Functional recovery of stored platelets after transfusion.

BACKGROUND: Platelet (PLT) concentrates are prophylactically given to prevent major bleeding complications. The corrected count increment (CCI) is currently the only tool to monitor PLT transfusion efficacy. PLT function tests cannot be performed in patients with thrombocytopenia. Therefore, an optimized agonist-induced assay was used to determine PLT function, in patients with severe thrombocytopenia before and after transfusion. STUDY DESIGN AND METHODS: PLT reactivity toward adenosine diphosphate (ADP), thrombin receptor-activating peptide SFLLRN (TRAP), and convulxin (CVX) was assessed by flow cytometry. P-selectin expression was measured on PLTs from 11 patients with thrombocytopenia before and 1 hour after transfusion, on stored PLTs, and on stored PLTs incubated for 1 hour in whole blood from patients ex vivo. RESULTS: The mean (±SEM) CCI after 1 hour was 11.4 (±1.5). After transfusion, maximal agonist-induced PLT P-selectin expression was on average 29% higher for ADP (p = 0.02), 25% higher for TRAP (p = 0.007), and 24% higher for CVX (p = 0.0008). ADP-induced reactivity of stored PLTs increased with 46% after ex vivo incubation (p = 0.007). These PLTs also showed an overall higher P-selectin expression compared to PLTs 1 hour after transfusion (p = 0.005). After normalization for this background expression, a similar responsiveness was observed. CONCLUSIONS: Our study shows recovery of PLT function after transfusion in patients with thrombocytopenia. The majority of functional PLTs measured after transfusion most likely represents stored transfused PLTs that regained functionality in vivo. The difference in baseline P-selectin expression in vivo versus ex vivo suggests a rapid clearance from circulation of PLTs with increased P-selectin expression.

Platelets of patients with chronic kidney disease demonstrate deficient platelet reactivity in vitro.

BACKGROUND: In patients with chronic kidney disease studies focusing on platelet function and properties often are non-conclusive whereas only few studies use functional platelet tests. In this study we evaluated a recently developed functional flow cytometry based assay for the analysis of platelet function in chronic kidney disease. METHODS: Platelet reactivity was measured using flow cytometric analysis. Platelets in whole blood were triggered with different concentrations of agonists (TRAP, ADP, CRP). Platelet activation was quantified with staining for P-selectin, measuring the mean fluorescence intensity. Area under the curve and the concentration of half-maximal response were determined. RESULTS: We studied 23 patients with chronic kidney disease (9 patients with cardiorenal failure and 14 patients with end stage renal disease) and 19 healthy controls. Expression of P-selectin on the platelet surface measured as mean fluorescence intensity was significantly less in chronic kidney disease patients compared to controls after maximal stimulation with TRAP (9.7 (7.9-10.8) vs. 11.4 (9.2-12.2), P=0.032), ADP (1.6 (1.2-2.1) vs. 2.6 (1.9-3.5), P=0.002) and CRP (9.2 (8.5-10.8) vs. 11.5 (9.5-12.9), P=0.004). Also the area under the curve was significantly different. There was no significant difference in half-maximal response between both groups. CONCLUSION: In this study we found that patients with chronic kidney disease show reduced platelet reactivity in response of ADP, TRAP and CRP compared to controls. These results contribute to our understanding of the aberrant platelet function observed in patients with chronic kidney disease and emphasize the significance of using functional whole blood platelet activation assays.

Highly pathogenic avian influenza virus H5N1 infects alveolar macrophages without virus production or excessive TNF-alpha induction.

Highly pathogenic avian influenza virus (HPAIV) of the subtype H5N1 causes severe, often fatal pneumonia in humans. The pathogenesis of HPAIV H5N1 infection is not completely understood, although the alveolar macrophage (AM) is thought to play an important role. HPAIV H5N1 infection of macrophages cultured from monocytes leads to high percentages of infection accompanied by virus production and an excessive pro-inflammatory immune response. However, macrophages cultured from monocytes are different from AM, both in phenotype and in response to seasonal influenza virus infection. Consequently, it remains unclear whether the results of studies with macrophages cultured from monocytes are valid for AM. Therefore we infected AM and for comparison macrophages cultured from monocytes with seasonal H3N2 virus, HPAIV H5N1 or pandemic H1N1 virus, and determined the percentage of cells infected, virus production and induction of TNF-alpha, a pro-inflammatory cytokine. In vitro HPAIV H5N1 infection of AM compared to that of macrophages cultured from monocytes resulted in a lower percentage of infected cells (up to 25% vs up to 84%), lower virus production and lower TNF-alpha induction. In vitro infection of AM with H3N2 or H1N1 virus resulted in even lower percentages of infected cells (up to 7%) than with HPAIV H5N1, while virus production and TNF-alpha induction were comparable. In conclusion, this study reveals that macrophages cultured from monocytes are not a good model to study the interaction between AM and these influenza virus strains. Furthermore, the interaction between HPAIV H5N1 and AM could contribute to the pathogenicity of this virus in humans, due to the relative high percentage of infected cells rather than virus production or an excessive TNF-alpha induction.

