Modulation of experimental T cell autoimmunity in the nervous system with emphasis on nasal tolerance

Abstract

Experimental autoimmune neuritis (EAN) and encephalomyelitis (EAE) are animal models of Guillian-Barré syndrome (GBS) and multiple sclerosis (MS), representing human demyelinating diseases of the peripheral nervous system (PNS) and central nervous system (CNS), respectively. CD4+ T cells recognizing myelin antigens and producing cytokines play central roles in the pathogenesis of both EAN and EAE and perhaps of GBS and MS. Current treatments of GBS and MS lack specificity and have significant adverse effects, imposing limits on their use. More selective or specific immunotherapies are searched for. In this study, we tested different therapeutic strategies in EAN and EAE. Subcutaneous (s.c.) injection of IL-10, a major Th2 cytokine, delayed onset, shortened duration and suppressed severity of clinical EAN. PNS myelin antigen P2 protein-reactive IFN-r secreting as well as IFN-γ, TNF-α, IL-1ß and IL-6 but not IL-4mRNA expressing lymph node cells were reduced by IL-10 treatment compared to untreated control EAN rats, consistent with a down-regulation of P2 specific Th1 responses in IL-10 treated rats. S.c. injection of Linomide (LS-2616, quinoline-3-carboxamide) prevented onset and suppressed ongoing EAN. Macrophages from EAN rats exposed to Linomide in vitro and in vivo showed reduced IFN-γ- and lipopolysacchande (LPS)-induced IL-1ß,TNF-α and IL-6 mRNA expression and reduced LPS-induced nitric oxide production by macrophages. Linomide, however, did not affect macrophage death and release of lactate dehydrogenase. Pretreatment with bovine myelin basic protein (MBP) by the nasal route dose-dependently prevented the development of actively induced protracted-relapsing EAE in DA rats.This protection was associated with reduced numbers of MBP-reactive IFN-γ secreting Th1-like splenocytes, decreased levels of anti-MBP IgG2b but elevated IgG1 antibody levels in serum. Nasal pretreatment with MBP also reduced numbers of MBP-reactiveTNF-α mRNA expressing cells both in CNS and spleen, while numbers of IL-4 and/orTGF-ß mRNA expressing cells were augmented. However, when the same or a higher dose of MBP was administered nasally to treat ongoing EAE, the severity of the acute phase of disease was enhanced, in conjunction with augmented levels of MBP-reactiveIFN-γ secreting Th1-like splenocytes. Actively induced EAE in Lewis rats with guinea pig (gp) MBP was also prevented by pretreatment nasally with gp-MBP or the encephalitogenic gp-MBP peptides 68-86+ 87-99, but not with bovine MBP or a non-encephalitogenic gp-MBP peptide 110-128.Lymph node cells from the protected rats showed reduced proliferation, reduced numbers of MBP-reactive IFN-r secreting, and IFN-γ and/or TNF-α mRNA expressing cells. Splenocytes from rats pretreated with a very low dose of gp-MBP but not high dose of gp-MBP or its peptides tolerized rats transferred protection of EAE. Lymph node cells from low dose gp-MBP-tolerized rats had much higher numbers of MBP-reactiveIL-4 mRNA expressing cells compared with control rats or rats tolerized with highdose gp-MBP or its encephalitogenic peptides.

We conclude that (1) s.c. injection of IL-10 can suppress clinical EAN. This suppression is associated with down-regulation of Th1 responses and macrophage functions, and upregulated Th2 responses. (2) Linomide suppresses clinical EAN and may exert its actions in EAN by suppressing certain macrophage functions. (3) Nasal administration of small amounts of antigens is a highly efficient approach in inducing clinically relevant tolerance. The mechanisms of nasal tolerance are either anergy/deletion of antigen-specific T cells or induction of IL-4 and/or TGF-ß related regulatory mechanisms depending on the property and dosage of antigens administered. Immunotherapy via induction of nasal tolerance could be complicated by the differential tolerogenic effects of antigens and the fact that transient activation of T cells may precede nasal tolerance induction. Only those antigens or peptides with high efficacy in inducing nasal tolerance and activating regulatory elements without inducing further activation of autoreactive T cells are candidates for future clinical use.