Schwann cell-specific regulation of IL-1 and IL-1Ra during EAN: possible relevance for immune regulation at paranodal regions.

We reported Schwann cell (SC)-specific autoregulation of IL-1 in vitro [J. Neuroimmunol. 74 (1997a)]. Whether SC resume this autoregulatory potential in vivo and what significance it may have for processes leading to inflammation and demyelination of the peripheral nerve remain obscure. Therefore, we examine SC-specific autoregulation of IL-1alpha, IL-1beta and their natural antagonist IL-1 receptor antagonist (IL-1Ra) during experimental autoimmune neuritis (EAN), a model for the human Guillain-Barre syndrome. Autoregulation of IL-1 by SC was analyzed in both, actively induced and adoptively transferred, EAN. Sciatic nerves were sampled before the onset of clinical signs, 2 to 11 days post immunization (dpi), with P2 peptide, and during clinically manifest disease, 11 to 15 dpi. In adoptively transferred EAN, sciatic nerves were analyzed at preclinical stage, 2 to 4 days post P2 peptide-specific cell transfer (dpt) and during clinical manifested phase, 5 to 10 dpt. In both models, IL-1alpha and IL-1beta were expressed by SC, during preclinical EAN. IL-1Ra was not detectable in SC at preclinical stage. Further development and progression to clinically manifest disease was accompanied by SC-specific expression of IL-1Ra. Although present in other cells in the nerve, IL-1alpha and IL-1beta were hardly detectable in SC during clinical EAN. IL-1Ra immunoreactivity highly co-localized with myelin associated glycoprotein (MAG), one of the markers for paranodal regions, sites essential for proper impulse transmission. Paranodes are also primary sites where activated macrophages make contact with SC, prior to infiltration.SC-specific autoregulation of IL-1 and IL-1Ra is suggestive of its relevance for immune regulation at paranodes during EAN.

Induced upregulation of IL-1, IL-1RA and IL-1R type I gene expression by Schwann cells.

We analyzed two distinct phenotypes of Schwann cells (SC), non-differentiated and differentiated, for their ability to produce IL-1alpha and IL-1beta, and to express message for IL-1 receptor antagonist (IL-IRA) and IL-1R type I, in vitro. SC were stimulated with: lipopolysaccharide (LPS), products of activated splenocytes (ASP), products from LPS stimulated SC (SCP), rat recombinant IL-1beta (rrIL-1beta) or dexamethasone. IL-1alpha, IL- 1beta and IL-1RA mRNA levels were highly upregulated after stimulation with LPS, ASP, SCP or rrIL-1beta. SC constitutively expressed low levels of message for IL-1alpha and IL-1beta but not IL-1RA. Specific mRNAs for both IL-1 isotypes were highly upregulated 2 to 4 h after LPS stimulation and then decreased and were undetectable by 24 h. IL-1RA mRNA was detectable after 6 h of LPS stimulation and was maximally upregulated at 24 h. IL-1 gene expression was inducible in both SC phenotypes. IL-1beta could be detected by immunofluorescence in SC, one to three days after LPS stimulation. At the same time IL-1 bioactivity was maximal in SC supernatants. Treatment with either SCP, rrIL-1beta or dexamethasone induced upregulation of IL-1R type I mRNA with maximal expression between 2 to 4 h, in SC. Inducible expression of genes for IL-1alpha, IL-1beta, IL-1RA and IL-1R type I in both differentiated and non-differentiated SC suggest autocrine and paracrine regulation of IL-1 by SC.

Experimental allergic encephalomyelitis. T cell trafficking to the central nervous system in a resistant Thy-1 congenic mouse strain.

BACKGROUND: The understanding of recognition events that underlie the migration of antigen-specific T cells to a target organ during immune-mediated damage will be integral to the therapy of a number of human conditions of proven or suspected autoimmune etiology. In experimental allergic encephalomyelitis (EAE), the laboratory model of the human demyelinating disease, multiple sclerosis, previous studies have concentrated on susceptible strains and have shown that myelin-specific T cells play an early, key role in central nervous system (CNS), lesion formation. Not known in this model is whether in EAE-resistant strains, similar antigen-specific T cells possess the ability to recognize CNS endothelium and infiltrate the CNS. EXPERIMENTAL DESIGN: Myelin basic protein (MBP)-responsive T cells derived from mice of the C57BL/6 strain (bearing the Thy-1.2 allele) were adoptively transferred to the Thy-1.1 congenic strain C57BL/Ka. Some recipients were given a subsequent challenge with MBP in adjuvant, a protocol recently shown to break resistance in this strain and cause EAE. On the basis of the difference in Thy-1 allele, T cell trafficking was followed in this EAE-resistant congenic strain following the different sensitization protocols. RESULTS: In C57BL/Ka mice receiving adoptively transferred C57BL/6 cells followed by MBP challenge, donor MBP-responsive Thy-1.2+ lymphocytes were detected by immunocytochemistry in the Thy-1.1 host CNS and also in peripheral lymphoid organs. In mice given MBP-sensitized cells without additional antigen challenge, although Thy-1.2+ cells were found in the spleen and lymph nodes, similar cells could not be found in the CNS, and animals displayed neither clinical nor pathologic signs of EAE. Donor T lymphocytes appeared in the host CNS with clinical onset, 10 to 14 days after challenge. When mice went into remission, Thy-1.2+ lymphocytes could not be found in the CNS, but were still present in peripheral lymphoid organs up to 3 months after challenge. From the total number of infiltrating cells, T cell receptor-alpha beta+ cells constituted 27% in perivascular cuffs, 15% in meninges, and 13% in the parenchymal infiltrates in the spinal cord. Thy-1.2+ cells contributed up to about 40% of total T cell receptor-alpha beta+ lymphocytes. Approximately 60% of all infiltrating T cells expressed L3T4 (helper/inducer), whereas 18% expressed Lyt-2 (suppressor/cytotoxic). The majority of infiltrating cells were memory and activated cells expressing on their surface Pgp-1 and CD 25. Immunostaining for cytokines showed that the majority of infiltrating cells belonged to the TH1 subset and contained interferon-gamma and tumor necrosis factor-alpha, while a minority were positive for interleukin-4. CONCLUSIONS: These results suggest that: (a) T lymphocytes from an EAE-resistant strain of mouse are capable of homing to the CNS; (b) T lymphocytes from an EAE-resistant strain express phenotypic characteristics, activation, memory, and cytokine profiles similar to infiltrating cells derived from susceptible strains; and (c) the presence of donor T cells in the recipient CNS correlates with clinical and histopathologic signs of EAE.

