The high lectin-binding capacity of human secretory IgA protects nonspecifically mucosae against environmental antigens

The anti-infectious role of human milk may be, at least partly, ascribed to its content in secretory IgA. As lectins are present in various infectious antigens, the binding of different types of IgA to three lectins (concanavalin A, peanut agglutinin, wheat germ agglutinin) was studied by Elisa. The specificity of those bindings was assessed by inhibitory experiments performed with the corresponding oligosaccharides. The following were found for the three lectins: (1) the lectin-binding capacity of colostrum secretory IgA was markedly greater than that of normal plasma IgA1 (p less than 0.001); (2) the lectin-binding capacity of polymeric IgA1 was greater than that of monomeric IgA1 (p less than 0.001). This property of mucosal IgA may be responsible of a nonimmune opsonization able to prevent the early step of some infectious mucosal diseases, i.e. the attachment of bacteria to epithelial cells by lectin-like bonds and also the penetration into the body of some antigens able to favor the development of allergy. Milk mucosal IgA, present in significant amounts in human colostrum and mature milk - but not in infant formulas - may therefore play an important polyvalent protective role in newborns.

Evidence for a role of accessible galactosyl or mannosyl residues of Fc domain in the in vivo clearance of IgG antibody-coated autologous erythrocytes in the rat

The potential role of accessible galactosyl or mannosyl residues of IgG in the clearance of IgG-coated autologous red blood cells (IgG-RBCs) by the spleen and the liver was investigated in the rat using rabbit anti-rat RBC IgG antibody molecules differing from each other by their capacity to bind in vitro to peanut agglutinin (PNA) and concanavalin A (Con A), i.e., two lectins that specifically bind to beta-galactosyl and alpha-mannosyl residues of Fc domain, respectively. Those IgG molecules [IgG(PNA) or IgG(Con A)] were separated from the starting anti-RBC IgG antibody batch [IgG(total)] by affinity chromatography on lectin columns. Each IgG-RBC preparation was labeled with 99mTc, and was reinjected iv with autologous rat RBCs labeled with 111In to correct for 99mTc present in the blood contained in each organ. The mean specific spleen uptakes per gram of the three IgG-RBC preparations increased according to the level of RBC sensitization but were at least 10 times higher in each instance than the mean specific liver uptake per gram. Consistent with the clearance curves of IgG(PNA)-RBCs, the mean specific splenic uptake per gram of those RBCs was significantly increased as compared to the same parameters determined using either IgG(total)-RBCs or IgG(Con A)-RBCs. In contrast, the mean specific liver uptakes per gram of IgG(PNA)-RBCs, of IgG(Con A)RBCs, or of IgG(total)-RBCs were not significantly different under otherwise identical experimental conditions. The increase in the splenic removal of IgG(PNA)-RBCs was C3 independent. Furthermore, splenic macrophages isolated from rats were able to bind in vitro significantly more IgG(PNA)-RBCs than IgG(total)-RBCs or IgG(Con A)-RBCs. These data therefore support the concept that, in the rat, the kinetic of removal of IgG-RBCs from the bloodstream by the Fc receptors of splenic mononuclear phagocytes may vary according to the nature of accessible carbohydrates located in the Fc domain of IgG antibody molecules coating the erythrocytes.

Effects of mannose and mannose derivatives on the clearance of IgG antibody-coated erythrocytes in the rat

The effects of D-mannose, mannose dimers, mannan, or lactotransferrin [a glycoprotein containing mannose alpha-(1,6) linkages] infusion on the clearance of IgG-coated, 99mTc-labelled, autologous red blood cells (IgG-RBC) by the spleen and liver were investigated in the rat. Untreated autologous rat RBC labelled with 111In were simultaneously injected to correct for 99mTc present in the blood contained in each organ. In normal rats, the mean specific spleen uptake (per g) of IgG-RBC was about 10 times higher than the mean specific liver uptake (per g). Consistent with the clearance curves of IgG-RBC, the mean specific splenic uptake of those RBC significantly decreased after D-mannose, mannose dimers, mannan, or lactotransferrin injections, compared with that measured in normal rats or in control rats receiving i.v. physiological saline, 5% or 15% glucose. In contrast, the mean specific liver uptake of IgG-RBC remained unchanged under otherwise identical experimental conditions. The splenic blockade induced by mannan and mannose derivatives was dose-dependent, C3-independent and spontaneously reversible within 42 hr. Splenic macrophages isolated from mannose- or mannan-treated animals expressed a decreased receptor activity for the Fc domain of IgG, whereas no consistent effect on the C3 receptors was noted. These data show a transient and specific impairment of the Fc(IgG)-receptor function of rat splenic macrophages after the i.v. injection of D-mannose or of mannose derivatives. They support the concept that simple sugar compounds can exhibit immunoregulatory activities in vivo, as has been already shown in vitro.

