Accumulation Of Immune Complexes Research Articles

The immune response to the parasitic nematode Trichinella and the ways to escape it. From experimental studies to implications for human infection.

The review describes different aspects of the host immune response to Trichinella, not only at the intestinal level on which most of the studies have focused until now, but also in the muscles which represent the final target of host invasion. The role of antibodies, T cells, mast cells, eosinophils and neutrophils, respectively, in immune reaction to this nematode is considered, in the light of the recent data derived from experimental models, both "in vivo" and more recently "in vitro" and when available, from clinical observations. A section is also devoted to the principal escape mechanisms from host immune responses, described in Trichinella, which are in part common to other parasites, in part peculiar. Two groups of mechanisms are described: antigen-dependent, such as anatomic seclusion, antigen stage-specificity, shedding and renewal and molecular mimicry, and those directly affecting the host immune response. Of the latter, some act at central level like immune suppression, polyclonal activation and eosinophilia induction, others interfere with effector functions as in the case of host leukocyte modification, immune complex accumulation, blocking antibody production or complement assembly blocking. The antigenic composition of the different stages is the subject of another section which has the aim to give an overview of the principal antigens described up to now, without giving too many biochemical details, but just illustrating the candidates for possible vaccines. Finally, the perspectives for vaccination are described. Most of the results described are derived from the experimental studies, but their implications in human infection are relevant.

Systemic lupus erythematosus patients under immunosuppressive treatment express high levels of the immunoglobulin lambda variable IGLV8S1 gene with silent somatic mutations

Systemic lupus erythematosus (SLE) patients express high titers of somatically mutated serum autoantibodies against nuclear structures including double-stranded DNA. These somatic mutations accumulate codons for basic amino acids in the immunoglobulin variable regions of both, heavy and light chains, facilitating binding to nucleic acids. The variable (V) immunoglobulin lambda 8 (IGLV8S1) gene contributes to autoreactive B-cell repertoire of auto-immune patients. Accumulation of immune complexes of these anti-DNA autoantibodies causes severe systemic inflammation in SLE. The current treatment of lupus disease is based on immunosuppressive drugs, but the precise role for this therapy remains to be defined. To evaluate the in vivo effect of combined immunosuppressive treatment on B-lymphocytes repertoire of SLE patients, we have developed an approach using the IGLV8S1 gene as a marker. The transcription of this gene in treated SLE patients was increased. However, we observed a trend, in these patients, to conserve complementarity determining regions (CDRs) and framework regions (FRs) of Vλ8 polypeptide light chain deduced sequence, from its germline counterpart. Sequencing IGLV8S1 cDNA of untreated SLE patients, taken as a control for treatment effect, displayed a decreased frequency of silent somatic mutations (consequently high frequency of replacement mutations) in the Vλ8 polypeptide chain deduced sequence. These data suggest that the immunosuppressive drug treatment modulates the positive selection of somatically mutated Vλ8 light chain.

Receptor mediated endocytosis by mesangial cells modulates transmigration of macrophages.

