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The experimental autoimmune encephalomyelitis (EAE) model is indispensable for autoimmunity research, but model-specific T cell dynamics are sparsely studied. We used next-generation immunosequencing across lymphoid organs, blood and spinal cord in response to immunization with myelin basic protein (MBP) to study T cell repertoires and migration patterns. Surprisingly, most spinal cord T cells were unique to the individual animal despite the existence of shared MBP-specific clones, suggesting a previously underestimated T cell diversity. Almost complete emigration of pathogenic clones from blood to spinal cord indicates that blood is not a suitable compartment to study EAE-mediating T cells., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The immunomodulatory effects of the IL-27 and IL-33 and the anti-inflammatory effects of ginger have been reported in some studies. The aim was to evaluate the effects of the ginger extract on the expression of IL-27 and IL-33 in a model of experimental autoimmune encephalomyelitis (EAE). In PBS-treated EAE mice the expression of IL-27 P28 was significantly lower whereas the expression of IL-33 was significantly higher than unimmunized control mice. In 200 and 300 mg/kg ginger-treated EAE groups the expression of IL-27 P28 and IL-27 EBI3 was significantly higher whereas the expression of IL-33 was significantly lower than PBS-treated EAE mice. The EAE clinical symptoms and the pathological scores were significantly lower in ginger-treated EAE groups. These results showed that the ginger extract modulates the expression of the IL-27 and IL-33 in the spinal cord of EAE mice and ameliorates the clinical symptoms of disease., (Copyright © 2014 Elsevier B.V. All rights reserved.)

To investigate whether AQP4 autoantibodies (AQP4-Ab) are causative for neuromyelitis optica (NMO), the production of AQP4-Ab and clinical experimental autoimmune encephalomyelitis (EAE) was investigated in mice administered with mouse AQP4 antigen or myelin oligodendrocyte glycoprotein (MOG35-55) alone, and in combination. Eight- to twelve-week-old female C57BL/6 mice were randomly immunized with encephalitogenic mixture containing 300 μg of MOG35-55 or AQP4 antigen alone, and in combination in complete Freund's adjuvant supplemented with H37Ra M. tuberculosis. The incidence of EAE, Weaver 15 scores, and body weight was evaluated. ELISA was used to detect serum mouse AQP4-Ab. Mice injected with MOG35-55 and MOG33-35 plus AQP4 antigen began to show EAE symptoms 12 days after immunization. The incidence of EAE was 91.6%, and 62.5%, for MOG35-55 alone and MOG33-35 plus AQP4 antigen groups, respectively, while AQP4 antigen alone didn't develop EAE. In all but the control group, serum AQP4-Ab levels were increased, and correlated positively with Weaver 15 score (rs=0.713, p=0.000) and negatively with body weight changes (rs=-0.415, p=0.011). Injection of human NMO sera positive for AQP4-Ab exacerbated MOG-induced EAE. Our results suggest that AQP4-Ab can be produced in MOG-induced MS model, and itself is not sufficient for the development of EAE, implying that NMO might be a subtype or transition from MS., (Published by Elsevier B.V.)

Multiple sclerosis (MS) is a demyelinating disease of the CNS involving T cell targeting of myelin antigens. During pregnancy, women with MS experience decreased relapses followed by a post partum disease flare. Using murine experimental autoimmune encephalomyelitis, we recapitulate pregnancy findings in both relapsing and progressive models. Pregnant mice produced less TNF-α, IL-17 and exhibited reduced CNS pathology relative to non-pregnant controls. Microparticles, called exosomes, shed into the blood during pregnancy were isolated and found to significantly suppress T cell activation relative to those from non-pregnant controls. These results demonstrate the immunosuppressive potential of pregnancy and serum-derived pregnancy exosomes., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Ovarian hormones, including progesterone, are known to have immunomodulatory and neuroprotective effects which may alter the disease course of experimental autoimmune encephalomyelitis (EAE). In the current study, we examined the treatment potential of progesterone beginning at the onset of EAE symptoms. Progesterone treated animals showed reduced peak disease scores and cumulative disease indices, and decreased inflammatory cytokine secretion (IL-2 and IL-17). In addition, increased production of IL-10 was accompanied by increased numbers of CD19+ cells and an increase in CD8+ cells. Decreased chemokine and chemokine receptor expression in the spinal cord also contributed to decreased lesions in the spinal cord., (Copyright 2010 Elsevier B.V. All rights reserved.)

