Soluble IgG Research Articles

Intractable pruritus in HIV infection: immunologic characterization.

Severe, intractable pruritus, often associated with erythematopapular skin lesions and hypereosinophilia, is a condition observed in some nonatopic, HIV-infected patients. We performed immunovirologic analyses of this condition. Immunologic (mitogen-stimulated production of cytokines, tumor necrosis factor-alpha [TNF-alpha], and soluble CD23; serum levels of soluble CD23, ICAM-1, TNF-alpha, IgG, IgE, and IgA) and virologic (HIV viral load) parameters were analyzed in six patients with therapy-resistant pruritus. Hypereosinophilia was present in all these patients. Results were compared to those of seven HIV-seropositive individuals similar to the first one in terms of CD4 counts and clinical staging, but without pruritus. Hypereosinophilia; hyper-IgE and hyper-IgA; augmented interleukin (IL)-4, IL-5, and sCD23; and reduced interferon-gamma production by mitogen-stimulated peripheral blood mononuclear cells (PBMC) were detected when patients with pruritus were compared to HIV controls. HIV viral load was also augmented in patients in whom pruritus was present. The results suggest that therapy-resistant, intractable pruritus accompanied by hypereosinophilia may be used to define a subset of HIV-seropositive individuals showing prototypic hyperactivation of humoral immunity, and in whom augmented HIV viral load is present.

Aminopeptidase activity in human nasal mucosa

Background: Aminopeptidases activate bradykinin and degrade many inflammatory peptides. Objective: The objective of this study was to identify the types of aminopeptidase activities in human nasal mucosa. Methods: Human nasal mucosa was homogenized (n = 12), and cytoplasmic (S2) and membrane-rich (P2) fractions were obtained. Several aminopeptidase (Ap) activities were defined by (1) substrate specificity with leucine-enkephalin (leu-Ap) and alanine-nitroanilide (ala-Ap), (2) inhibitor studies with puromycin and bestatin, (3) enzyme activity histochemistry (zymography), (4) immunohistochemistry, and (5) gel electrophoresis. Human volunteers had methacholine, histamine, and allergen nasal provocations to determine the mechanisms controlling nasal aminopeptidase secretion in vivo. Results: P2 was the largest reservoir of puromycin-resistant aminopeptidase activity (630 pmol leu-enk/min/mg protein). S2 contained 32 pmol leu-enk/min/mg activity, with 80% representing puromycin-resistant activity and 20% puromycin-sensitive aminopeptidase (PS-Ap). Ala-Ap was detected in both P2 and S2 fractions and was localized by zymography to epithelial and gland cells. Anti–rat brain–soluble PS-Ap IgG detected immunoreactive material in epithelium, glands, and endothelium. In nasal provocation studies, leu-AP correlated with glandular exocytosis but not vascular leak. Conclusions: The predominant aminopeptidase in human nasal epithelial and submucosal gland cells was membrane-bound puromycin-resistant aminopeptidase. A novel soluble puromycin-resistant aminopeptidase and lower amounts of soluble PS-Ap were also detected. (J Allergy Clin Immunol 1998;102:741-50.)

Expression and Characterization of a 70-kDa Fragment of the Insulin Receptor That Binds Insulin: MINIMIZING LIGAND BINDING DOMAIN OF THE INSULIN RECEPTOR

In order to characterize regions of the insulin receptor that are essential for ligand binding and possibly identify a smaller insulin-binding fragment of the receptor, we have used site-directed mutagenesis to construct a series of insulin receptor deletion mutants. From 112 to 246 amino acids were deleted from the alpha-subunit region comprising amino acids 469-729. The receptor constructs were expressed as soluble insulin receptor IgG fusion proteins in baby hamster kidney cells and were characterized in binding assays by immunoblotting and chemical cross-linking with radiolabeled insulin. The shortest receptor fragment identified was a free monomeric alpha-subunit deleted of amino acids 469-703 and 718-729 (exon 11); the mass of this receptor fragment was found by mass spectrometry to be 70 kDa. This small insulin receptor fragment bound insulin with an affinity (Kd) of 4.4 nM, which is similar to what was found for the full-length ectodomain of the insulin receptor (5.0 nM). Cross-linking experiments confirmed that the 70-kDa receptor fragment specifically bound insulin. In summary we have minimized the insulin binding domain of the insulin receptor by identifying a 70-kDa fragment of the ectodomain that retains insulin binding affinity making this an interesting candidate for detailed structural analysis.

