Antibody association with a novel model for primary progressive multiple sclerosis: induction of relapsing-remitting and progressive forms of EAE in H2s mouse strains

Monoclonal MOG-reactive autoantibody from progressive EAE has the characteristics of a natural antibody

A.SW mice sensitized with myelin oligodendrocyte glycoprotein (MOG)92-106 is an animal model for progressive multiple sclerosis (MS). We isolated MOG-reactive monoclonal antibodies that were immunoglobulin (Ig)M and polyreactive, similar to natural autoantibodies. Upon analysis of the variable (V) light chains and the diversity (D) and joining (J) regions of V heavy chains, we found they were identical to germ line Vkappa19/28, Jkappa5, DFL16.1e and JH4, respectively. The sequence of the VH region had 99.7% and 100% identity at the nucleotide and amino acid levels, respectively, compared with the germ line encoded antibody, P3, of the Q52 family. Although A strain mice have been reported to have an insertion in BAFF-R, the receptor for BAFF (B cell activation factor from the tumor necrosis factor family), which could explain our results, A.SW mice have no mutations in BAFF-R.

Massive apoptosis in lymphoid organs in animal models for primary and secondary progressive multiple sclerosis

The mechanism(s) responsible for generating the different forms of multiple sclerosis, primary progressive (PP) and secondary progressive (SP) versus relapsing-remitting (RR), is not well understood. Using myelin oligodendrocyte glycoprotein (MOG)(92-106), we have established animal models that mimic the different types of multiple sclerosis. A.SW mice develop PP or SP-experimental allergic encephalomyelitis (EAE) with large areas of demyelination and high titers of MOG antibody whereas SJL/J mice develop RR-EAE with perivascular T cells and mild demyelination. In A.SW progressive EAE, we found atrophy of the thymus, spleen, and lymph nodes with depletion of T and B cells and massive apoptosis, as demonstrated by immunohistochemistry, terminal dUTP nick-end labeling, and DNA agarose gel electrophoresis. To test whether lymphoid apoptosis itself contributes to disease progression, we injected SJL/J mice with apoptotic thymocytes. Injection of apoptotic cells resulted in greater than 20% of mice developing SP-EAE with ataxia. SJL/J mice with SP-EAE had large areas of demyelination, high MOG antibody titers and atrophic lymphoid organs. Spleen cells from mice with progressive EAE produced less interferon-gamma than those from RR-EAE when stimulated with mitogen. We suggest that induction of lymphoid apoptosis alters the balance of Th1 versus Th2 immune responses and increases MOG antibody production, leading to exacerbation of demyelination and subsequent disease progression.

Immunology of multiple sclerosis

Multiple sclerosis (MS) develops in young adults with a complex predisposing genetic trait and probably requires an inciting environmental insult such as a viral infection to trigger the disease. The activation of CD4+ autoreactive T cells and their differentiation into a Th1 phenotype are a crucial events in the initial steps, and these cells are probably also important players in the long-term evolution of the disease. Damage of the target tissue, the central nervous system, is, however, most likely mediated by other components of the immune system, such as antibodies, complement, CD8+ T cells, and factors produced by innate immune cells. Perturbations in immunomodulatory networks that include Th2 cells, regulatory CD4+ T cells, NK cells, and others may in part be responsible for the relapsing-remitting or chronic progressive nature of the disease. However, an important paradigmatic shift in the study of MS has occurred in the past decade. It is now clear that MS is not just a disease of the immune system, but that factors contributed by the central nervous system are equally important and must be considered in the future.

Primary progressive multiple sclerosis

PURPOSE OF REVIEW

The present article reviews the currently ongoing scientific debate on the specific characteristics of primary progressive multiple sclerosis.

RECENT FINDINGS

The most important observations come from the studies using magnetic resonance imaging showing involvement of the normal-appearing brain tissue and also from the clinical and magnetic-resonance-imaging descriptions in longitudinal studies.

SUMMARY

Progress in the diagnosis of primary progressive multiple sclerosis has been made. Long- and short-term natural history are now better known, which will allow the designing of clinical trials in the near future. Magnetic-resonance-imaging studies have demonstrated damage of the normal-appearing brain tissue, which may explain in part the apparent clinical and radiological paradox, common to all clinical forms of multiple sclerosis but perhaps more evident in the primary progressive form. Preliminary results from exploratory trials seem to indicate that these patients should no longer be excluded from therapeutic trials.

