Role of the cervical lymphatics in the Th2-type hierarchy of CNS immune regulation

Harms and benefits of lymphocyte subpopulations in patients with acute stroke

Lymphocytes are major players in the development of innate and adaptive immune responses but their behavior in patients with acute stroke has received little attention.

EXPERIMENTAL PROCEDURES

Using flow cytometry we identified total lymphocytes, T cells, helper T (Th) cells, cytotoxic T lymphocytes (CTL), natural killer (NK) cells, B cells, and regulatory T (Treg) cells in 46 consecutive patients with acute stroke within a median of 180 min of clinical onset, and at days 2, 7, and 90. Daily neurological score (National Institutes of Health Stroke Scale), diffusion-weighted imaging on brain magnetic resonance imaging, functional impairment, and stroke-associated infection (SAI) at day 7 were assessed. Apoptosis in lymphocyte subsets, tumor necrosis factor (TNF) -alpha/interleukin (IL) -4 production in stimulated Th and CTL, cluster of differentiation 86 (CD86) (B7-2) expression in B cells, cortisol and metanephrine in serum were measured. Multivariate analyses were used to evaluate SAI, and stroke outcome.

RESULTS

Increased apoptosis and a fall of T, Th, CTL, B, and Treg cells were observed after stroke. Severer stroke on admission and SAI disclosed a greater decline of T, Th, and CTL cells. Increased cortisol and metanephrine was associated with severe stroke and SAI, and inversely correlated with T, and CTL. T cells, and CTL were correlated with infarct growth. Stroke but not SAI resulted in lower TNF-alpha production in Th cells. SAI showed the greatest fall of lymphocytes, T, Th, and CTL, but not B cells, or Treg. Poor outcome was associated with reduced levels of B cells, and increased expression of CD86 in B cells, but not with SAI.

CONCLUSION

Lymphopenia and increased apoptosis of T, Th, CTL, Treg and B cells are early signatures after human stroke. A decreased cellular response after stroke is a marker of ongoing brain damage, the stress response, and a higher risk of infection. A lower humoral response is predictor of poorer long-term outcome.

Immunotherapy of malignant brain tumors

Despite aggressive multi-modality therapy including surgery, radiation, and chemotherapy, the prognosis for patients with malignant primary brain tumors remains very poor. Moreover, the non-specific nature of conventional therapy for brain tumors often results in incapacitating damage to surrounding normal brain and systemic tissues. Thus, there is an urgent need for the development of therapeutic strategies that precisely target tumor cells while minimizing collateral damage to neighboring eloquent cerebral cortex. The rationale for using the immune system to target brain tumors is based on the premise that the inherent specificity of immunologic reactivity could meet the clear need for more specific and precise therapy. The success of this modality is dependent on our ability to understand the mechanisms of immune regulation within the central nervous system (CNS), as well as counter the broad defects in host cell-mediated immunity that malignant gliomas are known to elicit. Recent advances in our understanding of tumor-induced and host-mediated immunosuppressive mechanisms, the development of effective strategies to combat these suppressive effects, and a better understanding of how to deliver immunologic effector molecules more efficiently to CNS tumors have all facilitated significant progress toward the realization of true clinical benefit from immunotherapeutic treatment of malignant gliomas.

Preclinical assessment of therapeutic antibodies against human CD40 and human interleukin-12/23p40 in a nonhuman primate model of multiple sclerosis

BACKGROUND

Proinflammatory cytokines, such as interleukin (IL)-12 and IL-23, and costimulatory molecules on antigen-presenting cells (APC), such as CD40, are critical to autoreactive T cell activation by APC, and hence, are considered relevant targets of therapy for immune-mediated inflammatory diseases (IMID).

OBJECTIVE

The current review discusses the preclinical evaluation of two novel immunotherapeutic monoclonal antibodies (mAbs), one directed against human IL-12/23p40 and the other against CD40. As the antibodies only recognize their target molecule in primates, the efficacy could not be tested in rodent models.

RESULTS

As a preclinical IMID model for the in vivo evaluation of both mAbs, we have used the experimental autoimmune/allergic encephalomyelitis (EAE) model in common marmoset monkeys (Callithrix jacchus). Both mAbs show beneficial activities in the EAE model when administered early in disease development as well as after the onset of brain inflammation. The treatment effects were evaluated using a combination of quantitative magnetic resonance imaging and a series of ex vivo and immunopathological evaluations.

CONCLUSION

The promising effects during ongoing disease in a relevant preclinical IMID model illustrate the potential of these two antibodies as treatment of IMID, in particular for multiple sclerosis on which disease EAE has been modeled.

Solutes, but not cells, drain from the brain parenchyma along basement membranes of capillaries and arteries: significance for cerebral amyloid angiopathy and neuroimmunology

Elimination of interstitial fluid and solutes plays a role in homeostasis in the brain, but the pathways are unclear. Previous work suggests that interstitial fluid drains along the walls of arteries.

AIMS

to define the pathways within the walls of capillaries and arteries for drainage of fluid and solutes out of the brain.

METHODS

Fluorescent soluble tracers, dextran (3 kDa) and ovalbumin (40 kDa), and particulate fluospheres (0.02 microm and 1.0 microm in diameter) were injected into the corpus striatum of mice. Brains were examined from 5 min to 7 days by immunocytochemistry and confocal microscopy.

RESULTS

soluble tracers initially spread diffusely through brain parenchyma and then drain out of the brain along basement membranes of capillaries and arteries. Some tracer is takenf up by vascular smooth muscle cells and by perivascular macrophages. No perivascular drainage was observed when dextran was injected into mouse brains following cardiac arrest. Fluospheres expand perivascular spaces between vessel walls and surrounding brain, are ingested by perivascular macrophages but do not appear to leave the brain even following an inflammatory challenge with lipopolysaccharide or kainate.

CONCLUSIONS

capillary and artery basement membranes act as 'lymphatics of the brain' for drainage of fluid and solutes; such drainage appears to require continued cardiac output as it ceases following cardiac arrest. This drainage pathway does not permit migration of cells from brain parenchyma to the periphery. Amyloid-beta is deposited in basement membrane drainage pathways in cerebral amyloid angiopathy, and may impede elimination of amyloid-beta and interstitial fluid from the brain in Alzheimer's disease. Soluble antigens, but not cells, drain from the brain by perivascular pathways. This atypical pattern of drainage may contribute to partial immune privilege of the brain and play a role in neuroimmunological diseases such as multiple sclerosis.

