Circulating anti-entactin antibodies in patients with glomerulonephritis

Amino acid sequence homology between thyroid autoantigens and central nervous system proteins: Implications for the steroid-responsive encephalopathy associated with autoimmune thyroiditis

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Alpha-enolase, aldehyde reductase-I and dimethylargininase-I are SREAT autoantigens.

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Molecular mimicry between thyroid and CNS autoantigens is hypothesized in SREAT.

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Homology with TSH-R, Tg and TPO exists for 6, 27 and 47 of 46,809 CNS-proteins.

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The above homologies are often in epitope-containing parts of thyroid autoantigens.

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Most of the above proteins are expressed in CNS regions which are altered in SREAT.

A few patients with Hashimoto’s thyroiditis or Graves’ disease develop a multiform syndrome of the central nervous system (CNS) termed Hashimoto’s encephalopathy or steroid-responsive encephalopathy associated with autoimmune thyroid disease (HE/SREAT). They have high levels of thyroid autoantibodies (TgAb, TPOAb and/or TSH-R-Ab) in blood and cerebrospinal fluid. Autoantibodies against alpha-enolase, aldehyde reductase-I (AKRIA) and/or dimethylargininase-I (DDAHI), proteins expressed in the CNS among other tissues, were detected in the blood and, when searched, in the cerebrospinal fluid of HE/SREAT patients. Recently, we reported that alpha-enolase, AKRIA and DDAHI share local sequence homology with each of the three autoantigens (TgAb, TPOAb, TSH-R-Ab), often in epitope-containing segments of the thyroid autoantigens. We hypothesized that there might be additional CNS-expressed proteins homologous to thyroid autoantigens, possibly overlapping known epitopes of the thyroid autoantigens. We used bioinformatic methods to address this hypothesis.

Six, 27 and 47 of 46,809 CNS-expressed proteins share homology with TSH-R, Tg and TPO, respectively. The homologous regions often contain epitopes, and some match regions of thyroid autoantigens which have homology with alpha-enolase, AKRIA and/or DDAHI. Several of the aforementioned proteins are present in CNS areas that show abnormalities at neuroimaging in HE/SREAT patients. Furthermore, autoantibodies against some of the said six, 27 and 47 proteins were reported to be associated with a number of autoimmune diseases.

Not only we validated our hypothesis, but we think that such a variety of potential CNS targets for thyroid Ab against epitopes contained in regions that have local homology with CNS proteins may explain the polymorphic phenotypes of HE/SREAT. Only when elevated amounts of these Ab are synthesized and trespass the blood-brain barrier, HE/SREAT appears. This might explain why HE/SREAT is so relatively rare.

Crescentic Glomerulonephritis: an update on Pauci-immune and Anti-GBM diseases

Crescentic glomerulonephritis (GN) in a renal biopsy is a widely accepted "critical diagnosis" in Anatomic Pathology practice. Prompt biopsy evaluation and notification of the referring physician is essential to facilitate rapid therapeutic intervention. The differential diagnostic categories of crescentic GN include pauci-immune GN, anti-glomerular basement membrane (GBM) nephritis and immune complex-mediated GN, distinguished from one another by immunofluorescence and electron microscopic study of the renal biopsy. Immune complex-mediated GN is characterized by abundant glomerular deposits and encompasses several diseases including but not limited to lupus nephritis, cryoglobulinemic GN and immunoglobulin A nephropathy. Pauci-immune GN, with paucity of deposits, correlates closely with antineutrophil cytoplasmic antibody disease due to the identifiable circulating pathogenic antineutrophil cytoplasmic antibody in most patients. Recent studies have identified other antibodies in pauci-immune GN and implicated infectious organisms in triggering autoimmunity in a susceptible host by molecular mimicry of host antigens. Anti-GBM nephritis is a rare but potentially life-threatening autoimmune disease with circulating antibodies against GBM epitopes in α3 chain of type IV collagen. It is characterized by a linear immunoglobulin G deposition along GBM on immunofluorescence microscopy. Environmental triggers including infections and solvent exposure seem to change the tertiary structure of the type IV collagen α345 hexamer in GBM, expose neoepitopes, and initiate autoimmunity. Even in light of advances in understanding of pathophysiology and serologic testing, renal biopsy remains the mainstay of diagnosis of crescentic GN.