Converting relapsing remitting to secondary progressive experimental allergic encephalomyelitis (EAE) by ultraviolet B irradiation

We induced experimental allergic encephalomyelitis (EAE) in SJL/J mice, an animal model for multiple sclerosis (MS), using myelin oligodendrocyte glycoprotein (MOG)(92-106) peptide, following ultraviolet (UV) irradiation. While all control mice developed relapsing-remitting (RR)-EAE, UV irradiation induced secondary progressive (SP)-EAE in some of the mice. Although mild demyelination was observed with T cell infiltration in RR-EAE, large demyelinating lesions developed in SP-EAE with massive macrophage and neutrophil infiltration and immunoglobulin deposition, but with little T cell infiltration. UV irradiation induced higher anti-MOG antibody responses. In SP-EAE, lymphoproliferative responses and interferon-gamma production were decreased without alteration of interleukin-4.

Sex differences in experimental autoimmune encephalomyelitis in multiple murine strains

Multiple sclerosis (MS) is more prevalent in women than men. We evaluated seven different mouse strains commonly used in the study of autoimmune diseases, for sex differences in the disease course of experimental autoimmune encephalomyelitis (EAE). Greater severity of EAE was observed in the female SJL immunized with two different peptides of myelin proteolipid protein (PLP) and myelin oligodendrocyte glycoprotein (MOG) as well as in the female ASW relative to males. Female NZW mice showed a greater incidence of EAE than males. However, male B10.PL and PL/J mice showed more severe disease than females. No sex differences were noted in the C57BL/6 or NOD strains.

T cell and antibody responses in remitting–relapsing experimental autoimmune encephalomyelitis in (C57BL/6×SJL) F1 mice

To characterize T cell and antibody responses in remitting-relapsing experimental autoimmune encephalomyelitis (RR-EAE), we compared myelin oligodendrocyte glycoprotein (MOG)-induced RR-EAE in C57BL/6 (B6) x SJL (F1) mice and chronic-progressive EAE (CP-EAE) in B6 mice at week 8 p.i. when clinical scores were comparable. Although these two strains exhibited similar inflammation/demyelination pattern and MOG-induced T cell responses, RR-EAE mice produced significantly higher levels of anti-MOG IgG1/IgG2a antibodies. Further, lymphocytes of RR-EAE mice proliferated vigorously to the secondary epitope myelin basic protein (MBP) 1-11. These results support a potential involvement of anti-MOG antibodies and epitope spreading in T cell responses in the development of MOG-induced RR-EAE model.

Distinct roles for IP-10/CXCL10 in three animal models, Theiler's virus infection, EAE, and MHV infection, for multiple sclerosis: implication of differing roles for IP-10

Theiler's murine encephalomyelitis virus (TMEV) causes demyelination with inflammation of the central nervous system (CNS) in mice and is used as an animal model for multiple sclerosis (MS). Interferon-gamma inducible protein-10 kDa (IP-10) is a CXC chemokine and a chemoattractant for CXCR3+ T cells. IP-10 mRNA is expressed in the CNS during TMEV infection. However, administration of anti-IP-10 serum caused no difference in clinical signs, inflammation, demyelination, virus persistence or anti-virus antibody response in TMEV infection, while levels of virus specific and autoreactive lymphoproliferation increased. This likely reflects a difference in the pathogenesis of TMEV infection from that of two other animal models for MS, mouse hepatitis virus infection and experimental allergic encephalomyelitis (EAE), where blocking of IP-10 resulted in clinical and histological improvement with suppression of antigen specific lymphoproliferation. In this review, we compare and contrast the roles of IP-10 between the three animal models for MS, and discuss the relevance to MS patients with different clinical courses.

Axonal injury heralds virus-induced demyelination

Axonal pathology has been highlighted as a cause of neurological disability in multiple sclerosis. The Daniels (DA) strain of Theiler's murine encephalomyelitis virus infects the gray matter of the central nervous system of mice during the acute phase and persistently infects the white matter of the spinal cord during the chronic phase, leading to demyelination. This experimental infection has been used as an animal model for multiple sclerosis. The GDVII strain causes an acute fatal polioencephalomyelitis without demyelination. Injured axons were detected in normal appearing white matter at 1 week after infection with DA virus by immunohistochemistry using antibodies specific for neurofilament protein. The number of damaged axons increased throughout time. By 2 and 3 weeks after infection, injured axons were accompanied by parenchymal infiltration of Ricinus communis agglutinin I(+) microglia/macrophages, but never associated with perivascular T-cell infiltration or obvious demyelination until the chronic phase. GDVII virus infection resulted in severe axonal injury in normal appearing white matter at 1 week after infection, without the presence of macrophages, T cells, or viral antigen-positive cells. The distribution of axonal injury observed during the early phase corresponded to regions where subsequent demyelination occurs during the chronic phase. The results suggest that axonal injury might herald or trigger demyelination.