Clinical Value of Soluble IgG Fc Receptor Type III in Plasma From Patients With Chronic Idiopathic Neutropenia

Previous studies have shown that the plasma level of soluble IgG Fc receptor type III (sFcγRIII) is a measure of the total body neutrophil mass. The aim of this study was to determine whether the plasma level sFcγRIII is associated with the risk of contracting bacterial infections in patients with neutropenia. We collected blood from 66 patients suffering from acquired idiopathic neutropenia, whose blood was sent to our laboratory for diagnostic evaluation of neutropenia (neutrophil count <1,500 cells/μL). Soluble FcγRIII levels were measured in plasma. Genotype distibutions of FcγR polymorphisms were determined. Clinical data were obtained from the patient files. Patients were assessed as to whether or not they had suffered from a bacterial infection 3 months before to 3 months after a single sFcγRIII measurement. In addition, longitudinal data were obtained from 21 patients. Of the 66 neutropenic patients who were included, 15 had suffered from a bacterial infection in the period 3 months before to 3 months after sFcγRIII measurement. The age and sex distribution was equal among the groups with and without infections, as were the genotype frequencies of neutrophil FcγR polymorphisms. Both neutrophil count and plasma level sFcγRIII were significantly lower in the patient group with infections, compared with the noninfected group (P = .03 and P < .0001, respectively). No infections were reported for patients who had plasma sFcγRIII levels above 100 arbitrary units (AU; normal value, 30 to 200). After matching each infected patient with two noninfected patients having the same neutrophil count, sFcγRIII plasma levels remained significantly lower in the group with infections (P = .0001). For the patients who were followed in time, no infections were reported when sFcγRIII levels were above 100 AU. In conclusion, our population of patients with chronic idiopathic neutropenia with plasma sFcγRIII levels above 100 AU did not show an increased risk of contracting bacterial infections.

Clinical Value of Soluble IgG Fc Receptor Type III in Plasma From Patients With Chronic Idiopathic Neutropenia

AbstractPrevious studies have shown that the plasma level of soluble IgG Fc receptor type III (sFcγRIII) is a measure of the total body neutrophil mass. The aim of this study was to determine whether the plasma level sFcγRIII is associated with the risk of contracting bacterial infections in patients with neutropenia. We collected blood from 66 patients suffering from acquired idiopathic neutropenia, whose blood was sent to our laboratory for diagnostic evaluation of neutropenia (neutrophil count <1,500 cells/μL). Soluble FcγRIII levels were measured in plasma. Genotype distibutions of FcγR polymorphisms were determined. Clinical data were obtained from the patient files. Patients were assessed as to whether or not they had suffered from a bacterial infection 3 months before to 3 months after a single sFcγRIII measurement. In addition, longitudinal data were obtained from 21 patients. Of the 66 neutropenic patients who were included, 15 had suffered from a bacterial infection in the period 3 months before to 3 months after sFcγRIII measurement. The age and sex distribution was equal among the groups with and without infections, as were the genotype frequencies of neutrophil FcγR polymorphisms. Both neutrophil count and plasma level sFcγRIII were significantly lower in the patient group with infections, compared with the noninfected group (P = .03 and P < .0001, respectively). No infections were reported for patients who had plasma sFcγRIII levels above 100 arbitrary units (AU; normal value, 30 to 200). After matching each infected patient with two noninfected patients having the same neutrophil count, sFcγRIII plasma levels remained significantly lower in the group with infections (P = .0001). For the patients who were followed in time, no infections were reported when sFcγRIII levels were above 100 AU. In conclusion, our population of patients with chronic idiopathic neutropenia with plasma sFcγRIII levels above 100 AU did not show an increased risk of contracting bacterial infections.

Neutrophil Fc gamma and complement receptors involved in binding soluble IgG immune complexes and in specific granule release induced by soluble IgG immune complexes.