Haplotype matching is not an essential requirement to achieve remyelination of demyelinating CNS lesions

Transplantation of oligodendrocyte precursor cells (OPCs) results in efficient remyelination in animal models of demyelination. However, the experiments so far undertaken have not addressed the need for tissue-type matching to achieve graft-mediated remyelination. Examination of MHC expression (main determinant of allograft rejection) by OPCs showed nondetectable levels under standard culture conditions and upregulation of MHC Class I expression only upon exposure to interferon gamma. We therefore hypothesized that MHC matching of OPC grafts may not be crucial to achieve transplant-mediated remyelination. Transplant experiments performed using a nonself repairing toxin-induced demyelination model showed that, similarly to allogeneic neurons, survival of allogeneic oligodendrocyte lineage cells is influenced by donor-host haplotype combination and graft composition. Transplantation of allogeneic mixed glial cell cultures resulted in remyelination failure by 1 month postengraftment due to a rejection response targeting both myelinating oligodendrocytes and OPCs, suggesting that inflammation-induced upregulation of OPC MHC I expression results in susceptibility to cytotoxic T cell attack. In contrast, remyelination persisted for at least 2 months following transplantation of OPC-enriched cultures whose overall MHC expression level was significantly decreased. While OPC-enriched preparations elicited delayed type hypersensitivity responses in hosts sensitized to alloantigens, allografting of such preparations into a central nervous system demyelinating lesion did not result in recipient priming. We conclude that while allografted oligodendrocyte lineage cells become targets of a graft rejection response once this response has been initiated, transplantation of OPC-enriched preparations can evade priming against alloantigens and graft rejection. This finding indicates that close tissue matching may not be an essential requirement for successful transplant-mediated remyelination.

Challenge with innate and protein antigens induces CCR7 expression by microglia in vitro and in vivo

Since activated microglia are able to phagocytose damaged cells and subsequently express major histocompatibility complex class II (MHC-II) and co-stimulatory proteins, they are considered to function as antigen presenting cells (APCs) in the central nervous system. The maturation and migratory potential of professional APCs is associated with the expression of chemokine receptor CCR7. We therefore investigated whether the immunological activation of microglia induces CCR7 expression. We here present that activation of cultured microglia by both the innate antigen lipopolysaccharide and protein antigen ovalbumin rapidly induces CCR7 expression, accompanied by increased MHC-II expression. Moreover, it is shown that CCR7 expression in IBA-1 positive cells is induced during the symptom onset and progression of experimental autoimmune encephalomyelitis, a rodent model for multiple sclerosis. These results suggest that microglia express CCR7 under specific inflammatory conditions, corroborating the idea that microglia develop into APCs with migratory potential toward lymphoid chemokines.

What is immune privilege (not)?

The 'immune privilege' of the central nervous system (CNS) is indispensable for damage limitation during inflammation in a sensitive organ with poor regenerative capacity. It is a longstanding notion which, over time, has acquired several misconceptions and a lack of precision in its definition. In this article, we address these issues and re-define CNS immune privilege in the light of recent data. We show how it is far from absolute, and how it varies with age and brain region. Immune privilege in the CNS is often mis-attributed wholly to the blood-brain barrier. We discuss the pivotal role of the specialization of the afferent arm of adaptive immunity in the brain, which results in a lack of cell-mediated antigen drainage to the cervical lymph nodes although soluble drainage to these nodes is well described. It is now increasingly recognized how immune privilege is maintained actively as a result of the immunoregulatory characteristics of the CNS-resident cells and their microenvironment.

The human CMV-UL86 peptide 981–1003 shares a crossreactive T-cell epitope with the encephalitogenic MOG peptide 34–56, but lacks the capacity to induce EAE in rhesus monkeys

Rhesus monkeys immunized with MOG(34-56), a dominant T-cell epitope from myelin/oligodendrocyte glycoprotein, develop an acute neurological disease resembling acute disseminated encephalomyelitis (ADEM) in humans. The typical large demyelinated lesions and mononuclear infiltrates in the monkey brains are caused by MOG(34-56) T-cells. We show that MOG(34-56)-reactive CD4+ and CD8+ T-cells are induced in monkeys immunized with a peptide from the human CMV major capsid protein (UL86; 981-1003), that shares sequence similarity with MOG(34-56). Monkeys sensitized against the viral peptide and subsequently challenged with MOG(34-56) display histological signs of encephalitis, but do not show overt neurological signs.

The importance of regional lymph nodes for mucosal tolerance

The immune system is organized as a number of distinct lymphoid organs interconnected by recirculating lymphocytes. These organs, such as lymph nodes, spleen, and gut-associated Peyer's patches, are compartmentalized, providing separate niches for T and B cells. In addition, regional compartmentalization of lymphoid organs themselves exists, leading to the distinction between the mucosal and the systemic immune systems. This distinction not only reflects the anatomical localization but also is based on functional differences, with predominant tolerance induction via mucosal routes and immunity seen after systemic antigen exposure. These differences are associated with regional differences in the lymphoid organs and with environmental conditions of the tissues in which the immune system functions. Recirculation patterns of lymphocytes differ between mucosal and systemic lymphoid organs, and more insight into the mechanisms that imprint this behavior has been generated recently. Differences in dendritic cells have been observed between mucosal and systemic sites, and knowledge on how local factors contribute to the immune system is emerging. From our studies on mucosal tolerance in mouse models, it has become evident that regional lymph nodes draining the mucosa are important sites to direct immune responses. Here, we discuss the way regional lymph nodes contribute to the direction of immune responses and what is known about the local factors and cell behavior that form the basis for these differences.

What is the blood-brain barrier (not)?

In 1900, summarizing his experiments with toxins and Ehrlich's earlier observations with intravital dyes, the Berlin physician Lewandowski concluded that "brain capillaries must hold back certain molecules". Illustrating this phenomenon with persuasive beauty, the subsequently evolving metaphor of a 'Bluthirnschranke' (blood-brain barrier, BBB) gained wide acceptance, but the extension of its meaning into the context of inhibiting leukocyte recruitment into the brain is imprecise. On the basis of the original work by Ehrlich, Lewandowski and Goldmann we re-define the BBB as a capillary barrier for solutes, and clarify that leukocyte recruitment requires two differentially regulated steps: (i) passage across postcapillary venules into Virchow-Robin spaces, and (ii) subsequent progression across the glia limitans into the neuropil. We propose that the second step frequently involves perivascular antigen-recognition and the induction of ectoenzymes, for example matrix metalloproteinases (MMPs).

