T-cell apoptosis in inflammatory neuromuscular disorders associated with human immunodeficiency virus infection

Muscle-fiber apoptosis in neuromuscular diseases

Muscle-fiber loss is a characteristic of many progressive neuromuscular disorders. Over the past decade, identification of a growing number of apoptosis-associated factors and events in pathological skeletal muscle provided increasing evidence that apoptotic cell-death mechanisms account significantly for muscle-fiber atrophy and loss in a wide spectrum of neuromuscular disorders. It became obvious that there is not one specific pathway for muscle fibers to undergo apoptotic degradation. In contrast, certain neuromuscular diseases seem to involve characteristic expression patterns of apoptosis-related factors and pathways. Furthermore, there are some characteristics of muscle-fiber apoptosis that rely on the muscle fiber itself as an extremely specified cell type. Multinucleated muscle fibers with successive muscle-fiber segments controlled by individual nuclei display some specifics different from apoptosis of mononucleated cells. This review focuses on the expression patterns of apoptosis-associated factors in different primary and secondary neuromuscular disorders and gives a synopsis of current knowledge.

Apoptotic Cell Death in Experimental Autoimmune Encephalomyelitis

Particularly in the vulnerable CNS with a low capacity for regeneration specialized mechanisms must be active for the fast and gentle elimination of dysregulated autoaggressive immune cells. In EAE, local apoptosis of autoimmune T-cells has been identified as a safe means for the removal of these unwanted cells. T-cell apoptosis in situ followed by phagocytic clearance of apoptotic remnants by glia assures a minimum of detrimental bystander damage to the local parenchyma and down-regulates the local inflammatory reaction. The pharmacological augmentation of local apoptosis of inflammatory effector cells might gain therapeutic importance also in human neuroimmunological diseases such as multiple sclerosis.

Polymyositis and dermatomyositis

The inflammatory myopathies, commonly described as idiopathic, are the largest group of acquired and potentially treatable myopathies. On the basis of unique clinical, histopathological, immunological, and demographic features, they can be differentiated into three major and distinct subsets: dermatomyositis, polymyositis, and inclusion-body myositis. Use of new diagnostic criteria is essential to discriminate between them and to exclude other disorders. Dermatomyositis is a microangiopathy affecting skin and muscle; activation and deposition of complement causes lysis of endomysial capillaries and muscle ischaemia. In polymyositis and inclusion-body myositis, clonally expanded CD8-positive cytotoxic T cells invade muscle fibres that express MHC class I antigens, which leads to fibre necrosis via the perforin pathway. In inclusion-body myositis, vacuolar formation with amyloid deposits coexists with the immunological features. The causative autoantigen has not yet been identified. Upregulated vascular-cell adhesion molecule, intercellular adhesion molecule, chemokines, and their receptors promote T-cell transgression, and various cytokines increase the immunopathological process. Early initiation of therapy is essential, since both polymyositis and dermatomyositis respond to immunotherapeutic agents. New immunomodulatory agents currently being tested in controlled trials may prove promising for difficult cases.

Expression of calcium-binding proteins MRP8 and MRP14 in inflammatory muscle diseases

The pathophysiological role of infiltrating macrophages and their subtypes in idiopathic inflammatory myopathies such as dermatomyositis, polymyositis, and inclusion body myositis is not fully clear. Monocytes exhibit various phenotypes with different functional properties such as release of pro- or anti-inflammatory mediators. Expression of myeloid-related proteins MRP8 and MRP14, two calcium-binding S100-proteins, characterizes a proinflammatory subtype of macrophages. We immunohistochemically investigated expression of MRP8 and MRP14 in muscle biopsies of 33 patients with dermatomyositis, polymyositis, and inclusion body myositis. We found a clear association of expression of MRP8 and MRP14 by infiltrating macrophages with degeneration of myofibers. Because MRP8 and MRP14 are secreted by activated macrophages we investigated if these proteins would have direct extracellular effects on myocytes. We found that the purified MRP8/MRP14 complex inhibited proliferation and differentiation of C2C12 myoblasts and that it induced apoptosis via activation of caspase-3 in a time- and dose-dependent manner. These results indicate that in the course of inflammatory myopathies, activated macrophages can promote destruction and impair regeneration of myocytes via secretion of MRP8/MRP14.

Immunotherapy in autoimmune neuromuscular disorders

Important progress has been made in our understanding of the cellular and molecular processes underlying autoimmune neuromuscular diseases that has led us to identify targets for rational therapeutic intervention. Although antigen-specific immunotherapy is not yet available, old and new immunomodulatory treatments, alone or in combination, provide effective immunotherapy for most autoimmune disorders. In parallel, the achievements of molecular medicine provide more specific yet largely experimental therapeutic tools that need to be tested in the human diseases. Here we review the principles and targets of immunotherapy for autoimmune neuromuscular disorders, address applications and practical guidelines, and give an outlook on future developments.

Oxides and apoptosis in inflammatory myopathies

Reactive oxygen intermediates (ROI) and nitric oxide (NO(.)) are produced in abundance in the inflammatory muscle diseases of autoimmune origin polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM). However, their role in the pathogenesis of these diseases is so far not clear. In contrast to demyelinating neuropathies, there is no convincing evidence for oxide-induced apoptosis either in myocytes or in lymphocytes and phagocytes in inflammatory myopathies. On the contrary, NO(.) released at low concentrations at target sites may even have cell-protective effects. A major mechanism of protection from apoptosis in both myocytes and inflammatory cells seems to be the upregulation of anti-apoptotic proteins like Bcl-2. Caution is warranted to apply antioxidative and anti-apoptotic agents to patients with inflammatory myopathies as long as the pathogenic role of oxides and apoptosis in the individual case is not resolved.

