Immune Complex Trapping Research Articles

Pathogenesis and treatment of glomerulonephritis-an update.

This review updates current concepts of the genetic risk factors, etiologic events, nephtitogenic responses and treatment of the major immunologically mediated types of glomerulonephritis (GN). These include post-infectious GN, IgA nephropathy, anti-glomerular basement membrane (GBM) antibody disease, ANCA-associated vasculitis (AAV) and lupus nephritis. Although the etiology(s) of most GNs remain undefined, many are now believed to be initiated by environmental insults, particularly infectious processes, that trigger host responses in genetically susceptible individuals which lead to GN. Mechanistic concepts of these diseases have evolved from earlier views that most were consequent to glomerular trapping of preformed immune complexes to the current view that most of these diseases are auto-immune in nature mediated by both antibodies and T cells reactive with self-antigens. Therapy of GN has lagged behind advances in understanding pathogenesis. Newly appreciated roles for older mediators like complement and complement regulatory proteins offer new therapeutic targets.

Newly Diagnosed White Man With HIV-Associated Lupus-Like Nephropathy

AbstractAlthough HIV-associated nephropathy (HIVAN) is the most common form of glomerulopathy found in HIV-infected patients, other lesions have been reported. Lupus-like glomerulonephritis is a lesion that presents with diffuse proliferative immune-complex trapping with lupus-like features instead

Scrapie Affects the Maturation Cycle and Immune Complex Trapping by Follicular Dendritic Cells in Mice

Transmissible spongiform encephalopathies (TSEs) or prion diseases are infectious neurological disorders of man and animals, characterised by abnormal disease-associated prion protein (PrPd) accumulations in the brain and lymphoreticular system (LRS). Prior to neuroinvasion, TSE agents often accumulate to high levels within the LRS, apparently without affecting immune function. However, our analysis of scrapie-affected sheep shows that PrPd accumulations within the LRS are associated with morphological changes to follicular dendritic cells (FDCs) and tingible body macrophages (TBMs). Here we examined FDCs and TBMs in the mesenteric lymph nodes (MLNs) of scrapie-affected mice by light and electron microscopy. In MLNs from uninfected mice, FDCs could be morphologically categorised into immature, mature and regressing forms. However, in scrapie-affected MLNs this maturation cycle was adversely affected. FDCs characteristically trap and retain immune complexes on their surfaces, which they display to B-lymphocytes. In scrapie-affected MLNs, some FDCs were found where areas of normal and abnormal immune complex retention occurred side by side. The latter co-localised with PrPd plasmalemmal accumulations. Our data suggest this previously unrecognised morphology represents the initial stage of an abnormal FDC maturation cycle. Alterations to the FDCs included PrPd accumulation, abnormal cell membrane ubiquitin and excess immunoglobulin accumulation. Regressing FDCs, in contrast, appeared to lose their membrane-attached PrPd. Together, these data suggest that TSE infection adversely affects the maturation and regression cycle of FDCs, and that PrPd accumulation is causally linked to the abnormal pathology observed. We therefore support the hypothesis that TSEs cause an abnormality in immune function.

The Effects of Host Age on Follicular Dendritic Cell Status Dramatically Impair Scrapie Agent Neuroinvasion in Aged Mice

Following peripheral exposure, many transmissible spongiform encephalopathy (TSE) agents accumulate first in lymphoid tissues before spreading to the CNS (termed neuroinvasion) where they cause neurodegeneration. Early TSE agent accumulation upon follicular dendritic cells (FDCs) in lymphoid follicles appears critical for efficient neuroinvasion. Most clinical cases of variant Creutzfeldt-Jakob disease have occurred in young adults, although the reasons behind this apparent age-related susceptibility are uncertain. Host age has a significant influence on immune function. As FDC status and immune complex trapping is reduced in aged mice (600 days old), we hypothesized that this aging-related decline in FDC function might impair TSE pathogenesis. We show that coincident with the effects of host age on FDC status, the early TSE agent accumulation in the spleens of aged mice was significantly impaired. Furthermore, following peripheral exposure, none of the aged mice developed clinical TSE disease during their lifespans, although most mice displayed histopathological signs of TSE disease in their brains. Our data imply that the reduced status of FDCs in aged mice significantly impairs the early TSE agent accumulation in lymphoid tissues and subsequent neuroinvasion. Furthermore, the inefficient neuroinvasion in aged individuals may lead to significant levels of subclinical TSE disease in the population.