The ability of normal human monocytes to phagocytose IgG-coated red blood cells is related to the number of accessible galactosyl and mannosyl residues in the Fc domain of the anti-red blood cell IgG antibody molecules

The percentage of normal human monocytes (MCs) that are able to form rosettes with, and subsequently phagocytose, IgG-coated red blood cells (RBCs) has been determined in vitro using five batches of anti-RBC IgG antibodies. These antibodies differed from each other by their capacity to bind to lectins recognizing two of the oligosaccharide structures of the Fc domain, namely, peanut agglutinin (PNA) and concanavalin A (ConA) which specifically bind to beta-galactosyl and alpha-mannosyl residues, respectively. The threshold between high (H) and low (L) binding capacities (BC) was arbitrarily fixed at 15% of mean specific binding. For each level of RBC sensitization tested (1500-6000 Ab molecules/one RBC), the percentage of MCs binding at least three IgG-RBCs was similar whatever the IgG Ab preparations used. In contrast, the percentage of MCs capable of phagocytosing at least three IgG-RBCs coated with 3000, 4500 and 6000 IgG/cell, as well as the phagocytosis index (number of IgG-RBCs ingested/100 MCs) of IgG-RBCs coated with 1500, 3000, 4500 and 6000 IgG/cell, were significantly lower (P less than 0.01 at least) using IgG Ab molecules with either [(PNA-H)(ConA-H)] BC, [(PNA-L) (ConA-H)] BC or with [(PNA-L)(ConA-L)] BC than the corresponding values measured using RBCs coated with IgG Ab molecules exhibiting [(PNA-H)(ConA-L)] BC. The binding to MCs of 125I-labelled anti-RBC IgG Ab molecules exhibiting different binding profiles to PNA and to ConA was studied by Scatchard plot analysis. A single class of binding sites was observed in each case. MCs bound a mean of 23,000 IgG molecules with a mean association constant (Ka) for IgG binding of about 1.4 X 10(8) M-1. These data indicate that terminal (and/or accessible) galactosyl and mannosyl residues of IgG Ab molecules play a role in the ingestion of IgG-RBCs by human MCs, despite the fact IgG Ab binding to IgG(Fc) receptors is not significantly affected. Thus, when studying the phagocytosis of IgG-coated RBC by human MC monolayers, the assay should be performed not only using similar RBC/MC ratios and IgG coating values, but also with IgG antibodies having comparable mean PNA and ConA binding capacities.

Acute experimental glomerulonephritis induced by the glomerular deposition of circulating polymeric IgA-concanavalin A complexes

The perfusion of polymeric or secretory IgA-Concanavalin A complexes into the aorta of rats led to a mannose-dependent binding of both IgA and lectin to the glomerular capillary wall, as shown by double immunolocalization experiments, by quantitative analysis of the amount of radiolabelled complexes bound per g of kidney, and by blocking experiments with the corresponding carbohydrate. Rats injected with amounts of those complexes as low as 500 micrograms developed, one hour later, a focal and segmental proliferative glomerulonephritis characterized by the deposition of injected complexes and of rat C3 and rat fibrin/fibrinogen in most glomeruli; focal thrombosis and small areas of necrosis in 10 to 15% of glomeruli, confined to the periphery of a single lobule of the tuft and segmental infiltration of these glomeruli by polymorphonuclear leucocytes and platelets. At the same time, many mesangial cells exhibited a hyperactive appearance, and red blood cells were noted in tubular lumens. In contrast, rats similarly injected with either monomeric IgA-ConA complexes, multimeric or secretory IgA-peanut agglutinin complexes or polymeric or monomeric IgA aggregates of comparable apparent molecular weight did not develop obvious glomerular lesions within one hour. The data indicate that performed polymeric IgA-ConA complexes can specifically bind to glomerular structures in vivo and trigger acute glomerular lesions locally, analogous to those observed in some glomerular diseases associated with a cryoglobulinaemia.