Myelin ingestion alters macrophage antigen-presenting function in vitro and in vivo.

During MS, phagocytosing myelin-containing macrophages arise and lie in close proximity to T cells. To date, it has not been addressed whether these myelin-laden macrophages have the capacity to present antigens to T cells and whether this contributes to inflammation in disease. We demonstrate that in vitro-generated human and mouse myelin-laden macrophages expressed MHC class I and II and costimulatory molecules and are thus well equipped for antigen presentation. Human myelin-laden macrophages exhibited normal endocytosis of particulate and soluble antigens. In addition, human myelin-laden macrophages elicited active T cell proliferation of naïve as well as memory T cells. Furthermore, mouse myelin-laden macrophages induced primary antigen-specific CD4(+) T cell proliferation in vivo but transiently diminished IFN-γ release. Functionally, MOG peptide-loaded myelin-laden mouse macrophages modestly but significantly reduced the severity of MOG peptide-induced EAE. These data show that myelin uptake results in the induction of a population of macrophages that retains antigen-presenting capacity and limits autoimmune-mediated disease.

Myelin ingestion by macrophages promotes their motility and capacity to recruit myeloid cells.

Myelin-laden macrophages reside within the CNS, the CSF and in the CNS-draining lymph nodes during MS and EAE, suggesting migration of these macrophages between these compartments and interaction with other cells. Since chemokines and their receptors are pivotal for leukocyte trafficking, we addressed whether myelin ingestion affects chemotaxis of mouse macrophages in vitro. Myelin ingestion enhanced expression of CCR7 and CXCR3 on macrophages and migration towards CCL21 and CXCL10. Furthermore, myelin-laden macrophages released chemoattractants resulting in enhanced migration of myeloid cells in vitro. Our data demonstrate that myelin-laden macrophages have increased motility and suggest trafficking between anatomical compartments in vivo.

Differential expression of adenosine A3 receptors controls adenosine A2A receptor-mediated inhibition of TLR responses in microglia.

Microglia activation is a prominent feature in many neuroinflammatory disorders. Unrestrained activation can generate a chronic inflammatory environment that might lead to neurodegeneration and autoimmunity. Extracellular adenosine modulates cellular activation through adenosine receptor (ADORA)-mediated signaling. There are four ADORA subtypes that can either increase (A(2A) and A(2B) receptors) or decrease (A(1) and A(3) receptors) intracellular cyclic AMP levels. The expression pattern of the subtypes thus orchestrates the cellular response to extracellular adenosine. We have investigated the expression of ADORA subtypes in unstimulated and TLR-activated primary rhesus monkey microglia. Activation induced an up-regulation of A(2A) and a down-regulation of A(3) receptor (A(3)R) levels. The altered ADORA-expression pattern sensitized microglia to A(2A) receptor (A(2A)R)-mediated inhibition of subsequent TLR-induced cytokine responses. By using combinations of subtype-specific agonists and antagonists, we revealed that in unstimulated microglia, A(2A)R-mediated inhibitory signaling was effectively counteracted by A(3)R-mediated signaling. In activated microglia, the decrease in A(3)R-mediated signaling sensitized them to A(2A)R-mediated inhibitory signaling. We report a differential, activation state-specific expression of ADORA in microglia and uncover a role for A(3)R as dynamically regulated suppressors of A(2A)R-mediated inhibition of TLR-induced responses. This would suggest exploration of combinations of A(2A)R agonists and A(3)R antagonists to dampen microglial activation during chronic neuroinflammatory conditions.

Surgical excision of CNS-draining lymph nodes reduces relapse severity in chronic-relapsing experimental autoimmune encephalomyelitis.