Enhanced capture of extramembranous IgM and IgG on B cells in the NOD mouse--implications for immune complex trapping

Binding of various antibody isotypes to B cells through either FcgammaRs or complement receptors has been attributed to play several roles, e.g. in immune complex (IC) transportation and regulation of B cell receptor signaling. We have revealed a novel B cell intrinsic receptor for IgM and IgG which is present in C57BL/6 (B6) mice and is more abundant in non-obese diabetic (NOD) mice. As a consequence, the level of extramembranous IgG monomers and IgM pentamers on peripheral blood B cells from NOD mice was significantly higher compared with B6 mice. The effect of this aberration was that all B cells in peripheral blood of (NOD.IgH(a) x B6(IgH(b)))F(1) mice carried both IgM allotypes on their surface. In addition, analysis of IC binding using IgG- or IgM-opsonized bacterial particles revealed a higher degree of binding in NOD mice compared with B6. We hypothesize that this novel Ig-binding receptor is part of the normal immune system function. The aberrant function in the NOD mouse could contribute to the development of Type 1 diabetes by altering normal B cell functions such as activation, IC transportation and B cell homeostasis.

Immunofluorescence staining for the detection of immunoglobulins and complement (C3) in dogs with renal disease

Renal cortical biopsies from 74 dogs with different degrees of renal failure were studied by immunofluorescence to assess the frequency and extent of the deposition of immunoglobulins G, M and...

Follicular dendritic cells stimulated by collagen type I develop dendrites and networks in vitro

Follicular dendritic cells (FDCs) reside in germinal centers in which their dendrites interdigitate and form non-mobile networks. FDC purification requires the use of collagenase and selection columns and leaves FDCs without detectable dendrites when examined by light microscopy. We have reasoned that isolated FDCs might reattach to a collagen matrix, extend their processes, and form immobile networks in vitro. As a test for this, cells were plated on collagen type I, laminin, biglycan, and hyaluronan. After 12 h, 80%-90% of FDCs adhered to all tested matrices but not to plastic. Within 2 weeks, FDCs adhering to type I collagen had spread out and had begun to acquire processes with occasional interconnections. By day 30, most FDCs had fine processes that formed networks through interdigitation with neighboring cells. FDC identity was confirmed by FDC-M1 labeling, immune complex trapping, and retention by FDCs in the networks. Scanning electron microscopy confirmed that groups of FDCs were in networks composed of convolutions and branching dendrites emanating from FDC cell bodies. In vivo, collagen type I was co-localized with FDCs, 5 h after challenge of immune mice with antigen. However, 2 days later, the collagen type I fibers were largely found at the periphery of the active follicles. Flow cytometry established the expression of CD29 and CD44 on FDCs; this may have partly mediated FDC-collagen interactions. Thus, we report, for the first time, that FDCs attach to collagen type I in vitro and regenerate their processes and networks with features in common with networks present in vivo.

Follicular dendritic cell (FDC)‐FcγRIIB engagement via immune complexes induces the activated FDC phenotype associated with secondary follicle development

Follicular dendritic cell (FDC)-FcgammaRIIB levels are up-regulated 1-3 days after challenge of actively immunized mice with Ag. This kinetics suggested that memory cells are not driving this response, prompting the hypothesis that immune complex (IC)-FDC interactions lead to FDC activation. To test this, mice passively immunized with anti-OVA Ab were OVA challenged to produce IC. After 3 days, levels of IC, FcgammaRIIB, ICAM-1, and VCAM-1 on FDC were analyzed. FDC were also stimulated with IC in vitro, and mRNA for FcgammaRIIB, ICAM-1, and VCAM-1 was quantified by quantitative RT-PCR. IC labeling in passively immunized WT and FcgammaRIIB-/- mice revealed five to six FDC-reticula per LN midsagittal section. In WT mice, these IC-bearing FDC-reticula corresponded with FDC-reticula labeling for FcgammaRIIB, ICAM-1, and VCAM-1. Increases in these molecules on IC-stimulated FDC were confirmed by flow cytometry. In marked contrast, in FcgammaRIIB-/- mice, no increased VCAM-1 or ICAM-1 was seen on IC-bearing FDC-reticula or on purified FDC. Addition of IC in vitro resulted in dramatic increases in mRNA for FcgammaRIIB, ICAM-1 and VCAM-1 in WT FDC, but not in FDC from FcgammaRIIB-/- mice, 2.4G2-pretreated WT FDC, B cells, or macrophages. Thus, although FDC-FcgammaRIIB was not essential for IC trapping, engagement of FDC-FcgammaRIIB with IC initiated an FDC activation pathway.