The changing spectrum of rheumatic disease in human immunodeficiency virus infection

CONTEXT

Although it has been known for over 15 years that a number of rheumatic diseases occur in patients with human immunodeficiency virus (HIV) infection, increasing knowledge about these disorders and advances in HIV treatment need to be considered in approaching patients with HIV-associated rheumatic disease.

OBJECTIVE

To examine the clinical, pathologic, and therapeutic features of HIV-associated rheumatic diseases in the context of what is known about the immunology of HIV infection.

DATA SOURCES

The author's own extensive collection of references, supplemented by PubMed Medline searches for articles in English-language journals published between 1985 and 2000. The indexing term HIV and the following coindexing terms were used for searching: arthritis, Reiter's syndrome, psoriatic arthritis, rheumatoid arthritis, osteonecrosis, vasculitis, pulmonary hypertension, myositis, myopathy, fibromyalgia, septic arthritis, parotid enlargement, diffuse infiltrative lymphocytosis syndrome, systemic lupus erythematosus, septic arthritis, mycobacterial arthritis, fungal arthritis, autoantibodies, anti-cardiolipin antibodies, and anti-neutrophilic cytoplasmic antibodies.

STUDY SELECTION

All papers identified in the literature search were reviewed. Studies presenting data that merely confirmed previous studies were not included in the analysis.

DATA EXTRACTION

All identified papers were abstracted by the author. Letters to the editor were included only if a new observation had been made.

DATA SYNTHESIS

This was a qualitative review of papers published, with new knowledge about these disorders summarized and presented.

RESULTS

Despite new treatments for HIV, reports of rheumatic diseases presenting in AIDS patients persist, especially in HIV-associated arthritis, diffuse infiltrative lymphocytosis syndrome, HIV-associated vasculitis, and polymyositis. However, new HIV treatments may ameliorate these diseases.

CONCLUSIONS

The spectrum of HIV-associated rheumatic disease remains a diagnostic and therapeutic challenge for the clinician. The impact of changes in HIV treatment on these disorders requires further assessment.

T-cell anti-apoptotic mechanisms in inflammatory myopathies

Recent studies have shown an up-regulation of the Fas/Fas ligand system in inflammatory myopathies. In myositis, however, the major Fas-mediated cytotoxicity which activates caspases bypasses apoptosis. We therefore evaluated the expression of proteins promoting cell survival, such as bcl-2, bcl-x(l) and cyclin-dependent kinase inhibitors, on muscle biopsies from 14 patients with polymyositis, dermatomyositis, inclusion body myositis and HIV-associated myositis. Our data demonstrate that inflammatory cells are immunoreactive for bcl-x(l), p16 and p57, three apoptosis-preventing proteins. Hence, we assume that these proteins might protect T cells from apoptotic nuclear changes. Our results could explain the non-self-limiting nature of inflammatory myopathies.

Expression of human IAP-like protein in skeletal muscle: a possible explanation for the rare incidence of muscle fiber apoptosis in T-cell mediated inflammatory myopathies

In Polymyositis (PM) and sporadic Inclusion Body Myositis (s-IBM), the CD8(+) cytotoxic T cells invade the muscle membrane and release perforin and granzyme B to induce cell death. Although granzyme B is a direct activator of executioner caspases, there is no convincing evidence of apoptosis in the muscle fibers of these patients. To search for an explanation, we examined the muscle expression of the human IAP-Like Protein (hILP), an evolutionarily conserved cell death suppressor, that exerts major anti-apoptotic effects by inhibiting the executioner caspases. Muscle biopsy specimens from patients with inflammatory myopathies and controls were studied with: (a) immunocytochemistry using antibodies against hILP and caspase-3 in single and double-labeled confocal laser microscopy; (b) immunoblotting of muscle extracts immunoreacted with anti-hILP antibodies; and (c) subcellular fractionation of muscle lysates immunoreacted with antibodies against hILP. We found that hILP is expressed on the sarcolemmal region and co-localizes with dystrophin. Caspase-3 is undetectable. Subcellular fractionation of the muscle specimens confirmed that hILP is a membrane-associated protein. By immunoblotting, the 57 kD hILP was abundantly expressed in the normal as well as the diseased muscles. We conclude that in s-IBM and PM the expression of hILP, a major cell death suppressor, on the muscle membrane may prevent the induction of apoptosis by the autoinvasive cytotoxic T cells on the cell surface, by inhibiting the caspase activation.

Mechanisms of immune regulation in the peripheral nervous system

The peripheral nervous system (PNS) is a target for heterogenous immune attacks mediated by different components of the systemic immune compartment. T cells, B cells, and macrophages can interact with endogenous, partially immune-competent glial cells and contribute to local inflammation. Cellular and humoral immune functions of Schwann cells have been well characterized in vitro. In addition, the interaction of the humoral and cellular immune system with the cellular and extracellular components in the PNS may determine the extent of tissue inflammation and repair processes such as remyelination and neuronal outgrowth. The animal model experimental autoimmune neuritis (EAN) allows direct monitoring of these immune responses in vivo. In EAN contributions to regulate autoimmunity in the PNS are made by adhesion molecules and by cytokines that orchestrate cellular interactions. The PNS has a significant potential to eliminate T cell inflammation via apoptosis, which is almost lacking in other tissues such as muscle and skin. In vitro experiments suggest different scenarios how specific cellular and humoral elements in the PNS may sensitize autoreactive T cells for apoptosis in vivo. Interestingly several conventional and novel immunotherapeutic approaches like glucocorticosteroids and high-dose antigen therapy induce T cell apoptosis in situ in EAN. A better understanding of immune regulation and its failure in the PNS may help to develop improved, more specific immunotherapies.