Accumulation of immune complexes in the mesangium is a common finding. Since migration of macrophages (Mphi) in the mesangium has been demonstrated to be an important event in the development of glomerular lesions, we studied the role of immune complexes and mesangial cell (MC) interaction in the transmigration (Tm) of Mphi. To determine the effect of MC and immune complexes (aggregated IgG, IgGAg) on transmigration of Mphi. MC were incubated with or without IgGAg in the lower compartment of a modified Boyden Chamber. To determine the effects of the secretory products (as a result of endocytosis of IgGAg by mesangial cells), MC-IgAg conditioned media was prepared and placed in the lower compartment of the Boyden chamber. We evaluated the effects of MC alone, MC + IgGAg, or MC-IgGAg conditioned media on the transmigration of macrophages across a filter. To determine the effect of free radicals on MC-IgAg endocytosis-induced Mphi migration we evaluated the effect of free radical scavengers such as dimethyl thiourea (DMTU) and tetramethylthiourea (TMTU) in MC-IgAg endocytosis-induced Mphi migration. To determine the role of chemokines in MC-IgAs endocytosis-induced Mphi migration we evaluated the effect of ani-MCP-1 antibodies on MC-IgAg endocytosis-induced Mphi migration, and also studied the effects of IgAg on MC mRNA expression of MCP-1 and RANTES. In addition, we evaluated the role of Fc receptors and actin cytoskeleton of MC in transmigration of Mphi. Mesangial cell endocytosis of IgG aggregates (IgGAg) is associated with enhanced (P < 0.001) transmigration of Mphi (control, 11.2 +/- 0.2 vs. MC + IgGAg, 22.1 +/- 0.9 migrated Mphi/field). IgGAg also induced MC mRNA expression for RANTES and MCP-1 on MC. DMTU and TMTU attenuated (P < 0.001) the MC + IgGAg-induced migration of Mphi as well as IgGAg-induced mRNA expression for RANTES and MCP-1. MC and IgGAg interaction products (MC-IgGAg conditioned media) also increased (P < 0.01) transmigration of Mphi (control, 18.3 +/- 1.7 vs. MC-IgGAg conditioned media, 30.7 +/- 0.6 Mphi/field). This effect of MC-IgGAg conditioned media on the migration of macrophages was dose dependent. Anti-MCP-1 antibody partially inhibited MC-IgGAg-induced migration of macrophages. MC and monomeric IgG (MIgG) interaction (MC-MIgG conditioned media) showed a lower (P < 0.05) migration of Mphi, when compared to the MC-IgGAg conditioned media. MC-IgGAg conditioned media prepared from cytochalasin B pretreated MCs also showed a lower (P < 0.001) migration of Mphi when compared with MC-IgGAg conditioned media-induced migration. These results indicate that MC-IgGAg conditioned media-induced transmigration of macrophages may be mediated through the generation of RANTES and MCP-1 by MC.

Pathogenesis and mechanisms of inflammation in the childhood rheumatic diseases.

The presence of CD4+ cells in the synovium of children with juvenile rheumatoid arthritis has led to the generally accepted hypothesis that aberrant activation or regulation of acquired immunity is central to the pathogenesis of this family of diseases; however, this hypothesis remains unproven, and, indeed, a specific role for T cells in the process of chronic synovitis in rheumatoid disease has yet to be identified for either adults or children. In contrast, processes associated with innate immunity are undeniably involved in the pathophysiology of chronic synovitis in both rheumatoid arthritis and juvenile rheumatoid arthritis. The presence of neutrophils in the synovial fluid, complement activation, and immune complex accumulation in the synovial fluid and serum all indicate an active inflammatory process. It is reasonable to hypothesize, therefore, that there are important clues to the cause of juvenile rheumatoid arthritis to be gleaned from a more careful study of inflammation or innate immunity. This review will focus on the roles of complement, immune complexes, and the vascular endothelium in the pathogenesis of juvenile rheumatoid arthritis. In so doing, it will reexamine the dogma of the central role of the T cell in juvenile rheumatoid arthritis disease pathogenesis and offer new paradigms with which to understand this and other rheumatic diseases of childhood.

Effect of enalapril therapy on glomerular accumulation of immune complexes and mesangial matrix in experimental glomerulonephritis in the nonhuman primate