Lactoferrin (LF) is a multifunctional protein present in secretory fluids of mammals and circulating neutrophils. Beside anti-inflammatory properties, LF was found to inhibit some autoimmune disorders. In this investigation we studied effects of oral administration of LF on experimental autoimmune encephalomyelitis (EAE) in Lewis rats. LF was given in drinking water as 0.25% solution beginning the day of elicitation of EAE or with a seven-day delay. The effects of LF were evaluated by the following criteria: clinical score, lymph node cell number, serum cytokine levels and histopathological changes. We found that LF treatment led to a significant acceleration of the recovery process, particularly on days 16-18 following elicitation of EAE. The delayed administration of LF was less effective in reducing the score of EAE. In addition, cell number of the inguinal lymph nodes of untreated EAE rats, almost 3 times higher as compared with control, naïve rats, was normalized by LF treatment. Furthermore, LF decreased elevated serum concentrations of tumor necrosis factor alpha and transforming growth factor beta. The histological analysis of the spinal cord revealed reduction in the number and size of inflammatory foci in LF-treated rats. In summary, treatment of EAE Lewis rats with LF reduced the clinical symptoms and accelerated the recovery of animals.

We sequentially analyzed the serum IgG response against normal mouse brain during experimental autoimmune encephalomyelitis in SJL/J mice injected with CFA, Bordetella pertussis toxin (BPT) and proteolipid protein 139-151 peptide, compared with mice that received CFA and BPT or were uninjected. Dynamic changes were observed from day 0 to day 28 in the 3 groups. Six highly discriminant antigenic bands (kappa=0.974) were identified. Three non-myelin proteins were characterized (mitochondrial aconitase hydratase 2, phosphoglycerate mutase 1, brain specific pyruvate deshydrogenase). The IgG response against two of them was less frequent in EAE whereas it was associated with multiple sclerosis in our previous work.

Erythropoietin (EPO) mediates a wide range of neuroprotective activities, including amelioration of disease and neuroinflammation in rat models of EAE. However, optimum dosing parameters are currently unknown. In the present study, we used a chronic EAE model induced in mice by immunization with the myelin oligodendrocyte glycoprotein peptide (MOG35-55) to compare the effect of EPO given with different treatment schedules. EPO was administered intraperitoneally at 0.5, 5.0 or 50 microg/kg three times weekly starting from day 3 after immunization (preventive schedule), at the onset of clinical disease (therapeutic schedule) or 15 days after the onset of symptoms (late therapeutic schedule). The results show that EPO is effective even when given after the appearance of clinical signs of EAE, but with a reduced efficacy compared to the preventative schedule. To determine whether this effect requires the homodimeric EPO receptor (EPOR2)-mediated hematopoietic effect of EPO, we studied the effect of carbamylated EPO (CEPO) that does not bind EPOR2. CEPO, ameliorated EAE without changing the hemoglobin concentration. Another non-erythropoietic derivative, asialoEPO was also effective. Both EPO and CEPO equivalently decreased the EAE-associated production of TNF-alpha, IL-1beta and IL-1Ra in the spinal cord, and IFN-gamma by peripheral lymphocytes, indicating that their action involves targeting neuroinflammation. The lowest dosage tested appeared fully effective. The possibility to dissociate the anti-neuroinflammatory action of EPO from its hematopoietic action, which may cause undesired side effects in non-anemic patients, present new avenues to the therapy of multiple sclerosis.

Inhibition of alpha(4)beta(1) integrin blocks immune cell influx into the CNS providing benefit to patients with multiple sclerosis and in animal model systems. We have used this mechanism to examine whether the presence of inflammatory cells suppresses spontaneous myelin repair in experimental autoimmune encephalomyelitis. We observed (1) 87% of plaques showed remyelination after 40 days of treatment; (2) myelin repair occurred in half of the total lesion area; (3) half of the animals regained motor function. There was no significant repair or gain of motor function in vehicle-treated animals. Therefore, prolonged inhibition of CNS inflammation, in the absence of targeted myelin repair, facilitates mechanisms of spontaneous remyelination.

