Inflammatory cerebrospinal fluid T cells have activation requirements characteristic of CD4+CD45RA- T cells

Basic principles of neuroimmunology

The brain is an immune-privileged organ such that immune cell infiltration is highly regulated and better tolerating the introduction of antigen to reduce risk of harmful inflammation. Thus, the composition and the nature of the immune response is fundamentally different in the brain where avoiding immunopathology is prioritized compared to other peripheral organs. While the principle of immune privilege in the central nervous system (CNS) still holds true, the role of the immune system in the CNS has been revisited over the recent years. This redefining of immune privilege in the brain is a result of the recent re-discovery of the extensive CNS meningeal lymphatic system and the identification of resident T cells in the brain, meningeal layers, and its surrounding cerebrospinal fluid (CSF) in both humans and rodents. While neuro-immune interactions have been classically studied in the context of neuroinflammatory disease, recent works have also elucidated unconventional roles of immune-derived cytokines in neurological function, highlighting the many implications and potential of neuro-immune interactions. As a result, the study of neuro-immune interactions is becoming increasingly important in understanding both CNS homeostasis and disease. Here, we review the anatomically distinct immune compartments within the brain, the known mechanisms of leukocyte trafficking and infiltration into the CNS and unique transcriptional and functional characteristics of CNS-resident immune cells.

CSF-resident CD4+ T-cells display a distinct gene expression profile with relevance to immune surveillance and multiple sclerosis

The CNS has traditionally been considered an immune privileged site, but is now understood to have a system of immune surveillance, predominantly involving CD4+ T-cells. Identifying functional differences between CNS and blood CD4+ T-cells, therefore, have relevance to CNS immune surveillance as well as to neurological conditions, such as multiple sclerosis, in which CD4+ T-cells play a central role. Here, CD4+ T-cells were purified from CSF and blood from 21 patients with newly diagnosed treatment-naïve multiple sclerosis and 20 individuals with non-inflammatory disorders using fluorescence-activated cell sorting, and their transcriptomes were profiled by RNA sequencing. Paired comparisons between CD4+ T-cells from CSF and blood identified 5156 differentially expressed genes in controls and 4263 differentially expressed in multiple sclerosis patients at false discovery rate <5%. Differential expression analysis of CD4+ T-cells collected from the CSF highlighted genes involved in migration, activation, cholesterol biosynthesis and signalling, including those with known relevance to multiple sclerosis pathogenesis and treatment. Expression of markers of CD4+ T-cell subtypes suggested an increased proportion of Th1 and Th17 cells in CSF. Gene ontology terms significant only in multiple sclerosis were predominantly those involved in cellular proliferation. A two-way comparison of CSF versus blood CD4+ T-cells in multiple sclerosis compared with non-inflammatory disorder controls identified four significant genes at false discovery rate <5% (CYP51A1, LRRD1, YES1 and PASK), further implicating cholesterol biosynthesis and migration mechanisms. Analysis of CSF CD4+ T-cells in an extended cohort of multiple sclerosis cases (total N = 41) compared with non-inflammatory disorder controls (total N = 38) identified 140 differentially expressed genes at false discovery rate < 5%, many of which have known relevance to multiple sclerosis, including XBP1, BHLHE40, CD40LG, DPP4 and ITGB1. This study provides the largest transcriptomic analysis of purified cell subpopulations in CSF to date and has relevance for the understanding of CNS immune surveillance, as well as multiple sclerosis pathogenesis and treatment discovery.

Comprehensive immunophenotyping of cerebrospinal fluid cells in patients with neuroimmunological diseases

We performed unbiased, comprehensive immunophenotyping of cerebrospinal fluid (CSF) and blood leukocytes in 221 subjects referred for the diagnostic work-up of neuroimmunological disorders to obtain insight about disease-specific phenotypes of intrathecal immune responses. Quantification of 14 different immune cell subsets, coupled with the assessment of their activation status, revealed physiological differences between intrathecal and systemic immunity, irrespective of final diagnosis. Our data are consistent with a model where the CNS shapes intrathecal immune responses to provide effective protection against persistent viral infections, especially by memory T cells, plasmacytoid dendritic cells, and CD56(bright) NK cells. Our data also argue that CSF immune cells do not simply reflect cells recruited from the periphery. Instead, they represent a mixture of cells that are recruited from the blood, have been activated intrathecally and leave the CNS after performing effector functions. Diagnosis-specific differences provide mechanistic insight into the disease process in the defined subtypes of multiple sclerosis (MS), neonatal onset multisystem inflammatory disease, and Aicardi-Goutières syndrome. This analysis also determined that secondary-progressive MS patients are immunologically closer to relapsing-remitting patients as compared with patients with primary-progressive MS. Because CSF immunophenotyping captures the biology of the intrathecal inflammatory processes, it has the potential to guide optimal selection of immunomodulatory therapies in individual patients and monitor their efficacy. Our study adds to the increasing number of publications that demonstrate poor correlation between systemic and intrathecal inflammatory biomarkers in patients with neuroimmunological diseases and stresses the importance of studying immune responses directly in the intrathecal compartment.