The present study is a prospective, controlled, blinded trial of enalapril therapy in experimental immune complex (IC)-mediated glomerulonephritis (GN) in the nonhuman primate (cynomolgus monkey [CYn]). Two groups of CYNs were studied: those with established GN (study A) and those in which GN was being induced (study B). In study A, 12 CYNs had GN established by 8 or 10 weeks of daily intravenous infusion of bovine gamma-globulin (BGG). These CYNs were then assigned to either 4 weeks of daily oral enalapril therapy (n = 6) or daily oral placebo therapy (n = 6). The daily BGG infusions were continued during the 4 weeks of enalapril or placebo therapy. At the start of the enalapril/placebo protocol, the two groups were similar with respect to proteinuria and level of precipitating antibody to BGG, which determined the daily BGG dose. Renal biopsy was performed in each CYN at the start and end of the 4-week period of enalapril/placebo protocol. In study 13, 15 normal CYNs were immunized to BGG over a period of 4 weeks. The CYNs were then assigned to daily oral enalapril therapy (n = 8) or placebo therapy (n = 7) based on level of precipitating antibody to BGG. At this point, daily intravenous BGG was begun along with daily enalapril or placebo for 8 weeks. Renal biopsy was performed in each CYN before and at the end of this 8-week period. In study A, enalapril therapy was associated with a significant decrease in mesangial matrix volume (mean change, −27.7%; P = 0.031) and a trend toward decreased mesangial matrix deposits (mean change, −34.1%; P = 0.188). By contrast, in CYNs receiving placebo therapy, mesangial matrix volume increased compared with the enalapril group ( P = 0.002) and mesangial deposits were unchanged. In study B, both the enalapril and placebo groups showed significant increases in mesangial matrix volume, mesangial deposits, mesangial cell volume, and capillary wall deposits during the 8 weeks of daily BGG infusion. However, none of the differences between the groups achieved statistical significance. Changes in mesangial cell volume and capillary wall deposits were also evaluated in study A and study B, but were not found to be different between the enalapril and placebo groups. In both study A and study B, blood pressure was lower in the enalapril groups. In conclusion, in the initial phase of IC-GN induction (0 to 8 weeks), enalapril therapy does not significantly influence the glomerular accumulation of mesangial matrix or immune deposits. However, in established IC-GN (after 8 weeks of GN induction), enalapril therapy significantly decreases the further accumulation of mesangial matrix and may decrease the further accumulation of mesangial deposits. Whether this benefit of enalapril therapy was related to lower blood pressure or to other effects of angiotensin-converting enzyme (ACE) inhibition was not determined in this study.

Morphine enhances deposition of ferritin-antiferritin complexes in the glomerular mesangium.

Since increased mesangial accumulation of matrix has been considered to be an important event in the development of focal glomerulosclerosis, we investigated whether morphine, an active metabolite of heroin, can modulate mesangial accumulation of immune complexes. Control or morphine-dependent rats were administered intraperitoneal ferritin (8 mg/100 g body weight) daily for 6 weeks. Body weight, blood pressure, serum creatinine, 24-hour urinary protein and creatinine excretion rates were measured at 3-week intervals. Rats were sacrificed at the end of 6 weeks and kidney tissue was studied by light, immunofluorescence and electron microscopy. Serum creatinine levels and urinary protein excretion rates were not different between control and morphine-dependent rats. All morphine-dependent rats developed hematuria, whereas only 1 control rat developed hematuria. Light microscopy revealed no proliferation of mesangial cells and only a minimal increase in the mesangial matrix. Electron-microscopic studies showed deposition of immune complexes in the mesangial region. Mesangial cells showed aggregation of ferritin in lysosomes. Immunofluorescence studies revealed the presence of IgG staining predominantly in the mesangial region. The majority (60%) of morphine-dependent rats showed a diffuse mesangial deposition of IgG when compared to control rats (83%) who showed only focal deposition. These results indicate that morphine enhances deposition of immune complexes in the mesangium. Morphine-induced matrix but may also change its quality. This may play a pathogenic role in the development of glomerular lesions in patients who abuse opiates.

Circulating immune complexes in renal injury.