T- and B-cell responses to myelin oligodendrocyte glycoprotein in experimental autoimmune encephalomyelitis and multiple sclerosis

The identification of myelin oligodendrocyte glycoprotein (MOG) as a target for autoantibody-mediated demyelination in experimental autoimmune encephalomyelitis (EAE) resulted in the re-evaluation of the role of B cell responses to myelin autoantigens in the immunopathogenesis of multiple sclerosis. MOG is a central nervous system specific myelin glycoprotein that is expressed preferentially on the outermost surface of the myelin sheath. Although MOG is only a minor component of CNS myelin it is highly immunogenic, inducing severe EAE in both rodents and primates. In rat and marmoset models of MOG-induced EAE demyelination is antibody-dependent and reproduces the immunopathology seen in many cases of MS. In contrast, in mice inflammation in the CNS can result in demyelination in the absence of a MOG-specific B cell response, although if present this will enhance disease severity and demyelination. Clinical studies indicate that autoimmune responses to MOG are enhanced in many CNS diseases and implicate MOG-specific B cell responses in the immunopathogenesis of multiple sclerosis. This review provides a summary of our current understanding of MOG as a target autoantigen in EAE and MS, and addresses the crucial question as to how immune tolerance to MOG may be maintained in the healthy individual.

Cytokine and IL-12 receptor mRNA discriminate between different clinical subtypes in multiple sclerosis

Little is known about the involvement of cytokines in the pathogenesis of primary progressive (PP) multiple sclerosis (MS). We evaluated in this cross-sectional study whether IL-18, IL-12p35, IL-12p40, TNF-alpha, IFN-gamma, IL-10, IL-4, TGF-beta, IL-12Rbeta1, and IL-12Rbeta2 mRNA expression in unstimulated white blood cells showed significant differences between relapsing-remitting (RR), secondary progressive (SP) and PP MS patients, and healthy controls. All clinical subtypes showed unique mRNA expression patterns as compared to the controls. Both RR and SP patients displayed increased levels of IL-12p40, IL-18, and TGF-beta mRNA compared to controls, whereas PP patients showed only increased IL-18 mRNA levels. Both in PP and SP patients, IFN-gamma and IL-10 mRNA were decreased compared to RR patients and controls. PP patients were unique in that they showed decreased IL-12Rbeta1 mRNA. In conclusion, our data show that the assessment of cytokine (receptor) mRNA profiles is useful to discriminate between the different clinical subtypes and suggest that different cytokines are involved in the pathogenesis of PP MS as compared to RR and SP MS.

Viruses can silently prime for and trigger central nervous system autoimmune disease

Although many viruses have been isolated from patients with multiple sclerosis (MS), as yet, no one agent has been demonstrated to cause MS. In contrast, epidemiological data indicate that viral infections are associated with exacerbations of MS. Here, we present data showing that virus infections can subclinically prime animals for central nervous system (CNS) autoimmune disease; long after the original infection has been eradicated, a nonspecific challenge/infection can trigger an exacerbation. The priming infectious agent must show molecular mimicry with self-CNS antigens such as glial fibrillary acidic protein (GFAP), myelin associated glycoprotein (MAG) or myelin proteolipid protein (PLP). The subsequent challenge, however, may be nonspecific; complete Freund's adjuvant (CFA), or infection with a recombinant vaccinia virus encoding an irrelevant protein, could trigger CNS disease. In the CNS, we could detect a mononuclear cell infiltration, but no demyelination was found. However, if the pathogenesis of MS is similar to that of this novel animal model for CNS autoimmune disease, our findings could help explain why exacerbations of MS are often associated with a variety of different viral infections.

Immune responses against the myelin/oligodendrocyte glycoprotein in experimental autoimmune demyelination

Myelin/oligodendrocyte glycoprotein (MOG) is a surface-exposed antigen of myelin and an important target for autoimmune responses which mediate inflammatory demyelination in the central nervous system. Experimentally, MOG induces strong pathogenic T cell responses in many strains of laboratory animals. Immunological studies in humans also identify MOG as a surprisingly prevalent antigenic molecule among the myelin proteins. In addition, the encephalitogenic properties of MOG are linked to the induction of antibody responses which have been demonstrated to directly promote central nervous system demyelination, a hallmark neuropathological feature in disorders such as human multiple sclerosis. Factors responsible for autoimmunity to MOG likely include genetic influences as well as other mechanisms, which are the subject of intense investigation. This article reviews experimental data currently available on specificity and pathogenic roles of T cell and antibody responses against MOG, which have implications relevant to multiple sclerosis and related disorders.