Despite lack of classical lymphatic vessels in the central nervous system (CNS), cells and antigens do reach the CNS-draining lymph nodes. These lymph nodes are specialized to mediate mucosal immune tolerance, but can also generate T- and B-cell immunity. Their role in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE) therefore remains elusive. We hypothesized that drainage of CNS antigens to the CNS-draining lymph nodes is vital for the recurrent episodes of CNS inflammation. To test this, we surgically removed the superficial cervical lymph nodes, deep cervical lymph nodes, and the lumbar lymph nodes prior to disease induction in three mouse EAE models, representing acute, chronic, and chronic-relapsing EAE. Excision of the CNS-draining lymph nodes in chronic-relapsing EAE reduced and delayed the relapse burden and EAE pathology within the spinal cord, which suggests initiation of CNS antigen-specific immune responses within the CNS-draining lymph nodes. Indeed, superficial cervical lymph nodes from EAE-affected mice demonstrated proliferation against the immunizing peptide, and the deep cervical lymph nodes, lumbar lymph nodes, and spleen demonstrated additional proliferation against other myelin antigen epitopes. This indicates that intermolecular epitope spreading occurs and that CNS antigen-specific immune responses are differentially generated within the different CNS-draining lymphoid organs. Proliferation of splenocytes from lymphadenectomized and sham-operated mice against the immunizing peptide was similar. These data suggest a role for CNS-draining lymph nodes in the induction of detrimental immune responses in EAE relapses, and conclusively demonstrate that the tolerance-inducing capability of cervical lymph nodes is not involved in EAE.

Brain antigens in functionally distinct antigen-presenting cell populations in cervical lymph nodes in MS and EAE.

Drainage of central nervous system (CNS) antigens to the brain-draining cervical lymph nodes (CLN) is likely crucial in the initiation and control of autoimmune responses during multiple sclerosis (MS). We demonstrate neuronal antigens within CLN of MS patients. In monkeys and mice with experimental autoimmune encephalomyelitis (EAE) and in mouse models with non-inflammatory CNS damage, the type and extent of CNS damage was associated with the frequencies of CNS antigens within the cervical lymph nodes. In addition, CNS antigens drained to the spinal-cord-draining lumbar lymph nodes. In human MS CLN, neuronal antigens were present in pro-inflammatory antigen-presenting cells (APC), whereas the majority of myelin-containing cells were anti-inflammatory. This may reflect a different origin of the cells or different drainage mechanisms. Indeed, neuronal antigen-containing cells in human CLN did not express the lymph node homing receptor CCR7, whereas myelin antigen-containing cells in situ and in vitro did. Nevertheless, CLN from EAE-affected CCR7-deficient mice contained equal amounts of myelin and neuronal antigens as wild-type mice. We conclude that the type and frequencies of CNS antigens within the CLN are determined by the type and extent of CNS damage. Furthermore, the presence of myelin and neuronal antigens in functionally distinct APC populations within MS CLN suggests that differential immune responses can be evoked.

Differentiation of primary adult microglia alters their response to TLR8-mediated activation but not their capacity as APC.

Activated microglia are found in a variety of neuroinflammatory disorders where they have attributed roles as effector as well as antigen-presenting cells (APC). Critical determinants for the multifaceted role of microglia are the differentiation potential of microglia and their mode of activation. In this study, we have investigated the effects of M-CSF and GM-CSF-mediated differentiation of adult primate microglia on their cellular phenotype, antigen presentation, and phagocytic function as well as on Toll-like receptor (TLR)-mediated responses. We show that although cell morphology and expression levels of activation markers were markedly different, differentiation with either factor yielded microglia that phenotypically and functionally resemble macrophages. Both M-CSF and GM-CSF-differentiated microglia were responsive to TLR1/2, 2, 3, 4, 5, 6/2, and 8-mediated activation, but not to TLR7 or 9-mediated activation. Intriguingly, M-CSF-differentiated microglia expressed higher levels of TLR8-encoding mRNA and protein, and produced larger amounts of proinflammatory cytokines in response to TLR8-mediated activation as compared to GM-CSF-differentiated microglia. While differentiation of adult microglia by growth factors that can be produced endogenously in the central nervous system is thus unlikely to change their APC function, it can alter their innate responses to infectious stimuli such as ssRNA viruses. Resident primate microglia may thereby help shape rather than initiate adaptive immune responses.

