Experimental mercury-induced glomerulonephritis

Changes in the renal function after acute mercuric chloride exposure in the rat are associated with renal vascular endothelial dysfunction and proximal tubule NHE3 inhibition

Mercury is an environmental pollutant and a threat to human health. Mercuric chloride (HgCl₂)-induced acute renal failure has been described by several reports, but the mechanisms of renal dysfunction remain elusive. This study tested the hypothesis that HgCl₂ directly impairs renal vascular reactivity. Additionally, due to the mercury toxicity on the proximal tubule, we investigated whether the HgCl₂-induced natriuresis is accompanied by inhibition of Na⁺/H⁺ exchanger isoform-3 (NHE3). We found that 90-min HgCl₂ infusion (6.5 μg/kg i.v.) remarkably increased urinary output, reduced GFR and renal blood flow, and increased vascular resistance in rats. "In vitro" experiments of HgCl₂ infusion in isolated renal vascular bed demonstrated an elevation of perfusion pressure in a concentration- and time-dependent manner, associated with changes on the endothelium-dependent vasodilatation and the flow-pressure relationship. Moreover, by employing "in vivo" stationary microperfusion of the proximal tubule, we found that HgCl₂ inhibits NHE3 activity and increases the phosphorylation of NHE3 at serine 552 in the renal cortex, in line with the HgCl₂-induced diuresis. Changes in renal proximal tubular function induced by HgCl₂ were parallel to increased urinary markers of proximal tubular injury. Besides, atomic spectrometry showed that mercury accumulated in the renal cortex. We conclude that acute HgCl₂ exposure causes renal vasoconstriction that is associated with reduced endothelial vasodilator agonist- and flow-mediated responses and inhibition of NHE3-mediated sodium reabsorption. Thus, our data suggest that HgCl₂-induced acute renal failure may be attributable at least in part by its direct effects on renal hemodynamics and NHE3 activity.

Risk HLA-DQA1 and PLA(2)R1 alleles in idiopathic membranous nephropathy

BACKGROUND

Idiopathic membranous nephropathy is a major cause of the nephrotic syndrome in adults, but its etiologic basis is not fully understood. We investigated the genetic basis of biopsy-proven cases of idiopathic membranous nephropathy in a white population.

METHODS

We performed independent genomewide association studies of single-nucleotide polymorphisms (SNPs) in patients with idiopathic membranous nephropathy from three populations of white ancestry (75 French, 146 Dutch, and 335 British patients). The patients were compared with racially matched control subjects; population stratification and quality controls were carried out according to standard criteria. Associations were calculated by means of a chi-square basic allele test; the threshold for significance was adjusted for multiple comparisons (with the Bonferroni method).

RESULTS

In a joint analysis of data from the 556 patients studied (398 men), we identified significant alleles at two genomic loci associated with idiopathic membranous nephropathy. Chromosome 2q24 contains the gene encoding M-type phospholipase A(2) receptor (PLA(2)R1) (SNP rs4664308, P=8.6×10(-29)), previously shown to be the target of an autoimmune response. Chromosome 6p21 contains the gene encoding HLA complex class II HLA-DQ alpha chain 1 (HLA-DQA1) (SNP rs2187668, P=8.0×10(-93)). The association with HLA-DQA1 was significant in all three populations (P=1.8×10(-9), P=5.6×10(-27), and P=5.2×10(-36) in the French, Dutch, and British groups, respectively). The odds ratio for idiopathic membranous nephropathy with homozygosity for both risk alleles was 78.5 (95% confidence interval, 34.6 to 178.2).

CONCLUSIONS

An HLA-DQA1 allele on chromosome 6p21 is most closely associated with idiopathic membranous nephropathy in persons of white ancestry. This allele may facilitate an autoimmune response against targets such as variants of PLA2R1. Our findings suggest a basis for understanding this disease and illuminate how adaptive immunity is regulated by HLA.

Cluster of systemic lupus erythematosus (SLE) associated with an oil field waste site: a cross sectional study

BACKGROUND

This is a community comparison study that examines persons living in a subdivision exposed to petroleum products and mercury.

METHODS

We compared their health status and questionnaire responses to those living in another community with no known exposures of this type.

RESULTS

Pristane house dust among the exposed homes was higher than in the comparison communities. The exposed subdivision has higher ambient air mercury levels compared to the control community. The prevalence of rheumatic diseases (OR = 10.78; CI = 4.14, 28.12) and lupus (OR = 19.33; CI = 1.96, 190.72) was greater in the exposed population compared to the unexposed. A higher prevalence of neurological symptoms, respiratory symptoms and several cardiovascular problems including stroke (OR = 15.41; CI = 0.78, 304.68) and angina (OR = 5.72; CI = 1.68, 19.43) was seen.

CONCLUSION

There were statistically significant differences in B cells, Natural Killer Cells, gamma glutamyl transferase, globulin and serum calcium levels between control and exposed subjects.