The new orally active drug laquinimod (ABR-215062) was evaluated in experimental autoimmune encephalomyelitis (EAE) in the Lewis rat. EAE shares important immunological and clinical features with multiple sclerosis (MS). Doses of 16, 1.6 and 0.16 mg/kg/day laquinimod dose-dependently inhibited disease and showed better disease inhibitory effects as compared to roquinimex (Linomide). Furthermore, laquinimod inhibited the inflammation of both CD4+ T cells and macrophages into central nervous tissues, i.e. the spinal cord. It also changed the cytokine balance in favour of TH2/TH3 cytokines IL-4, IL-10 and TGF-beta. Laquinimod therefore represents a new orally active immunoregulatory drug without general immunosuppressive properties with a potential for the treatment of severe autoimmune diseases like MS.

FTY720 is a prodrug for FTY-phosphate, an agonist at four of the five known receptors for sphingosine-1-phosphate (S1P). We show that administration of either FTY720 or FTY-P to SJL mice with established relapsing-remitting experimental autoimmune encephalitis (EAE) results in a rapid and sustained improvement in their clinical status, and a reversal of changes in expression of mRNAs encoding some myelin proteins and inflammatory mediators. EAE produced by adoptively transferring lymph node cells from immunized mice to naïve hosts is similarly ameliorated by FTY-P. Treatment with FTY-P is accompanied by a dose-responsive peripheral lymphopoenia.

A gender difference prevails in some murine strains of experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis (MS). Our results showed that castration of SJL males, a strain characterized by decreased susceptibility of males as compared to females, displayed increased disease severity. In contrast, castration had no effect on disease in C57BL/6 males, a strain in which no gender difference in EAE is observed. Regardless of whether endogenous androgens were protective in a given genetic background, supplemental androgen treatment was protective in gonadally intact males of both strains. These data provide a basis for the novel therapeutic use of supplemental testosterone for men with MS.

To study alterations in the morphology of spinal perivascular macrophages (SPM) during experimental allergic encephalomyelitis (EAE), we labelled SPM by intracerebroventricular (i.c.v.) injection of horseradish peroxidase (HRP). As earlier electron microscopical analysis had shown severely damaged SPM, we suspected that each inflammatory process is accompanied by the death of SPM. To prove this hypothesis, we compared the numerical density of resident SPM (i.c.v. labelled in red by Fluoro-Ruby) with that of monocytes/macrophages recruited to the perivascular space (i.c.v. labelled in green by Fluoro-Emerald). At the peak of paraparesis, the density of resident SPM was reduced by 33%. Since this reduction contrasted sharply with earlier data indicating a massive increase in the density of SPM during EAE, we checked our findings after general or selective suppression of the immune response to myelin autoantigens with the drugs dexamethasone and copaxone, respectively. Dexamethasone treatment commenced after evident paraparesis accelerated recovery, but did not influence SPM density. Immunisation with copaxone completely prevented the occurrence of EAE (monitored by video-based motion analysis of tail motility); the subsequent histological analysis revealed no reduction in SPM density. Based on this inverse correlation between the severity of EAE and the density of resident macrophages, we conclude that SPM plays an important role in the pathogenesis of EAE.

The ability of sex hormones to regulate cytokine production is well established, but the ability of cytokines to regulate sex hormone production has only begun to be investigated. We measured sex hormones in mice with passive experimental autoimmune encephalomyelitis (EAE) and in multiple sclerosis (MS) patients with sexual dysfunction. Abnormally low serum testosterone levels were found in male mice with EAE and in male MS patients, while serum estrogen levels in female mice with EAE were normal. An inverse relationship between cytokine and testosterone levels in male mice with EAE, coupled with an increase in serum luteinizing hormone (LH) levels, suggests that inflammatory cytokines suppress testosterone production by a direct effect on testicular Leydig cells. Gender differences in the sensitivity of the hypothalamic-pituitary-gonadal (HPG) axis to inflammation may be an important factor regulating the duration and severity of central nervous system (CNS) autoimmunity.