Brain-derived human immunodeficiency virus-1 Tat exerts differential effects on LTR transactivation and neuroimmune activation.

Molecular diversity within brain-derived HIV-1 sequences is highly variable depending on the individual gene examined and the neurological status of the patient. Herein, we examined different brain-derived human immunodeficiency virus (HIV)-1 tat sequences in terms of their effects on LTR transactivation and host gene induction in neural cells. Astrocytic and monocytoid cells co-transfected with prototypic tat clones derived from non-demented (ND) (n = 3) and demented (HAD) (n = 3) AIDS patients and different HIV-LTR constructs revealed that LTR transactivation mediated by tat clones derived from HAD patients was decreased (p < 0.05). A Tat-derived peptide containing the amino acid 24-38 domain from a ND clone caused down-regulation of the LTR transactivation (p < 0.05) in contrast to peptides from other Tat regions derived from HAD and ND tat clones. Both brain-derived HAD and ND tat constructs were able to induce the host immune genes, MCP-1 and IL-1beta. Microarray analysis revealed several host genes were selectively upregulated by a HAD-derived tat clone including an enzyme mediating heparan sulphate synthesis, HS3ST3B1 (p < 0.05), which was also found to be increased in the brains of patients with HAD. Expression of the pro-apoptotic gene, PDCD7, was reduced in cells transfected with the HAD-derived tat clone and moreover, this gene was also suppressed in monocytoid cells infected with a neurotropic HIV-1 strain. Thus, mutations within the HIV-1 tat gene may exert pathogenic effects contributing to the development of HAD, which are independent of its effects on LTR transactivation.

Phagocytes containing a disease-promoting Toll-like receptor/Nod ligand are present in the brain during demyelinating disease in primates.

Recent studies claim a central role for Toll-like receptor (TLR) ligands in stimulating autoimmune disease by activation of antigen-presenting cells in the target organ, but it is unclear if and how TLR ligands reach target organs. Most evidence comes from rodent models, and it is uncertain whether this principle holds in primates. Here we identify which cells contain peptidoglycan (PGN) in multiple sclerosis brain and in two nonhuman primate experimental autoimmune encephalomyelitis (EAE) models with different disease courses: acute (rhesus monkey) versus chronic disease (marmoset). Because persistence of TLR ligands in the central nervous system might be consequential for disease progression, we also determined the expression of two major PGN-degrading enzymes, ie, lysozyme and N-acetylmuramyl-l-alanine amidase. Distinct phagocyte subsets, including granulocytes, macrophages, and dendritic cells, contained PGN in the brain and coexpressed the inflammatory cytokine interleukin-12. The number of phagocytes carrying PGN increased in acute and chronic EAE compared with control animals, with the highest number of PGN-containing cells in acute EAE brain. Lytic enzymes were scarcely expressed in monkey and multiple sclerosis brain, favoring PGN persistence. PGN stimulated interleukin-12p70 release by leukocytes from all three primate species. The presence of PGN in the inflamed brain may have major implications because TLR2/Nod ligation potentially promotes inflammation and disease progression.

Proteinase-activated receptor 2 modulates neuroinflammation in experimental autoimmune encephalomyelitis and multiple sclerosis.

The proteinase-activated receptors (PARs) are widely recognized for their modulatory properties of inflammation and neurodegeneration. We investigated the role of PAR2 in the pathogenesis of multiple sclerosis (MS) in humans and experimental autoimmune encephalomyelitis (EAE) in mice. PAR2 expression was increased on astrocytes and infiltrating macrophages in human MS and murine EAE central nervous system (CNS) white matter (P < 0.05). Macrophages and astrocytes from PAR2 wild-type (WT) and knockout (KO) mice exhibited differential immune gene expression with PAR2 KO macrophages showing significantly higher interleukin 10 production after lipopolysaccharide stimulation (P < 0.001). PAR2 activation in macrophages resulted in the release of soluble oligodendrocyte cytotoxins (P < 0.01). Myelin oligodendrocyte glycoprotein-induced EAE caused more severe inflammatory gene expression in the CNS of PAR2 WT animals (P < 0.05), together with enhanced T cell proliferation and interferon gamma production (P < 0.05), compared with KO littermates. Indeed, PAR2 WT animals showed markedly greater microglial activation and T lymphocyte infiltration accompanied by worsened demyelination and axonal injury in the CNS compared with their PAR2 KO littermates. Enhanced neuropathological changes were associated with a more severe progressive relapsing disease phenotype (P < 0.001) in WT animals. These findings reveal previously unreported pathogenic interactions between CNS PAR2 expression and neuroinflammation with ensuing demyelination and axonal injury.