Mechanisms of immune-deposit formation and the mediation of immune renal injury

The passive trapping of preformed immune complexes is responsible for some forms of glomerulonephritis that are associated with mesangial or subendothelial deposits. The biochemical characteristics of circulating antigens play important roles in determining the biologic activity of immune complexes in these cases. Examples of circulating immune complex diseases include the classic acute and chronic serum sickness models in rabbits, and human lupus nephritis. Immune deposits also form "in situ". In situ immune deposit formation may occur at subepithelial, subendothelial, and mesangial sites. In situ immune-complex formation has been most frequently studied in the Heymann nephritis models of membranous nephropathy with subepithelial immune deposits. While the autoantigenic target in Heymann nephritis has been identified as megalin, the pathogenic antigenic target in human membranous nephropathy had been unknown until the recent identification of neutral endopeptidase as one target. It is likely that there is no universal antigen in human membranous nephropathy. Immune complexes can damage glomerular structures by attracting circulating inflammatory cells or activating resident glomerular cells to release vasoactive substances, cytokines, and activators of coagulation. However, the principal mediator of immune complex-mediated glomerular injury is the complement system, especially C5b-9 membrane attack complex formation. C5b-9 inserts in sublytic quantities into the membranes of glomerular cells, where it produces cell activation, converting normal cells into resident inflammatory effector cells that cause injury. Excessive activation of the complement system is normally prevented by a series of circulating and cell-bound complement regulatory proteins. Genetic deficiencies or mutations of these proteins can lead to the spontaneous development of glomerular disease. The identification of specific antigens in human disease may lead to the development of fundamental therapies. Particularly promising future therapeutic approaches include selective immunosuppression and interference in complement activation and C5b-9-mediated cell injury.

Filter Function and Immune Complex Trapping in Splenic Ellipsoids

The role of splenic ellipsoids in the trapping of particulate material and immune complexes was investigated in mink (Mustela vison). The ellipsoids were prominent, with typical features such as a permeable endothelium and a discontinuous basement membrane surrounded by a sheath of macrophages and reticular cells. Ellipsoidal trapping of circulating particles was demonstrated 10 min after intracardiac injection of colloidal carbon and fluorescent microspheres. Preformed peroxidase-antiperoxidase immune complexes were detected in ellipsoids 10 min and also 1 h after intracardiac injection. Erythrocytes were frequently observed in the ellipsoidal sheath, and many phagocytized fragments of erythrocytes were found in the ellipsoidal macrophages. It was concluded that mink ellipsoids are effective blood filters with a role in retention of circulating particulate material, and that mammalian splenic ellipsoids also have the ability to trap immune complexes.

Murine Scrapie Infection Causes an Abnormal Germinal Centre Reaction in the Spleen

Follicular dendritic cells (FDCs) of the lymphoreticular system play a role in the peripheral replication of prion proteins in some transmissible spongiform encephalopathies (TSEs), including experimental murine scrapie models. Disease-specific PrP (PrP d) accumulation occurs in association with the plasmalemma and extracellular space around FDC dendrites, but no specific immunological response has yet been reported in animals affected by TSEs. In the present study, morphology (light microscopical and ultrastructural) of secondary lymphoid follicles of the spleen were examined in mice infected with the ME7 strain of scrapie and in uninfected control mice, with or without immunological stimulation with sheep red blood cells (SRBCs), at 70 days post-inoculation or at the terminal stage of disease (268 days). Scrapie infection was associated with hypertrophy of FDC dendrites, increased retention of electron-dense material at the FDC plasma membrane, and increased maturation and numbers of B lymphocytes within secondary follicles. FDC hypertrophy was particularly conspicuous in immune-stimulated ME7-infected mice. The electron-dense material was associated with PrP d accumulation, as determined by immunogold labelling. We hypothesize that immune system changes are associated with increased immune complex trapping by hypertrophic FDCs expressing PrP d molecules at the plasmalemma of dendrites, and that this process is exaggerated by immune system stimulation. Contrary to previous dogma, these results show that a pathological response within the immune system follows scrapie infection.