Rat strains vary in their susceptibility to experimental autoimmune encephalomyelitis (EAE) and in many cases, factors other than MHC antigens are thought to play a role in this. We found that PVG rats, which have a very low susceptibility to EAE, were rendered highly susceptible to clinical disease when treated with N-methylarginine (NMA) an inhibitor of nitric oxide synthase (NOS). The clinical course of the ensuing disease in NMA-treated PVG rats was in most cases fulminating in nature and accompanied by some mortality. Following immunisation with myelin basic protein (MBP)-complete Freund's adjuvant (CFA), PVG rats developed higher serum levels of the surrogate markers of nitric oxide production, reactive nitrogen intermediates (RNI; nitrite and nitrate), than did their Lewis counterparts. This in vivo finding was reflected in vitro, where the levels of RNI produced in 24, 48 and 72 h IFN-gamma-stimulated spleen cell cultures for PVG rats were significantly higher than those for Lewis rats. A mechanism by which increased NO production might protect PVG rats against clinical EAE was suggested by the finding that lymph node cells, isolated from NMA-treated MBP-immunised PVG rats, proliferated in response to MBP at a rate approximately 3 x greater than those from MBP-immunised, saline treated rats. Thus, the greater number of MBP-specific T cells generated in the NOS inhibitor-treated vs. untreated rats could account for their increased susceptibility to developing clinical EAE. The findings in this study suggest that NO plays a role in protecting PVG rats against developing EAE.

We previously observed Th1-dominated response in the central nervous system (CNS) of mice during the course of experimental allergic encephalomyelitis (EAE) with a semiquantitative reverse transcriptase-polymerase chain reaction (RT/PCR) analysis. We report here that mRNA levels for both inflammatory cytokines including interleukin (IL)-1beta, IL-2, IL-6, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and TNF-beta and immunoregulatory cytokines including IL-4, IL-10 and transforming growth factor (TGF)-beta were up-regulated in the preclinical and/or acute phase but down-regulated in the recovery phase of EAE in lymph node (LN) of mice. Similar profiles for cytokine mRNA levels were also observed in spleen and peripheral blood mononuclear cells (PBMC). The present study also showed that a significant down-regulation of the mRNA level for IL-6 in the acute phase as compared with the preclinical phase, and a significant reduction of the mRNA level for TGF-beta in the preclinical and acute phase as compared with the corresponding mRNA levels in the control mice treated with complete Freund's adjuvant alone were characteristic in peripheral immune organs of mice with EAE. These results indicate that no particular bias in cytokine production occurred in peripheral immune organs of mice with actively induced relapsing EAE, and that the relative reduction in production of TGF-beta or IL-6 in peripheral circulation might participate in the induction or remission of EAE, respectively. Our results using the animal model of multiple sclerosis (MS) suggested that the mRNA levels for IL-6 and TGF-beta in PBMC from patients with MS may be a good indicator to assess the disease activity or to predict relapse.

We have recently reported that the oral administration of myelin basic protein (MBP) prior to encephalitogenic challenge results in suppression of experimental autoimmune encephalomyelitis (EAE). We examined the serum and salivary antibody responses to MBP in orally tolerant rats using an avidin-biotin enzyme-linked immunosorbent assay. Serum anti-MBP IgA and IgG, but not IgM levels are suppressed in orally tolerant versus control rats. This suppression is time dependent and is confined to the period when animals would otherwise be manifesting EAE clinical signs. In contrast, there is an increase in salivary anti-MBP IgA levels in MBP-fed rats relative to vehicle-fed controls. Thus, MBP-induced unresponsiveness is demonstrable at the humoral level, and moreover, a discrete compartmentalization between the serum and salivary anti-MBP responses exists.

When experimental autoimmune encephalomyelitis (EAE) is induced by adoptive transfer of myelin basic protein (MBP)-specific lymphocytes the splenic noradrenergic and adrenocortical responses mirror in most respects those that occur following sensitization with spinal cord and Freund's adjuvant (CFA), despite the absence of the primary immune challenge. An early drop in splenic noradrenaline (NA), observed only when purified protein derivative-primed cells are transferred may reflect a vigorous proliferative response in vitro, not observed with MBP-specific cells. However, serum corticosterone (CS) levels and the density of splenocyte beta-adrenergic receptors were increased in both experimental groups within 3 days of cell inoculation. The stress of clinical signs of EAE resulted in highly significant increases in both splenic NA and plasma CS. Thus adoptively transferred EAE provides a well-delineated model of autoimmune disease for investigating the immunomodulatory role of the neural and endocrine systems.

Peripheral blood mononuclear cells (PBMC) from strain 13 guinea pigs at various stages of chronic relapsing experimental allergic encephalomyelitis (CREAE) showed significantly reduced reactivity to the polyclonal T cell mitogens, phytohaemagglutinin and concanavalin A. Serum taken at the same time revealed an increase in inhibitors of lymphocyte mitogenesis. The factors identified appeared to inhibit the initial stages of lymphocyte proliferation: they were not cytotoxic for lymphocytes nor were they complement-dependent.

