Relationship of kidney function to immunopathology in chronic serum sickness of rats

Differential expression of collagen type IV alpha-chains in the tubulointerstitial compartment in experimental chronic serum sickness nephritis

The expression of collagen type IV chains in the renal tubulointerstitium was investigated during the development of chronic serum sickness (CSS) in rats, a model for immune complex-mediated renal disease. Immunohistochemical studies showed increased expression of alpha4(IV) collagen early during disease development, followed by an increase in alpha1(IV) through alpha3(IV) collagen subchain expression, especially in the tubular basement membrane. Dot-blot and in situ hybridization analysis showed a transient increase in steady-state mRNA levels for all collagen IV subchains during the development of CSS, which was most abundant for alpha1(IV), alpha2(IV), and alpha4(IV). Statistical correlations were found between the mRNA levels of alpha1(IV) and alpha2(IV) collagen and between alpha3(IV) and alpha4(IV), in line with the results of others which showed that these chains are co-distributed as heterotrimer collagen type IV molecules. However, additional correlations were found between the mRNA levels coding for alpha1(IV) and alpha3(IV) collagen, and between alpha1(IV) and alpha4(IV) mRNAs in the course of CSS. These abnormal correlations support the hypothesis that changes occur in the co-expression of the collagen IV subchains during the development of CSS. In addition, a strong correlation was found between the presence in the tubulointerstitium of alpha1(IV) and alpha2(IV) collagen chains, on the one hand, and the tubulointerstitial influx of R73+ and ED1+ cells, on the other, suggesting the involvement of inflammatory cells in the observed alterations in matrix production. Changes in the relative abundance of collagen IV chains in disease states may perturb the collagen IV network in the tubulointerstitial compartment and thereby play a role in the development of renal failure.

Glomerular sequence of events concerning monocyte/macrophage accumulation and ICAM-1 expression during experimental serum sickness nephritis in the rat

Serum sickness nephritis was induced in Fischer rats by preimmunization and repeated immunization with chicken egg albumin. This experimental model is characterized by marked accumulation of monocytes/macrophages (MO) and deposition of immune complexes (IC) in glomeruli during the inflammatory stage and, thereafter, the advancement to glomerulosclerosis. The correlations between glomerular tissue damage, MO participation, intercellular adhesion molecule-1 (ICAM-1) expression and IC deposition were analyzed during the long-term disease process. The grade of ICAM-1 expression was well correlated with MO accumulation and IC deposition, and its distribution was observed on the glomerular endothelial layer, mesangium, and along the parietal epithelial layer of the Bowman's capsule. It is suggested that glomerular MO accumulation is largely affected by the ICAM-1 expression on glomeruli and, underneath such adhesion molecules, MO may play a role in subendothelial or mesangial migration, mesangial cell activation, inducing sclerosis and monocytic-epithelial crescent formation.

Glomerular macrophage phagocytic activity in experimental immune complex nephritis

In rats with the proliferative immune complex glomerulonephritis of chronic serum sickness, kidney function deteriorates in three clearly distinguishable and discrete stages: mild, moderate and severe. The macrophage component of glomerular inflammation in each stage is also quantitatively and qualitatively distinct, with abnormal phenotypic markers appearing in the moderate stage and increasing in the severe stage. To determine whether there were distinct functional differences among macrophages from the three stages, Fc gamma receptor-mediated phagocytic capacity was measured. The phagocytic capacity of glomerular macrophages increased significantly in the moderate stage, then significantly decreased, as rats progressed to severe chronic serum sickness. This decline in phagocytic function was not associated with a decrease in the expression of Fc gamma receptors on the glomerular macrophage cell surface. Furthermore, the phagocytic function of peritoneal macrophages from rats with severe chronic serum sickness was not impaired. Whether or not this attenuation of glomerular macrophage phagocytic capacity is the cause, or result, of renal disease progression remains unclear. It may indicate a potentially protective role for intraglomerular macrophages, and can serve as an additional functional marker of disease progression.