Cerebrospinal fluid is an efficient route for establishing brain infection with feline immunodeficiency virus and transfering infectious virus to the periphery

Like human immunodeficiency virus (HIV), feline immunodeficiency virus (FIV) invades and infects the central nervous system (CNS) soon after peripheral infection. The appearance of viral RNA is particularly prominent in the cerebrospinal fluid (CSF), suggesting an efficient route of virus transfer across the blood-CSF barrier. This raises the concern whether this route can establish a stable viral reservoir and also be a source of virus capable of reseeding peripheral systems. To examine this possibility, 200 mul of cell-free NCSU1 FIV or FIV-infected choroid plexus macrophages (ChP-Mac) was directly injected into the right lateral ventricle of the brain. Negative controls were sham inoculated with uninfected ChP-Mac or virus-free culture supernatant and positive controls were infected systemically by intraperitoneal (i.p.) injection. Intracerebroventricular (i.c.v.) inoculation with cell-free FIV resulted in high levels of plasma FIV RNA detected as early as 1 to 2 weeks post inoculation in all cats. In each case, the plasma viremia preceded the detection of CSF viral RNA. Compared to i.p. cats, i.c.v. cats had 32-fold higher CSF viral loads, 8-fold higher ratios of CSF to plasma viral load, and a 23-fold greater content of FIV proviral DNA in the brain. No FIV RNA was detected in plasma or CSF from the cats inoculated with FIV-infected ChP-Mac but an acute inflammatory response and a slight suppression of the CD4+:CD8+ ratio were observed. These results indicate that free FIV circulating in the CSF promotes infection of the CNS and provides a highly efficient pathway for the transfer of infectious virus to the periphery.

The B cell response in multiple sclerosis

Multiple sclerosis (MS) plaques and CSF contain increased amounts of intrathecally synthesized IgG, manifest as oligoclonal bands (OCBs) after protein electrophoresis. OCBs are not unique to MS and are also produced in infectious diseases of the CNS, in which the oligoclonal IgG has been shown to be antibody directed against the disease-causing agent. Thus, analysis of antibody specificity may identify the causative agent/antigen in MS. This review discusses recent studies that have analyzed the phenotypes of B cells in MS which infiltrate the CNS and the molecular features of their antigen-binding regions. Together with histologic studies showing the presence of ectopic lymphoid follicles in the meninges of some MS patients, this data supports the notion of a targeted and compartmentalized humoral response in MS.

Altered neuroantigen-specific cytokine secretion in a Th2 environment reduces experimental autoimmune encephalomyelitis

Activation of Th2 cells suppresses clinical experimental autoimmune encephalitis (EAE), demyelination and expression of genes associated with Th1-mediated inflammation. Despite both reduced central nervous system inflammation and IFN-gamma induced MHC class II expression by microglia, the composition of CNS infiltrates in Th2-protected mice were similar to mice with EAE. Analysis of the CNS infiltrating cells by flow cytometry suggests that protection did not correlate with abrogation of CD4+ T cell recruitment, preferential recruitment of donor Th2 cells or an increased frequency of CD25+ CD4+ T cells. By contrast, protection correlated with an increased frequency of neuroantigen-specific Th2 cells infiltrating the CNS. These data suggest that a peripheral Th2 cytokine environment influences both potential antigen presenting cells as well as recruitment and/or retention of neuroAg-specific Th2 CD4+ T cells.

Evidence of antibody production in the rat cervical lymph nodes after antigen administration into the cerebrospinal fluid

We previously showed histologically that, in the rat, the cerebrospinal fluid drains from the subarachnoid space along the olfactory nerves to the nasal lymphatics and empties into the superficial and deep cervical lymph nodes. The present study was performed to investigate whether these lymph nodes play a role in the immune response of the central nervous system. For this purpose, keyhole limpet hemocyanin conjugated with fluorescein isothiocyanate (KLH-FITC) was administered into the subarachnoid space of the rat brain, and the time-kinetics and location of FITC and anti-FITC antibody forming cells in the cervical lymph nodes were studied histologically and immunohistochemically. FITC fluorescence was detected in superficial and deep cervical lymph nodes as well as the subarachnoid space and the nasal mucosa 2 h after FITC-KLH injection into the subarachnoid space. The specific antibody-forming cells first appeared in both the superficial and deep cervical lymph nodes on the 4th day after antigen administration although the reaction was more intense in the deep than in the superficial cervical lymph nodes. These cells were located in the medullary cords of the cervical lymph nodes. The number of antibody forming cells increased thereafter, reached a peak around the day 6, and then declined on day 10. These findings indicate that antigens introduced in the cerebrospinal fluid are drained into the cervical lymph nodes through the nasal lymphatics and initiate the antigen-specific immune response there. Thus, the cervical lymph nodes probably act as a monitoring site for cerebrospinal fluid and play a major role in the central nervous system immune response.

Failed central nervous system regeneration: a downside of immune privilege?

Immunity is required to eliminate dangerous or degenerated material and to support regeneration, but also causes significant parenchymal damage. In the eye and the brain, in which cornea and lens poorly regenerate and neurons are hardly replaceable, early transplantation experiments demonstrated remarkable tolerance to various grafts. This "immunologically privileged status" (Billingham and Boswell, 1953) may reflect evolutionary pressure to downmodulate certain actions of immune cells within particularly vulnerable tissues. As an example, tolerating certain "neurotrophic" viruses may often be a more successful strategy for survival than the elimination of all infected neurons. While several constitutive and inducible signals maintaining or re-establishing immune tolerance within the brain have been identified, it has also become evident that the resulting anti-inflammatory environment limits certain beneficial effects of neuroinflammation such as neurotrophin secretion or glutamate buffering by T-cells and the clearance of growth-inhibiting myelin or amyloid. Following spinal cord injury, the costs and benefits of neuroinflammation seem to come close because enhancing as well as suppressing innate or adaptive immunity caused amelioration and aggravation of functional regeneration in similar experiments. Evaluating such balances has also begun in (animal models of) Alzheimer's disease, central nervous system trauma, and stroke, and the appreciation of the beneficial side of neuroinflammation has caused a rethinking of the ill-defined use of immune suppressants. As dual roles for individual molecules have been recognized (Merrill and Benveniste, 1996), we are uncovering an already fine-tuned system, but the challenge remains to further support beneficial immune cascades without causing additional damage, and vice versa.

Intrathecal antibody production in a mouse model of Lyme neuroborreliosis

Intrathecal antibody (ITAb) production is a common feature of neurological diseases, yet very little is known about its mechanisms. Because ITAb is prominent in human Lyme neuroborreliosis (LNB), in the present study we established a mouse model of LNB to study ITAb production. We injected different strains of Borrelia burgdorferi into a variety of mouse strains by the intracerebral (i.c.) route to develop the model. Spirochetal infection and ITAb production were identified by complementary methods. This study demonstrates that the mouse model of LNB can be utilized to test hypotheses related to the mechanisms of ITAb production.