Evidence that the phagocytosis mediated by the peanut agglutinin-like activity of IgG(Fc) receptors of human monocytes is selectively modulated by estradiol and natural estrogens

The percentage of human monocytes (MCs) that are able to form rosettes with, and to phagocytose, IgG-coated sheep red blood cells (IgG-SRBCs) has been first determined in vitro by a classical rosette assay in 12 postmenopausal (PM) women. Half of them never received any suppletive estrogen (E) therapy at the time of testing, whereas the other six were chronically treated with E. Three different preparations of the same anti-SRBC IgG antibody batch were coated to SRBCs: the first one was the starting antibody preparation [IgG(total] and the other two were purified by affinity chromatography either on Sepharose-concanavalin A (Con A) or on agarose-peanut agglutinin (PNA) columns specifically recognizing terminal, and/or accessible, alpha-mannosyl [IgG(Con A)] or beta-galactosyl [IgG(PNA)] residues of the Fc domain, respectively. The three IgG preparations exhibited similar hemagglutinating antibody titers (1/100). All experiments were conducted using a coating range of 5000 to 6000 IgG antibody molecules per SRBC. In PM women with E, the rosetting capacity of autologous MCs (percentage of MCs rosetting at least three IgG-SRBCs), their phagocytosing capacity (percentage of MCs ingesting at least three IgG-SRBCs), and the phagocytosis index (number of SRBCs ingested/100 MCs) were similar for each IgG-SRBC preparation considered. In contrast, in PM women without E, the capacity of MCs to phagocytose IgG(PNA)-SRBCs, as well as the phagocytosis index measured with those SRBCs, was strongly reduced (P less than 0.01 at least), when compared to the same parameters determined using IgG(total)-SRBCs and IgG(Con A)-SRBCs.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased intestinal permeability to (51 Cr) EDTA is correlated with IgA immune complex-plasma levels in children with IgA-associated nephropathies

Intestinal permeability was investigated in 10 normal young adults, in 11 control children and in 9 children presenting with either Berger disease (4 cases) or Henoch-Schönlein nephritis (5 cases), making use of (51 Cr) EDTA as a probe molecule. All subjects exhibited a normal creatinine clearance at the time of testing. After oral administration of (51 Cr) EDTA, 24-hour urine radioactivity was measured and results were expressed in percentage of the oral dose administered. Means and SD were 2.35% +/- 0.77, 2.51% +/- 0.70, and 5.10% +/- 2.35 for normal adults, control children and patients with IgA-associated nephropathies, respectively. The differences of permeability between controls and patients were statistically significant (p less than 0.01). In addition, a significant, direct, linear correlation has been established between the percentage of (51 Cr) EDTA excreted in 24-hour urine and IgA immune complex-plasma levels. Our results therefore support the hypothesis that increased gut permeability could play a role in the pathogenesis of IgA-associated nephropathies.

The spontaneous ability of normal human IgG to inhibit the Fc receptors of normal human monocytes is related to their binding capacity to lectins

The lectin-binding capacity of 96 normal human IgG, assessed by solid-phase radioimmunoassay, strikingly varied according to the lectin considered. Indeed, half of the IgG samples exhibited peanut agglutinin (PNA)- and pokeweed mitogen-specific binding capacities superior or equal to 4%, whereas less than 15% of IgG similarly bound to concanavalin A (Con A) and to phytohemagglutinin. The ability of those IgG to inhibit the Fc receptor (Fc-R) function of human monocytes, measured by a classical rosette assay, was inversely correlated to their binding ratios to PNA and Con A only. By affinity chromatography, three groups of IgG were separated: the IgG purified on agarose-PNA columns slightly reduced the Fc-R function (40-45% inhibition); the IgG purified on Sepharose-Con A columns exhibited the highest inhibitory properties (80-85% inhibition); the IgG that did not bind to PNA and Con A columns possessed intermediate inhibitory properties (65-70% inhibition). The different effect of IgG on Fc receptors was conserved when monocytes were first treated by trypsin and was unrelated to their specific binding to human monocytes, to their subclasses, and to their C1q- or protein A-binding capacities. Incubation of monocytes with D-galactose (10 mM) significantly improved their capacity to form IgG rosettes, whereas their incubation with D-mannose (10 mM) significantly reduced the Fc-R function. Scatchard plots of 125I-IgG1 myeloma protein binding to monocytes were linear under basal conditions, as well as after a prior incubation of the cells with D-galactose or D-mannose. Monocytes bound about 16,000 molecules of IgG1 per cell in each instance. In contrast, the mean association constant (Ka) for IgG1 binding was 2.59 +/- 0.50 X 10(8) M-1 under basal conditions, 4.4 +/- 0.75 X 10(8) M-1 after D-galactose incubation, and 1.35 +/- 0.50 X 10(8) M-1 after D-mannose incubation. These data suggest that the level of human monocyte Fc-R function blockade induced by human IgG depends mainly on the presence of "accessible" galactosyl or mannosyl residues in the Fc domain and that the modulation of the Fc-R function induced by these carbohydrates is due to a change in the affinity rather than in the number of single class of high-affinity binding sites.