Normal Induction but Attenuated Progression of Germinal Center Responses in BAFF and BAFF-R Signaling–Deficient Mice

The factors regulating germinal center (GC) B cell fate are poorly understood. Recent studies have defined a crucial role for the B cell–activating factor belonging to TNF family (BAFF; also called BLyS) in promoting primary B cell survival and development. A role for this cytokine in antigen-driven B cell responses has been suggested but current data in this regard are limited. A BAFF receptor expressed by B cells (BAFF-R/BR3) is defective in A/WySnJ mice which exhibit a phenotype similar to BAFF-deficient (BAFF−/−) animals. Here, we show that although GC responses can be efficiently induced in both A/WySnJ and BAFF−/− mice, these responses are not sustained. In BAFF−/− mice, this response is rapidly attenuated and accompanied by perturbed follicular dendritic cell development and immune complex trapping. In contrast, analysis of the A/WySnJ GC response revealed a B cell autonomous proliferative defect associated with reduced or undetectable Ki67 nuclear proliferation antigen expression by GC B cells at all stages of the response. These data demonstrate a multifaceted role for the BAFF pathway in regulating GC progression.

Age-related depression of FDC accessory functions and CD21 ligand-mediated repair of co-stimulation.

Morphological and kinetic studies of immune complex (IC) trapping by follicular dendritic cells (FDC) show marked age-related deficits. We postulated that a reduction in trapped IC, which generate CD21 ligands (L) on FDC, would lead to inadequate FDC-Ag-B cell interactions resulting in depressed Ab responses. To determine whether the age-related defect was the result of the aging of FDC or changes in the in vivo microenvironment of FDC (i.e. aging B and T cells), FDC-B cell-T cell-Ag interactions were studied in in vitro germinal centers where various combinations of old and young cells could be compared. Since we reasoned that reduced IC on FDC would generate less CD21L needed to stimulate the B cell co-receptor via CD21, we also examined the role of complement (C'). The hypothesis that aging reduces the accessory activity of FDC was tested with increasing numbers of FDC from young (12 weeks) or old (20 months) mice in the presence of young (12 weeks) B and T lymphocytes. The Ag-specific stimulatory activity of FDC was studied using the OVA-specific Ab response which was reduced by 40-50% in the presence of old FDC. Antigen-independent FDC-mediated co-stimulation was studied by using LPS to stimulate B-lymphocytes to produce immunoglobulin (Ig). In the presence of old FDC, co-stimulation was decreased by 70-80% in the LPS system. Incubation of aged FDC with IC and C' to provide FDC with CD21L restored co-stimulatory activity to near normal levels. In marked contrast, no defects in old B and T cells were apparent. The data suggest that the Ag handling capacity and co-stimulatory activity of old FDC become defective with aging and this appears to be a consequence of reduced trapping and presentation FDC-Ag and CD21L to B cells.

Ontogeny of the Follicular Dendritic Cell Phenotype and Function in the Postnatal Murine Spleen

Follicular dendritic cells (FDCs) represent a unique cell population of antigen trapping cells restricted to follicles within the secondary lymphoid tissues. FDCs appear to be involved in the formation of primary follicles during the ontogeny of lymphoid tissue. We sought to determine the kinetics and tissue distribution of cells in the spleen of newborn mice expressing various differentiation antigens restricted to FDCs using immunohistochemistry with monoclonal antibodies (mAb) against FDCs and in vivo immune complex binding and retention. The earliest FDC-specific marker displayed was the antigenic determinant recognized by the FDC-M1 mAb, which was detectable by Day 3 prior to follicle formation on cells located around the peripheral part of the developing white pulp. The appearance of CD21/35 (complement receptor Type 2 and 1, CR1.2) was observed at the end of the first week, revealing a focal pattern in B-cell-rich areas. In addition, at that time there were some FDC-M1-positive cells in the nonfollicular part of the periarteriolar region. The administration of anti-horseradish peroxidase antibody followed by soluble antigen HRP into 7-day-old newborn mice resulted in the trapping and retention of immune complexes onto FDCs even in the absence of Fcγ receptors. The appearance of another FDC-specific marker, FDC-M2, was observed during the second week after birth and was restricted on the cells located in the same area as CR1.2 cells. The Fcγ receptor Type II appeared on FDCs after the second postnatal week. The above sequence of phenotypic maturation could also be observed in newborns after lethal irradiation at Day 3. This indicates that not only mature FDCs but also their precursors are highly radioresistant, and their phenotypic maturation follows a programmed path that requires only a small number of mature B cells.