Glial grafting for demyelinating disease

Remyelination of demyelinated central nervous system (CNS) axons is considered as a potential treatment for multiple sclerosis, and it has been achieved in experimental models of demyelination by transplantation of pro-myelinating cells. However, the experiments undertaken have not addressed the need for tissue-type matching in order to achieve graft-mediated remyelination since they were performed in conditions in which the chance for graft rejection was minimized. This article focuses on the factors determining survival of allogeneic oligodendrocyte lineage cells and their contribution to the remyelination of demyelinating CNS lesions. The immune status of the CNS as well as the suitability of different models of demyelination for graft rejection studies are discussed, and ways of enhancing allogeneic oligodendrocyte-mediated remyelination are presented. Finally, the effects of glial graft rejection on host remyelination are described, highlighting the potential benefits of the acute CNS inflammatory response for myelin repair.

Choroid plexus selectively accumulates T-lymphocytes in normal controls and after peripheral immune activation

We determined T-lymphocyte migration into brain and choroid plexus (CPx) after enterotoxin-induced systemic immune activation. CPx T-lymphocytes/mm2 in control mice were > 3 logs more numerous than brain and increased by as much as 150-fold by post-enterotoxin Day 3 (p < 0.01). Flow cytometry of pooled CPx confirmed post-enterotoxin increases. Brain T-lymphocytes increased up to 17-fold after SEB and accumulated in subependymal and periventricular brain. T cell apoptosis was absent. These results show preferential T-lymphocyte migration to CPx over brain and suggest that brain T cells may be derived from the CPx by direct migration or by cerebrospinal fluid dissemination.

Factors affecting delivery of antiviral drugs to the brain

Although the CNS is in part protected from peripheral insults by the blood-brain barrier and the blood-cerebrospinal fluid barrier, a number of human viruses gain access to the brain, replicate within this organ, or sustain latent infection. The efficacy of antiviral drugs towards the cerebral viral load is often limited as both blood-brain interfaces impede their cerebral distribution. For polar compounds, the major factor restricting their entry lies in the tight junctions that occlude the paracellular pathway across these barriers. For compounds with more favourable lipid solubility properties, CNS penetration will be function of a number of physicochemical factors that include the degree of lipophilicity, size and ability to bind to protein or red blood cells, as well as other factors inherent to the vascular and choroidal systems, such as the local cerebral blood flow and the surface area available for exchange. In addition, influx and efflux transport systems, or metabolic processes active in both capillary endothelial cells and choroid plexus epithelial cells, can greatly change the bioavailability of a drug in one or several compartments of the CNS. The relative importance of these various factors with respect to the CNS delivery of the different classes of antiviral drugs is illustrated and discussed.

Reduced immunoglobulin E and allergy among adults with glioma compared with controls

We and others have reported previously that adults with glioma are 1.5- to 4-fold less likely than controls to report a variety of allergic conditions. The consistent nature of this relationship calls for a biological explanation so that preventative or therapeutic modalities can be explored. We enrolled 403 newly diagnosed adult glioma cases in the San Francisco Bay Area over a 3-year period using a population-based cancer registry and 402 age/gender/ethnicity frequency-matched controls identified via random digit dialing. We assessed total, food-specific, and respiratory-specific IgE in available case (n = 228) and control (n = 289) serum samples. IgE levels were associated with gender, age, smoking status, and ethnicity among cases and/or controls. Among the cases, IgE levels were not associated with aspects of glioma therapy including radiation, chemotherapy, or tumor resection. Total IgE levels were lower in cases than controls: age/gender/ethnicity/education/smoking-adjusted odds ratio (OR) for elevated versus normal total IgE was 0.37 [95% confidence interval (CI), 0.22-0.64]. For the food panel, OR was 0.12 (95% CI, 0.04-0.41). For the respiratory panel, OR was 0.76 (95% CI, 0.52-1.1). Among respiratory allergies, late age of onset (>12 years) but not IgE levels defined a group with strong associations with risk (OR, 0.50; 95% CI, 0.33-0.75). These results corroborate and strengthen our findings of an inverse association between allergic reactions and glioma by showing a relationship with a biomarker for allergy and cancer for the first time. Furthermore, the results indicate a complex relationship between allergic disease and glioma risk that varies by allergen and allergic pathology.

Th2-biased immune response in cervical lymph nodes: Animal models of Graves’ disease might administer autoantigen to body regions where lymphatics drain to cervical lymph nodes

It is believed that cervical lymph nodes have an important impact on Th2-biased immune response to central nervous system (CNS)-derived antigens. Obstruction of these nodes prior to a CNS-infusion of antigen markedly lowers the level of serum antibody response to the antigen. Graves' disease is a Th2-biased autoimmunity in which autoantibodies against thyrotropin receptor stimulate thyroid hormone production. The reasons for the distinct Th2-biased immune response in this hyperthyroidism are not fully understood, whereas most of the other human organ-specific autoimmune diseases are believed to be Th1 mediated. It is suggested that the drainage of the thyroid lymphatics to cervical lymph nodes may play a role in the Th2-polarized immune response of Graves' disease. Thus, the generation of Graves' disease models by immunization may become more feasible if animals are administered the autoantigen to body regions whose lymph is drained to cervical lymph nodes.

The link between T helper balance and lymphoproliferative disease

Lymphoproliferative disorders comprise a heterogeneous group of neoplasms whose behaviors range from indolent to very aggressive. The increased incidence seen in the context of immunodeficiency provides evidence that the host immune system plays a vital role in their pathogenesis. We believe that T-helper (Th)-2 dominant states favor development of lymphoproliferative disorders, including lymphoma, and conversely T-helper (Th)-1 immunity protects against lymphoproliferative disease. The age distribution of lymphomas favors childhood and post-reproductive senescence, suggesting that exposure to these periods of Th-2 bias constitutes a key risk factor for developing the disease. The tendency of lymphomas to arise in Th-2 biased locations such as mucosal interfaces, immunoprivileged sites, and regions of B-cell differentiation may likewise reflect a corresponding spatial predilection. Various clinical conditions or treatments that shift Th1/Th2 balance, including HIV infection, transplant-related immune suppression, and autoimmune disorders, can also influence the status of lymphoproliferative diseases.