T HE IMMUNOLOGIC basis of most forms of glomerulonephritis (GN) is well established. Immune-mediated glomerulonephritis in humans was initially defined by the pattern of glomerular immune deposits observed by immunofluorescence microscopy. Linear immunoglobulin (1g)G deposits along the glomerular basement membrane (GBM) were thought to be and have since been proven to be the result of antibodies binding directly to intrinsic renal antigens. In contrast, granular immune deposits were thought to result from passive trapping of circulating immune complexes (CIC). Following considerable controversy, it is now well established that granular immune deposits can arise from several mechanisms. In some cases, like anti-GBM disease, antibodies bind directly to intrinsic renal antigens; however, when the antigen is discontinuously distributed in the glomerulus, granular rather than linear deposits result. This is one form of in situ immune complex (IC) formation. Alternatively, granular immune deposits can be composed primarily of nonrenal antigens and their antibodies and reflect the formation of antigen-antibody (immune) complexes in the circulation and their localization within renal structures. The dynamics of formation of these complexes in the circulation, their trapping, rearrangement, and further accretion within the glomerulus, and the immunochemical characteristics that determine their ability to initiate renal injury are the focus of this article. The considerable progress that has been made in the previous 40 years in our understanding of immunecomplex mediated glomerulonephritis (ICGN) has been extensively reviewed previously and the reader is referred to those reviews for additional background. ‘-I2 The pathogenic potential of nonrenal circulating antigens is dependent on unique biochemical characteristics of the antigen as well as the nature of the immune response elicited by the antigen. Glomerular properties such as the high rate of blood flow, transcapillary hydraulic pressure gradient, fixed-negative charges within the capillary wall, and the unique set of extracellular matrix and cell surface proteins all contribute to the potential for macromolecular interactions that facilitate glomerular IC accumulation. The efficiency of the mononuclear phagocyte system for clearance of CIC is critically important, because glomerular IC accumulation increases when phagocyte function is impaired or overwhelmed.3~‘3~‘4 The dynamic equilibrium that exists between IC formation, clearance, and tissue accumulation is further illustrated in Fig 1 and discussed below. Despite our considerable knowledge, many questions remain unanswered. Early studies2*‘4-16 focused on quantitation of CIC as correlates of disease activity. These studies found the presence of CIC in the absence of disease manifestations and suggested that only subsets of IC were pathogenic. It was initially thought that CIC analysis would lead to antigen identification in human ICGN and thereby elucidate the etiologic agent and lead to an obvious approach to prevention and treatment. Early studies of serum sickness in the rabbit shed light on why our original hopes have not been fulfilled. Rabbits given identical antigen with identical dosage schedules develop a wide variety of histological forms and variable severity of ICGN. This indicated the critical importance of the individual animal’s immune response to the ultimate development of renal disease. Most current attempts to understand the pathogenic mechanisms responsible for ICGN are focused on basic concepts of regulation of the immune response and the unique biochemical characteristics of IC and their constituents that convey the capacity to deposit in the kidney (nephrotropic) and initiate injury (nephritogenic). In light of this, the antigen features that dictate antibody specificity, regulation of antibody synthesis, and the structure,

Proteolytic machinery of glomerular epithelial cells against IgG

Accumulation of immune complexes in the subepithelial region of the glomerular basement membrane results in the lesion of membranous nephropathy. The inefficient handling of immune complexes by the glomerular epithelial cell was investigated by studying the mechanism of IgG proteolysis by the intracellular proteases of cultured epithelial cells. Radiolabelled IgG was incubated with extracts of cells and the digestion of IgG was monitored by SDS-PAGE analysis. Prolonged incubation of IgG with the cell extracts resulted in only partial degradation of the IgG. The enzyme responsible for the breakdown was determined to be the lysosomal cathepsin D based on the pH optimum and the presence of aspartate in the active site of the enzyme. SDS-PAGE analysis of the digestion fragments revealed that a large proportion of the incompletely degraded IgG was the (Fab) 2 fragment, which was resistant to further proteolysis. This could be one of the possible explanations for the slow removal of IgG from the subepithelial location of the basement membrane.

Effect of isologous and autologous insulin antibodies on in vivo bioavailability and metabolic fate of immune-complexed insulin in Lou/M rats.

