Polyclonal IgM and IgA block in vitro complement deposition mediated by anti-ganglioside antibodies in autoimmune neuropathies

Hyperbaric oxygen therapy improves recovery at acute motor axonal neuropathy case

Acute motor axonal neuropathy (AMAN) is a rare immune-mediated disorder characterized by acute flaccid paralysis with elevated levels of GM1 antibodies. It is also known as a subtype of the Guillain-Barre syndrome (GBS) and develops since antigen s serve as antibodies in the spinal cord. We report a case diagnosed as AMAN with symptoms of ascending limb symmetrical weakness. A neurological examination revealed a flaccid paralysis with multiple cranial nerve palsies. Electromyography showed an axonal type of GBS. The patient refused bone marrow fluid aspiration. Intravenous immunoglobulin was administered at the high care unit. Unfortunately, despite the standard therapy, an optimal recovery was not obtained. Hyperbaric oxygen (HBO) therapy has been known to be common in illnesses and some clinical diseases. Although it has not been indicated for peripheral neuropathy, a remarkable recovery was soon visible in the HBO-treated AMAN case. The HBO mechanisms involved here are anti-inflammation and immunomodulation.

Therapeutic Monoclonal Antibody Therapies in Chronic Autoimmune Demyelinating Neuropathies

Autoimmune diseases of the peripheral nervous system have so far been treated mainly with exogenous high-dose intravenous immunoglobulins (IVIg), that act through several mechanisms, including neutralization of pathogenic autoantibodies, modulation of lymphocyte activity, interference with antigen presentation, and interaction with Fc receptors, cytokines, and the complement system. Other therapeutic strategies have recently been developed, in part to address the increasing shortage of IVIg, prime among which is the use of B cell depleting monoclonal antibodies, or small molecule inhibitors targeting the B-cell specific kinases. Rituximab, a chimeric monoclonal antibody against CD20 + B lymphocytes, is currently the most used, especially in anti-MAG antibody neuropathy and autoimmune neuropathies with antibodies to nodal/paranodal antigens that are unresponsive to IVIg. After several reports of its efficacy in chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), rituximab is currently under investigation in three Phase 2 trials in CIDP. In addition, the possible role of complement activation in the pathogenesis of chronic autoimmune neuropathies has brought into consideration drugs that can block the complement cascade, such as eculizumab, a monoclonal antibody already assessed in acute polyradiculoneuropathies, and approved for myasthenia gravis. Preliminary data on eculizumab in multifocal motor neuropathy have been published, but randomized controlled studies are pending. Moreover, the neonatal Fc receptor, that recycles IgGs by preventing their lysosome degradation, is an important and attractive pharmacological target. Antibodies against FcRn, which reduce circulating IgG (both pathogenic and non-pathogenic) have been developed. The FcRn blocker efgartigimod, a humanized IgG1-derived Fc fragment, which competitively inhibits the FcRn, has recently been approved for the treatment of myasthenia gravis and is currently under investigation in CIDP. In addition, the anti-human FcRn monoclonal antibody rozanolixizumab is currently being assessed in phase 2 trials in CIDP. However, none of the abovementioned monoclonal antibodies is currently approved for treatment of any immune-mediated neuropathies. While more specific and individualized therapies are being developed, the possibility of combined treatments targeting different pathogenic mechanisms deserves consideration as well.

Acute Motor Axonal Neuropathy Improvement 20 Days After Hyperbaric Oxygen Therapy

We reported a rare case demonstrating that the hyperbaric oxygen chamber provided faster clinical improvement in a patient with a variant of Guillain-Barre Syndrome (GBS). A patient with progressive, acute weakness of upper extremity locomotor muscles and with difficulty breathing and swallowing was diagnosed with axonal GBS. Despite life-saving conventional therapies, there was no significant improvement until day 5. During hyperbaric oxygen therapy, there were daily gradual improvements until day 20, at which time the patient was capable of walking slowly without using a walking aid.