Combining cytotoxic and immune-mediated gene therapy to treat brain tumors

Glioblastoma (GBM) is a type of intracranial brain tumor, for which there is no cure. In spite of advances in surgery, chemotherapy and radiotherapy, patients die within a year of diagnosis. Therefore, there is a critical need to develop novel therapeutic approaches for this disease. Gene therapy, which is the use of genes or other nucleic acids as drugs, is a powerful new treatment strategy which can be developed to treat GBM. Several treatment modalities are amenable for gene therapy implementation, e.g. conditional cytotoxic approaches, targeted delivery of toxins into the tumor mass, immune stimulatory strategies, and these will all be the focus of this review. Both conditional cytotoxicity and targeted toxin mediated tumor death, are aimed at eliminating an established tumor mass and preventing further growth. Tumors employ several defensive strategies that suppress and inhibit anti-tumor immune responses. A better understanding of the mechanisms involved in eliciting anti-tumor immune responses has identified promising targets for immunotherapy. Immunotherapy is designed to aid the immune system to recognize and destroy tumor cells in order to eliminate the tumor burden. Also, immune-therapeutic strategies have the added advantage that an activated immune system has the capability of recognizing tumor cells at distant sites from the primary tumor, therefore targeting metastasis distant from the primary tumor locale. Pre-clinical models and clinical trials have demonstrated that in spite of their location within the central nervous system (CNS), a tissue described as 'immune privileged', brain tumors can be effectively targeted by the activated immune system following various immunotherapeutic strategies. This review will highlight recent advances in brain tumor immunotherapy, with particular emphasis on advances made using gene therapy strategies, as well as reviewing other novel therapies that can be used in combination with immunotherapy. Another important aspect of implementing gene therapy in the clinical arena is to be able to image the targeting of the therapeutics to the tumors, treatment effectiveness and progression of disease. We have therefore reviewed the most exciting non-invasive, in vivo imaging techniques which can be used in combination with gene therapy to monitor therapeutic efficacy over time.

APCs in the anterior uveal tract do not migrate to draining lymph nodes

The migration of APCs from sites of infection and their maturation are critical elements in the generation of immune responses. However, the paths by which intraocular Ags migrate to draining lymph nodes are not known because the eye has limited lymphatic vessels. To date, only dendritic cells from the cornea and conjunctiva have been shown to emigrate. We demonstrate that phagocytic APCs in the anterior uveal tissues of the murine eye that ingest fluorescent latex beads do not migrate to regional lymph nodes. The beads are ingested in the uveal tract by cells expressing MHC class II, CD11c, or F4/80. Using intravital time-lapse videomicroscopy to monitor iris APC migration after anterior chamber injection of fluorescent Ag, fluorescently labeled APCs fail to move at multiple observation times, even in the presence of Ag and LPS. Whereas an as yet unidentified ocular nonphagocytic APC subset might migrate from the anterior uveal tissues, it is more probable that immune responses in the draining lymph nodes are engendered by soluble Ag escaping the eye through interstitial spaces. The inability of anterior uveal tissue APCs to migrate to lymph nodes may contribute to deviant immune responses that dominate after Ags are introduced into the anterior chamber.

Initiation of Immune Responses in Brain Is Promoted by Local Dendritic Cells

The contribution of dendritic cells (DCs) to initiating T cell-mediated immune response in and T cell homing into the CNS has not yet been clarified. In this study we show by confocal microscopy and flow cytometry that cells expressing CD11c, CD205, and MHC class II molecules and containing fluorescently labeled, processed Ag accumulate at the site of intracerebral Ag injection. These cells follow a specific pattern upon migrating out of the brain. To track their pathway out of the CNS, we differentiated DCs from bone marrow of GFP-transgenic mice and injected them directly into brains of naive C57BL/6 mice. We demonstrate that DCs migrate from brain to cervical lymph nodes, a process that can be blocked by fixation or pertussis toxin treatment of the DCs. Injection of OVA-loaded DCs into brain initiates a SIINFEKL (a dominant OVA epitope)-specific T cell response in lymph nodes and spleen, as measured by specific tetramer and LFA-1 activation marker staining. Additionally, a fraction of activated SIINFEKL-specific T cells home to the CNS. Specific T cell homing to the CNS, however, cannot be induced by i.v. injection of OVA-loaded DCs alone. These data suggest that brain-emigrant DCs are sufficient to support activated T cells to home to the tissue of DC origination. Thus, initiation of immune reactivity against CNS Ags involves the migration of APCs from nervous tissue to peripheral lymphoid tissues, similarly to that in other organs.

B and T cells in the brains of autoimmune mice

Systemic lupus erythematosus (SLE) is an autoimmune disorder that can involve the central nervous system (CNS). Recently, we reported the presence of autoantibodies bound to the brain tissue of murine models of lupus; MRL/lpr and BXSB. We postulated that the source of these autoantibodies was in part due to in situ production, caused by the entry of B and T cells. Frozen brain sections of MRL/lpr and BXSB at 1 and 4 months of age were stained for CD3 (T cells) and CD19 (B cells) markers using an immunofluorescent antibody binding assay. Confocal fluorescence microscopy showed both CD3(+) and CD19(+) cells at 4 months of age only in MRL/lpr mice. There were no lymphocytes seen in the other autoimmune model, BXSB. Results suggest a difference in the mechanisms by which autoantibodies access the brain in these two autoimmune models of lupus.

Trafficking of superparamagnetic iron oxide particles (Combidex) from brain to lymph nodes in the rat

Central nervous system (CNS) drainage may occur via connections to the vasculature, but in animal models up to 50% occurs via perivascular, perineural and primitive lymphatic drainage to cervical lymph nodes. We evaluated efflux of particles from the brain to cervical lymph nodes in normal rats, using Combidex iron oxide-based magnetic resonance imaging (MRI) agent. After intracerebral, intraventricular, intracarotid or intravenous injection of Combidex in normal Long Evans rats, particle localization was assessed by MRI and histochemistry for iron and the dextran coat (n = 27). Intraventricular or intracerebral injection, but not intracarotid administration of Combidex (100 micro g), resulted in MRI signal changes in the deep cervical lymph nodes around the carotid artery, and, less strongly, in the superficial cervical nodes. Within 2 h of Combidex administration, iron was histologically localized in cervical lymph nodes, with patched staining of capsule and peripheral sinus consistent with delivery via multiple afferent lymphatic vessels. Lymph node staining in groups receiving CNS Combidex was significantly different from controls (P < 0.0001) and was significantly localized in the deep vs. superficial cervical lymph nodes (P = 0.0003). The trafficking of the superparamagnetic iron particles from the CNS in the rat could be visualized by MRI and histology. Combidex provides a powerful tool to rapidly assess drainage of virus-sized particles from the CNS.

Self-tolerance in the immune privileged CNS: lessons from the entorhinal cortex lesion model

Upon peripheral immunization with myelin epitopes, susceptible rats and mice develop T cell-mediated demyelination similar to that observed in the human autoimmune disease multiple sclerosis (MS). In the same animals, brain injury does not induce autoimmune encephalomyelitis despite massive release of myelin antigens and early expansion of myelin specific T cells in local lymph nodes, indicating that the self-specific T cell clones are kept under control. Using entorhinal cortex lesion (ECL) to induce axonal degeneration in the hippocampus, we identified possible mechanisms of immune tolerance after brain trauma. Following ECL, astrocytes upregulate the death ligand CD95L, allowing apoptotic elimination of infiltrating activated T cells. Myelin-phagocytosing microglia express MHC-II and the costimulatory molecule CD86, but lack CD80, which is found only on activated antigen presenting cells (APCs). Restimulation of invading T cells by such immature APCs (e.g. CD80 negative microglia) may lead to T cell anergy and/or differentiation of regulatory/Th3-like cells due to insufficient costimulation and presence of high levels of TGF-beta and IL-10 in the CNS. Thus, T cell -apoptosis, -anergy, and -suppression apparently maintain immune tolerance after initial expansion of myelin-specific T lymphocytes following brain injury. This view is supported by a previous metastatistical analysis which rejected the hypothesis that brain trauma is causative of MS (Goddin et al., 1999). However, concomitant trauma-independent proinflammatory signals, e.g., those evoked by clinically quiescent infections, may trigger maturation of APCs, thus shifting a delicate balance from immune tolerance and protective immune responses to destructive autoimmunity.

