Myeloperoxidase-specific plasma cell depletion by bortezomib protects from anti-neutrophil cytoplasmic autoantibodies-induced glomerulonephritis

Impact of intravenous immunoglobulin on the dopaminergic system and immune response in the acute MPTP mouse model of Parkinson's disease

Intravenous immunoglobulin (IVIg) is a blood-derived product, used for the treatment of immunodeficiency and autoimmune diseases. Since a range of immunotherapies have recently been proposed as a therapeutic strategy for Parkinson’s disease (PD), we investigated the effects of an IVIg treatment in a neurotoxin-induced animal model of PD. Mice received four injections of MPTP (15 mg/kg) at 2-hour intervals followed by a 14-day IVIg treatment, which induced key immune-related changes such as increased regulatory T-cell population and decreased CD4⁺/CD8⁺ ratio. The MPTP treatment induced significant 80% and 84% decreases of striatal dopamine concentrations (P < 0.01), as well as 33% and 40% reductions in the number of nigral dopaminergic neurons (P < 0.001) in controls and IVIg-treated mice, respectively. Two-way analyses of variance further revealed lower striatal tyrosine hydroxylase protein levels, striatal homovanillic acid concentrations and nigral dopaminergic neurons (P < 0.05) in IVIg-treated animals. Collectively, our results fail to support a neurorestorative effect of IVIg on the nigrostriatal system in the MPTP-treated mice and even suggest a trend toward a detrimental effect of IVIg on the dopaminergic system. These preclinical data underscore the need to proceed with caution before initiating clinical trials of IVIg in PD patients.

Animal models of anti-neutrophil cytoplasmic antibody-associated vasculitis

Antibodies against neutrophil proteins myeloperoxidase (MPO) and proteinase 3 are thought to cause disease in anti-neutrophil cytoplasmic antibody (ANCA) vasculitis. There have been a number of recent developments in the animal models of ANCA vasculitis in both mice and rats. These include models based on an immune response to MPO generated in MPO-deficient mice, with other models using MPO-sufficient mice and rats. In addition, there is a report of the use of humanized mice where immunodeficient mice have been engrafted with human haematopoietic stem cells and injected with patient ANCA. Antibodies to another protein lysosomal-associated protein-2 have been found in patients with ANCA vasculitis, and evidence from a rat model suggests that they are also pathogenic. These models all have advantages and disadvantages, which are discussed. We also consider what these models have taught us about the pathogenesis of ANCA vasculitis. Experiments using genetically modified mice and pharmacological inhibition have given insights into disease mechanisms and have identified potential therapeutic targets. Toll-like receptor stimulation modifies disease by acting both at the level of tissue injury and in the generation of the autoimmune response. Complement is also potentially important with data to support the role of the alternative pathway and C5a in particular. Intracellular pathways have been examined, with a role showing p38 mitogen-activated protein kinase and phosphatidylinositol 3-kinase γ. Serine proteases are now known to contribute to disease by release of interleukin-1β in ANCA-activated neutrophils and monocytes. Other potential therapies studied in these models include the use of bortezemib and strategies to modify antibody glycosylation.

Proteasome inhibitors as immunosuppressants: biological rationale and clinical experience

Accumulating evidence supports the potential of proteasome inhibitors as immunosuppressants. Proteasome inhibitors interfere with antigen processing and presentation, as well as with the signaling cascades involved in immune cell function and survival. Both myeloma and healthy plasma cells appear to be highly susceptible to proteasome inhibitors due to impaired proteasomal activity in both cell types. As a consequence, these agents can be used to reduce antibody production and thus prevent antibody-induced tissue damage. Several clinical studies have explored the potential of bortezomib, a peptide boronate proteasome inhibitor, for treating immune disorders, such as antibody-mediated organ rejection and graft-versus-host disease (GVHD), with encouraging results. Here, we discuss the biological rationale for the use of proteasome inhibitors as immunosuppressive agents and review the clinical experience with bortezomib in immune-mediated diseases.

Pathogenesis of ANCA-associated vasculitis: recent insights from animal models

PURPOSE OF REVIEW

To provide an update on animal models of antineutrophil cytoplasmic autoantibody (ANCA)-mediated vasculitis and highlight recent insights gained from studies in these models pertaining to immunopathogenesis.

RECENT FINDINGS

Animal models support the pathogenic potential of myeloperoxidase (MPO)-ANCA. Alternative pathway complement activation has been identified as a novel inflammatory pathway in disease induction and a potential target for intervention. Interventions targeting B cells, antibodies, and signal transduction pathways may hold promise as well. The role of T cells is beginning to be explored, and studies indicate a prominent role for Th17 responses. The link between infection and ANCA vasculitis is well established. In animal models, Toll-like receptor (TLR)4 ligation is involved in disease induction. Ligation of TLRs contributes to the initiation of anti-MPO autoimmune responses in which TLR2 activation induces a Th17 response and TLR9 activation directs a Th1 response. An animal model for PR3-ANCA vasculitis is not available yet but models with a humanized immune system are being developed and show promising first results.

SUMMARY

Animal models of MPO-ANCA vasculitis have contributed substantially to our understanding of disease immunopathogenesis and have illuminated novel targets for intervention. The development of PR3-ANCA animal models remains a challenge but recent observations in humanized model systems offer hope.