Selective binding of peripheral blood lymphocytes to the walls of cerebral vessels in frozen sections of human brain

Dual destructive and protective roles of adaptive immunity in neurodegenerative disorders

Inappropriate T cell responses in the central nervous system (CNS) affect the pathogenesis of a broad range of neuroinflammatory and neurodegenerative disorders that include, but are not limited to, multiple sclerosis, amyotrophic lateral sclerosis, Alzheimer’s disease and Parkinson’s disease. On the one hand immune responses can exacerbate neurotoxic responses; while on the other hand, they can lead to neuroprotective outcomes. The temporal and spatial mechanisms by which these immune responses occur and are regulated in the setting of active disease have gained significant recent attention. Spatially, immune responses that affect neurodegeneration may occur within or outside the CNS. Migration of antigen-specific CD4+ T cells from the periphery to the CNS and consequent immune cell interactions with resident glial cells affect neuroinflammation and neuronal survival. The destructive or protective mechanisms of these interactions are linked to the relative numerical and functional dominance of effector or regulatory T cells. Temporally, immune responses at disease onset or during progression may exhibit a differential balance of immune responses in the periphery and within the CNS. Immune responses with predominate T cell subtypes may differentially manifest migratory, regulatory and effector functions when triggered by endogenous misfolded and aggregated proteins and cell-specific stimuli. The final result is altered glial and neuronal behaviors that influence the disease course. Thus, discovery of neurodestructive and neuroprotective immune mechanisms will permit potential new therapeutic pathways that affect neuronal survival and slow disease progression.

Central memory CD4+ T cells dominate the normal cerebrospinal fluid

BACKGROUND

To use cerebrospinal fluid (CSF) immune phenotyping as a diagnostic and research tool, we have set out to establish reference values of white blood cell (WBC) subsets in CSF.

METHODS

We assessed the absolute numbers and percentages of WBC subsets by 6-color flow cytometry in paired CSF and blood samples of 84 individuals without neurological disease who underwent spinal anaesthesia for surgery. Leukocyte (i.e., lymphocytes, granulocytes, and monocytes), lymphocyte (i.e., T [CD4(+) and CD8(+) ], NK, NKT and B cells), T cell (i.e., naïve, central memory, effector memory, and regulatory) and dendritic cell subsets (i.e., myeloid and plasmacytoid) were studied.

RESULTS

CSF showed a predominance of T cells, while granulocytes, B and NK cells were relatively rare compared to blood. The majority of T cells in CSF consisted of CD4(+) T cells (∼70%), most of them (∼90%) with a central memory phenotype, while B cells were almost absent (<1%). Among the small population of dendritic cells in CSF, those of the myeloid subtype were more frequent than plasmacytoid dendritic cells (medians: 1.7% and 0.4% of leukocytes, respectively), whilst both subsets made up 0.2% of leukocytes in blood.

CONCLUSIONS

This study reports reference values of absolute numbers and percentages of WBC subsets in CSF, which are essential for further investigation of the immunopathogenesis of neuro-inflammatory diseases. Furthermore, the relative abundance of CD4(+) T cells, mainly with a central memory phenotype, and the presence of dendritic cells in CSF suggests an active adaptive immune response under normal conditions in the central nervous system (CNS).

The modelling of mononuclear phagocyte-connective tissue adhesion in vitro: application to disclose a specific inhibitory effect of Leishmania infection

In this work, we have developed an adhesion assay to study interactions between mononuclear phagocytes and connective tissue in vitro and show its potential use to study diseases caused by intracellular microorganisms. The assay reproduces most of the characteristics of macrophage adhesion to connective tissue in vivo, such as: preferential adhesion to inflamed connective tissue, divalent cation and integrin dependence, and up-regulation upon cell activation. The phagocyte adhesion to connective tissue was inhibited by infection with Leishmania (58+/-22%, p < 0.05) and was not affected by infection with Mycobacterium or by endocytosis of latex beads. Manganese partially reverted the loss in adherence produced by Leishmania infection, indicating that the mechanisms regulating the function of integrins are affected by cell infection with Leishmania. This assay might be a useful tool for the study of the mechanisms by which mononuclear phagocytes play a role in the immune-inflammatory response and in the development of lesions.