Relation between biological IgA abnormalities and mesangial IgA deposits in isolated hematuria in childhood

Indications for renal biopsies in isolated hematuria in childhood remain difficult to define. Their limitation to patients presenting with either a macroscopic or a familial hematuria [Trachtman et al. 1984] bears the potential risk of missing the diagnosis of IgA-associated nephropathies (Berger disease and Henoch-Schönlein nephritis) which may manifest themselves by microscopic hematuria only. In order to reevaluate the association between biological IgA abnormalities and mesangial IgA deposits, iterative and concomitant determinations of IgA plasma levels, of IgA immune complexes and of IgA production by lymphocytes in vitro have been performed over a one-year period in two groups of hematuric children presenting with mesangial IgA deposits (14 cases) or not (13 cases). The incidence of positivity of each test was significantly higher in the former group of patients than in the latter. However, the best discrimination between both groups was observed when the three tests were repeated and/or considered together (97% vs 15% of positivity). In Berger disease and Henoch-Schönlein nephritis, IgA immune complexes were the only IgA abnormality more frequently detected in patients presenting with hematuria than in patients presenting with no hematuria at the time of testing. It is proposed to add IgA abnormalities to macroscopic or familial hematuria as indications for renal biopsies in isolated hematuria in childhood.

Increased concanavalin A-binding capacity of immunoglobulin G purified from sera of patients with rheumatoid arthritis

A solid phase radioimmunoassay was set up for direct measurement of the binding capacity of human IgG to three lectins recognizing different carbohydrates of the Fc domain, i.e. peanut agglutinin (PNA), Concanavalin A (Con A) and pokeweed mitogen (PWM) which mainly bind to beta-galactose, alpha-mannose and dimers of N-acetyl-beta-glucosamine respectively. The mean specific binding of the 96 normal IgG tested to PNA and to PWM was statistically higher (P less than 0.001) than that to Con A, whereas no significant differences were observed between the mean specific bindings to PNA and to PWM. A statistically significant linear negative correlation could be established only between the relative bindings (expressed in percentage of the total binding to the three lectins) to PNA and to PWM (r = -0.65, P less than 0.001). The mean specific binding of IgG purified from 34 patients suffering from rheumatoid arthritis (RA) to PNA and to Con A was statistically higher (P less than 0.001) than that reached with PWM, whereas no significant differences were noted between their mean binding capacities to PNA and to Con A. When compared to normal IgG, only four out of 34 RA IgG exhibited a significantly higher binding capacity to PNA, whereas all but one RA IgG possessed a significantly higher binding capacity to Con A. Accordingly, the mean specific binding of RA IgG to Con A was significantly higher than that of normal IgG (P less than 0.001). Besides (and contrary to normal IgG), a statistically significant negative linear correlation was noted between the relative bindings of RA IgG to PNA and to Con A (r = -0.89, P less than 0.001). All the five RA IgG tested exhibited an abnormal circular dichroism. Our data suggest that, by altered steric conformation and glycosylation, mannosyl-residues of RA IgG become prominent or terminal or both, and are therefore able to react more effectively with Con A than normal IgG do.

Urinary excretion of neutral proteinases in nephrotic rats with a glomerular disease

A proliferative glomerulonephritis was induced in rats pre-immunized with rabbit IgG by injecting intravenously a sub-nephrotoxic dose of rabbit anti-glomerular basement membrane (GBM) IgG (A rats). Most rats (80%) developed a severe proteinuria (greater than 100 mg/24 hr) within two to five days after the injection of anti-GBM IgG. At the same time, microscopic examination of the kidneys revealed a glomerular infiltration by mononuclear phagocytes and a prominent decrease in the intensity of the colloidal iron reaction in glomeruli. A non-proliferative glomerular disease was induced in another group of rats (B rats) by intraperitoneal administration of aminonucleoside of puromycin. A marked proteinuria (greater than 100 mg/24 hr) occurred after six days in 90% of animals. Histochemical studies then revealed a decrease in staining intensity of glomeruli for polyanion. No glomerular hypercellularity was noted. In normal rats and in non-proteinuric A or B rats, the 24 hour urinary excretion of neutral proteinases ranged from 1.4 to 7.8 units (mean value +/- SEM, 4.69 +/- 0.60, N = 11), that of laminin ranged from 100 to 3,900 ng (mean value +/- SEM, 1,154 +/- 325, N = 10), and that of type IV collagen ranged from 160 to 420 ng (mean value +/- SEM, 306 +/- 26.5 ng, N = 8). In proteinuric rats from groups A (N = 11) and B (N = 9), the 24 hour urinary excretion of neutral proteinases significantly increased (mean values +/- SEM, 38.55 +/- 8.66 U for A rats and 42.17 +/- 7.92 U for B rats) and ran parallely with that of proteins, laminin and type IV collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro studies on the Fc-receptor function of mononuclear phagocytes in rheumatoid arthritis: relation between the Fc-receptor blockade and the concanavalin A-binding capacity of autologous immunoglobulin G