In situ processing and distribution of intracerebrally injected OVA in the CNS

Drainage and retention of brain-derived antigens are important factors in initiating and regulating immune responses in the central nervous system (CNS). We investigated distribution, immunological processing and retention of intracerebrally infused protein antigen, ovalbumin (OVA), and the subsequent recruitment of CD8(+) T cells into the CNS. We found that protein antigens infused into the CNS can drain rapidly into the cervical lymph node and initiate antigen-specific immune response in the periphery. A portion of the antigens are also retained by CD11b/MAC-1(+) cells in the brain parenchyma where they are recognized by antigen-specific CD8(+) T cells.

Brain tumor immunotherapy: an immunologist's perspective

Key concepts in brain tumor immunotherapy are reviewed. "Immunotherapy" can refer to a fully-developed, tumor-specific immune response, or to its individual cellular or molecular mediators. The immune response is initiated most efficiently in organized lymphoid tissue. After initiation, antigen-specific T lymphocytes (T cells) survey the tissues--including the brain. If the T cells re-encounter their antigen at a tumor site, they can be triggered to carry out their effector functions. T cells can attack tumor in many ways, directly and indirectly, through cell-cell contact, secreted factors, and attraction and activation of other cells, endogenous or blood-borne. Recent work expands the list of candidate tumor antigens: they are not limited to cell surface proteins and need not be absolutely tumor-specific. Once identified, tumor antigens can be targeted immunologically, or in novel ways. The immune response is under complex regulatory control. Most current work aims to enhance initiation of the response (for example, with tumor vaccines), rather than enhancing the effector phase at the tumor site. The effector phase includes a rich, interactive set of cells and mediators; some that are not usually stressed are of particular interest against tumor in the brain. Within the brain, immune regulation varies from site to site, and local neurochemicals (such as substance P or glutamate) can contribute to local control. Given the complexity of a tumor, the brain, and the immune response, animal models are essential, but more emphasis should be given to their limitations and to step-by-step analysis, rather than animal "cures".

Neuroimmunomodulation and immune privilege: the role of neuropeptides in ocular immunosuppression

Regional immunoregulatory mechanisms insure that the most effective immune defense mounted is in proportion with preserving unique tissue functionalities. Immune-privileged tissues, such as the eye, are tissue sites of extreme regional immunoregulation. They have evolutionarily adapted several mechanisms to prevent the induction of inflammation within their tissue microenvironment. With over half a century of experimental examinations of ocular immune privilege, only recently have we come to understand that neuropeptides constitutively present in ocular tissues are part of the mechanisms of immune privilege.

Determinants of human B cell migration across brain endothelial cells

Circulating B cells enter the CNS as part of normal immune surveillance and in pathologic states, including the common and disabling illness multiple sclerosis. However, little is known about the molecular mechanisms that mediate human B cell interaction with the specialized brain endothelial cells comprising the blood-brain barrier (BBB). We studied the molecular mechanisms that regulate the migration of normal human B cells purified ex vivo, across human adult brain-derived endothelial cells (HBECs). We found that B cells migrated across HBECs more efficiently than T cells from the same individuals. B cell migration was significantly inhibited by blocking Abs to the adhesion molecules ICAM-1 and VLA-4, but not VCAM-1, similar to the results previously reported for T cells. Blockade of the chemokines monocyte chemoattractant protein-1 and IL-8, but not RANTES or IFN-gamma-inducible protein-10, significantly inhibited B cell migration, and these results were correlated with the chemokine receptor expression of B cells measured by flow cytometry and by RNase protection assay. Tissue inhibitor of metalloproteinase-1, a natural inhibitor of matrix metalloproteinases, significantly decreased B cell migration across the HBECs. A comprehensive RT-PCR comparative analysis of all known matrix metalloproteinases and tissue inhibitors of metalloproteinases in human B and T cells revealed distinct profiles of expression of these molecules in the different cell subsets. Our results provide insights into the molecular mechanisms that underlie human B cell migration across the BBB. Furthermore, they identify potential common, and unique, therapeutic targets for limiting CNS B cell infiltration and predict how therapies currently developed to target T cell migration, such as anti-VLA-4 Abs, may impact on B cell trafficking.

Secondary lymphoid organ chemokines are elevated in the cerebrospinal fluid during central nervous system inflammation

Secondary lymphoid organ chemokines have been implicated in chronic inflammation. Their expression in the central nervous system (CNS) has not been studied. Here, levels of secondary lymphoid organ chemokines CCL19 (Exodus-3, MIP-3beta), CCL21 (Exodus-2, 6Ckine, SLC) and CXCL12 (SDF-1alpha) were analysed by ELISA in cerebrospinal fluid (CSF) and plasma from patients with multiple sclerosis (MS); acute optic neuritis (ON) with oligoclonal IgG in the CSF (i.e., first bout of MS); acute ON without oligoclonal IgG (non-MS-type ON); other inflammatory neurological diseases (OIND); and non-inflammatory neurological diseases (NIND). NIND CSF contained CCL19 and CXCL12, while CCL21 was not detected. Intrathecal production of CCL19 and CCL21 was elevated in MS, MS-type ON, and OIND, but not in non-MS-type ON. In MS, CSF levels of CCL19 weakly correlated with CSF cell counts. Intrathecal production of CXCL12 was elevated only in OIND. The role of elevated CCL19 and CCL21 in MS could be retention of mature dendritic cells (DC) in the CNS, recruitment of nai;ve T cells and activated B cells, as well as de novo formation of secondary lymphoid structures in MS plaques.

Immune responses to RNA-virus infections of the CNS

A successful outcome for the host of virus infection of the central nervous system (CNS) requires the elimination of the virus without damage to essential non-renewable cells, such as neurons. As a result, inflammatory responses must be tightly controlled, and many unique mechanisms seem to contribute to this control. In addition to being important causes of human disease, RNA viruses that infect the CNS provide useful models in which to study immune responses in the CNS. Recent work has shown the importance of innate immune responses in the CNS in controlling virus infection. And advances have been made in assessing the relative roles of cytotoxic T cells, antibodies and cytokines in the clearance of viruses from neurons, glial cells and meningeal cells.

