Inhibition of experimental autoimmune encephalomyelitis in Lewis rats by nasal administration of encephalitogenic MBP peptides: synergistic effects of MBP 68-86 and 87-99

Induction of mucosal tolerance by inhalation of soluble peptides withdefined T cell epitopes is receiving much attention as a means ofspecifically down-regulating pathogenic T cell reactivities in autoimmuneand allergic disorders. Experimental autoimmune encephalomyelitis (EAE)induced in the Lewis rat by immunization with myelin basic protein (MBP)and Freund's adjuvant (CFA) is mediated by CD4+ T cells specific for theMBP amino acid sequences 68-86 and 87-99. To further define the principlesof nasal tolerance induction, we generated three different MBP peptides(MBP 68-86, 87-99 and the non- encephalitogenic peptide 110-128), andevaluated whether their nasal administration on day -11, -10, -9, -8 and -7prior to immunization with guinea pig MBP (gp-MBP) + CFA confers protectionto Lewis rat EAE. Protection was achieved with the encephalitogenicpeptides MBP 68-86 and 87-99, MBP 68-86 being more potent, but not with MBP110-128. Neither MBP 68-86 nor 87-99 at doses used conferred completeprotection to gp-MBP-induced EAE. In contrast, nasal administration of amixture of MBP 68-86 and 87-99 completely blocked gp-MBP-induced EAE evenat lower dosage compared to that being used for individual peptides. Ratstolerized with MBP 68-86 + 87-99 nasally showed decreased T cell responsesto MBP reflected by lymphocyte proliferation and IFN-gamma ELISPOT assays.Rats tolerized with MBP 68-86 + 87-99 also had abrogated MBP-reactiveIFN-gamma and tumor necrosis factor-alpha mRNA expression in lymph nodecells compared to rats receiving MBP 110-128 nasally, while similar lowlevels of MBP-reactive transforming growth factor-beta and IL-4 mRNAexpressing cells were observed in the two groups. Nasal administration ofMBP 68-86 + 87-99 only slightly inhibited guinea pig spinal cordhomogenate-induced EAE, and passive transfer of spleen mononuclear cellsfrom MBP 68-86 + 87-99-tolerized rats did not protect naive rats from EAE.Finally, we show that nasal administration of MBP 68-86 + 87-99 can reverseongoing EAE induced with gp-MBP, although higher doses are requiredcompared to the dosage needed for prevention. In conclusion, nasaladministration of encephalitogenic MBP peptides can induce antigen-specificT cell tolerance and confer incomplete protection to gp-MBP-induced EAE,and MBP 68-86 and 87-99 have synergistic effects. Non-regulatory mechanismsare proposed to be responsible for tolerance development after nasalpeptide administration.