The Fc-receptor (Fc-R) function of monocytes isolated from 19 control subjects and from 30 patients presenting with a rheumatoid arthritis (RA) was assessed in vitro by a classical rosette assay using IgG-coated sheep red blood cells. In RA patients, the percentage of monocytes forming rosettes was significantly lower than in controls (34.4 +/- 20.4 versus 67.4 +/- 4.5%; P less than 0.001). The blockade observed was reversed by a prior trypsin treatment of RA monocytes, the percentage of recovery being correlated with the IgG plasma levels. Besides, IgG purified from the serum of four RA patients bound a mean of 7.3, 5.2, 1.6, and 1.6 times more than normal IgG did onto concanavalin A (Con A), peanut agglutinin (PNA), phytohemagglutinin (PHA), and pokeweed mitogen (PWM), respectively. Although similar amounts of 125I-labeled normal and RA IgG were bound to normal monocytes, RA IgG inhibited more efficiently than normal IgG the Fc-R function of normal monocytes, for all concentrations tested (10 to 100 micrograms/100 microliters). A prior treatment of RA IgG by alpha-mannosidase, but not by beta-galactosidase, significantly reduced their inhibitory properties. The incubation of monocytes with D-mannose or mannan reduced their capacity to form rosettes. The percentage of monocytes forming rosettes in the presence of both mannan and normal IgG was significantly lower than that measured in the presence of normal IgG only. On the contrary, the rosetting capacity of monocytes in the presence of both RA IgG and mannan was the same as that calculated in the presence of RA IgG only. The inhibitory effect of RA IgG was not related to their abnormal circular dichroism. Our data suggest that the greater ability of RA IgG to block the Fc-R function of monocytes probably depends on the presence of a greater number of accessible mannosyl residues on the glycosidic side chains located in the Fc domain of the molecules.

Elevated antigalactosyl antibody titers reflect renal injury after gold or D-penicillamine in rheumatoid arthritis

Titers of circulating antigalactosyl antibodies (a-Gal Ab) were assessed by passive hemagglutination using rabbit red blood cells in 40 normal subjects, in 14 patients with immunodeficient states, in 47 patients with active rheumatoid arthritis (RA), and in 15 patients with an Henoch-Schönlein disease (HS). Titers of controls ranged from 1:16 to 1:64. All immunodeficient patients exhibited very low titers (1:1). On the contrary, the existence of an enhanced humoral immune response status, as observed in RA, was not reflected by a parallel increase of a-Gal Ab titers. However, in this disease, a strong relationship existed between titers exceeding control values (greater than 1:64) and the prior occurrence of renal injury under gold or D-penicillamine therapy. Lastly, the discovery of elevated titers (greater than 1:64) in HS only when renal involvement occurred further suggests that such antibodies reflect a renal injury.

Sequential measurements of the reticulo-endothelial system function in Henoch-Schönlein disease of childhood. Correlations with various immunological parameters

Different immunological parameters were studied in 16 children suffering from Henoch-Schönlein purpura. The following results were observed during the acute phases in some patients: (1) an increase in C3d plasma levels; (2) the presence of circulating immune complexes (CIC); (3) an increase in IgA plasma levels and (4) an impairment of the reticuloendothelial system (RES) function assessed by an in vitro and an in vivo test. After the acute phase, all the altered parameters were almost normalized in recovering patients. On the contrary, all 5 patients with persistent urinary findings or relapsing purpura continued to present increased IgA plasma levels and/or CIC and/or impaired RES function. Our results therefore show that, in Henoch-Schönlein disease of childhood, a correlation exists between persisting clinical signs and persisting high IgA plasma levels, CIC and RES function impairment.

Electron microscopic studies in a long-term follow-up of a case of congenital nephrotic syndrome

A boy presenting with a severe congenital nephrotic syndrome diagnosed by histological analysis at the age of 3 weeks was biopsied again 7 years later. The ultrastructural glomerular basement membrane abnormalities depicted in the first biopsy were no longer present in the second one. The number of completely hyalinized glomeruli was not significantly decreased. The GFR remained normal, but a moderate persistent, non-selective proteinuria (800 mg/24 h) was noted without oedema. The patient however developed a progressive perceptive deficit of hearing.