Neural activity in the spleen in the pre-clinical stage of experimental allergic encephalomyelitis (EAE) mirrored that of animals immunized with complete Freund's adjuvant (CFA) alone. In response to immune challenge the splenic noradrenaline content fell significantly, accompanied by an increase in lymphocyte beta-receptor density. The response of the pituitary-adrenal axis was reflected in increased circulating levels of corticosterone in both experimental groups; this was amplified by the stress of clinical signs leading to a 2-fold increase in animals with EAE. The increased, potentially immunosuppressive concentration of noradrenaline in the spleen during the acute stage may also represent a recovery mechanism and indicate how neuroimmune interactions could influence the relapsing-remitting nature of chronic inflammatory demyelinating disease.

Cholesterol esters and free cholesterol were determined in the serum of guinea pigs with experimental allergic encephalomyelitis (EAE). EAE was induced by immunization with myelin basic protein (MBP) and galactocerebroside (GC). The results showed an increased content of cholesterol arachidonate and cholesterol linoleate during the period of clinical signs of EAE in comparison with the content of cholesterol esters in EAE induced by MBP without galactocerebroside. The content of free cholesterol was significantly reduced. Histological analyses showed intensive inflammatory lesions and demyelination which were not found in EAE induced by MBP without galactocerebroside.

An animal model which might help to study multiple sclerosis has long been sought. With chronic relapsing experimental allergic encephalitis (EAE), the search seems to have brought hope and evidence of comparable pathology whether concerned with clinical or neuropathological results, but no study of the cerebrospinal fluid (CSF) electrophoretic pattern has been made so far. A new sensitive method enables to study the CSF proteins: unconcentrated CSF proteins after agar gel electrophoresis are stained with silver reagents. The silver technique allows to follow the evolution of the inflammatory reaction in chronic relapsing EAE as well as in the acute form of EAE. This technique provides an additional approach to the study of EAE and an argument in favor of chronic relapsing EAE in guinea pigs as a model for multiple sclerosis.

The pathology of acute experimental allergic encephalomyelitis is characterized by perivascular cellular infiltrates in the central nervous system. Our hypothesis is that this immuno-pharmacological process can activate the circulating and tissular kallikrein-kinin systems. We studied 21 New Zealand rabbits inoculated with a homogenate of guinea-pig spinal cord in complete Freund's adjuvant. Each animal underwent radioimmunoassay for arterial blood bradykinin, des-Arg9-bradykinin and des-Phe8-des-Arg9-bradykinin during the acute or subacute clinical phase of encephalomyelitis. Immediately after blood sampling, all animals had their complete central nervous system dissected out and prepared for staining and histological study. The number of hematoxylin-eosin-stained perivascular cellular infiltrates was counted at eight levels of the central nervous system, from the hypothalamic to sacral spinal segments. We demonstrated a positive significant (P less than or equal to 0.02) correlation (r = 0.55) between the number of perivascular cellular infiltrates and blood level of the biologically active kinin bradykinin.

Juvenile strain-13 guinea pigs challenged with whole central nervous system (CNS) tissue in complete Freund's adjuvant (CFA) developed chronic-relapsing (CR) experimental allergic encephalomyelitis (EAE). The animals that recovered from the first clinical episode were divided into three groups. One group was left untreated, one group was treated with three intracardiac injections of 100 micrograms glutaraldehyde-fixed myelin basic protein (MBP)-liposomes (MBP-L-GA) given once a week, and one group was treated with cytochrome c-liposomes (CYC-L-GA). The animals treated with MBP-liposomes were very well protected against further relapses. In vitro proliferative responses of peripheral blood lymphocytes (PBL) were performed repeatedly on most animals. The lymphocytes exhibited excellent proliferative responses to MBP, proteolipid apoprotein (PLP) and whole myelin, as well as to purified protein derivative (PPD) and concanavalin-A (ConA). High proliferative responses were recorded over the entire period of observation which lasted 12-22 months, each time the animals were tested in remission or in full relapse. However, a sharp decrease in proliferative responses was observed in most animals when the assay was performed 24-48 h before to 24 h after entering a relapse. The results demonstrate the presence of long-term and sustained cell-mediated responses to two distinct neuroantigens, and show fluctuations of both neuroantigen-specific and nonspecific responses concordant with a well-defined phase of the disease. Isoelectric focusing and immunofixation was performed on sera and cerebrospinal fluids obtained at the time of sacrifice. The pattern showed clear oligoclonal IgG bands (OB) in the samples obtained from untreated, CYC-L-GA-treated as well as in the MBP-L-GA-treated animals.