Oral, perioral and systemic pathosis in HgCl2-induced autoimmunity in the BN rat

Male BN rats were repeatedly skin-injected with HgCl2 solution and sacrificed after 6, 9, 14, 21, 28 or 24 days. Mononuclear cell infiltrates were observed in the oral mucosa and in lacrimal, salivary and thyroid glands from 6-9 days onwards, with a peak at 14-21 days. Immunohistochemistry identified these cells as predominantly T cells with some NK cells but very few B cells. Reversible parenchymal changes were observed but there was no obvious persistent tissue destruction. Serum titers of IgE, IgG1, anti-laminin and anti-DNP, but not IgG2a antibodies, were raised and peaked at 14-21 days. However, there was no correlation, within animals, between these titers and the extent of mononuclear cell infiltration. Mercury was histochemically detected within dendritic cells/macrophages in the connective tissue stroma of the glands and in the oral mucosa, but no correlation was found between the distribution of mercury and the degree of inflammation. We conclude that the accumulation of mononuclear cells in oral and perioral tissues of HgCl2-treated BN rats does not represent a local immune response to tissue-retained Hg. Instead, we propose that the extravasation represents an epiphenomenon that is not necessarily deleterious to the infiltrated organ.

Contact stomatitis to mercury associated with spontaneous mononuclear cell infiltrates in brown Norway (BN) rats with HgCl2-induced autoimmunity

Light microscopy and immunocytochemistry have been used to study the tissue reaction to non-irritant concentrations of mercury painted onto the oral mucosa of genetically mercury-sensitive BN rats. Low-dose skin injections of HgCl2 in BN rats result in an autoimmune syndrome, including also a spontaneous migration of T lymphocytes into the oral mucosa. Our results show that such infiltrates confer an increased degree of reactivity (contact stomatitis) to HgCl2 painted onto the BN (Hg) rat oral mucosa. In contrast, results were negative in the LEW rat strain, which is also resistant to development of autoimmunity to skin-injected mercury. The possible involvement of mucosal mercury-loaded macrophages is discussed. The results are also discussed with respect to possible etiologic and pathogenetic mechanisms involved in the development of dental material (amalgam)-associated lichenoid lesions of human oral mucosa.

Histochemical visualization of mercury in the oral mucosa, salivary and lacrimal glands of BN rats with HgCl2-induced autoimmunity

BN, but not LEW, rats treated with subcutaneous injections of mercuric chloride (HgCl2) develop an autoimmune syndrome with infiltration of mononuclear cells into various organs including the oral mucosa. In the present study, we have utilized autometallographic techniques to visualize mercury in the oral mucosa, salivary and lacrimal glands of mercury-sensitive BN and -non-sensitive LEW rats injected with HgCl2. Mercury was deposited intracellularly in dendritic cells that were scattered throughout the lamina propria and submucosal connective tissue of both rat strains. In addition, mercury was detected in dendritic cells appearing within small cell clusters in the juxtaepithelial connective tissue of BN oral mucosa. In salivary and lacrimal glands, mercury was found in dendritic cells scattered throughout the stroma as well as in mononuclear cell foci. Mercury was also found in ductal epithelium. No staining was seen in any of the non-mercury-treated controls. Phenotypic analysis revealed that most mercury-laden cells were ED2+ resident macrophages and that some, but not all, of these cells expressed MHC class II antigens (RT1B).

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.

Interferon gamma-mediated renal MHC expression in mercuric chloride-induced glomerulonephritis

In rodents, mercuric chloride (HgCl2) causes an autoimmune disorder with glomerulonephritis (GN), and represents an animal model for the pathogenesis of GN. We have tested the hypothesis that HgCl2 induces major histocompatibility complex (MHC) expression in renal parenchymal cells, and studied the kinetics of this induction and its temporal relation to the development of immune complex deposition in the glomeruli. Mice treated with doses of HgCl2 between 2 and 3.2 mg/kg three times for one week had increased renal expression of MHC class I and class II (at the mRNA and the product levels). Class I induction was observed in proximal tubule cells, endothelial cells and glomerular cells. Class II induction was seen mainly in interstitial cells and, to a lesser extent, in tubule cells. Renal MHC expression was maximal at one week, decreased progressively after the second week of HgCl2 administration, and reached basal levels by 23 weeks. In contrast, the amount of lymphocyte infiltration in the kidney increased from the first to the fifth week and was followed by the appearance of glomerular immune deposits from the third week on. Glomerular immune complex deposits were maximal at five weeks and, by 23 weeks, immune deposits in HgCl2-treated mice were only slightly increased over those observed in the sham group. Renal MHC induction by HgCl2 was significantly reduced by treatment with monoclonal antibody against interferon gamma.(ABSTRACT TRUNCATED AT 250 WORDS)

Experimental models of autoimmune diseases

Several experimental models of autoimmune diseases have been studied which often mimic the human situation. Autoreactive T cells that emerge either spontaneously or after immunization have been identified in several situations. The main lesson from these models is that these autoreactive T cells are negatively controlled in the normal situation and that a defect either inherited or acquired in this regulatory circuit is responsible for autoimmunity.