Inflammation in the central nervous system: the role for dendritic cells

Dendritic cells (DCs) are a subclass of antigen-presenting cells critical in the initiation and regulation of adaptive immunity against pathogens and tumors, as well as in the triggering of autoimmunity. Recent studies have provided important knowledge regarding distribution of DCs in the central nervous system (CNS) and their role in intrathecal immune responses. DCs are present in normal meninges, choroid plexus, and cerebrospinal fluid, but absent from the normal brain parenchyma. Inflammation is accompanied by recruitment and/or development of DCs in the affected brain tissue. DCs present in different compartments of the CNS are likely to play a role in the defence against CNS infections, and also may contribute to relapses/chronicity of CNS inflammation and to break-down of tolerance to CNS autoantigens. CNS DCs can therefore be viewed as a future therapeutic target in chronic inflammatory diseases such as multiple sclerosis.

Vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide promote in vivo generation of memory Th2 cells

Functionally active effector T cells are generated through clonal expansion. Most effector T cells are later eliminated, whereas a small number survive and differentiate into memory T cells. The mechanisms by which some effector T cells escape apoptosis and become memory T cells are not understood. Neuropeptides such as the vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) inhibit antigen-induced apoptosis of CD4 T cells. By using an in vivo long-term experimental model, in which CD4 T cells from TRC-transgenic mice were transferred into hosts, we demonstrate that VIP and PACAP induce the survival and/or generation of antigen-specific CD4 T cells with a memory Th2 phenotype. This was confirmed by the fact that transgenic CD4 T cells were recovered only from mice that received Th2, but not Th1 effector cells, in the presence of VIP or PACAP. In vitro, VIP/PACAP support the survival of Th2, but not Th1, cell lines through an inhibition of antigen-induced apoptosis. The role of neuropeptides in the biased development of Th2 memory cells is particularly relevant in view of the immune deviation existing in immune-privileged sites such as the brain and eye, where Th2, but not Th1, responses occur in nonpathological conditions.

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) as modulators of both innate and adaptive immunity

The structurally related neuropeptides VIP and PACAP are released within the lymphoid organs following antigenic stimulation, and modulate the function of inflammatory cells through specific receptors. In activated macrophages, VIP and PACAP inhibit the production of pro-inflammatory agents (cytokines, chemokines, and nitric oxide), and stimulate the production of the anti-inflammatory cytokine IL-10. These events are mediated through the VIP/PACAP effects on de novo expression or nuclear translocation of several transcription factors, i.e., NFkappaB, CREB, c-Jun, JunB, and IRF-1. The in vivo administration of VIP/PACAP results in a similar pattern of cytokine and chemokine modulation, which presumably mediates the protective effect of VIP/PACAP in septic shock. In addition, VIP/PACAP reduce the expression of the co-stimulatory molecules B7.1/B7.2, and the subsequent stimulatory activity of macrophages for T-helper cells. In T-cells expressing specific VIP/PACAP receptors, VIP and PACAP inhibit the expression of FasL through effects on NFkappaB, NFAT, and Egr2/3. The reduction of FasL expression has several biological consequences: inhibition of antigen-induced cell death in CD4 T-cells, inhibition of the FasL-mediated cytotoxicity of CD8 and CD4 effectors against direct and bystander targets, and promotion of long-term memory Th2 cells, through a positive effect on the survival of Th2, but not Th1, effectors. The various biological effects of VIP and PACAP are discussed within the range of a general anti-inflammatory model.

Cerebrospinal fluid affects phenotype and functions of myeloid dendritic cells

Myeloid (CD11c+) dendritic cells (DC) are present in cerebrospinal fluid (CSF), as well as in the meninges and choroid plexus. Functional studies of these DC are hindered or impossible. To obviate this problem, we investigated the effects of CSF supernatants from patients with non-inflammatory neurological diseases (NIND), multiple sclerosis (MS), bacterial meningitis (BM) and Lyme meningoencephalitis (LM) on immature monocyte-derived DC (moDC) from healthy donors. CSF supernatants caused maturation of moDC (MS > LM > NIND > BM), as reflected by a decrease in CD1a, and an increase in HLA-DR, CD80 and CD86 expression. The maturation effect of MS CSF and LM CSF could be blocked by anti-TNF-alpha MoAb or recombinant human IL-10. moDC cultured with BM CSF either remained immature or turned into CD14+ macrophage-like cells and were relatively inefficient at inducing T cell responses in vitro. In contrast, moDC cultured with LM CSF induced strong Th1 responses. Both BM CSF and LM CSF contained IFN-gamma, a cytokine that augments IL-12 production by moDC and hence should confer an ability to induce a Th1 response. However, BM CSF also contained high levels of IL-10, which could antagonize the effects of IFN-gamma on moDC. moDC cultured with MS CSF induced a higher production of IFN-gamma from T cells compared to moDC cultured with NIND CSF or BM CSF. In summary, soluble factors present in the CSF may influence the phenotype and functions of meningeal, choroid plexus and CSF DC which, in turn, may have an impact on the character of intrathecal T cell responses.

History of allergies among adults with glioma and controls

The causes of most adult gliomas are essentially unknown. Previous studies have indicated associations between immune system factors and the incidence of adult glioma, specifically that those individuals with certain allergic conditions may have decreased risk of glioma. We obtained detailed allergy histories for 405 adults newly diagnosed with glioma in the San Francisco Bay Area from 1997-1999 and 402 age-gender-ethnicity frequency-matched population-based controls. Seventy-nine percent of eligible cases or their proxies and 74% of eligible controls completed in-person interviews about allergies, age at onset, frequency, duration and severity. Overall, cases were less likely than controls to report any allergy (72% vs. 85%; odds ratio [OR] = 0.5 [0.3-0.7]); for self-reported cases (n = 269), OR = 0.7 (0.4-0.97) and for proxy-reported cases, OR = 0.3 (0.2-0.5). Pollen, dairy and nut allergies were significantly less common in cases than controls and most other allergens had odds ratios of less than one. There were no apparent trends with numbers of symptoms, route of exposure of allergen or reported severity of allergy, but there was a significant dose-response with increasing numbers of allergens (p < 0.0001 for linear trend among all cases vs. controls and p = 0.02 among self-reported cases only vs. controls). Although our work displays strong and consistent associations, future efforts must attempt to establish whether an immune system typified by proclivity to allergies, or an immunologic consequence of the allergies themselves, might be capable of preventing nascent brain tumors. The dominance of humoral immunity in the central nervous system is consistent with either of these models. Alternatively, common genetic or environmental causes for allergies and gliomagenesis may mediate or confound these observed inverse risks for allergies and gliomas, or other explanations may exist. Future work might reveal an important role for immunologic factors in gliomagenesis and potential preventative and/or therapeutic modalities.