The presence of tumor necrosis factor alpha (TNF alpha)/cachectin was investigated in 180 paired cerebrospinal fluid (CSF) and serum samples from patients with neurological diseases, and in five paired CSF and serum samples of Macaca cynomolgus monkeys with acute monophasic experimental autoimmune encephalomyelitis (AMEAE). TNF alpha was never detected in human CSF, even when an extensive demyelination was documented (active multiple sclerosis, acquired immunodeficiency syndrome (AIDS) dementia complex). Only one Macaca with AMEAE had detectable levels of TNF alpha in CSF but not in serum, suggesting an intrathecal synthesis of this cytokine in AMEAE.

The myelin/oligodendrocyte glycoprotein (MOG) is a target antigen for autoantibody-mediated demyelination in chronic relapsing experimental allergic encephalomyelitis (CREAE) in the Strain 13 guinea pig. Anti-idiotypic antibodies directed against a demyelinating MOG-specific monoclonal antibody (8-18C5) have identified a cross-reactive idiotype in 10/10 CREAE sera. In nine of these sera inhibition studies demonstrated that this idiotype was at or in close proximity to the combination site of guinea pig anti-MOG autoantibodies. This cross-reactive anti-MOG idiotype may represent an important target for the anti-idiotypic regulation of demyelinating antibody responses in CREAE.

A monoclonal antibody against the human interleukin-2 receptor (anti-Tac) has been found to cross-react with an antigen on the surface of guinea pig leucocytes. Cells marking with anti-Tac and with an anti-pan T cell monoclonal antibody have been quantitated in the peripheral blood and cerebrospinal fluid (CSF) of guinea pigs with chronic relapsing experimental allergic encephalomyelitis (CR-EAE). T cells account for about 90% of peripheral blood leucocytes in all animals whilst in the CSF, T cells are the major contributor only when there is a pleocytosis. The proportion of T cells marking with anti-Tac, a measure of T cell activation, in blood and CSF of control animals is 12%, rising to 23% in blood in the post-acute phase of the disease. However, a fall in the blood Tac/T ratio to 13% occurs during the first 10 days of relapse with a subsequent rise to 30-35%. This change is related to the time after onset of relapse irrespective of the subsequent course of the disease. From first relapse onwards CSF lymphocytes show a greater level of activation than lymphocytes from paired peripheral blood samples but the proportion of Tac+ cells in CSF does not increase with increasing CSF pleocytosis. The data is consistent with migration of activated T cells from blood to CSF at the onset of relapse.

The spontaneous chemiluminescence activity (CL-A) of peripheral mononuclear cells (MNC) was examined in Lewis rats with acute experimental allergic encephalomyelitis (EAE), compared to rats immunized with complete adjuvant (n = 11) and healthy animals (n = 16). In rats with EAE, CL-A increased sharply 8-9 days after immunization (3420 +/- 3124 counts/10 s, n = 16) at the time of flattening of the weight curve. This CL-A peak was compared to that of animals immunized with complete adjuvant: 765 +/- 441 counts/10 s (P = 0.01) and healthy rats: 450 +/- 172 counts/10 s (P = 0.0001). After this initial peak in EAE rats, CL-A decreased almost to normal values when animals lost weight (746 +/- 251 counts, n = 19) and tail paralysis developed (557 +/- 251 counts/10 s, n = 15). CL-A increased again with the onset of paralysis of the extremities (1527 +/- 990 counts/10 s, n = 11), followed by a decrease as the clinical course deteriorated. Finally, CL-A approached normal values as the animals improved. A significant increase in the number of meningeal (P less than 0.01) and perivascular (P less than 0.01) cells in the CNS coincided with the initial CL-A peak. Gel filtration of the serum of rats with increased CL-A revealed at least one substance, with a molecular weight between 13,700 and 43,000 Da, which stimulated the CL-A of normal mononuclear cells.