The in vivo bioavailability, distribution, and metabolic fate of 125I-labeled insulin complexed to isologous and autologous antibodies were studied in inbred Lou/M rats. There was an impaired bioavailability of the 125I-insulin bound to the isologous and autologous antibodies. Very little of the 125I-insulin in these immune complexes could bind to insulin receptors on hepatocytes or renal tubular cells and be degraded, because the amounts of 125I from degraded 125I-insulin in the blood or secreted into the stomach were markedly attenuated in both cases for at least 30 min after injection. There was a simultaneous accumulation of 125I-insulin immune complexes in the liver and the kidneys of Lou/M rats injected with 125I-insulin complexed with isologous antibodies or when insulin-immunized Lou/M rats were injected with 125I-insulin during the same interval. The impaired bioavailability of immune-complexed insulin and altered distribution of radioactivity due to the accumulation of immune complexes in the liver and kidney were also observed in previous experiments in which Lewis rats were injected with xenogenic guinea pig and homologous insulin antibodies. These observations are therefore submitted as evidence that the Lou/M rat is a valid model in which to study the bioavailability of insulin immune complexed to isologous, homologous, and xenogenic antibodies and the metabolic fate of the respective insulin-antibody immune complexes.

Effect of prostaglandins on immune complex interaction with glomerular cells in vitro.

Previous studies demonstrated that prostaglandins of the E1 (PGE1) series reduced immune complex (IC) accumulation and inflammation in murine glomeruli in IC glomerulonephritis (GN). This study examines the effect of PGE1 on IC interaction with cultured rabbit glomerular cells and heparan sulfate synthesis by the cells. IC were formed with antigen chemically modified to produce a cationic (CAT) charge or left unmodified (UM). CAT IC binding to cells was greater than UM IC in the absence of PGE1. CAT IC binding to cells was increased by PGE1 while UM IC interaction was not affected. Prolonged exposure of cells to PGE1 enhanced CAT IC binding. Heparan sulfate synthesis by the cells was not affected by the concentrations of PGE1 employed. The findings suggest the benefit provided by PGE1 in murine IC GN may not be due to a direct effect on glomerular cells which reduces glomerular IC accumulation.

Spontaneous glomerulonephritis in rabbits: Role of a glomerular capillary antigen

Overt glomerulonephritis, detected by abnormal proteinuria, occurred in 3.3% of young (2.5 kg) male New Zealand White (NZW) rabbits. Histologically, mild to moderate mixed membranous and proliferative glomerulonephritis was observed. Glomerular deposits of IgG and C3 and electron microscopic findings were not typical of circulating immune complex accumulation, nor did they suggest anti-glomerular basement membrane (GBM) antibody. Segmental and less intense glomerular deposits of IgG were found in up to 48% of nonproteinuric NZW rabbits of the same age; histologic changes were minimal. IgG antibodies in sera from proteinuric rabbits or eluted from their kidneys reacted by indirect immunofluorescence with antigens distributed (discontinuously) along the glomerular capillary walls, and in some cases within the walls of small arteries of normal rabbit kidney sections. By indirect immunoperoxidase electron microscopy, the reactive antigens were present at the surfaces of the epithelial cell foot processes where they abut the GBM. This spontaneous glomerulonephritis appears to involve fixation of antibodies to antigens distributed in a discontinuous pattern in the glomerular capillary wall. The mechanism would be much like that causing anti-GBM antibody glomerulonephritis, except that the glomerular antigen is different. Possibly some forms of glomerulonephritis develop in humans as a result of a similar process.

The macrophage-phagocyte system in rabbits with experimentally induced serum sickness: functional studies.