Cellular and sub-cellular localisation of PrP in the lymphoreticular system of mice and sheep.

Using immunocytochemistry or immunogold electron microscopy, abnormal PrP accumulation was found in lymphoreticular tissues of Suffolk sheep naturally exposed to scrapie and in the spleens of ME7 infected C57 BL mice at 70 days after infection and at the terminal stage of disease at 170 days. Clinically diseased scrapie affected sheep show widespread PrP accumulation within tingible body macrophages (TBMs) and follicular dendritic cells (FDCs) of secondary lymphoid follicles. Serial tonsillar biopsies taken from 171 ARQ/ARQ sheep at 4 months of age did not contain abnormal PrP accumulations but 80% of biopsies were positive by 14 months. In contrast, whole body necropsies of sheep not previously biopsied failed to detect PrP in the tonsil of sheep at 4, 8, 12 or 16 months of age. These findings suggest that the biopsy procedure of susceptible sheep but not resistant sheep may induce tonsillar infection. In spleen of mice both at 70 and 170 dpi, accumulations of PrP were found within lysosomes of TBMs and also at the plasma-lemma of FDCs. In the light zone of follicles of terminally diseased mice, all FDC dendrites were arranged in the form of highly reactive or hyperplastic labrynthine glomerular complexes. PrP was consistently seen between FDC dendrites in association with abundant electron dense antigen-antibody complexes. At 70 days after challenge, labrynthine complexes were rare and invariably labelled for PrP. However, sparse PrP labelling was also seen on simple FDC dendrites at this stage. These observations suggests that scrapie infected FDCs continually release PrP from the cell surface where it accumulates in excess in association with trapped immune complexes and dendritic extension. It is likely that TBMs acquire lysosomal PrP following phagocytosis of effete FDC processes or from the extracellular space. We suggest that the normal function of PrP may involve cell process extension or immune complex trapping.

Development of immune complex trapping: experimental study of lymphoid follicles and germinal centers newly induced by exogenous stimulants in mouse popliteal lymph nodes.

The development of immune complex trapping in newly-induced lymphoid follicles of draining popliteal lymph nodes was investigated in young adult mice, which had been given bilateral injection of hemocyanin (KLH) or phytohemagglutinin (PHA), each absorbed onto alumina. HRP-anti-HRP immune complex was injected into the footpad 1 day before sacrifice. Using three series of semi-serial cryostat sections prepared from each popliteal node, the number of lymphoid follicles in each node was counted, and follicular localization of the in vivo injected and in vitro applied immune complexes in each follicle was determined. By day 5, a large germinal center had developed within each preexisting follicle. A large number of 'new' secondary follicles, each containing a small PNA-positive germinal center, appeared outside pre-existing follicles, from day 5 through day 11 in KLH-treated nodes, and from day 7 through day 14 in PHA-treated nodes. Shortly after their appearance, new secondary follicles showed no in vitro or in vivo trapping, but subsequently, many of the new follicles began to display in vitro trapping, at first weakly but later intensely. Occurrence of in vivo trapping in new follicles took some time and was first recognized when new follicles showed intense in vitro trapping. At day 21 or 25, many of the new follicles showed both in vitro and in vivo trapping. It was concluded that in lymph nodes treated with a stimulant, secondary follicles containing germinal centers can be formed de novo in the extrafollicular zone where the follicular trapping microenvironment is absent, but subsequently the microenvironment capable of trapping immune complexes develops at the site of formation of new follicles.

