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ESSENTIALS OF DIAGNOSIS
Systemic lupus erythematosus (SLE): this diagnosis is based on presence of at least four clinical and laboratory features: rash, photosensitivity, mucosal ulcers, arthritis, serositis or renal, neurologic, hematologic, immunologic disorder, or antinuclear antibody; while not formal criteria, complement components, C3 and/or C4, are commonly depressed.
Lupus nephritis (LN): this diagnosis often represents an exception to the usual basal requirement for a formal diagnosis SLE based on systemic disease criteria; diagnosis of LN is made on the basis of urinary findings (hematuria, cellular casts, and/or proteinuria), autoantibodies (antinuclear and/or anti-DNA), and kidney biopsy showing immune complex mediated glomerulonephritis.
LN spans a spectrum of pathology and cases are assigned to one of six major classes, along with semiquantitative scores to reflect degrees of activity and chronicity.
Deposition of nephritogenic immune complexes that characteristically starts in the mesangium may extend into the subendothelial space in the case of proliferative LN, or presumptively qualitatively different types of immune complexes may form in the subepithelial space in the case of membranous nephropathy, along tubular basement membranes in the case of interstitial nephritis, or in vascular bed in the case of lupus vasculopathy.
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GENERAL CONSIDERATIONS
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Lupus nephritis (LN) develops in the majority of patients with systemic lupus erythematosus (SLE). The clinical spectrum ranges from mild and indolent to severe and progressive glomerulonephritis. Autoantibodies to a range of constitutive nuclear antigens contribute to the diagnosis of SLE. Anti-DNA antibodies appear to be the most nephritogenic, although other autoantibodies are clearly involved in many cases of LN.
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The main determinants of the occurrence, form, and severity of LN derive from the quantity and affinity of circulating immune complexes for glomerular structures. Immune complexes initially accumulate in the mesangial interstices. Deposits may be limited to the mesangium in mild LN (Classes I and II, Mesangial Lupus Nephritis). Complexes may spill over into the subendothelial space where they evoke inflammatory processes and endocapillary hypercellularity (Classes III, Focal, and Class IV, Diffuse Proliferative Lupus Nephritis). The pathogenesis of Class V, Membranous Lupus Nephropathy, is less well understood. The leading hypothesis for formation of the characteristic subepithelial immune complex deposits is that autoantibodies react with either constitutive or planted antigens expressed on podocyte membranes. Mononuclear cells (macrophages and lymphocytes) are typically present in the tubulointerstitial compartment. Thus, there is inference that imprecisely defined cell-mediated immune mechanisms may contribute to the pathogenesis of LN.
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Understanding of the complex mechanisms leading to LN continues to evolve. Current models are based on a multitude of factors which include the following: genetic susceptibility, epigenetic modifiers, loss of self-tolerance to nuclear antigens, overactive and dysregulated lymphoid cells, overproduction of stimulatory cytokines and circulating growth factors, hyperglobulinemia and autoantibody production, ready availability of nuclear antigens from high rates of apoptotic cell death, overproduction and impaired clearance of immune complexes, complement activation, inflammation, coagulation, repair and fibrosis. Extrapolating from the complexity of this ...