Fc-receptor function in minimal change nephrotic syndrome of childhood

This study was undertaken to establish whether the Fc-receptor function of circulating monocytes (CM) and/or of splenic macrophages (SM) is modified during the course of minimal change nephrotic syndrome (MCNS) of childhood. The Fc-receptor function of SM was ascertained by measuring the spleen to liver uptake ratio 40 min after IV injection of heat-damaged autologous erythrocytes labeled with 99Tc, whereas the Fc-receptor function of CM was determined by a "rosetting" test. The Fc-receptor function was followed in six girls presenting with a MCNS and receiving no therapy at the time of testing. The Fc-receptor function of SM was decreased in five patients during an acute phase of MCNS. In four of these five patients, the Fc-receptor function of CM was also altered. No significant correlations were observed between the Fc-receptor blockade and the C3, C3d, C4, C3PA or immune complex-plasma levels. The Fc-receptor blockade was persistent in three girls during remission. A prior incubation of CM with trypsin did not completely reverse the Fc-receptor blockade. Further studies are now being pursued in order to determine whether this persisting abnormality is inherited and mainly observed in relapsing nephrotic syndrome.

Accumulation of several basement membrane proteins in glomeruli of patients with preeclampsia and other hypertensive syndromes of pregnancy. Possible role of renal prostaglandins and fibronectin

The glomerular lesions of preeclampsia consist of swelling of endothelial cells, interposition of mesangial cells and matrix between the endothelial cells and the glomerular basement membrane, and organization of subendothelial deposits of incompletely characterized material. Fibrin and immunoglobulins have previously been localized to these deposits. Laminin, a large basement membrane glycoprotein, type IV collagen, fibronectin, and a basement membrane proteoglycan were found in moderate amounts in the mesangium and prominently in the thickened glomerular capillary walls of patients with preeclampsia or other hypertensive syndromes of pregnancy. Fibrin showed the same pattern of distribution as that of fibronectin. The material deposited in the subendothelial layer of the capillary loops thus consists not only of plasma-derived proteins but also structural components of the glomerular basement membrane and of the mesangial matrix. Type I collagen deposits were demonstrated only in mesangium of pregnant patients with chronic or recurrent hypertension. Glomerular epithelial and mesangial cells synthesize in vitro the basement membrane proteins that accumulate in glomeruli of pregnant hypertensive patients. We have tested the influence of some of the pathophysiologic changes occurring during preeclampsia on the biosynthesis of collagen by rat glomerular epithelial and mesangial cells. Addition of indomethacin to the cultures transiently inhibited the synthesis of prostaglandins (PGE2) and of collagen. Addition of exogenous fibronectin to the media stimulated the production of collagen by mesangial and epithelial cells. Alterations in the metabolism of prostaglandins and the increased deposition of fibronectin observed during preeclampsia could thus play a pathogenic role in the accumulation of basement membrane proteins in glomeruli of these patients.

Fc-receptor function in Henoch-Schönlein disease of childhood

The Fc-receptor function of circulating monocytes (CM) and/or of splenic macrophages (SM) was followed in eight children presenting with rheumatoid purpura. The Fc-receptor of CM and/or of SM was decreased in all cases during the acute phase of the disease without any correlation with the plasma values of C3, C4, C3PA or immune complexes. When a clinical improvement occurred, a reversal of the Fc-receptor blockade was noted. In contrast, the Fc-receptor function remained abnormal in three children with persistent nephritis. The sequential measurement of Fc-receptor function may be of predictive value in rheumatoid purpura of childhood.

Evidence for a particular binding capacity of rat peritoneal macrophages to rat glomerular mesangial cells in vitro

The adhesion of normal rat peritoneal macrophages to normal rat glomerular epithelial or mesangial cells has been studied in vitro after a 60 min incubation at 37 degree C. After washing, the cell preparations were examined by phase contrast or scanning electron microscopy. Quantitative studies were also performed using macrophages labelled with 99mTc tin colloids. Peritoneal macrophages predominantly adhered to the cultured mesangial cells. The percent-age of labelled macrophages adhering to these cells was about 10 times higher than that of labelled macrophages adhering to the cultured epithelial cells. This percentage increased proportionally to the number of labelled macrophages added, and was strongly reduced by the prior incubation of macrophagic cells with aggregated IgG, with anti-fibronectin IgG, or with F(ab')2 fragments of anti-fibronectin IgG. Furthermore, the macrophage-mesangial cell interaction was significantly reduced by the prior incubation of mesangial cells with anti-fibronectin IgG or with F(ab')2 fragments of anti-fibronectin IgG. The data demonstrate that normal rat peritoneal macrophages preferentially adhere in vitro to normal rat glomerular mesangial cells, and that this binding may be modulated, at least, by: (a) the Fc receptor binding activity of macrophages; (b) the fibronectin molecules available at the surface of macrophages and of mesangial cells.