Immunology of viral-vector-mediated gene transfer into the brain: an evolutionary and developmental perspective

The immune system imposes limitations on gene transfer into the brain. Viral vectors injected into the brain's ventricular system elicit innate and adaptive immune responses. However, when injected directly into the brain parenchyma, they elicit only transient inflammation owing to the absence of dendritic cells, which transport antigen to lymph nodes and present it to naive T cells to initiate adaptive immune responses. This article explores the evolutionary and developmental basis of brain immune responses and their implications for viral-vector-mediated neurological gene therapy. Elucidating the cellular and molecular basis of these differential reactions is essential to the long-term success of neurological gene therapy.

Recruitment of dendritic cells to the cerebrospinal fluid in bacterial neuroinfections

Dendritic cells (DC) accumulate in the CNS during inflammation and may contribute to local immune responses. Two DC subsets present in human cerebrospinal fluid (CSF) are probably recruited from myeloid (CD11c(+)CD123(dim)) and plasmacytoid (CD11c(-)CD123(high)) blood DC. In bacterial meningitis and especially in Lyme meningoencephalitis, numbers of myeloid and plasmacytoid DC in CSF were increased, compared to non-inflammatory neurological diseases, and correlated with chemotactic activity of CSF for immature monocyte-derived DC (moDC). Multiple DC chemoattractants, including macrophage inflammatory protein (MIP)-1beta, monocyte chemotactic protein (MCP)-1, MCP-3, RANTES and stromal cell-derived factor (SDF)-1alpha were elevated in CSF in these two neuroinfections. Chemotaxis of immature moDC induced by these CSFs could be partially inhibited by mAbs against CXCR4, the receptor for SDF-1alpha, and CD88, the receptor for C5a. SDF-1alpha present in CSF also chemoattracted mature moDC, which in vivo could correspond to a diminished migration of antigen-bearing DC from the CSF to secondary lymphoid organs. Regulation of DC trafficking to and from the CSF may represent a mechanism of controlling the CNS inflammation.

Evidence for a compartmentalized B cell response as characterized by IgG epitope specificity in human ocular toxoplasmosis

Infectious agents in the eye induce both a local and a systemic humoral immune response. Previously, differences in Ag recognition were observed between systemic and ocular derived IgG of patients with ocular toxoplasmosis. This finding implied a nonrandom distribution of IgG-producing B cells in the inflamed eye. In the present study, we compared the intraocular and systemic B cell responses of patients with ocular toxoplasmosis to a single Toxoplasma gondii Ag. Two series of C-terminally deleted recombinant T. gondii GRA-2 proteins were constructed to delineate IgG B cell epitopes of paired ocular and serum samples. Differences in epitope region recognition between the ocular and systemic compartment were detected in 9 of 13 patients. The difference in distribution of GRA-2 epitopes between paired samples is indicative of a local GRA-2 specific B cell population functionally different from the systemic GRA-2-specific B cell population. Our results suggest a selective activation of a subset of B cells locally in nonlymphoid tissue.

Immune surveillance of mouse brain perivascular spaces by blood-borne macrophages

Virchow-Robin's perivascular spaces lie between the basement membrane around pericytes and the basement membrane at the surface of the glia limitans of the brain vessels. They are directly connected to the subpial space and harbour a population of cells distinct from pericytes, perivascular microglia and other cells within perivascular spaces (e.g. T cells and mast cells) in their ability to quickly phagocytose particles from the cerebrospinal fluid (CSF). Morphology, function, and cell surface proteins of these perivascular cells suggest an origin from the monocyte/macrophage lineage. It is currently unclear to what extent these brain perivascular cells represent a resident population of histiocytes or undergo continuous supplementation from blood monocytes. Using transplants of green-fluorescent-protein (GFP)-transfected bone marrow cells, we therefore investigated the replacement of perivascular cells by blood-borne macrophages in adult mice. GFP-positive cells in the perivascular spaces were found as early as 2 weeks post transplantation. The substitution of host perivascular cells by donor-derived macrophages was then evaluated using immunocytochemistry and intraventricular injection of hydrophilic rhodamine-fluorescent tracers. Such tracers diffuse along perivascular spaces and are subsequently phagocytosed by perivascular cells leading to stable phagocytosis-dependent labelling. Thus, the population of newly immigrated macrophages could be related to the total number of perivascular macrophages. This approach revealed a continuous increase of donor-derived perivascular cells. At 14 weeks post transplantation, all perivascular cells were donor-derived. These data show that brain perivascular cells are a population of migratory macrophages and not resident histiocytes.

Basic principles of immunological surveillance of the normal central nervous system

Unlike most bodily organs, the central nervous system (CNS) exists behind a blood-tissue barrier designed to minimize the passage of cells and macromolecules into the neural parenchyma. Yet, the CNS is routinely and effectively surveyed by the immune system. This review examines the mechanisms and participants in this immunological surveillance mechanism. The nature of the healthy blood-brain barrier, factors modifying it, and its central position in determining the number and nature of leukocytes permitted to enter, are considered. In addition the role in surveillance played by lymphatic drainage, migrating T and B lymphocytes, and elements of the monocyte/macrophage/microglia family are considered. While all these participants are known to be important in responding to a CNS antigen and/or establishing a site of inflammation in the nervous system, they also are major elements in maintaining the homeostasis of the CNS and permitting the necessary immunological surveillance of that organ.

Brain granulomas in neurocysticercosis patients are associated with a Th1 and Th2 profile

Neurocysticercosis (NCC) is a common central nervous system (CNS) infection caused by Taenia solium metacestodes. Despite the well-documented importance of the granulomatous response in the pathogenesis of this infection, there is limited information about the types of cells and cytokines involved. In fact, there has been limited characterization of human brain granulomas with any infectious agent. In the present study a detailed histological and immunohistochemical analysis of the immune response was performed on eight craniotomy specimens where a granuloma surrounded each T. solium metacestode. The results indicated that in all the specimens there was a dying parasite surrounded by a mature granuloma with associated fibrosis, angiogenesis, and an inflammatory infiltrate. The most abundant cell types were plasma cells, B and T lymphocytes, macrophages, and mast cells. Th1 cytokines were prevalent and included gamma interferon, interleukin-18 (IL-18), and the immunosuppressive, fibrosis-promoting cytokine transforming growth factor beta. The Th2 cytokines IL-4, IL-13, and IL-10 were also present. These observations indicate that a chronic immune response is elicited in the CNS environment with multiple cell types that together secrete inflammatory and anti-inflammatory cytokines. In addition, both collagen type I and type III deposits were evident and could contribute to irreversible nervous tissue damage in NCC patients.