Homing of T cells to the central nervous system throughout the course of relapsing experimental autoimmune encephalomyelitis in Thy-1 congenic mice.

Chronic relapsing experimental allergic encephalomyelitis (EAE) was induced in Thy-1.1 congenic SJL/J mice by the adoptive transfer of myelin basic protein (MBP)-responsive lymph node cells from Thy-1.2 SJL/J mice. The Thy-1 congenic mouse strain was constructed on the SJL (Thy-1.2) background by the initial cross with the AKR (Thy-1.1) strain and does not reject Thy-1.2+ T cells. Quantitative immunocytochemical analysis of the central nervous system (CNS) of Thy-1.1 recipients showed preferential trafficking of Thy-1.2+ T cells to the meninges and white matter, beginning prior to onset of clinical signs. At 7 days post-transfer (dpt), Thy-1.2+ donor cells constituted 2.5% of the infiltrating cells and reached peak values (ca. 10%) during the first attack. At later stages (up to ten relapses), Thy-1.2+ T cells constituted 2-5% of the infiltrate. In control mice injected with irrelevant antigen-stimulated Thy-1.2+ T cells, only the occasional Thy-1.2+ T cell could be demonstrated up to 14 dpt. This is the first study showing unequivocally the presence of MBP-stimulated, adoptively transferred T cells within the CNS of recipients throughout the course of EAE, particularly during later relapsing stages. These results indicate that the persistent presence of antigen-specific T cells may be required for the recruitment of non-CNS antigen-responsive immune cells.

A saturable mechanism for transport of immunoglobulin G across the blood-brain barrier of the guinea pig.

The existence of an immunological blood-brain barrier to homologous blood-borne immunoglobulin G (IgG) was investigated in the guinea pig using a vascular brain perfusion technique in situ. Cerebrovascular unidirectional transfer constants (Kin) for 125I-labeled IgG (2.5 micrograms/ml) estimated from the multiple-time brain uptake data, ranged from 0.53 to 0.58 ml min-1 g-1 X 10(3) in the parietal cortex, hippocampus, and caudate nucleus, the transfer rate being some 10 times higher than that for [3H]dextran (MW 70,000). In the presence of 4 mg/ml unlabeled IgG, unidirectional blood to brain transfer of 125I-IgG was markedly inhibited. Immunohistochemical analysis of the brain tissue after vascular perfusion with unlabeled IgG revealed a distribution of the blood-borne immunoglobulin in the endothelial cells of microvessels and in the surrounding perivascular tissue. It is concluded that there is a specific transfer mechanism for IgG at the blood-brain barrier in the guinea pig, which is saturated at physiological plasma levels of IgG.

Blood-brain barrier permeability changes during acute allergic encephalomyelitis induced in the guinea pig.

Blood-brain barrier permeability to homologous serum 125I-IgG and to D-[3H]mannitol was studied by means of the brain vascular perfusion method in guinea pigs with experimental allergic encephalomyelitis (EAE). EAE was induced with homologous myelin basic protein (MBP) after pretreatment with foreign protein and muramyl dipeptide (MDP). The results suggest a significant comparable increase in IgG blood-to-brain clearance in the parietal cortex, hippocampus, and caudate nucleus, during vascular perfusion of the brains of animals, after 7 and 20 days of EAE. On the other hand, unidirectional transfer of mannitol in the same period of EAE was markedly augmented only in the hippocampus, but no significant changes in the parietal cortex or caudate nucleus were observed. Cerebrospinal fluid (CSF)/serum ratios for IgG and albumin were both significantly increased, suggesting an increase in blood-CSF barrier permeability, but more for albumin than for IgG. The results were confirmed by immunohistochemical determination of the IgG deposits in the brains of EAE animals, during vascular perfusion with unlabeled homologous IgG. An important role of the blood-brain barrier for the central nervous system immunoglobulin homeostasis during EAE is suggested.