Effects of a diet deficient in essential fatty acids on the glomerular hypercellularity occurring in the course of nephrotoxic serum nephritis in rats

An accelerated model of nephrotoxic serum nephritis (NTN) was induced in two groups of Sprague-Dawley rats on the following regimens: (a) a diet deficient in essential fatty acids that contained 20% coconut oil (rats A); (b) a diet supplemented with essential fatty acids that contained 20% safflower oil (rats B). Animals from both groups developed a severe proteinuria reaching its maximum 4 days after the injection of nephrotoxic serum (NTS). Kidney tissue was studied by light and immunofluorescent microscopy 2 to 21 days after NTS injection. The glomeruli of rats A exhibited much more fibrinoid deposition than did those of rats B. A comparable glomerular infiltration by mononuclear cells was observed in both groups of animals between the 2nd and 5th day following the injection of NTS. The number of intrinsic glomerular cells incorporating 3H-thymidine in vivo, however, was significantly lower in rats A than it was in rats B. The outgrowth capacity of glomerular cells in vitro was significantly lower in glomerular explants from rats A than it was in glomerular explants from rats B. These findings demonstrate that, in this model of rat NTN, a diet deficient in essential fatty acids has no major effects on the course of the disease during the first 3 weeks following NTS injection. They further show that the proliferation of intrinsic glomerular cells can be modulated by altering prostaglandin metabolism.

Proliferative glomerulonephritis in rats: evidence that mononuclear phagocytes infiltrating the glomeruli stimulate the proliferation of endothelial and mesangial cells

A proliferative, non-crescentic, glomerulonephritis (GN) was induced in rats preimmunized with rabbit IgG by injecting a sub-nephrotoxic dose of rabbit anti-GMA IgG. Control rats either received anti-GBM IgG only, or were totally irradiated (800 rads, kidneys protected) 2 days before the second injection. All the GN rats developed a severe proteinuria within 2-4 days after the injection of anti-GBM IgG, contrarily to the control rats. At the same time, many mononuclear cells, of predominantly extra-renal origin, infiltrated the glomeruli. Glomeruli were isolated from GN, normal and control rats and were cultivated in RPMI medium. In normal and control rats cultures, epithelial and mesangial cells were observed. In GN rat cultures, not only epithelial and mesangial cells, but also endothelial and macrophagic cells were identified; the outgrowth capacity of the mesangial cells was enhanced. These data were particularly evident in cultures of GN glomeruli isolated within 2-4 days after the induction of the renal disease, exactly when the glomeruli were infiltrated by a large number of mononuclear phagocytes. It is suggested that the mononuclear phagocytes infiltrating the glomeruli of rats with this model of GN stimulate the proliferation of endothelial and mesangial cells in vitro.

Tissue culture of normal rat glomeruli: contractile activity of the cultured mesangial cells

Rat glomerular epithelial and mesangial cells, and rat skin fibroblasts, were cultured in RPMI medium containing 15% decomplemented fetal bovine serum. They were incubated for 1 h at 37 degrees C with 2 mM [Ca2+]. At that time, their response to various concentrations of angiotensin II, norepinephrine and carbamylcholine was studied by phase contrast microscopy. Only the mesangial cells exhibited contractile activity in the presence of 10(-10) M angiotensin II and 10(-6) M norepinephrine, as demonstrated by the reduction of their length or, more frequently, by modification of their shape. No contractile activity was observed in the presence of 10(-5) M carbamylcholine. The percentage of contractile cells increased proportionally to the concentration of angiotensin II, reaching about 35% with 10(-6) M angiotensin II. The contractile activity was reversible. Specific inhibitors, i.e. Sar1-ala8-angiotensin II and phenoxybenzamine, when administered in concentrations 10 to 100-fold higher than that of the corresponding agonists, completely blocked the contractile response. This competitive effect was also reversible. The data, therefore, suggest that mesangial cells in culture display some functional properties of smooth muscle cells.