Differential expression of beta1 and beta2 integrins and L-selectin on CD4+ and CD8+ T lymphocytes in human blood: comparative analysis between isolated cells, whole blood samples and cryopreserved preparations

Flow cytometric analysis was used to compare the expression of adhesion molecules on human CD4+ and CD8+ T lymphocytes in isolated blood mononuclear cells (MNCs) in whole blood samples and in cryopreserved MNC preparations. Examination of MNCs revealed that the CD11b and CD11c components of the beta2 integrins were preferentially expressed on CD8+ T cells, whereas CD62L was present on more CD4+ T cells. All CD4+ and CD8+ T lymphocytes were positive for CD11a but the CD8+ population had a higher intensity of expression of CD11a and also CD11b. Virtually identical results were obtained with T cells in whole blood samples. In relation to the beta1 integrins, the only difference between isolated CD4+ and CD8+ T cells was that the latter subset had a greater proportion of cells bearing CD49d. The naive cell marker CD45RA was present on the majority of CD8+ T cells whereas CD45RA and the memory marker CD45RO were evenly distributed within the CD4+ T cell subset. Although cryopreservation of lymphocytes did not modify the expression of beta1 and beta2 integrins it produced a marked reduction in the percentage of CD4+ and CD8+ T cells bearing CD62L. With regard to endothelial interactions, it appears that cryopreserved lymphocytes are suitable for inclusion in studies of integrin-mediated adhesion but not for those relating to tethering or recognition of addressins on high endothelial venules. Differences in adhesion molecule expression between CD4+ and CD8+ T lymphocytes could underlie the selective extravasation of these subsets into sites of infection and inflammation.

Pulsatile flow regulates monocyte adhesion to oxidized lipid-induced endothelial cells

Oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (ox-PAPC), a component of minimally modified low density lipoprotein, induces monocyte adhesion to endothelial cells. It is not known whether the upstroke slopes of pulsatile flow, defined as shear stress slew rates (tau(r)/tauT)), can regulate monocyte binding to ox-PAPC-treated bovine aortic endothelial cells (BAECs). At 60 cycles per minute, ox-PAPC-treated BAECs were exposed to 3 conditions representing known vascular conditions: (1) high shear stress slew rates (tau(r)/tau(T)=293 dyne. cm(-2). s(-1)), with time-averaged shear stress=50 dyne/cm(2); (2) low shear stress slew rate (tau(r)/tau(t)=71 dyne. cm(-2). s(-1)), with identical time-averaged shear stress; and (3) reversing oscillating flow (0+/-2.6 mm Hg). Reverse transcription-polymerase chain reaction and quantification were performed for monocyte chemoattractant protein-1 (MCP-1) mRNA expression. High tau(r)/tau(t) reduced monocyte binding to ox-PAPC-treated BAECs by 64+/-3.2% compared with static conditions, and low tau(r)/tau(t) reduced monocyte binding by 31+/-3.4%, whereas oscillating flow increased monocyte binding by 22+/-1.7% (P<0.005). High partial tau(r)/tau(t) downregulated MCP-1 expression by 33+/-8%, and low partial tau(r)/tau(t) downregulated MCP-1 expression by 15+/-4%, but oscillating flow upregulated MCP-1 by 13+/-5%. These results suggest that shear stress slew rates regulate monocyte binding by modulating the expression of a potent monocyte chemoattractant.

Factors modifying the migration of lymphocytes across the blood-brain barrier

Characterising the factors that control the entry of leucocytes into tissue in response to inflammatory or microbial insult continues to generate considerable interest. Of all the tissues studied it is probably that of the CNS which is the most fascinating because of the specialised properties of its blood vessel walls, which constitute the blood-brain barrier (BBB). In health, very few leucocytes penetrate the BBB but in disorders such as MS the barrier becomes compromised with the result that there is an intense infiltration of the CNS by T lymphocytes whose subsequent activity appears to underlie the onset and progression of disease. The purpose of this article is to summarise and assess recent literature pertaining to how lymphocytes bind to cerebral endothelial cells, migrate across the blood vessel walls and enter the CNS parenchyma. Particular emphasis is devoted to the cellular and molecular aspects of these events and addressing the questions of whether certain subsets of circulating T lymphocytes are more favourably disposed than others to CNS infiltration and whether entry is dependent upon the initial expression of distinct groups of adhesion molecules and upon the generation of chemotactic factors. This article also focuses upon identifying the key stages of lymphocyte migration across the BBB and their susceptibility to antagonism by therapeutic agents. It is intended that the review will provide a useful source of information and offer additional insights into the mechanisms controlling lymphocyte passage across the BBB during pathological disturbance.

