Mechanisms of action of intravenous immunoglobulin (IVIG)

Clinical presentation and immunological features of Post-Malaria Neurologic Syndrome: a case report and review of literature

Background

Malaria still represents a major health threat, in terms of both morbidity and mortality. Complications of malaria present a diversified clinical spectrum, with neurological involvement leading to the most serious related-conditions. The authors recently encountered a case of a 60-year old Italian man presenting with confusion, language disturbances and Parkinson-like syndrome 3 weeks after complete remission from severe Plasmodium falciparum cerebral malaria. Chemical and microbiological analysis revealed aseptic meningitis, diffuse encephalitis and abnormal immune-activation. Re-infection and recrudescence of infection were excluded. Further analysis excluded paraneoplastic and autoimmune causes of encephalitis. A diagnosis of Post-Malaria Neurological Syndrome (PMNS) was finally formulated and successfully treated with high dose of steroids.

Methods

A systematic research of current literature related to PMNS was performed.

Results

151 cases of PMNS were included, the majority of which occurred after severe P. falciparum infections. Four main clinical pattern were identified: 37% of the cases presented as “classical” PMNS, 36% presented as delayed cerebellar ataxia (DCA), 18% resembled acute inflammatory demyelinating polyneuropathy (AIDP), and 8% presented as acute disseminated encephalomyelitis (ADEM)-like form. Differentiation between different forms was not always simple, as clinical and radiological findings frequently overlap. Overall, in almost all of the tested cases, cerebrospinal fluid was found pathological; EEG revealed nonspecific encephalopathy in 30% of classical PMNS and 67% ADEM; imaging tests were found abnormal in 92% of ADEM-like forms. Pathogenesis remains unclear. An autoimmune mechanism is the most corroborated pathogenic hypothesis. Overall, the majority of PMNS cases revert without specific treatment. In most severe forms, high dose steroids, intravenous immunoglobulins, and plasmapheresis have been shown to improve symptoms.

Conclusions

PMNS is a disabling complication of malaria. The overall incidence is not known, due to frequent misdiagnosis and under-reporting. Pathogenesis is not also fully understood, but rapid response to immune-modulating treatment along with similarities to auto-immune neurological disease, strongly support a dysregulated immunological genesis of this condition. The lack of randomized controlled studies regarding therapeutic approaches is a major unmet need in this setting. A systematic collection of all the PMNS cases would be desirable, in order to increase awareness of this rare condition and to prospectively investigate the most appropriate management.

Immunoglobulin for Treating Bacterial Infections: One More Mechanism of Action

The mechanisms underlying the effects of immunoglobulins on bacterial infections are thought to involve bacterial cell lysis via complement activation, phagocytosis via bacterial opsonization, toxin neutralization, and antibody-dependent cell-mediated cytotoxicity. Nevertheless, recent advances in the study of the pathogenicity of Gram-negative bacteria have raised the possibility of an association between immunoglobulin and bacterial toxin secretion. Over time, new toxin secretion systems like the type III secretion system have been discovered in many pathogenic Gram-negative bacteria. With this system, the bacterial toxins are directly injected into the cytoplasm of the target cell through a special secretory apparatus without any exposure to the extracellular environment, and therefore with no opportunity for antibodies to neutralize the toxin. However, antibodies against the V-antigen, which is located on the needle-shaped tip of the bacterial secretion apparatus, can inhibit toxin translocation, thus raising the hope that the toxin may be susceptible to antibody targeting. Because multi-drug resistant bacteria are now prevalent, inhibiting this secretion mechanism is an attractive alternative or adjunctive therapy against lethal bacterial infections. Thus, it is not unreasonable to define the blocking effect of anti-V-antigen antibodies as the fifth mechanism for immunoglobulin action against bacterial infections.

The natural antibody repertoire of sharks and humans recognizes the potential universe of antigens

In ancestral sharks, a rapid emergence in the evolution of the immune system occurred, giving jawed-vertebrates the necessary components for the combinatorial immune response (CIR). To compare the natural antibody (NAb) repertoires of the most divergent vertebrates with the capacity to produce antibodies, we isolated NAbs to the same set of antigens by affinity chromatography from two species of Carcharhine sharks and from human polyclonal IgG and IgM antibody preparations. The activities of the affinity-purified anti-T-cell receptor (anti-TCR) NAbs were compared with those of monoclonal anti-TCR NAbs that were generated from a systemic lupus erythematosus patient. We report that sharks and humans, representing the evolutionary extremes of vertebrate species sharing the CIR, have NAbs to human TCRs, Igs, the human senescent cell antigen, and to numerous retroviral antigens, indicating that essential features of the combinatorial repertoire and the capacity to recognize the potential universe of antigens is shared among all jawed-vertebrates.

Differentiation of multiple sclerosis subtypes: implications for treatment

There has been tremendous progress in the immunomodulatory treatment of multiple sclerosis (MS) during recent years. With the introduction of interferon-beta, glatiramer acetate and mitoxantrone (recently registered for MS in the US), there are at least three therapeutic strategies that have proven effective in large phase III studies. However, not all patients with MS respond well to treatment with these drugs. This may largely be a consequence of disease heterogeneity. From a clinical perspective, patients with different disease courses show different treatment responses. Patients with relapsing-remitting MS are more likely to respond to immunomodulatory therapy than those with a progressive disease course. Studies of patients with secondary progressive MS have yielded inconsistent results and, so far, there has been no positive phase III study of immunomodulatory therapy in patients with primary progressive MS. Pathological evidence indicates that subtyping based on clinical findings alone does not reflect actual disease heterogeneity. In a large series of biopsy and autopsy specimens, at least four subtypes could be identified with respect to oligodendrocyte/myelin pathology and immunopathology. As long as the only method of identifying subtypes of disease is histopathology, differential therapy will remain a future goal. Thus, there is an urgent need for in vivo markers of immunopathogenesis in an individual patient that would allow treatment to be specifically directed towards a given pathological focus. However, at least from a theoretical point of view, some therapeutic approaches appear very attractive. Plasmapheresis and/or intravenous immunoglobulins could most plausibly be the best approach for the immunopathological subtype of MS, which is characterised by antibody and complement deposition next to demyelinated axons, in order to remove antibodies. The subtype of MS that is associated with heavy macrophage activation, T cell infiltration and expression of inflammatory mediator molecules, including tumour necrosis factor-alpha, may be most likely to respond to immunomodulation with interferon-beta or glatiramer acetate. There are other subtypes of MS in which viral infection or oligodendrocyte degeneration, rather than autoimmunity, appear to play a role. It is possible that these could benefit from antiviral therapy, oligodendrocyte protection or oligodendrocyte transplantation, although therapies based on these latter approaches have yet to be developed.