The critical role of IL-12p40 in initiating, enhancing, and perpetuating pathogenic events in murine experimental autoimmune neuritis.

Interleukin 12 (IL-12) is a proinflammatory cytokine with important immunoregulatory activities and is critical in determining the differentiation and generation of Th1 cells. For the present study, we investigated the role of endogenous IL-12 in the pathogenesis of experimental autoimmune neuritis (EAN), which is a CD4+ T-cell mediated autoimmune inflammatory disease of the peripheral nervous system. EAN is used as an animal model for Guillain-Barré syndrome of humans. Here, EAN was established in IL-12 p40 deficient mutant (IL-12-/-) C57BL/6 mice by immunization with P0 peptide 180-199, a purified component of peripheral nerve myelin, and Freund's complete adjuvant. In these IL-12-/- mice the onset of clinical disease was delayed, and the incidence and severity of EAN were significantly reduced compared to that in wild-type mice.The former group's clinical manifestations were associated with less P0-peptide 180-199 induced secretion of interferon-gamma (IFN-gamma) by splenocytes in vitro and low production of anti-P0-peptide 180-199 IgG2b antibodies in serum. Fewer IFN-gamma and TNF-alpha producing cells, but more cells secreting IL-4, were found in sciatic nerve sections from IL-12-/- mice, consistent with impaired Th1 functions and response. However, the IL-12 deficiency appeared not to affect P0 peptide 180-199-specific T-cell proliferation. These results indicate that IL-12 has a major role in the initiation, enhancement and perpetuation of pathogenic events in EAN by promoting a Th1 cell-mediated immune response and suppressing the Th2 response. This information augments consideration of IL-12 as a therapeutic target in Guillain-Barré syndrome and other T-cell-mediated autoimmune diseases.

Initiation and development of experimental autoimmune neuritis in Lewis rats is independent of the cytotoxic capacity of NKR-P1A+ cells.

Natural killer (NK) cells are implicated in T cell-mediated autoimmune diseases. Experimental autoimmune neuritis (EAN) is a CD4+ T cell-mediated animal model of the Guillain-Barré syndrome in human. The role of NK cells in the initiation and development of EAN remains unclear. In the present study, we demonstrate that anti-NKR-P1A monoclonal antibody (mAb) treatment in vivo did not affect the initiation and development of clinical EAN in Lewis rats induced by immunization with peripheral nerve myelin P0 protein peptide 180-199 and Freund's complete adjuvant, as well as the proportion of NKR-P1A+ cells (including NK cells and NKT cells) in the spleen. Furthermore, inflammatory cell infiltrations and demyelination in the peripheral nervous system (PNS) and in vitro P0 peptide 180-199-specific splenocyte proliferation were not different in anti-NKR-P1A mAb-treated rats compared to the control antibody-treated rats. The cytotoxic activity of NKR-P1A+ cells, determined by NK cell-sensitive K562 cells as target cells, decreased markedly in anti-NKR-P1A mAb-treated rats, suggesting that decrease of the cytotoxic activities of NKR-P1A+ cells is not sufficient to alter clinical EAN, although NKR-P1A+ cells may participate in the pathogenesis of T cell-mediated autoimmune diseases, such as EAN, by the mechanisms that involve the release of cytokines.

P0 glycoprotein peptides 56-71 and 180-199 dose-dependently induce acute and chronic experimental autoimmune neuritis in Lewis rats associated with epitope spreading.

Two synthetic peripheral nerve myelin P0 protein peptides, an immunodominant (amino acids 180-199) and a cryptic (amino acids 56-71) one, induced an acute or chronic course of experimental autoimmune neuritis (EAN) in Lewis rats, when given at low dose (50-100 microg/rat) or high dose (250 microg/rat), respectively. Corresponding to the different clinical course, pathological changes and immune responses were found: (1) Onset of clinical signs of P0 peptide 56-71 (P0 56-71) induced EAN was 1-3 days later than in P0 peptide 180-199 (P0 180-199) induced EAN at all immunizing doses, whereas the peak of the disease occurred at a similar time point post immunization (p.i.), i.e. at days 14-16 p.i. in P0 56-71 induced EAN and at day 16 p.i. in P0 180-199 induced EAN. (2) Intramolecular epitope spreading as assessed by delayed type hypersensitivity response occurred in P0 56-71 induced EAN at both low and high antigen doses and in P0 180-199 induced EAN at high antigen dose (250 microg/rat) only. (3) P0 180-199 stimulated higher levels of interferon-gamma production in P0 180-199 induced EAN than in P0 56-71 induced EAN and vice versa. (4) Histopathologic evaluation revealed a similar grade of mononuclear cell infiltration in the sciatic nerves of both types of EAN, but more severe demyelination was found in P0 180-199 induced EAN compared to P0 56-71 induced EAN. The results support the hypothesis that high dose autoantigen immunization induces extensive determinant spreading and chronic course of autoimmune diseases.

Antigen-specific immunosuppression: nasal tolerance to P0 protein peptides for the prevention and treatment of experimental autoimmune neuritis in Lewis rats.

Experimental autoimmune neuritis (EAN) is an autoimmune inflammatory demyelinating disease of the peripheral nervous system (PNS), and represents an animal model of the human Guillain-Barré syndrome (GBS). In this study, we report that nasal administration of the neuritogenic peptide 180-199 and of the cryptic peptide 56-71 of the rat neuritogenic P0 protein of peripheral nerve myelin prevents EAN and attenuates ongoing EAN. Both peptides effectively decreased the severity and shortened clinical EAN. Both a prophylactic and a therapeutic approach proved to be beneficial. These effects were associated with T and B cells hyporesponsiveness to the peptide antigens, reflected by downregulated Th1 cell responses (interferon-gamma secretion) and macrophage function, whereas Th2 cell responses (IL-4 secretion) and transforming growth factor-beta mRNA expression were upregulated.

T helper type 2 like cytokine responses to peptides from P0 and P2 myelin proteins during the recovery phase of Guillain-Barré syndrome.

T-lymphocytes are probably involved in the pathogenesis of Guillain-Barré syndrome (GBS). T-helper-1 (Th1) cytokines activate macrophages and induce a delayed type hypersensitivity (DTH) inflammatory response, consistent with the morphology of the demyelination in GBS. Th2 cytokines encourage antibody production and downregulate Th1 responses. To study the Th1/Th2 cytokines in relation to the clinical course of GBS an ELISPOT method for determination of single cells secreting interferon-gamma, IFN-gamma (Th1) or interleukin-4, IL-4 (Th2) was used. We serially investigated antigen-induced cytokine secretion from circulating T-cells stimulated with human peptides from the P0 and P2 proteins in seven patients and compared to results from seven serially investigated healthy controls. Most patients (five of seven) showed IL-4 responses during the plateau- or recovery-phase as compared to controls. One patient with a prolonged disease course, on the other hand, had an IFN-gamma dominated reactivity. We suggest that the IL-4 responses are beneficial in GBS, and may have a role in terminating the disease process in this self-limiting inflammatory disease.