Time course of IgM antibodies which block anti-myelin basic protein IgG antibodies associated with development of experimental autoimmune encephalomyelitis in rabbits

Evidence for spontaneous regulation of the humoral IgM anti-GM1 autoimmune response by IgG antibodies in multifocal motor neuropathy patients

BACKGROUND AND AIMS

Multifocal motor neuropathy (MMN) is a peripheral nerve disorder characterized by slow progressive distal asymmetric weakness with minimal or no sensory impairment. Currently, a vast evidence supports a direct pathogenic role of IgM anti-GM1 antibodies on disease pathogenesis. Patients with MMN seropositive for GM1-specific IgM antibodies have significantly more weakness, disability and axon loss than patients without these antibodies. During the screening for IgM anti-GM1 antibodies in a cohort of patients with neuropathy we noticed an absence or significant reduction of natural IgM anti-GM1 autoreactivity in some patients with MMN, suggesting a mechanism of self-control of autoreactivity. We aim to understand the lack of natural reactivity against GM1 in MMN patients.

METHODS

The presence of free IgM anti-GM1 reactivity or its complex to blocking IgG was analysed by combining high performance thin layer chromatography-immunostaining, soluble binding inhibition assays, Protein-G or GM1-affinity columns and dot blot assays.

RESULTS

We identified in MMN patients an immunoregulation of IgM anti-GM1 antibodies mediated by IgG immunoglobulins characterized by: (i) lack of natural IgM anti-GM1 autoreactivity as a result of a immunoregulatory IgG-dependent mechanism; (ii) presence of natural and disease-associated IgM anti-GM1/IgG blocking Ab complexes in sera; and (iii) high levels of IgG blocking against natural IgM anti-GM1 antibodies (Abs.

INTERPRETATION

Our observations unmask a spontaneous IgG-dependent mechanism of immunoregulation against IgM anti-GM1 antibodies that could explain, in part, fluctuations in the usually slowly progressive clinical course that characterizes the disease and, at the same time, allows the identification of an autoimmune response against GM1 ganglioside in seronegative patients.

Interaction between Gonadal Steroids and Neuroimmune System in Acute Experimental Autoimmune Encephalomyelitis (EAE) in Wistar Rats

Experimental autoimmune encephalomyelitis (EAE) is an inflammatory disease of the CNS mediated by autoreactive T lymphocytes directed against myelin antigens. Since neuroendocrine-immune dysfunction appears to contribute to the pathogenesis of autoimmune diseases, the present work was designed to study the effect of changes in the endocrine system on the development of acute EAE and the immune response against myelin basic protein (MBP). Intact and sham males and intact female Wistar rats showed the most severe clinical symptoms (acute period) 12-14 days post-inoculation (dpi). Then, they began gradually to recover, regaining the total ability to walk by 15-17 dpi. Male Wistar rats with altered levels of gonadal hormones by surgical castration showed an onset of the symptoms retarded 2-3 days with respect to the other EAE groups, showing neuropathological symptoms up to 27-28 dpi, and remaining with lower body weight even at 40 dpi. The castrated animals exhibited a specific delay in MBP-stimulated DTH reactivity that correlates with the delay in the onset of the clinical symptoms. Also significant lymphocyte proliferation to MBP was still present at 35 dpi that was absent in the sham group. The distribution of the IgG subclasses indicated that at 35 dpi castrated animals have a higher IgG2b/IgG1 ratio (35.1) in comparison to that presented by sham rats (4.8). Considering that at this time the castrated animals were not completely recuperated, these results could indicate an ongoing inflammatory immune response associated with Th1 activity in these animals. Also castrated animals developed antibodies to a diversity of MBP epitopes in comparison to sham rats, which presented a dominance of antibodies to MBP peptide p96-128. These results indicate that sex hormones levels regulate cell-mediated immunity and the specificity of anti-MBP antibodies related to the induction and development of acute EAE.

Antibodies which block anti-myelin basic protein antibodies associated with development of experimental autoimmune encephalomyelitis in Wistar rats

OBJECTIVE

In sera from normal rats and from rats injected with whole myelin in complete Freund adjuvant to induce EAE we study the presence of antibodies capable to inhibit the reactivity of autoantibodies directed to myelin basic protein (MBP).

METHODS

Sera from rats that developed or not clinical signs of EAE were obtained previously to immunization, at acute stage of the disease and when the animals were completely recuperated, and chromatographied on a protein G-Sepharose column to obtain the retained (IgG) fractions. Then these fractions were depleted of anti-MBP reactivity by affinity chromatography and the ability of these depleted sera to block the reactivity of anti-MBP IgG antibodies was analyzed by an immunoblot technique.

RESULTS

IgG fractions from preimmune sera inhibited the anti-MBP IgG reactivity associated to EAE. The analysis of sick EAE animals showed that the inhibitory activity faded away with the onset of the clinical signs but returned at its maximum value during the spontaneous remission. Animals that never developed clinical EAE did not show changes in the level of inhibitory activity that was similar to that observed in the preimmune sera.

CONCLUSIONS

The presence of IgG antibodies blocking the anti-MBP IgG reactivity correlates with the development of the clinical signs of EAE.

Age-related changes in the development of experimental autoimmune encephalomyelitis

A prominent feature of multiple sclerosis is its high incidence of onset in the third decade of life and its relatively rare onset in persons older than 50 years. In order to study age-related restriction of clinical expression, a comparative biochemical, immunological and histological study was undertaken during development of experimental autoimmune encephalomyelitis (EAE) in young (7 weeks) and middle-aged (15 months) Wistar rats. Young rats showed characteristic clinical signs 12-16 days postinduction, and then they spontaneously recuperated. In middle-aged rats, the incidence of clinical signs was significantly reduced, with a later onset of the disease. Similar biochemical and histological alterations were detected in both age groups, but they were present in a later stage in middle-aged animals. However, cellular and humoral immune responses to myelin basic protein (MBP) were observed 15 days postinduction in all EAE animals. The study of anti-MBP IgG isotype pattern in 7-week-old animals indicated a predominant Th1-type immune response during the acute stage of EAE, with antibodies predominantly recognizing the MBP 96-128 peptide. In contrast, 15-month-old animals showed a less prominent Th1 response, without any epitope dominance. The changes in immune function found in middle-aged animals may account for the different susceptibility and expression of EAE, and may also be relevant to the different clinical expression observed in multiple sclerosis with maturation.