The voltage-gated potassium channel Kv1.3 is highly expressed on inflammatory infiltrates in multiple sclerosis brain

Multiple Sclerosis (MS) is characterized by central nervous system perivenular and parenchymal mononuclear cell infiltrates consisting of activated T cells and macrophages. We recently demonstrated that elevated expression of the voltage-gated potassium channel, Kv1.3, is a functional marker of activated effector memory T (T(EM)) cells in experimental allergic encephalomyelitis and in myelin-specific T cells derived from the peripheral blood of patients with MS. Herein, we show that Kv1.3 is highly expressed in postmortem MS brain inflammatory infiltrates. The expression pattern revealed not only Kv1.3(+) T cells in the perivenular infiltrate but also high expression in the parenchyma of demyelinated MS lesions and both normal appearing gray and white matter. These cells were uniformly chemokine receptor 7 negative (CCR7(-)), consistent with an effector memory phenotype. Using double-labeling immunohistochemistry and confocal microscopy, we demonstrated colocalization of Kv1.3 with CD3, CD4, CD8, and some CD68 cells. The expression patterns mirrored in vitro experiments showing polarization of Kv1.3 to the immunological synapse. Kv1.3 was expressed in low to moderate levels on CCR7(+) central memory T cells from cerebrospinal fluid, but, when these cells were stimulated in vitro, they rapidly became Kv1.3(high)/CCR7(-) T(EM), suggesting that a subset of cerebrospinal fluid cells existed in a primed state ready to become T(EM). These studies provide further rationale for the use of specific Kv1.3 antagonists in MS.

Apoptosis-related fas antigen on memory T cells in aqueous humor of uveitis patients

To investigate the role of lymphocytes in the pathogenesis of uveitis, we analyzed the expression of memory markers, CD29 and CD45RO antigens, and apoptosis-related Fas antigen on T lymphocytes in the aqueous humor (AH) and peripheral blood (PB) from patients with uveitis. Using three-color flow cytometry, we assessed the number of T lymphocyte subsets that stained with fluorescence-conjugated anti-CD3, CD4, CD8, CD29, CD45RA, CD45RO, HLA-DR, and Fas monoclonal antibodies in the AH and PB from 19 patients with active uveitis who were diagnosed as having sarcoidosis, Vogt-Koyanagi-Harada disease, HLA-B27+ uveitis, or idiopathic uveitis. Cells from AH and PB were evaluated by light and electron microscopy before and after 6 h of incubation. The majority of lymphocytes in AH but not in PB, were CD3+HLA-DR+ (activated) T cells. The percentage of CD4+ lymphocytes was significantly higher in uveitic AH than in PBL (P < 0.01). While the percentage of CD4+ CD45RA+ (naive) cells within T cells was much lower in uveitic AH than in PB, the percentage of CD4+CD29+ or CD4+CD45RO+ (memory) cells was significantly higher in uveitic AH than in PBL (P < 0.01). Fas antigen was expressed preferentially on memory cells in uveitic AH. Apoptosis of cells in the AH was observed by microscopically following after incubation with no stimulation. Lymphocytes from the AH of patients with uveitis were more activated than those from PB. The majority of T lymphocytes from uveitic AH expressed memory markers and Fas antigen. Results suggest that an increase in the number of Fas+ memory T lymphocytes in AH is involved in the pathogenesis of uveitis.