Induction of type 2 salivary cystatin in immunological and chemical kidney injury

We have previously reported that isoproterenol induces type 2 salivary cystatin in both submandibular glands and kidney tubule cells of rats but not in any other organs examined. In the present study, we investigated whether this salivary protein is induced in other conditions that show kidney tubule injury. Immunocytochemistry, using a monospecific antiserum to this cystatin, revealed specific staining within the proximal tubule epithelium of the cortex as well as in the inner and outer stripe of the medulla of immunologically and chemically injured rats. Cystatin could not be detected in kidneys from healthy rats by means of immunocytochemistry. Weak staining was found in 3/3 kidneys of rats treated with turpentine and in 5/5 animals treated with potassium dichromate. In rats treated with puromycin, cystatin could not be demonstrated in 5/5 animals having proteinuria of less than 100 mg/24 h; however, moderate staining was observed in 4/5 puromycin-treated rats having proteinuria greater than 100 mg/24 h. In Heymann nephritis, cystatin was present in 7/31 kidneys with proteinuria lasting 6 to 15 weeks and in none (0/7) with proteinuria of shorter duration. Strong staining was also observed in 10/10 kidneys from rats with moderate-to-severe chronic serum sickness. This study shows that elaboration of type 2 cystatin in rats is not limited to salivary glands and, with our previous study, suggests that induction of this cysteine inhibitor may represent a local response to generalized tissue injury in both submandibular and renal tissues. These findings further demonstrate that induction of cystatin in salivary glands is not unique to these glands and suggest that induction of this cysteine proteinase inhibitor may represent a local response to tissue injury caused by diverse mechanisms.

Endogenous creatinine clearance in the rat: strain variation

The clearance of endogenous creatinine was examined in five strains of rats (Wistar, Wistar Kyoto, Spontaneously Hypertensive Rats, Biobreeding/Worcester diabetic prone and diabetic resistant rats). Creatinine clearance was compared with inulin clearance as the standard. Conditions for clearance measurements were also varied (anesthesia with constant infusion, overnight collection of urine, fed vs. unfed state, single-injection technique). The clearance of creatinine adequately reflects the glomerular filtration rate in three strains (Wistar, Wistar-Kyoto and the Spontaneously Hypertensive Rat). In the two strains of the Biobreeding/Worcester rat creatinine clearance is consistently lower than the inulin clearance. When creatinine clearance is measured from an overnight collection of urine with food withheld it is always lower than when food is present. This clearance should always be validated by comparison with inulin clearance measured simultaneously or under comparable conditions. The ease with which endogenous creatinine clearance can be measured makes it a reasonable method when large numbers of repeated determinations of glomerular filtration rate are required.

Progressive glomerular injury after recovery from acute glomerulonephritis in rats

To determine if an acute immunologic injury resembling poststreptococcal nephritis could lead to chronic renal injury, rats with immune-complex glomerulonephritis produced with cationic human gammaglobulin were followed for 48 weeks. During Week 1, animals developed severe proteinuria, hypoalbuminemia, and a diffuse proliferative/exudative glomerulitis. Substantial recovery, characterized by a significant decline in urinary protein excretion and normalization of plasma albumin concentration, occurred by Week 4. Subsequently, rats developed significantly elevated blood pressures and increasing proteinuria. Glomerular histology at Week 48 revealed minimal inflammation, significant hypertrophy, and considerable sclerosis. We conclude that chronic, progressive renal disease can evolve after apparent recovery from an acute immunologic insult. Further study of this model should provide clinically relevant information about the mechanisms underlying this process.

Glomerular macrophage proliferation in experimental immune complex nephritis

In immune complex nephritis, glomerular hypercellularity is known to result from the proliferation of intrinsic cells and from the infiltration of mononuclear cells, primarily macrophages. An immunohistochemical double-labeling procedure was used to determine whether macrophages were among the cells which may undergo mitosis within the glomerular tuft. The monoclonal antibody ED1 served as a macrophage marker; cells in the S-phase of mitosis were recognized by uptake of bromodeoxyuridine. Glomerular proliferation was studied in chronic serum sickness of LEW rats, an animal model of immune complex nephritis for which the relationship between immunopathology and pathophysiology has been well described. In normal glomeruli, resident mesangial macrophages accounted for an unexpectedly large proportion (greater than or equal to one-third) of the total mitotic activity. In immune complex glomerulonephritis, the rate of glomerular macrophage proliferation increased rapidly just at the onset of proteinuria and remained high throughout the remaining course of disease. Glomerular macrophages from rats with proliferative nephritis also divided more vigorously than normal in short term culture in vitro, while persistently expressing abnormal surface marker phenotypes. The proliferation of mesangial macrophages appears to be a prominent feature of the normal process of glomerular cell renewal. In hypercellular glomeruli, vigorous local proliferation could greatly amplify the potential of macrophages to cause damage.

