Antibodies to human myeloperoxidase in glomerular immune deposits of systemic lupus erythematosus

The many roles of myeloperoxidase: From inflammation and immunity to biomarkers, drug metabolism and drug discovery

This review provides a practical guide to myeloperoxidase (MPO) and presents to the reader the diversity of its presence in biology. The review provides a historical background, from peroxidase activity to the discovery of MPO, to its role in disease and drug development. MPO is discussed in terms of its necessity, as specific individuals lack MPO expression. An underlying theme presented throughout brings up the question of the benefit and burden of MPO activity. Enzyme structure is discussed, including accurate masses and glycosylation sites. The catalytic cycle of MPO and its corresponding pathways are presented, with a discussion of the importance of the redox couples of the different states of MPO. Cell lines expressing MPO are discussed and practically summarized for the reader, and locations of MPO (primary and secondary) are provided. Useful methods of MPO detection are discussed, and how these can be used for studying disease processes are implied through the presentation of MPO as a biomarker. The presence of MPO in neutrophil extracellular traps is presented, and the activators of the former are provided. Lastly, the transition from drug metabolism to a target for drug development is where the review concludes.

Clearance Deficiency and Cell Death Pathways: A Model for the Pathogenesis of SLE

Alterations of cell death pathways, including apoptosis and the neutrophil specific kind of death called NETosis, can represent a potential source of autoantigens. Defects in the clearance of apoptotic cells may be responsible for the initiation of systemic autoimmunity in several chronic inflammatory diseases, including systemic lupus erythematosus (SLE). Autoantigens are released mainly from secondary necrotic cells because of a defective clearance of apoptotic cells or an inefficient degradation of DNA-containing neutrophil extracellular traps (NETs). These modified autoantigens are presented by follicular dendritic cells to autoreactive B cells in germinal centers of secondary lymphoid organs. This results in the loss of self-tolerance and production of autoantibodies, a unifying feature of SLE. Immune complexes (IC) are formed from autoantibodies bound to uncleared cellular debris in blood or tissues. Clearance of IC by blood phagocytes, macrophages, and dendritic cells leads to proinflammatory cytokine secretion. In particular, plasmacytoid dendritic cells produce high amounts of interferon-α upon IC uptake, thereby contributing to the interferon signature of patients with SLE. The clearance of antinuclear IC via Fc-gamma receptors is considered a central event in amplifying inflammatory immune responses in SLE. Along with this, the accumulation of cell remnants represents an initiating event of the etiology, while the subsequent generation of autoantibodies against nuclear antigens (including NETs) results in the perpetuation of inflammation and tissue damage in patients with SLE. Here, we discuss the implications of defective clearance of apoptotic cells and NETs in the development of clinical manifestations in SLE.

Correlations of anti-dsDNA and anti-ribosomal P autoantibodies with lupus nephritis

Patients with systemic lupus erythematosus, with and without nephritis, were studied for their serological profiles. Patients were stratified into two groups defined by the presence or the absence of precipitating antibodies to ribosomal P proteins. It was found that 27 patients were positive for anti-P precipitins and the remaining 34 patients were studied for the presence of lesser amounts of anti-P antibodies by Western blot and ELISA tests. The nephritic patients were characterized most frequently by the presence of both autoantibodies to dsDNA and the ribosomal P proteins. In the group with anti-P precipitins, anti-dsDNA titers were much higher in the patients with nephritis than in those without nephritis. Thus, over a wide range of anti-ribosomal P antibody concentrations, the mutual occurrence of anti-P antibodies with anti-dsDNA antibodies was strongly associated with lupus nephritis.

Are antineutrophil cytoplasmic antibody-associated vasculitides pauci-immune?

The role of ICs in ANCA-associated vasculitides remains controversial. The ANCA-associated vasculitides are described as being pauci-immune. We hypothesize that the absence of ICs is a result of an exaggerated inflammatory response caused by the presence of ANCAs. We present evidence indicating that ICs may play a role in the initiation or relapses of the disease. The nature of the involved antigen(s) is not yet known. Possible candidates are reviewed and include ANCA antigens, AECA antigens, and staphylococcal antigens.