Sunday, 9 October 2011
Antiglomerular antibodies
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Antiglomerular antibodies are present in —
a)Good pasture syndrome (Al 90)
b)Focal gloumerulonephritis
c)Membramcous glomerulonephritis
d)Membrano proliferative glomerulonephritis
a)Good pasture syndrome (Al 90)
b)Focal gloumerulonephritis
c)Membramcous glomerulonephritis
d)Membrano proliferative glomerulonephritis
RPGN may be caused by a number of different diseases, some restricted to the kidney and others systemic. [34] Although no single mechanism can explain all cases, there is little doubt that in most cases the glomerular injury is immunologically mediated. Thus, a practical classification divides RPGN into three groups on the basis of immunologic findings (Table 21-6) . In each group, the disease may be associated with a known disorder or it may be idiopathic.
Type I RPGN is best remembered as anti-GBM disease and hence is characterized by linear deposits of IgG and, in many cases, C3 in the GBM, as previously described. In some of these patients, the anti-GBM antibodies cross-react with pulmonary alveolar basement membranes to produce
TABLE 21-6 — RAPIDLY PROGRESSIVE GLOMERULONEPHRITIS (RPGN)
TYPE 1 RPGN
Idiopathic
Goodpasture syndrome
TYPE II RPGN (immune complex)
Idiopathic
Postinfectious
Systemic lupus erythematosus
Henoch-Schonlein purpura (IgA)
Others
TYPE III RPGN (pauci-immune)
(ANCA associated)
Idiopathic
Wegener granulomatosis
Microscopic polyarteritis nodosa
the clinical picture of pulmonary hemorrhages associated with renal failure ( Goodpasture syndrome). The Goodpasture antigen, as noted, resides in the noncollagenous portion of the alpha3 chain of collagen type IV. What triggers the formation of these antibodies is unclear in most patients. Exposure to viruses or hydrocarbon solvents (found in paints and dyes) has been implicated in some patients, as have various drugs and cancers. Cigarette smoking appears to play a permissive role, since most patients who develop pulmonary hemorrhage are smokers. There is a high prevalence of certain HLA subtypes and haplotypes (e.g., HLA-DRB1), a finding consistent with the genetic predisposition to autoimmunity. [34]
Type II RPGN is an immune complex- mediated disease. It can be a complication of any of the immune complex nephritides, including postinfectious glomerulonephritis, SLE, IgA nephropathy, and Henoch-Schonlein purpura. In some cases, immune complexes can be demonstrated, but the underlying cause is undetermined. In all of these cases, immunofluorescence studies reveal the characteristic (“lumpy bumpy”) granular pattern of staining. These patients cannot usually be helped by plasmapheresis, and they require treatment for the underlying disease.
Type III RPGN, also called pauci-immune type, is defined by the lack of anti-GBM antibodies or immune complexes by immunofluorescence and electron microscopy. Most of these patients have antineutrophil cytoplasmic antibody (ANCA) in the serum, which, as we have seen (Chapter 12) , plays a role in some vasculitides. Hence, in some cases, type III RPGN is a component of a systemic vasculitis such as Wegener granulomatosis or microscopic polyarteritis. In many cases, however, pauci-immune crescentic glomerulonephritis is isolated and hence idiopathic. More than 90% of such idiopathic cases have C-ANCA or P-ANCA in the sera.
To summarize, all three types of RPGN may be associated with a well-defined renal or extrarenal disease, but in many cases (approximately 50%) the disorder is idiopathic. Of the idiopathic cases, about one fourth have anti-GBM disease (RPGN type I) without lung involvement; another one fourth have type II RPGN; and the remainder are pauci-immune or type III RPGN. The common denominator in all types of RPGN is severe glomerular injury.
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