Mononuclear cells in glomeruli and cytokines in urine reflect the severity of experimental proliferative immune complex glomerulonephritis

Immunohistochemical methods were used to investigate the role of macrophages in the progression of proliferative immune complex glomerulonephritis. The mononuclear cell component of glomerular inflammation was analysed in three different stages of chronic serum sickness, each of which was clearly distinguished by criteria of kidney function. Urinary excretion of the macrophage secretory products interleukin-1 and tumour necrosis factor was also evaluated in relation to the functional severity of kidney disease. T lymphocytes and macrophages began to accumulate in glomeruli at the onset of proteinuria, but not before. Urinary excretion of interleukin-1 also began with proteinuria. Proteinuria increased in direct correlation with increases in the number of glomerular macrophages. Development of the most severe stage of glomerulonephritis, characterized by cachexia, declining kidney function, and necrotizing glomerular pathology, was accompanied by the disappearance of T cells from glomeruli and the expression of highly abnormal phenotypes by most macrophages. In addition, there was a switch from urinary excretion of interleukin-1 to excretion of tumour necrosis factor. The progression of proliferative immune complex glomerulonephritis was associated with qualitative as well as quantitative changes in glomerular macrophage populations. Differentiation and/or activation of those glomerular macrophages may have resulted from local T cell-mediated immunoregulation. Measurements of urinary cytokine excretion provided a reliable means of monitoring disease progression. The local action of tumour necrosis factor probably contributed to declining kidney function in the most severe stage of disease.

A transition from proliferative to membranous glomerulonephritis in chronic serum sickness

Chronic serum sickness glomerulonephritis was induced in rats by daily i.v. administration of bovine serum albumin (BSA). Previous studies have shown that the disease progresses through three discrete stages: mild, moderate and severe. The diffuse, proliferative necrotizing glomerulonephritis of severe chronic serum sickness, which is accompanied by a decreased glomerular filtration rate and increased glomerular permeability to macromolecules, has an inevitable fatal outcome. In the experiments reported here, BSA injections were discontinued at the transition from moderate to severe glomerulonephritis, a point which was identified by decreased sodium excretion. Retrospectively, rats could be divided into two categories. Some, called non-survivors, continued to exhibit sodium retention. Those animals progressed rapidly to end-stage renal disease and died within two weeks of the cessation of antigen injections. Others, called survivors, returned to sodium balance and remained alive for many months. The development of progressive membranous glomerulonephritis, with prominent spike formation and disappearance of glomerular hypercellularity, was noted in all survivors. That change in histopathology occurred in the absence of both circulating BSA and precipitating antibodies to BSA. The transition of proliferative to membranous glomerulonephritis was accompanied by partial recovery of glomerular function, although proteinuria persisted. Maintenance of severe proteinuria did not appear to depend on an active immunological process.

Reabsorption of horseradish peroxidase by proximal tubules in rats with Heymann nephritis

The distribution of the histochemical protein tracer, horseradish peroxidase, was studied in proximal tubules of rats with Heymann nephritis. Peroxidase reabsorption was substantially reduced in stage 2 of Heymann nephritis, a period during which the brush border of proximal tubules is severely damaged by specific antibodies. Impairment of the reabsorption function could not be attributed either to proteinuria or disturbances of proximal tubule metabolism and appeared to result from loss of microvilli. Recovery of brush border membrane morphology in stage 4 of Heymann nephritis was not accompanied by recovery of the normal capacity to reabsorb peroxidase. Functional deficits resulting from immunologic injury to proximal tubules in Heymann nephritis may persist despite waning of the anti-brush border antibody response and regeneration of the brush border of proximal tubule cells.

Pathophysiology of the kidney in rats with Heymann nephritis

Alterations in kidney function were assessed early in the course of Heymann nephritis that was induced in rats by immunization with Fx1A, an extract prepared from rat kidney cortex. Whole kidney and single nephron function were evaluated by clearance and micropuncture techniques. Kidney function was studied in stage 1 of Heymann nephritis, before the onset of proteinuria, and in stage 2, when antibodies are deposited along the brush border of proximal tubules. Although overall kidney function was similar in rats in stage 1 and normal controls, glucose reabsorption was somewhat depressed in the first part of the proximal convoluted tubule in stage 1. Both whole kidney and single nephron glomerular filtration rates were depressed in stage 2. Proteinuria in stage 2 was characterized by an increased albumin sieving coefficient, which resulted in an elevated excretion of albumin. Furthermore, several proximal tubule functions (glucose and fluid reabsorption and PAH extraction) were substantially depressed in stage 2. These findings demonstrate that immunological injury to the proximal tubules in stage 2 of Heymann nephritis produces a significant impairment of proximal function.