Murine IgG1 Complexes Trigger Immune Effector Functions Predominantly via FcγRIII (CD16)

AbstractPreviously, we have demonstrated that phagocytosis of IgG1-coated particles by macrophages in vitro is impaired by deletion of FcγRIII in mice, suggesting that IgG1 may interact preferentially with FcγRIII. In the present study, the biologic relevance of this observation was addressed by triggering various effector functions of the immune system in FcγRIII−/− mice, using panels of mAbs of different IgG subclasses. Both binding and phagocytosis of IgG1-coated sheep or human erythrocytes by FcγRIII−/− macrophages in vitro were strongly impaired, indicating that the impaired ingestion of complexed IgG1 by FcγRIII−/−macrophages is due to a defect in binding. An in vivo consequence of the defective phagocytosis was observed by resistance of FcγRIII-deficient mice to experimental autoimmune hemolytic anemia, as shown by a lack of IgG1-mediated erythrophagocytosis in vivo by liver macrophages. Furthermore, trapping of soluble IgG1-containing immune complexes by follicular dendritic cells in mesenteric lymph nodes from FcγRIII−/− mice was abolished. Whole blood from FcγRIII−/− mice was unable to induce lysis of tumor cells in the presence of IgG1 antitumor Abs. Finally, IgG1 mAbs proved unable to mount a passive cutaneous anaphylaxis in FcγRIII−/− mice. Together, these results demonstrate that IgG1 complexes, either in particulate or in soluble form, trigger in vitro and in vivo immune effector functions in mice predominantly via FcγRIII.

Human placental Fc receptors and the trapping of immune complexes

Monomeric maternal antibodies are transmitted to the fetus, but most immune complexes are trapped in the placental stroma. The receptors responsible for trapping immune complexes appear to be FcγRIa, FcγRIIa, and FcγRIIIa on stromal macrophages, and FcγRII on fetal capillary endothelial cells.

The distribution, immune complex trapping ability and morphology of follicular dendritic cells in popliteal lymph nodes of aged rats.

Immune system function declines with age, and lymph nodes involute. The aims of the study were to describe the distribution of follicular dendritic cells (FDCs) in the lymphoid follicles of aged rats, and to determine whether these cells have reduced ability to trap immune complexes (ICs). Popliteal lymph nodes of rats aged 24-28 months were immunostained for S-100 protein as a marker of FDCs. Some rats were pretreated with peroxidase-anti-peroxidase complex (PAP) as an IC. FDCs were densely distributed in lymphoid follicles, which contained many primary follicles and a few secondary follicles. FDCs in primary follicles stained weakly for S-100 protein, and showed weak trapping, while those in secondary follicles stained strongly for both S-100 protein and trapping. Ultrastructurally, in involuted lymphoid follicles FDCs were atrophic. We conclude that FDCs in aged rats are densely distributed in involuted follicles and show reduced trapping ability and atrophic morphology. This seems to reflect the long life of FDCs and the reduced numbers of lymphoid cells in these follicles. We suggest that FDCs in aged rats may show some of their normal functions if fully developed germinal centers are induced, and may not play an important role in the process of involution of the follicles.

Destruction of follicular dendritic cells during chronic visceral leishmaniasis.

Follicular dendritic cells (FDCs) play a pivotal role in the germinal center (GC) response and in the development and regulation of B lymphocytes. Pathologic changes in GCs and a loss of FDCs have previously been noted in various viral infections, notably HIV-1. However, such changes have not been formally described in a chronic parasitic infection. In BALB/c mice infected with Leishmania donovani, parasites persist in the spleen for long periods, with associated splenomegaly. To examine the fate of FDC during the course of this chronic infection, we used 1) immunohistology, with FDC-specific mAbs; and 2) passive immunization with immune complexes, followed by light and electron microscopy. This study demonstrates that destruction of FDCs and a concomitant loss of GCs are associated with chronic visceral leishmaniasis. These pathologic effects are notable from 4 wk postinfection. At 8 wk postinfection and beyond, FDC are almost undetectable by both immunohistology and functional immune complex trapping. The loss of FDCs is associated with the infiltration of heavily parasitized macrophages into the GC, and reduction in parasite burden by chemotherapy is able to retard the process of FDC destruction. These data directly demonstrate for the first time the loss of FDCs during a chronic parasite infection and suggest a mechanism underlying the aberrant regulation of B cell function in murine visceral leishmaniasis.