Nasal administration of soluble antigens is an exciting means of specifically down-regulating pathogenic T-cell reactivities in autoimmune diseases. The mechanisms by which nasal administration of soluble antigens suppresses autoimmunity are poorly understood. To define further the principles of nasal tolerance induction, we studied the effects of nasal administration of myelin basic protein (MBP) on experimental autoimmune encephalomyelitis (EAE) in the Lewis rat. EAE is a CD4+ T-cell-mediated animal model for human multiple sclerosis. Nasal administration of guinea-pig (gp)-MBP at a dose as low as 30 gtg/rat can completely prevent gp-MBP-induced EAE, whereas nasal administration of bovine (b)-MBP is not effective even at a much higher dosage. Cellular immune responses, as reflected by T-cell proliferation and interferon-y (IFN-y)- ELISPOT, were suppressed in rats receiving the two different doses (30 and 600 Jig/rat) of gp-MBP, but not after administration of b-MBP. Rats tolerized with both doses of gp-MBP had also abrogated MBP-induced IFN-y mRNA expression in popliteal and inguinal lymph node mononuclear cells compared with rats receiving phosphate-buffered saline nasally. However, adoptive transfer revealed that only spleen mononuclear cells from rats pretreated with a low dose, but not from those pretreated with a high dose, of gp-MBP transferred protection to actively induced EAE. Low-dose (30 Jg/rat) gp-MBP-tolerized rats also had high numbers of interleukin-4 (IL-4) mRNA-expressing lymph node cells, while high-dose (600 Jg/rat) gp-MBP-tolerized rats had low numbers of IL-4 mRNA-expressing lymph node cells. Our data suggest an exquisite specificity of nasal tolerance. Dose-dependent mechanisms also relate to nasal tolerance induction and protection against EAE in the Lewis rat.

Myasthenia gravis (MG) and experimental autoimmune myasthenia gravis (EAMG) are caused by auto-antibodies against thenicotinic acetylcholine receptor (AChR) at the postsynaptic membrane. To evaluate the extent to which the humoral immune response againstAChR opcratcs in the pathogenesis of EAMG, we immunized B-cell knockout(儿MT) and wild type C57BL/6 mice with AChR in complete Freund's adjuvant. The ability of AChR-primed lymph node cells to proliferate and secreteIFN-/in response to AChR and itsdominant peptide a146-162 were intact in ktMT as in wild type mice. Similar levels of mRNA for IFN- IL-4 and IL-IO in AChR-reactivelymph node cells were detected in ktMT and wild type mice. However, htMT mice had no detectable anti-AChR antibodies and never devel-oped clinical EAMG. We conclude that B-cells are critically required for the genesis of clinical EAMG, but not for AChR-specific T-cellpriming

CTLA-4 appears to be a negative regulator of T cell activation and is implicated in T cell-mediated autoimmune diseases.Experimental autoimmune myasthenia gravis (EAMG), induced by immunization of C57BL/6 mice with acetylcholine receptor(AChR) in adjuvant, is an autoantibody-mediated disease model for human myasthenia gravis (MG). The production of anti-AChR Abs in MG and EAMG is T cell dependent. In the present study, we demonstrate that anti-CTLA-4 Ab treatment enhancesT cell responses to AChR, increases anti-AChR Ab production, and provokes a rapid onset and severe EAMG. To address possible mechanisms underlying the enhanced autoreactive T cell responses after anti-CTLA-4 Ab treatment, mice were immunized withthe immunodominant peptide a146–162 representing an extracellular sequence of the AChR. Anti-CTLA-4 Ab, but not control Ab,treatment subsequent to peptide immunization results in clinical EAMG with diversification of the autoantibody repertoire as wellas enhanced T cell proliferation against not only the immunizing a146–162 peptide, but also against other subdominant epitopes.Thus, treatment with anti-CTLA-4 Ab appears to induce determinant spreading, diversify the autoantibody repertoire, andenhance B cell-mediated autoimmune disease in this murine model of MG.

Background and Purpose—Cerebral ischemia is associated with inflammation involving accumulation of polymorphonuclearneutrophils. T cells have been suggested to contribute to the secondary progression of ischemic braininjury. Dendritic cells (DC) are potent regulators of immunity by activating and tolerizing T cells. DC have previouslybeen detected in rat meninges and choroid plexus. Hypothesizing that DC are involved in inflammation associated withcerebral ischemia, we investigated DC in the brain of Sprague-Dawley rats after permanent middle cerebral arteryocclusion (pMCAO) versus sham operation.Methods-All experimental rats (n 24) had the right MCA permanently occluded by inserting a nylon monofilamentthrough the right external carotid artery. Immunohistochemistry was used to detect DC (OX62), microglia/macrophages (OX42) that developed into DC, and activated DC expressing major histocompatibility complex class II (OX6) in the brain hemispheres at 1 hour to 6 days after pMCAO or sham operation.Results—Levels of DC were elevated at 1 hour in the ischemic versus sham hemispheres (P 0.001) and ischemic versusnonischemic hemispheres (P 0.001). Activated DC expressing major histocompatibility complex class II(OX62 OX6 ) were still elevated at 6 days after pMCAO in the ischemic versus nonischemic hemispheres (P 0.01).The area of brain lesion correlated with numbers of OX62 DC per 100-mm2 brain tissue section (r 0.79; P 0.0001). Conclusions-Increased levels of DC inthe brain after pMCAO and correlation between DC numbers and brain lesion areaindicate a role for DC in cerebral ischemia. This observation could constitute a basis for further studies on the role ofDC in inflammation related to cerebral ischemia.