Blood mononuclear cells in patients with HTLV-I-associated myelopathy: lymphocytes are highly activated and adhesion to endothelial cells is increased

We have investigated lymphocyte subpopulations and blood mononuclear cell (MNC) adhesion to activated endothelial monolayers in patients with human T lymphotropic virus type I (HTLV-I) associated myelopathy (HAM), in HTLV-I asymptomatic carriers (carriers), and in seronegative controls. HAM patients and carriers had higher levels of CD4(+)CD29(+) "memory cells" than controls (P < 0.05). The percentage of CD3(+)CD27(-) "primed T cell" was elevated in patients with HAM (P < 0.05), but not in carriers. HAM patients had higher levels of CD8(+)CD57(+) "cytotoxic cells" (P < 0.05) than controls and carriers. The percentages of CD4(+) cells coexpressing activation markers HLA-DR and CD25, and of CD8(+) cells expressing HLA-DR, were significantly higher in HAM patients and carriers than in controls. Functional experiments indicated that MNC from HAM patients adhered more to activated endothelial monolayers than MNC from carriers or controls. Blocking studies demonstrated that the adhesion molecules VLA-4 and ICAM-1 and also L-selectin all contributed to increased binding. Analysis of expression of molecules involved in adhesion indicated that in HAM patients, L-selectin (CD62L) expression on CD4(+) and CD8(+) subsets was lower than in controls. Interestingly, HAM patients had a lower percentage of CD4(+) subsets expressing L-selectin than carriers (P < 0.05). In contrast, the percentage of CD4(+) and CD8(+) cells expressing VLA-4 (CD49d) was found to be higher in both HAM patients and carriers compared with controls. After 2 days in culture without mitogen, the percentage of T cells expressing ICAM-1 (CD54) increased in culture in carriers and more profoundly in HAM, but not in controls (P < 0. 05). After culture, T cells expressing the early activation antigen CD69 were also increased in HAM and carriers (P < 0.05) but not in controls. Interestingly, the levels of CD8(+) cells coexpressing activation antigen HLA-DR and CD38 were higher in HAM patients compared with both carriers and controls (P < 0.05) after culture. These findings are consistent with the observations that HTLV-I produces chronic lymphocyte activation with increased adhesion. This may be sufficient to initiate events leading to central nervous system inflammation and ultimately to HAM.

LFA-3 (CD58) mediates T-lymphocyte adhesion in chronic inflammatory infiltrates

Previous studies have suggested that LFA-3 has an important role in a number of chronic inflammatory pathologies, although an active role for LFA-3 within in vivo inflammatory reactions has not previously been directly observed in humans. To assess the importance of LFA-3 in this process, this study used an adaptation of the Stamper-Woodruff lymphocyte adhesion assay to measure the binding of exogenous activated lymphocytes to the T-cell-dominated chronic inflammatory infiltrate of oral lichen planus. Antibody blockade experiments showed that anti-LFA-3 monoclonal antibody reduced lymphocyte adhesion by approximately 29%, while anti-ICAM-1 produced a reduction of 26%. These results thus suggest that both LFA-3 and ICAM-1 are likely to mediate cell-cell interactions within lesional tissues in vivo. Moreover, these findings are also the first to directly demonstrate that LFA-3-mediated adhesion, like that of ICAM-1, is functionally important in the molecular pathology of inflammatory mucosal disease.

Adhesion of mononuclear cells from multiple sclerosis patients to cerebral vessels in cryostat sections of normal human brain

Leukocyte extravasation across the blood-brain barrier is a critical event in the pathogenesis of multiple sclerosis (MS). This complex multistep process includes the adhesion of leukocytes to the endothelial cells of the central nervous system microvasculature. To investigate this phenomenon in MS, we developed a modified version of the frozen-section assay. Peripheral blood mononuclear cells (PBM) from 26 MS patients, 26 healthy controls and 10 patients with other inflammatory non- neurological diseases (OIND) were co-incubated with cryostat sections of normal brain white matter, immunohistochemically labelled with anti-CD45 antibody and counterstained with Giemsa stain. CD45-positive PBM adherent to transected microvasculature were counted with an automated image analyzer. MS patients showed an increased number of vessel-bound PBM (48.8 +/- 36.4) with respect to healthy controls (27.4 +/- 20.7, P = 0.01) and OIND patients (22.6 +/- 7.8, P = 0.01). Significant differences were also obtained counting the number of vessel-bound PBM as a percent of total vascular cells between MS patients (12.7 +/- 7.2%) and healthy controls (6.9 +/- 5.4%, P = 0.002) or OIND patients (7.4 +/- 4.4%, P = 0.03). We confirm that PBM from MS patients show an increased potential of binding to cerebral vessels. The frozen-section assay provides a unique tool to study in situ the molecular interactions of leukocytes with brain vascular structures.