A study of CD45RO, CD45RA and CD29 antigen expression on human decidual T cells in an early stage of pregnancy

The decidua is the place where the fertilized egg is implanted and where the immunocompetent cells of the mother come into direct contact with genetically disparate cells of the conceptus. Although the T cells in the decidua are exposed to fetal antigens, the fetus is not rejected by maternal immunocompetent cells. In the present study, we examined surface markers to determine whether the T cells in the human decidua are naive T cells without or memory T cells with a history of antigen stimulation. Although few T cells were present in the decidua, as compared to the peripheral blood, CD45RO+, CD29+ and CD45RA- CD4+ T cells as well as CD45RO+, CD29+ and CD45RA- CD8+ T cells, which are considered to be memory T cells, were in the majority, with only small numbers of CD45RO-, CD29- and CD45RA+ CD4+ and CD8+ cells, which are naive T cells, present. Also, the decidual mononuclear cells secreted IL-2 and IL-4. Since IL-4 is secreted only by memory T cells, it is suggested that in the decidua memory T cells increase in number and secrete cytokines, thereby in some way influencing the phenomenon of fertility.

Inhibition of human T lymphocyte proliferation and cytokine production by 1,25-dihydroxyvitamin D3. Differential effects on CD45RA+ and CD45R0+ cells

1,25-dihydroxyvitamin D3 (1,25-(OH)2 D3), the biologically active form of vitamin D3, has been shown to modulate lymphocyte functions in vitro. These effects are exerted through binding to specific receptors that are expressed in activated, but not in resting lymphocytes. 1,25-(OH)2 D3 inhibits lymphocyte proliferation, immunoglobulin production and the release of cytokines including interleukin-2 (IL-2) and interferon gamma (IFN gamma) by mitogen driven blood mononuclear cells (MNC). A distinction between CD45RA+ and CD45R0+ subsets of T cells has, however, proven extremely relevant in terms of immunoactivation and immunopathology. The present study was undertaken to evaluate effects of 1,25-(OH)2 D3 on proliferation and cytokine production by purified CD45RA+ and CD45R0+ T cells. 1,25-(OH)2 D3 caused a dose- and time-dependent reduction in phytohemagglutinin-(PHA) and poke-weed mitogen (PWM)-driven proliferation of purified CD45R0+ T cells. In contrast, proliferation of the CD45RA+ subset was unaffected by this treatment. Comparable levels of lymphotoxin (LT), IFN gamma and IL-2 were obtained in cultures of both subsets. 1,25-(OH)2 D3 reduced these levels, but the suppressive effect of the hormone was delayed in cultures of CD45RA+ T cells. The results suggest that the CD45R0+ subset is relatively more sensitive than CD45RA+ subset to the inhibitory effects of 1,25-(OH)2 D3. This finding may be of pharmacological interest, because the CD45R0+ subset plays a key role in immune activation and because these cells have been associated with the pathogenesis of autoimmune diseases such as rheumatoid arthritis and multiple sclerosis.

Distribution of IL-2R and CD45Ro expression on CD4+ and CD8+ T-lymphocytes in the peripheral blood of patients with posterior uveitis

Different lines of evidence support a major role for activated T-lymphocytes in the pathogenesis of posterior uveitis. The initial site of activation of these autoreactive T-cells, either locally in the eye or in the peripheral immune compartment, is still unknown. This study was undertaken to investigate whether with currently available techniques, it is possible to detect alterations in the levels and subsets of activated T-cells in the peripheral blood of patients with posterior uveitis. For this reason, 3-colour immunofluorescent staining was performed to assess the distribution of IL-2 receptors (IL-2R) and the CD45RO-antigen on CD4+ and CD8+ subsets of peripheral blood lymphocytes (PBLs) from patients with posterior uveitis (n = 29). Only the subgroup of patients with posterior uveitis as part of a systemic immune-mediated disease (sarcoidosis, Behçet's disease) (n = 9) showed a significant increase in IL-2R expression on peripheral blood lymphocytes (p less than 0.005) when compared to normals (n = 12). This increased expression was reflected much more significantly in the CD4+ (p less than 0.0005) rather than in the CD8+ subset (p less than 0.05) of lymphocytes. In contrast, no significant increase in CD45RO expression on either subset of T lymphocytes was found in any subgroup of posterior uveitis in comparison with normals.

Subset-specific co-stimulatory signals are required for IL-2 production but not growth inhibition responses by T cell hybrids specific for myelin basic protein

