxide) and acquired immunity (expression of MHC molecules and T-cell infiltration) are activated following VSV infection in the CNS.