Myelin-laden macrophages are anti-inflammatory, consistent with foam cells in multiple sclerosis.

Multiple sclerosis lesion activity concurs with the extent of inflammation, demyelination and axonal suffering. Pro-inflammatory myeloid cells contribute to lesion development, but the self-limiting nature of lesions implies as yet unidentified anti-inflammatory mechanisms. We addressed the hypothesis that myelin ingestion by myeloid cells induces a foamy appearance and confers anti-inflammatory function. First, we show that myelin-containing foam cells in multiple sclerosis lesions consistently express a series of anti-inflammatory molecules while lacking pro-inflammatory cytokines. Second, unique location-dependent cytokine and membrane receptor expression profiles imply functional specialization allowing for differential responses to micro-environmental cues. A novel human in vitro model of foamy macrophages functionally confirmed that myelin ingestion induces an anti-inflammatory programme. Foamy macrophages are unable to respond to prototypical inflammatory stimuli but do express molecules involved in suppression of inflammation. These findings provide novel insights into the mechanisms of lesion control and may open new roads to intervention.

Proinflammatory bacterial peptidoglycan as a cofactor for the development of central nervous system autoimmune disease.

Upon stimulation by microbial products through TLR, dendritic cells (DC) acquire the capacity to prime naive T cells and to initiate a proinflammatory immune response. Recently, we have shown that APC within the CNS of multiple sclerosis (MS) patients contain peptidoglycan (PGN), a major cell wall component of Gram-positive bacteria, which signals through TLR and NOD. In this study, we report that Staphylococcus aureus PGN as a single component can support the induction of experimental autoimmune encephalomyelitis (EAE) in mice, an animal model for MS. Mice immunized with an encephalitogenic myelin oligodendrocyte glycoprotein peptide in IFA did not develop EAE. In contrast, addition of PGN to the emulsion was sufficient for priming of autoreactive Th1 cells and development of EAE. In vitro studies demonstrate that PGN stimulates DC-mediated processes, reflected by increased Ag uptake, DC maturation, Th1 cell expansion, activation, and proinflammatory cytokine production. These data indicate that PGN-mediated interactions result in proinflammatory stimulation of Ag-specific effector functions, which are important in the development of EAE. These PGN-mediated processes may occur both within the peripheral lymph nodes as well as in the CNS and likely involve recognition by TLR on DC. Thus, PGN may provide a physiological trigger of DC maturation, and in this way disrupt the normal tolerance to self Ag. As such, PGN signaling pathways may serve as novel targets for the treatment of MS.

Gaucher cells demonstrate a distinct macrophage phenotype and resemble alternatively activated macrophages.

Although the existence of anti-inflammatory alternatively activated macrophages (aamphi) has been accepted widely based on in vitro studies, their in vivo location, phenotype, and function still are debated. Gaucher disease (GD) is caused by a genetic deficiency in the lysosomal enzyme glucocerebrosidase and is characterized by accumulation of glycosphingolipids in so-called Gaucher cells (GCs). By using immunohistochemical analysis, we investigated whether this results in an aamphi phenotype. GCs are macrophage-like cells, expressing acid phosphatase, CD68, CD14, and HLA class II, but not CD11b, CD40, or dendritic cell markers. GCs show infrequent immunoreactivity for mannose receptor GCs did not express proinflammatory cytokines such as tumor necrosis factor alpha and monocyte chemoattractant protein 1, but did express the aamphi markers CD163, CCL18, and interleukin-1 receptor antagonist. Furthermore, CD36 and signal receptor protein alpha, involved in lipid uptake, also were observed on GCs. Thus, GCs represent a distinctive population of myeloid cells that resemble aamphi but differ from previously described in vitro aamphi.

Marked elevation of the chemokine CCL18/PARC in Gaucher disease: a novel surrogate marker for assessing therapeutic intervention.

