Improving the sensitivity of myelin oligodendrocyte glycoprotein-antibody testing: exclusive or predominant MOG-IgG3 seropositivity-a potential diagnostic pitfall in patients with MOG-EM/MOGAD.

BACKGROUND: Myelin oligodendrocyte glycoprotein antibody-associated encephalomyelitis (MOG-EM; also termed MOG antibody-associated disease, MOGAD) is the most important differential diagnosis of both multiple sclerosis and neuromyelitis optica spectrum disorders. A recent proposal for new diagnostic criteria for MOG-EM/MOGAD explicitly recommends the use of immunoglobulin G subclass 1 (IgG1)- or IgG crystallizable fragment (Fc) region-specific assays and allows the use of heavy-and-light-chain-(H+L) specific assays for detecting MOG-IgG. By contrast, the utility of MOG-IgG3-specific testing has not been systematically evaluated. OBJECTIVE: To assess whether the use of MOG-IgG3-specific testing can improve the sensitivity of MOG-IgG testing. METHODS: Re-testing of 22 patients with a definite diagnosis of MOG-EM/MOGAD and clearly positive MOG-IgG status initially but negative or equivocal results in H+L- or Fc-specific routine assays later in the disease course (i.e. patients with spontaneous or treatment-driven seroreversion). RESULTS: In accordance with previous studies that had used MOG-IgG1-specific assays, IgG subclass-specific testing yielded a higher sensitivity than testing by non-subclass-specific assays. Using subclass-specific secondary antibodies, 26/27 supposedly seroreverted samples were still clearly positive for MOG-IgG, with MOG-IgG1 being the most frequently detected subclass (25/27 [93%] samples). However, also MOG-IgG3 was detected in 14/27 (52%) samples (from 12/22 [55%] patients). Most strikingly, MOG-IgG3 was the predominant subclass in 8/27 (30%) samples (from 7/22 [32%] patients), with no unequivocal MOG-IgG1 signal in 2 and only a very weak concomitant MOG-IgG1 signal in the other six samples. By contrast, no significant MOG-IgG3 reactivity was seen in 60 control samples (from 42 healthy individuals and 18 patients with MS). Of note, MOG-IgG3 was also detected in the only patient in our cohort previously diagnosed with MOG-IgA+/IgG- MOG-EM/MOGAD, a recently described new disease subvariant. MOG-IgA and MOG-IgM were negative in all other patients tested. CONCLUSIONS: In some patients with MOG-EM/MOGAD, MOG-IgG is either exclusively or predominantly MOG-IgG3. Thus, the use of IgG1-specific assays might only partly overcome the current limitations of MOG-IgG testing and-just like H+L- and Fcγ-specific testing-might overlook some genuinely seropositive patients. This would have potentially significant consequences for the management of patients with MOG-EM/MOGAD. Given that IgG3 chiefly detects proteins and is a strong activator of complement and other effector mechanisms, MOG-IgG3 may be involved in the immunopathogenesis of MOG-EM/MOGAD. Studies on the frequency and dynamics as well as the clinical and therapeutic significance of MOG-IgG3 seropositivity are warranted.

[Atypical monoclonal plasma cell hyperplasia. Infiltration of ZNS]. / Atypische monoklonale Plasmazellhyperplasie. Infiltration des ZNS.

Atypical monoclonal plasma cell hyperplasia is extremely rare in the central nervous system without involvement of bone or other systemic disease. This neuropathological entity was first described by Weidenheim and colleagues in 1989. It is considered an inflammatory pseudotumor that can evolve into malignant myeloma. We report on an atypical monoclonal plasma cell hyperplasia with bilateral occipital and cerebellar involvement in a 38-year-old woman. The diagnosis was confirmed by brain biopsy immunohistochemical and molecular tests.

Neuregulin-induced association of Sos Ras exchange protein with HER2(erbB2)/HER3(erbB3) receptor complexes in Schwann cells through a specific Grb2-HER2(erbB2) interaction.

Neuregulins are members of the epidermal growth factor family of related ligands that exert pleotropic effects during development on the Schwann cell lineage. The receptor complex activated by neuregulin in Schwann cells consists of HER2 (erbB2) and HER3 (erbB3). The intracellular signaling events that follow activation of the HER2/HER3 receptor complex in primary cells, and in particular in Schwann cells, are poorly understood. We have found that neuregulin induces the rapid association of the guanine nucleotide exchange factor SOS with the HER2/HER3 receptor complex. The association of SOS with the HER2/HER3 receptor complex is preceded by the rapid association of Grb2 with the HER2/HER3 receptor complex. Far Western analysis indicates that Grb2 and SOS bind exclusively to HER2 in the HER2/HER3 receptor complex.

Neuregulin: an oligodendrocyte growth factor absent in active multiple sclerosis lesions.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) which results in demyelination and axonal injury. Conventional therapy for MS is immune suppression in the absence of agents that promote neural and glial survival or remyelination. Neuregulins are a family of ligands that exert trophic effects on both neurons and glia. Using mice bearing a null mutation in the neuregulin gene, here we demonstrate that neuregulins are necessary for the normal development of oligodendrocytes. In addition, neuregulins are produced in the normal human CNS by astrocytes as well as neurons. Astrocyte-derived neuregulin is functionally active in bioassays and exists in secreted and membrane-associated beta-isoforms. In active and chronic active MS lesions, however, the expression of astrocyte neuregulin is dramatically reduced. The absence of neuregulin in active MS lesions may contribute to the paucity of remyelination in MS.

Axonal neuregulin signals cells of the oligodendrocyte lineage through activation of HER4 and Schwann cells through HER2 and HER3.

We are interested in the signaling between axons and glia that leads to myelination and maintenance of the myelin internode, and we have focused on the role of neuregulins and their receptors. Neuregulins are a family of ligands that includes heregulin, neu differentiation factor, glial growth factor, and the acetylcholine receptor-inducing activity. Three signal transducing transmembrane receptors for neuregulins, which bear significant homology to the EGF receptor, are currently known: HER2 (erbB2), HER3 (erbB3), and HER4 (erbB4). We have found that oligodendrocite-type II astrocyte (O2A) progenitor cells and mature oligodendrocytes express HER2 and HER4 but no HER3. Schwann cells express HER2 and HER3 but little HER4. In O2A progenitor cells and oligodendrocytes, recombinant neuregulin induces the rapid tyrosine phosphorylation of only HER4. HER2 is not phosphorylated in cells of the oligodendrocyte lineage, but a physical interaction between HER2 and HER4 was detected in coimmunoprecipitation experiments. In Schwann cells, neuregulin induces the phosphorylation of both HER2 and HER3. Coimmunoprecipitation experiments indicate that receptor activation in Schwann cells results in the formation of HER2:HER3 heterodimers. Neuregulin localized immunocytochemically was present on neurites of cultured dorsal root ganglion neurons, and it was released into the medium in a form that promoted receptor tyrosine phosphorylation. Neuregulins therefore meet important criteria expected of molecules involved in axonal-glial signaling. The use of unique neuregulin receptor combinations in oligodendrocytes and Schwann cells likely results in recruitment of different signaling pathways and thus provides a basis for different biological responses.