The pulmonary-renal syndrome: a poorly understood clinicopathologic condition

The co-existence of pulmonary hemorrhage and glomerulonephritis delineates a severe syndrome, often underestimated, resulting from several diseases and frequently associated with serum positivity for antineutrophil cytoplasmic antibodies (ANCA) or antiglomerular basement membrane (GBM) antibodies. The most common illness presenting as pulmonary-renal syndrome is systemic vasculitis. Moreover, the idiopathic pulmonary-renal syndrome is a distinctive clinicopathologic entity with different pathogenetic mechanisms. Tissue immunofluorescence studies are fundamental in distinguishing anti-GBM antibody-mediated forms from immune-complex-mediated and ANCA-associated forms. The type of glomerular or alveolar immunologic injury is the main factor determining the outcome and thus the prognosis of the pulmonary-renal syndrome. Development and improvement of appropriate serologic detection techniques have given reliable and early guidance for diagnosing these cases.

Circulating autoantibodies as serological markers in the differential diagnosis of pulmonary renal syndrome

OBJECTIVES

Pulmonary renal syndrome (lung haemorrhage and glomerulonephritis) is a fulminant condition that warrants a rapid diagnosis and treatment to prevent mortality and preserve renal functions. However, the patients frequently present with non-specific pulmonary symptoms in the early phase of the syndrome and the diagnosis is often missed. Recently, several autoantibodies have been described in association with various forms of glomerulonephritis. We evaluated the association as well as the diagnostic and the prognostic significance of these antibodies in pulmonary renal syndrome.

DESIGN

Retrospective clinical study.

SETTING

University Hospital.

SUBJECTS

Forty consecutive patients with biopsy verified glomerulonephritis and overt haemoptysis or pulmonary infiltrates compatible with lung haemorrhage.

INTERVENTIONS

Analysis of proteinase 3 antineutrophil cytoplasm antibodies (PR3-ANCA), myeloperoxidase (MPO)-ANCA, antiglomerular basement membrane (GBM) and anti-entactin antibodies.

RESULTS

Thirty-six (90%) patients possessed one or more autoantibodies. Twenty-seven (70%) patients had ANCA (PR3-ANCA, MPO-ANCA or both). The remaining positive patients (n = 9) had anti-GBM antibodies. Only two patients had anti-entactin antibodies, suggesting a poor association of these antibodies with PRS. The majority of patients with anti-GBM antibodies had a very poor clinical outcome (five irreversible renal failure; three deaths). On the other hand, despite no significant difference in clinical features or renal morphology from patients with anti-GBM antibodies, 19 patients (70%) with ANCA recovered completely following treatment.

CONCLUSIONS

Our study demonstrated that the presence of autoantibodies is a predominant feature of PRS and that the type of immunologic injury is of paramount importance in determining the course of illness in this syndrome. Analysis of the aforementioned antibodies can help in an early differential diagnosis and thus, in better management of PRS.

Significance of anti-entactin antibodies in patients with systemic lupus erythematosus and related disorders

OBJECTIVES

To further evaluate the association of anti-entactin antibodies with clinical manifestations in patients with systemic lupus erythematosus (SLE) and related disorders.

METHODS

Sera were analysed for anti-entactin antibodies from 79 patients with SLE, 38 patients with rheumatoid arthritis, 20 patients with progressive systemic sclerosis and five with Behçet's syndrome. Sera from 150 healthy blood donors and 20 patients with pneumonia were analysed as controls. To study the association of anti-entactin antibodies with severity and activity in SLE, 30 patients were assigned into three groups with 10 patients in each: (1) with mild manifestations; (2) severe disease without renal involvement and (3) frank lupus nephritis. Two blood samples from each patient were analysed, one from the active and the other from the inactive phase of the disease. Additionally, serial sera from 12 patients with SLE were also analysed.