We examined the effect of soluble IgG immune complex (IC) characteristics on the binding of IC to human neutrophils and IC-induced specific granule release of neutrophils via Fc gamma receptors (CD16 and CD32) and complement receptors (CR1 and CR3). A set of soluble IgG IC varying in size, IgG subclass, antigen epitope density and complement (C) incorporation were formed between 5-iodo-4-hydroxy-3-nitrophenacetyl (NIP) coupled to bovine serum albumin (BSA) and chimeric mouse-human anti-NIP monoclonal antibodies (mAb) of all four IgG subclasses. High and low epitope density IC of all four IgG subclasses induced specific granule release with C, but in the absence of C only IgG1 and IgG3 IC were functionally active. The Fc gamma and C receptors responsible for IgG IC-induced specific granule release and IC binding were determined using mAb specific for the ligand binding sites of CD16, CD32 and CR3, and recombinant soluble CR1. Each defined IC displayed a unique pattern of receptor preference, dependent upon subclass and antigenic epitope density. IC binding and IC-induced specific granule release was not mediated by the same receptor, or combination of receptors. High and low epitope density IgG3 IC binding and induction of specific granule release was mediated predominantly via CD16. Other IC subclasses bound differently, i.e. IgG1 IC used CD16 and CR3; IgG2 and IgG4 predominantly used complement receptors; but all three induced specific granule release via CD32. In vivo these results may translate into differential activation of neutrophils by soluble IC dependent upon their characteristics, leading to subtle nuances in the etiology, pathology and control of the immune response in IC-related diseases.

Stimulation of Intracellular Ca2+ Levels in Human Neutrophils by Soluble Immune Complexes

Soluble immune complexes bind to unprimed neutrophils and generate intracellular Ca2+ transients but fail to activate the NADPH oxidase. Following priming of the neutrophils with either tumor necrosis factor alpha or granulocyte-macrophage colony-stimulating factor, stimulation of the cells with the soluble immune complexes leads to an enhanced Ca2+ signal and significant secretion of reactive oxidants. The enhanced Ca2+ signal observed in primed neutrophils results from the influx of Ca2+ from the external environment and is partly sensitive to tyrosine kinase inhibitors. This is in contrast to the Ca2+ signal observed in unprimed neutrophils, which arises from the mobilization of intracellular stores. When the surface expression of FcgammaRIIIb on primed neutrophils was decreased either through incubation with Pronase or phosphoinositide-specific phospholipase C, the extra enhanced Ca2+ mobilization seen in primed cells was significantly lowered, while the initial rise in intracellular Ca2+ was unaffected. Depletion of FcgammaRIIIb had no significant effect on the Ca2+ transients in unprimed neutrophils. Cross-linking FcgammaRII, but not FcgammaRIIIb, induced increases in intracellular Ca2+ in unprimed neutrophils, while cross-linking either of these receptors increased Ca2+ levels in primed neutrophils. The FcgammaRII-dependent intracellular Ca2+ rise in primed cells was unaffected by incubation in Ca2+-free medium, whereas the FcgammaRIIIb-dependent transient was significantly decreased when Ca2+ influx was prevented in Ca2+-free medium supplemented with EGTA. Cross-linking either FcgammaRII or FcgammaRIIIb in primed or unprimed cells failed to stimulate substantial levels of inositol 1,4,5-trisphosphate production. These results indicate that following stimulation of primed neutrophils with soluble immune complexes the enhanced Ca2+ mobilization observed is the result of a functional activation of the glycosylphosphatidylinositol-linked FcgammaRIIIb.

Clinical value of soluble IgG Fc receptor type III (sFcγRIII) in plasma from patients with neutropenia

Clinical value of soluble IgG Fc receptor type III (sFcγRIII) in plasma from patients with neutropenia

Clinical value of soluble IgG Fc receptor type III (sFcγRIII) in plasma from patients with neutropenia

Clinical value of soluble IgG Fc receptor type III (sFcγRIII) in plasma from patients with neutropenia

Peripheral deletion of rheumatoid factor B cells after abortive activation by IgG.

Rheumatoid factor (RF) B cells proliferate during secondary immune responses to immune complexed antigen and antigen specific T cells, but higher affinity RFs are not detected except in patients with rheumatoid arthritis and other autoimmune diseases. Consequently, there must exist highly efficient mechanisms for inactivation of these higher-affinity RF B cell clones under normal circumstances. Exposure of transgenic mice expressing a human IgM RF to soluble human IgG in the absence of T cell help causes antigen specific B cell deletion in 2-3 days. The deletion is independent of the Fas/Fas ligand (FasL) pathway of apoptosis and is preceded by a phase of partial activation involving increase in cell size and expression of B7 and ICAM-1, and transient release of low levels of immunoglobulin. Complete B cell activation involving the formation of germinal centers and sustained high level RF secretion only occurs if T cell help is provided simultaneously. RF B cells exposed to tolerogen remain competent to secrete RF in vitro if provided with an appropriate antigenic stimulus and T cell help. Consequently, death of these cells is not preceded by anergy. Abortive activation/deletion of B cells by antigen in the absence of T cell-derived survival signals may represent the major mechanism for maintaining peripheral tolerance in B cells expressing higher affinity RF. The lack of anergy, and the potential for reactivation before death, provide a means for maintaining RF production under pathologic circumstances, such as may occur in the inflamed rheumatoid synovium.