Gaucher disease is characterized by storage of glucosylceramide in lysosomes of tissue macrophages as the result of an autosomal recessively inherited deficiency in glucocerebrosidase. Progressive accumulation of these glycolipid-laden Gaucher cells causes a variety of debilitating symptoms. The disease can be effectively treated by costly intravenous infusions with recombinant glucocerebrosidase. Chitotriosidase is massively secreted by Gaucher cells and its plasma levels are used to monitor efficacy of enzyme therapy. Broad-scale application is hampered by the common genetic defect in this surrogate marker. We report that in plasma of symptomatic patients with Gaucher disease the chemokine CCL18 is on average 29-fold elevated, without overlap between patient and control values (median control plasma level is 33 ng/mL, range, 10-72 ng/mL; median Gaucher plasma level is 948 ng/mL, range, 237-2285 ng/mL). Plasma CCL18 concentrations decrease during therapy, comparably to chitotriosidase levels. Immunohistochemistry demonstrates that Gaucher cells are the prominent source of CCL18. Plasma CCL18 levels can serve as alternative surrogate marker for storage cells in patients with Gaucher disease and monitoring of plasma CCL18 levels proves to be useful in determination of therapeutic efficacy, especially in patients who are deficient in chitotriosidase activity. The potential physiologic consequences of chronically elevated CCL18 in patients with Gaucher disease are discussed.

Up-regulation of proteinase-activated receptor 1 expression in astrocytes during HIV encephalitis.

Proteinase-activated receptor 1 (PAR-1) is a G protein-coupled receptor that is activated by thrombin and is implicated in the pathogenesis of inflammation. Although PAR-1 is expressed on immunocompetent cells within the brain such as astrocytes, little is known about its role in the pathogenesis of inflammatory brain diseases. Herein, we investigated PAR-1 regulation of brain inflammation by stimulating human astrocytic cells with thrombin or the selective PAR-1-activating peptide. Activated cells expressed significantly increased levels of IL-1 beta, inducible NO synthase, and PAR-1 mRNA. Moreover, supernatants of these same cells were neurotoxic, which was inhibited by an N-methyl-D-aspartate receptor antagonist. Striatal implantation of the PAR-1-activating peptide significantly induced brain inflammation and neurobehavioral deficits in mice compared with mice implanted with the control peptide or saline. Since HIV-related neurological disease is predicated on brain inflammation and neuronal injury, the expression of PAR-1 in HIV encephalitis (HIVE) was investigated. Immunohistochemical analysis revealed that PAR-1 and (pro)-thrombin protein expression was low in control brains, but intense immunoreactivity was observed on astrocytes in HIVE brains. Similarly, PAR-1 and thrombin mRNA levels were significantly increased in HIVE brains compared with control and multiple sclerosis brains. These data indicated that activation and up-regulation of PAR-1 probably contribute to brain inflammation and neuronal damage during HIV-1 infection, thus providing new therapeutic targets for the treatment of HIV-related neurodegeneration.

Transfer of central nervous system autoantigens and presentation in secondary lymphoid organs.

Dendritic cells are thought to regulate tolerance induction vs immunization by transferring Ags and peripheral signals to draining lymph nodes (LN). However, whether myelin Ag transfer and presentation in LN occurs during demyelinating brain disease is unknown. In this study, we demonstrate redistribution of autoantigens from brain lesions to cervical LN in monkey experimental autoimmune encephalomyelitis (EAE) and in multiple sclerosis (MS). Immunohistochemical analysis revealed significantly more cells containing myelin Ags in cervical LN of monkeys with EAE compared with those of healthy control monkeys. Myelin Ags were observed in cells expressing dendritic cell/macrophage-specific markers, MHC class II, and costimulatory molecules. Moreover, these cells were directly juxtaposed to T cells, suggesting that cognate interactions between myelin-containing APC and T cells are taking place in brain-draining LN. Indeed, myelin Ag-reactive T cells were observed in cervical LN from marmosets and rhesus monkeys. Importantly, these findings were paralleled by our findings in human tissue. We observed significantly more myelin Ag-containing cells in LN of individuals with MS compared with those of control individuals. These cells expressed APC markers, as observed in marmosets and rhesus monkeys. These findings suggest that during MS and EAE, modulation of T cell reactivity against brain-derived Ags also takes place in cervical LN and not necessarily inside the brain. A major implication is that novel therapeutic strategies may be targeted to peripheral events, thereby circumventing the blood-brain barrier.