RESULTS

Thirty one patients with SLE (39%) had IgG, IgM or both anti-entactin antibodies. Twenty three of these patients (29%) had biopsy verified glomerulonephritis and 12 (50%) were positive for anti-entactin antibodies. Of the remaining 56 patients without apparent renal involvement, 18 (36%) were positive for anti-entactin antibodies. (chi squared = 2.77, p > 0.05). With the exception of rheumatoid arthritis where six patients (24%) had IgM anti-entactin antibodies, the antibodies were present much less frequently in other diseases (two patients with systemic vasculitis whilst none of the patients with PSS or Behçet's syndrome). Only one patient with pneumonia and none of the 150 sera from healthy blood donors had anti-entactin antibodies. Among Group 1, three (30%) were positive for IgG or IgM anti-entactin antibodies. Six (60%) patients in group 2, and five patients (50%) in group 3 were positive for anti-entactin antibodies. However, the difference between the presence of anti-entactin antibodies between group 1 and 2 or between group 1 and 3 was not significant (p = 0.15 and 0.19 respectively). There was no significant correlation between the titres of anti-entactin antibodies and total serum concentration of IgG (r = 0.141, p > 0.10) and IgM. (r = 0.130, p > 0.10). Furthermore, no significant correlation was observed between SLE disease activity index (SLEDAI) scores and the titres of IgG (r = 0.067, p > 0.10) or IgM (r = -0.033, p > 0.10) anti-entactin antibodies.

CONCLUSION

The study demonstrates that anti-entactin antibodies are present in a significant number of patients with SLE and tend to be more common in those with severe disease, with or without nephritis, than in patients with mild disease manifestations. There is no correlation between the titre of anti-entactin antibodies and severity or activity of SLE.

Autoimmunity and glomerulonephritis

Autoimmunity is now unequivocally regarded as the predominant pathogenic process underlying most forms of primary and secondary glomerulonephritis in humans. Most of the investigations so far have been focused upon humoral mechanisms. Consequently, the role of cell-mediated immunity in nephritis is still incompletely understood. Nonetheless, as a result of contemporary studies, a number of previously unidentified auto-antibodies in association with glomerulonephritis have been discovered. However, apart from anti-NC1 antibodies in the classical Goodpasture syndrome, the exact role of these auto-antibodies in the pathogenesis of glomerulonephritis yet remains undefined. This fact, however, does not undermine the relevance of exploring these auto-antibodies. They have been of immense help in sub-classifying glomerulonephritis previously thought homogeneous (Figure 3). Besides, analysis of auto-antibodies has assisted tremendously in the early diagnosis of rapidly progressive glomerulonephritis. This, in turn, has aided in early commencement of therapy thus contributing to regression in morbidity and mortality resulting from these disorders. Moreover, investigation of these auto-antibodies is of enormous value for future studies aimed at understanding the pathogenic mechanisms involved in glomerulonephritis.

Antigenic specificities of glomerular-bound autoantibodies in membranous glomerulopathy induced by mercuric chloride

The present study describes the development of membranous glomerulopathy (MGP) with high proteinuria in DZB rats exposed to mercuric chloride (HgCl2). IgG1 and IgG2a antibodies, eluted from glomeruli with subepithelial immune deposits, bind to the interface of the GBM and epithelial cells. High reactivity to GBM was demonstrated by ELISA and Western blotting, which could be absorbed for 30% by laminin or laminin-associated extracellular matrix components. No reactivity was found with type IV collagen, fibronectin, heparan sulfate proteoglycans, or tubular brush border antigens. Absorption to GBM removed the reactivity to renal antigens. Passively transferred eluted antibodies bind in a predominantly linear pattern along the GBM, causing focal ultrastructural transformations of the podocytes. These results suggest that this type of HgCl2-induced MGP, associated with epithelial cell injury and proteinuria, is caused by autoantibodies to basement membrane components which are located at the epithelial cell-basement membrane interface and may be involved in cell-matrix binding.