Antibody-mediated complement activation in pathology and protection

Antibody-dependent complement activity is associated not only with autoimmune morbidity, but also with antitumor efficacy. In infectious disease, both recombinant monoclonal antibodies and polyclonal antibodies generated in natural adaptive responses can mediate complement activity to protective, therapeutic or disease-enhancing effect. Recent advances have contributed to the structural resolution of molecular complexes involved in antibody-mediated complement activation, defining the avid nature of participating interactions and pointing to how antibody isotype, subclass, hinge flexibility, glycosylation state, amino acid sequence and the contextual nature of the cognate antigen/epitope are all factors that can determine complement activity through impact on antibody multimerization and subsequent recruitment of complement component 1q. Beyond the efficiency of activation, complement activation products interact with various cell types that mediate immune adherence, trafficking, immune education and innate functions. Similarly, depending on the anatomical location and extent of activation, complement can support homeostatic restoration or be leveraged by pathogens or neoplasms to enhance infection or promote tumorigenic microenvironments, respectively. Advances in means to suppress complement activation by intravenous immunoglobulin (IVIG), IVIG mimetics and complement-intervening antibodies represent proven and promising exploratory therapeutic strategies, while antibody engineering has likewise offered frameworks to enhance, eliminate or isolate complement activation to interrogate in vivo mechanisms of action. Such strategies promise to support the optimization of antibody-based drugs that are able to tackle emerging and difficult-to-treat diseases by improving our understanding of the synergistic and antagonistic relationships between antibody mechanisms mediated by Fc receptors, direct binding and the products of complement activation.

Associations between tumor necrosis factor-α gene polymorphisms and the risk of Guillain-Barré syndrome and its subtypes: A systematic review and meta-analysis

This meta-analysis aimed to assess the relationship between tumor necrosis factor-α (TNF-α) polymorphisms and Guillain-Barré syndrome (GBS) or its subtypes of acute inflammatory demyelinating polyneuropathy (AIDP), acute motor axonal neuropathy (AMAN), and acute motor-sensory axonal neuropathy (AMSAN). A total of six studies with 1013 cases and 1029 controls were included. Our pooled data indicated that TNF-α 308G/A polymorphism was significantly associated with GBS, AMAN, and AMSAN but not with AIDP; TNF-α 857C/T polymorphism was significantly associated with AMAN but not with GBS or AIDP. Besides, no association was found between TNF-α 238G/A and 863C/A polymorphisms and GBS or its subtypes.

Monomeric Immunoglobulin A from Plasma Inhibits Human Th17 Responses In Vitro Independent of FcαRI and DC-SIGN

Circulating immunoglobulins including immunoglobulin G (IgG) and IgM play a critical role in the immune homeostasis by modulating functions of immune cells. These functions are mediated in part by natural antibodies. However, despite being second most abundant antibody in the circulation, the immunoregulatory function of IgA is relatively unexplored. As Th17 cells are the key mediators of a variety of autoimmune, inflammatory, and allergic diseases, we investigated the ability of monomeric IgA (mIgA) isolated from pooled plasma of healthy donors to modulate human Th17 cells. We show that mIgA inhibits differentiation and amplification of human Th17 cells and the production of their effector cytokine IL-17A. mIgA also suppresses IFN-γ responses under these experimental conditions. Suppressive effect of mIgA on Th17 responses is associated with reciprocal expansion of FoxP3-positive regulatory T cells. The effect of mIgA on Th17 cells is dependent on F(ab′)₂ fragments and independent of FcαRI (CD89) and DC-SIGN. Mechanistically, the modulatory effect of mIgA on Th17 cells implicates suppression of phosphorylation of signal transducer and activator of transcription 3. Furthermore, mIgA binds to CD4⁺ T cells and recognizes in a dose-dependent manner the receptors for cytokines (IL-6Rα and IL-1RI) that mediate Th17 responses. Our findings thus reveal novel anti-inflammatory functions of IgA and suggest potential therapeutic utility of mIgA in autoimmune and inflammatory diseases that implicate Th17 cells.