Flow cytometry of cerebrospinal fluid (CSF) lymphocytes: alterations of blood/CSF ratios of lymphocyte subsets in inflammation disorders of human central nervous system (CNS)

Flow cytometry was adapted to measure lymphocytes in human cerebrospinal fluid (CSF). The method was sufficiently precise, reproducible and accurate despite low cell counts. In lumbar CSF of controls with 500 to 3500 (10(3)/l) leukocytes, lymphocyte counts correlated with those in corresponding venous blood: blood/CSF ratios of approximately 2000 : 1 were found for total T cells (CD3+) and CD3+ HLA-DR-, CD3+4+, CD3+8+ subsets, ratios were increased for the lymphocyte subsets CD3+ HLA-DR+ < or = CD3+16+56+ < CD16+56+3- < CD8+3- << CD19+; CD8+4+ ratio was half of CD3+ ratio. Data indicate selective barriers (blood-brain and blood-CSF barriers) to blood lymphocyte subsets which favor the transfer of T subsets. Correlation of the subset ratios to the CD3+ ratio indicates distinct barrier properties which changed differently with acute and subacute inflammations and neuroimmunological diseases of central nervous system (CNS) in lumbar or ventricular CSF, but not with simple protein barrier disturbance. HLA DR+ T ratios were higher than HLA DR- T ratios only with controls and some neuroimmunological diseases. Lymphocyte barrier characteristics were related to protein leakage situated at the same barriers, indicating for the lymphocyte subsets selective transfer routes in control subjects and non-selective routes in patients with CNS inflammation where altered ratios revealed a mixture of both routes.

Soluble adhesion molecules in CSF are increased in children with severe head injury

Leukocyte-endothelial adhesion molecules, critical to the development of acute inflammation, are expressed in brain as part of the acute inflammatory response to traumatic brain injury (TBI). We measured the concentrations of the adhesion molecules P-selectin, ICAM-1, E-selectin, L-selectin, and VCAM-1 in ventricular cerebrospinal fluid (CSF) from children with severe TBI (Glasgow coma score < 8) and compared these findings with those from children with bacterial meningitis. P-selectin, an adhesion molecule associated with ischemia/reperfusion, was increased in children with TBI versus meningitis and control. Univariate and multivariate regression analyses demonstrated associations between CSF P-selectin and child abuse and age of < 4 years, and a significant, independent association between CSF intercellular adhesion molecule-1 (ICAM-1) and child abuse. These results are consistent with a specific acute inflammatory component to TBI in children. Future studies of secondary injury mechanisms and therapy after TBI should assess on the roles of P-selectin and ICAM-1 in injury and repair processes in brain after TBI.

Age-dependent changes in the expression of dopamine receptor subtypes in human peripheral blood lymphocytes

The pharmacological profile and the density of dopamine D3 and D5 receptor subtypes expressed by human peripheral blood lymphocytes of subjects of different ages (ranging from 20 to 75 years) were assessed using radioligand binding techniques. Dopamine D3 receptor was assayed with [3H]7-hydroxy-N,N-di-n-propyl-2-aminotetraline ([3H]7-OH-DPAT) as a ligand. Dopamine D5 receptor was assayed using [3HIR]-(+)-(-chloro-2,3,4,5, tetrahydro-5-phenyl-1H-3-benzazepin-al-hemimaleate) ([3H]SCH 23390) as a ligand. The affinity and the pharmacological profile of [3H]7-OH-DPAT and [3H]SCH 23390 at dopamine D3 and D5 receptor, respectively, were similar in subjects of different ages. The density of dopamine D3 receptor binding sites was slightly decreased in subjects of 30-39 years in comparison with younger individuals. A remarkable loss of dopamine D3 receptor was then found between 40 and 49 years of age in comparison with younger subjects. A further slight decrease was noticeable between 50 and 59 years of age. The number of [3H]7-OH-DPAT binding sites was then stabilized after 60 years of age. The density of dopamine D5 receptor binding sites did not show age-dependent changes. The above findings indicate the occurrence of a decline in the density of lymphocyte dopamine D3 but not D5 receptor between adult and mature subjects. The possibility that dopamine D3 receptor assay in peripheral blood lymphocytes may represent a tool for investigating dopamine receptor function in aging and age-related neurological disorders is discussed.