Two distinct types of T cell hybridomas (designated THYB-1 and T-HYB-2) were derived by fusing BW5147 thymoma cells with encephalitogenic T helper cells from Lewis rats. Both subsets required MHC-restricted presentation of determinants within the 72-86 peptide sequence of myelin basic protein (MBP) as a requisite signal for IL-2 production. Unlike THYB-1 hybrids, however, THYB-2 hybrids required additional accessory cell activities that were mediated by radiosensitive nonadherent (RS-NAdh) splenocytes (SPL). In this study, we describe two observations indicating that RS-NAdh SPL enable MBP-specific responses of THYB-2 hybrids by providing subset-specific co-stimulatory signals that act independently of antigen recognition pathways. First, RS-NAdh SPL were required by THYB-2 hybrids for MBP-stimulated IL-2 production but were not needed when MBP-specific inhibition of hybrid growth was used as an alternative measure of cellular activation. Second, PMA and ionomycin induced optimal IL-2 production by both THYB-1 hybrids and BW5147 thymoma cells but only stimulated low or marginal levels of IL-2 production by THYB-2 hybrids. Together, these observations indicate that RS-NAdh SPL were required for the specific response of IL-2 production regardless of whether the response was stimulated by antigen or by mitogens that bypass initial antigen recognition events. This study thereby provides additional evidence that distinct stimulus-response relationships define two T-helper cell lineages in experimental autoimmune encephalomyelitis.

The function of the CD2 protein is abnormal in multiple sclerosis

In active multiple sclerosis (MS), T cell adhesion to sheep red blood cells (SRBC) is deficient. The CD2 protein mediates adhesion to SRBC. Since ligands that bind CD2 can activate T cells, we studied adhesion and activation through CD2 in leukocytes from MS patients. Mononuclear cells (MNC) from patients with MS formed markedly fewer avid T cells (TA; T cells binding greater than or equal to 10 SRBC) than MNC from controls. CD2 antigen expression as measured by FACS analysis on T cells and on T cell subsets was equivalent in MS and controls and rose to a comparable extent in both groups after cell activation; yet activated MS MNC continued to form fewer TA than control cells. Avid rosette formation may be reduced by prostaglandins (PG) secreted by monocytes. Exposure to PG in vitro decreased TA% only in controls, suggesting refractoriness to exogenous PG in MS, perhaps because endogenous PG had already acted. The finding that indomethacin increased TA in MS cells favors this formulation. MNC were activated through CD2 using mAb 9-1 paired with mAb 9.6. Proliferation was significantly diminished in MNC from MS patients compared to MNC from normal controls. Thus, even though T cell membrane expression of CD2 appeared normal in MS, adhesion to SRBC and activation through the CD2 protein were defective.

Expression of CD45R0 (UCHL1) by CD4+ and CD8+ T cells as a sign of in vivo activation in infectious mononucleosis

CD45R0 (UCHL1), a member of leucocyte common antigen family, is expressed largely on previously activated or memory T cells. We examined CD45R0 expression of T cell subpopulations in patients with Epstein-Barr virus (EBV) induced infectious mononucleosis (IMN) as a sign of in vivo activation. Consistent with the notion that activated CD8+ T cells expand in acute IMN; the majority of CD8+ T cells in patients with acute IMN expressed CD45R0 to the similar extent to HLA-DR expression. Most CD4+ T cells in these patients also demonstrated marked expression of CD45R0 as well as HLA-DR antigens, compared with age-matched controls. Expression of CD45R0 by CD4+ T cells in patients with acute IMN was more notable than their HLA-DR expression. While predominant CD8+ T cells resulted in decreased percentages of CD4+ T cells, CD4+ T cells expressing CD45R0 were shown to be significantly elevated in absolute number. The results suggest that both CD4+ and CD8+ T cells may be activated by stimulation with EBV infection. The appearance of two T cell subpopulations expressing CD45R0 in acute IMN implies their immunoregulatory roles in the control of EBV-infected cells.

Age-related changes in the activation requirements of human CD4+ T-cell subsets

In agreement with previous studies, we found that the proliferative response of unfractionated T-cells to phytohaemagglutinin (PHA) was severely impaired in healthy aged individuals (70-85 years). On the other hand, we did not observe significant differences between aged and young adults in T-cell responsiveness to mab OKT3 (anti-CD3). PHA responses in "old" T-cells could be substantially improved, however, by the addition of recombinant interleukin-2 (rIL-2) or KOLT2 (anti-CD28 mab). When individual CD4+ T-cell subpopulations were isolated from young and old donors and stimulated with PHA in the presence of autologous accessory cells, age-related deficiencies were seen in both CD4+CD45RA+ (naive) and CD4+CD45RO+ (memory) cell populations. Further analysis using a panel of coactivators in cultures depleted of accessory cells identified specific abnormalities in the CD2 or alternate pathway of T-cell activation. These were predominantly seen in CD4+ naive T-cells. The capacity of rIL-2, KOLT2, and PMA to restore, at least partially, T-cell responsiveness in the aged suggests a defect(s) in an early signal transduction mechanism.