Effects of pooled human immunoglobulins in an animal model of neuromyelitis optica with chronic application of autoantibodies to aquaporin 4

Abstract

Neuromyelitis optica (NMO) is a relapsing, chronic inflammatory disease of the central nervous system (CNS) mainly affecting the spinal cord and the optic nerves. The discovery of highly specific associated autoantibodies (AB) to the osmotic-driven water channel aquaporin 4 (APQ4) led to the classification of NMO as a separate entity from multiple sclerosis [1,2]. AQP4 is an integral membrane protein, located on the abluminal side of astrocyte endfeet in the CNS. Immunopathology of typical NMO lesions show distinct deposition of immunoglobulin (Ig)G and activated complement, as well as immune cell infiltration resulting in tissue destruction. NMO lesions are also characterized by astrocyte depletion and loss of AQP4. Recent reports also suggest 'penumbra-like' regions adjacent to destructive areas, which are characterized by specific loss of AQP4 but preserved astrocytes [3]. Current treatment strategies for NMO patients consist of AB removal by plasma exchange or immunoadsorption and/or high-dose corticosteroids during acute relapses, and of B cell depletion with rituximab or immunosuppressive treatment with mitoxantrone or cyclophosphamide as an interval therapy. Furthermore, there is some clinical evidence for a favourable outcome with an interval treatment using eculizumab, a therapeutic monoclonal antibody that neutralizes complement protein C5 [4]. Together, these complex immunopathological features and the treatment response to either AB removal, B cell depletion or downstream complement inhibition point clearly towards an AB-mediated, target-directed pathomechanism. The aim of the current study was to evaluate the treatment effect of pooled human immunoglobulins (IVIg; Privigen ® ) in a rat model that focuses on the intrinsic pathogenic effects of AB to AQP4 induced by repetitive intrathecal (i.th.) application of purified patient IgG fractions.In previous studies we developed an animal model that proved to be useful to study AB-dependent pathomechanisms in the CNS in the living organism [5,6]. In adult female Wistar rats, i.th. catheters were inserted through the cerebellomedullary cistern, with the internal opening of the catheter right above the lumbar enlargement of the spinal cord whereas the external ending was facing outwards of the animal's occiput. When small amounts of high-dose NMOpatient IgG (10 μl volume of 100 mg/ml concentration) purified from patient plasma exchange material were administered in three series of five daily applications and a 2-day break in between (3 weeks in total), rats developed progressive disease signs starting with motor symptoms of unilateral hind limb paresis reaching to paraplegia in severe cases. Histologically, spinal cord areas near the catheter ending were characterized by intense IgG deposition and reduction of AQP4 immunoreactivity, but without obvious cell destruction, immune cell infiltration and astrocyte depletion. Thus, in this animal model without additional co-injection of complement factors, the intrinsic effects of AB to AQP4 mediated distinct immun...

Neuromyelitis optica study model based on chronic infusion of autoantibodies in rat cerebrospinal fluid

“…AQP4 antigen specificity was demonstrated by the absence of the effect of the control IgG and the dramatic decrease of the effect in AQP4-IgG-depleted IgG. Our study thus validates a concept that has been already suggested in NMO by several in vitro studies [ 12 – 14 , 24 ] and in animal models based on passive transfer of AQP4-IgG in the periphery [ 33 ] or iterative injection of AQP4-IgG directly into the spinal cord [ 21 , 34 ]. There are accumulative evidences for such intrinsic effect of autoantibody against surface antigens in other antibody-mediated CNS disorders.…”