Isolation and characterization of rat renal glomerular cells in vitro

Glomerular tufts were isolated from normal rat kidneys and were cultivated in RPMI 1640 medium supplemented with 15% fetal bovine serum. Studies on DNA synthesis demonstrated two peaks (A and B) of cell division. The cells of peak A grew as a monolayer until confluency, exhibited many junctional complexes and microvilli. They were very susceptible to the aminonucleoside of puromycin, as glomerular epithelial cells in vivo. They did not contain many bundles of intracellular microfilaments and were not stained by an anti-factor VIII serum. The cells of peak B formed both monolayered sheets and multilayered bands, exhibited no junctional complexes, but contained large bundles of intracellular fibrillar structures, which were strongly stained by an antimyosin antiserum. They were not stained by an anti-factor VIII antiserum. The B cells exhibited a contractile activity in response to 10(-9) M angiotensin II and were very susceptible to mitomycin C treatment, as glomerular mesangial cells in vivo. They synthesized large amounts of prostaglandins (mainly PGE2). The data suggest that the A cells are visceral epithelial cells, and that the B cells are smooth muscle-like cells derived from the glomerular mesangium.

Synthesis of collagen and fibronectin by glomerular cells in culture

The biosynthesis of collagen and fibronectin molecules by cultivated glomerular epithelial or mesangial cells was studied at confluency using radioactive proline or lysine as precursors. Collagen represented 0.5% of the total protein synthesized by the glomerular epithelial cells. About 60% of this collagenous protein were associated to the cell layer, whereas about 40% were secreted into the culture medium. Two major collagenous polypeptides were observed with apparent molecular weights of 185K and 170K, and were identified as two gene products of type IV procollagen. They exhibited ratios of 3- to 4-hydroxyproline, of total hydroxyproline to proline, and of hydroxylysine to lysine characteristic of type IV procollagen. They were degraded by bacterial collagenase. The patterns of peptides obtained after digestion of the 185K and 170K chains of this type IV procollagen with pepsin and V8 protease were identical to those obtained after digestion of type IV procollagen chains purified from a murine tumor (EHS sarcoma). Finally. a purified antibody to type IV collagen specifically immunoprecipitated the collagenous protein produced by the glomerular epithelial cells. By contrast, the mesangial cells synthesized about 5% of collagenous protein. 90% of this collagen were secreted into the cultured medium, whereas about 10% remained associated to the cell layer. Type I, III and IV procollagens were synthesized by the mesangial cells. Fibronectin was found in the medium and cell layer of both epithelial and mesangial cells. Fibronectin molecules were identified by their resistance to bacterial collagenase, their susceptibility to pepsin digestion, and their specific adherence to collagen. It was composed of disulfide-linked peptides of 220K daltons. The data therefore demonstrate that: (a) the glomerular epithelial and mesangial cells synthesize fibronectin molecules and type IV procollagen in vitro; (b) the cultivated mesangial cells also synthesize type I and III collagens. The implications of these findings in certain pathological circumstances, such as diabetes mellitus, are now being investigated.

Radioimmunologic method for detection of antitubular basement membrane antibodies

A radioimmunoassay for detection of antitubular basement membrane (TBM) antibodies was set up using a human TBM antigen (mol wt, 70,000 daltons), purified after collagenase treatment of the insoluble membrane by preparative polyacrylamide electrophoresis, and labeled with iodine 125. Free labeled antigens were separated from those bound to immunoglobulins by a 20% polyethylene glycol (mol wt, 6,000 daltons) solution. In the presence of normal human or Brown Norway rat sera, less than 10% of the labeled antigens were precipitated. In the presence of sera or of kidney eluates from rats immunized with human TBM, the precipitation of the labeled TBM antigens reached 73%, but in the presence of sera from two patients presenting with an interstitial nephritis and linear deposits along the TBM only, up to 47% of the same antigens were precipitated. In these two cases, the anti-TBM antibodies were mainly directed against the heteropolysaccharide-containing glycopeptides isolated from TBM, that is, against the noncollagenous polypeptides of the TBM antigens. Anti-TBM antibodies were sought in the sera of 52 normal blood donors and of 11 patients presenting with glomerulonephritis and linear deposits of immunoglobulins. The average percentage (+/- 1 SD) of labeled TBM antigens precipitated in the serum of normal blood donors was 7.1 +/- 1.2. Of the patients presenting with glomerulonephritis and linear deposits along the GBM, 9 out of 11 exhibited anti-TBM antibodies by radioimmunoassay; among these 9 patients, 8 also displayed linear deposits of IgG along the TBM. Absorption of anti-TBM and anti-GMB antibodies with particulate TBM or GBM, with both types of glycopeptides isolated from GBM or TBM, indicated that the anti-TBM antibodies were directed against the noncollagenous polypeptides of TBM but that the anti-GBM antibodies mainly reacted with the collagenous polypeptides of TBM and GBM. Finally, it was found that the sera of 2 patients out of 15 presenting with lupus nephritis contained a significant anti-TBM-binding activity, mainly directed against the noncollagenous material of TBM.