The objective of this study was to measure the phagocytic functions of the spleen and the liver and, if possible, to correlate them with the morphology and the immunohistology of these organs in rabbits with serum sickness. Serum sickness was induced by repeated intravenous injections of bovine serum albumin (BSA). Rabbits with acute serum sickness (stage A of serum sickness), with chronic serum sickness (stage C), rabbits in a stage of immunization between stage A and stage C (stage B), and rabbits that did not respond to the antigenic challenge [nonresponders (NR)], as well as nonimmunized (NI) rabbits were used. The function of the spleen and of the liver was measured by the clearances of 51Cr-labeled heat damaged (HE), periodate-treated (PE), or immunoglobulin G (IgG)-coated (IgGE) autologous erythrocytes. In NR rabbits the functions of the spleen and liver were normal. In rabbits in stage A of serum sickness the clearance of HE, the only one measured in this stage, was decreased. In rabbits in stage B the clearances of HE and IgGE were determined; both clearances were decreased. In rabbits in stage C, the clearances of HE and IgGE were decreased, while the time of clearance of 50% (T 1/2) of PE was not significantly prolonged. In addition, in rabbits in stages A, B, and C the ratio of whole spleen vs liver radioactivity was increased. In rabbits in stage B the clearance of HE returned to normal 3 days after discontinuation of BSA injections. While all animals with detectable morphologic and immunohistologic changes of the spleen and the liver had prolonged clearances of treated erythrocytes, some animals with similarly prolonged clearances lacked evidence of pathology of these organs. The results obtained indicate that: (1) In NI and in NR rabbits, treated erythrocytes are rapidly removed by the macrophage-phagocyte system (MPS) and preferentially by the liver. (2) In rabbits in stages A, B, and C of serum sickness the clearances of treated erythrocytes are significantly prolonged. Moreover, treated erythrocytes appear to be preferentially removed by the spleen, indicating that the ability of the spleen to clear treated erythrocytes is less impaired than that of the liver. (3) In stages A, B, and C of serum sickness the nonimmunologic clearance of autologous erythrocytes is as altered as the clearance that occurs via Fc receptors. (4) In rabbits in stage B of serum sickness recovery of MPS function occurs after the interruption of BSA injections, suggesting reversible damage.(ABSTRACT TRUNCATED AT 400 WORDS)

Complement-mediated defect in clearance and sequestration of sensitized, autologous erythrocytes in rodent malaria.

We investigated the ability of malaria-infected and normal mice to clear particulate immune complexes consisting of autologous erythrocytes sensitized with either IgG or complement. Normal mice rapidly clear autologous erythrocytes optimally sensitized with IgG and the liver plays a major role in their sequestration. Clearance of optimally sensitized erythrocytes is complement-dependent because cobra venom factor-treated, normal mice failed to clear these cells rapidly, unless they had been pre-treated with fresh mouse serum. In the initial phase of Plasmodium berghei infection, clearance of the optimally sensitized erythrocytes was markedly increased over that observed in normal mice. 2 wk after infection, however, clearance was minimal. This defect was most likely the consequence of the hypocomplementemia observed at this stage of infection since sensitized erythrocytes were removed rapidly from the blood if they had been coated with C3 in vitro before injection into malarial mice.The functional activity of the complement receptors of phagocytic cells was assayed in malarial mice by the injection of autologous erythrocytes coated with C3 and C4 in the absence of antibody. The complement-coated erythrocytes were rapidly removed from the blood, accumulated in the liver, and then gradually returned to the circulation. Similar patterns were observed in normal animals, but the degree of clearance was considerably higher in the malarial mice late in infection. It appears, therefore, that complement receptors remain functional throughout the infection. Erythrocytes suboptimally sensitized with IgG were cleared minimally by normal mice. This clearance was not complement-dependent and was mediated mainly by the spleen. During malaria, clearance of these particles was initially enhanced but later it was abolished.The association of hypocomplementemia with a major splenic defect in clearance late in malaria infection may explain the accumulation of immune complexes in pathological sites observed in this disease.

Human C4-binding protein. Association with immune complexes in vitro and in vivo.

C4-binding protein (bp), a glycoprotein with specific binding affinity for the activated form of C4 (C4b), has recently been isolated from human serum and partially characterized. This report demonstrates that C4-bp is incorporated into soluble immune complexes after complement activation in vitro. The reaction requires Ca++ ions and the presence of C4 in serum. Immunopathological studies of various forms of glomerulonephritis revealed intense C4-bp deposition in glomeruli from patients with immune-complex type of pathogenesis. C4-bp deposition was in close correlation with that of C4. These observations, together with the in vitro association of C4-bp to immune complexes, support the notion that the deposits in glomeruli represent the local accumulation of immune complexes.