A Competitive Enzyme-Linked Immunoassay for the Quantitation of Soluble Human Immunoglobulin G and Albumin in Nanogram Amounts

&lt;i&gt;Background:&lt;/i&gt; Some clinical and experimental questions require quantitation of soluble serum proteins in amounts lower than those which are detectable by radial immunodiffusion (RID) or nephelometry. &lt;i&gt;Materials and Methods:&lt;/i&gt; We describe a competitive enzyme-linked immunoassay (CELIA) for the quantitation of minor amounts of soluble human IgG and albumin. &lt;i&gt;Results:&lt;/i&gt; The assay enables the detection of IgG and albumin in the range of 5 to 125 ng/ml. &lt;i&gt;Conclusions:&lt;/i&gt; Besides its high sensitivity, the main advantage of this double-step technique is that the sample-specific primary antibody is not needed in an enzyme-conjugated form because of the use of a labelled secondary antibody.

Production of polyclonal antibody specific for human natriuretic peptide receptor B

Polyclonal antibody against human natriuretic peptide receptor B (NPR-B) was produced using as immunogen a soluble chimeric protein consisting of the extracellular domain of the receptor fused with Fc portion of human IgG. The antibody was purified with protein A column, and then subjected to an adsorption of anti-Fc antibody using IgG column. The purified antibody recognized human NPR-B but not the related receptor NPR-A. The antibody inhibited C-type natriuretic peptide (CNP)-mediated intracellular cGMP accumulation in a dose-dependent manner. With regard to specific activity for the neutralization, the antibody purified with IgG column was significantly stronger than that before the adsorption step, indicating that the purification of the antibody with IgG column was extremely effective to remove the contaminating anti-Fc antibody from anti-NPR-B antibody. Western blot analysis using the purified antibody revealed that while the native NPR-B exists as an oligomer, the truncated NPR-B lacking most of its cytoplasmic domain is a monomer. This finding suggests that the cytoplasmic region may be involved in the oligomerization of the receptor. The results in this study demonstrate that soluble IgG fusion protein is very effective and useful for generating specific antibodies to the proteins expressed on cell surface.

Specific activity of polypyrrole nanoparticulate immunoreagents: comparison of surface chemistry and immobilization options.

Polypyrrole-based colloids with differing surface chemistries were compared with respect to the specific activity of immobilized antibody. Monoclonal antibody to the alpha subunit of human chorionic gonadotropin (hCG) was modified by incorporation of cystamine into the Fc-carbohydrate, followed by reduction with dithiothreitol resulting in the generation of 4.5 free thiols per IgG. The reduced IgG was added to clean, unmodified and surface-modified polypyrrole colloids. Functionalized colloids included carboxylate-modified polypyrrole, poly[pyrrole-co-1-(2-carboxyethyl) pyrrole]-silica composite, and amine forms of the carboxylated colloids. The amine-functionalized colloids were subsequently treated with sulfosuccinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate to provide thiol-reactive maleimide surface groups. Following the conjugation of IgG to the colloids, bound and soluble antibody activity was quantitated using a sequentially competitive immunoassay for hCG, based on an automated commercial hCG kit. The results indicated that all forms of polypyrrole retained the equivalence of between 12 and 33 micrograms of IgG activity/mg of colloidal solids, relative to the unmodified soluble IgG.

Human recombinant CD4 and CD4-derived synthetic peptides agglutinate immunoglobulin-coated latex particles. Evidence that residues 25–28 and 35–38 of human CD4 form two separate immunoglobulin binding sites

It has been shown previously that amino acid residues 21–49 of the first extracellular domain of human CD4 form the core of an immunoglobulin (Ig) binding site. Synthetic peptides of human CD4 that encompass this region also bind Ig and, with higher affinity, antigen/antibody complexes. Synthetic peptides also enhance binding of both monomeric and aggregated Ig to monocytic U937 cells and Staphylococcus aureus Protein A. To better characterize the nature of the Ig binding site on CD4, we tested the ability of human recombinant CD4 (rCD4) to agglutinate polystyrene particles coated with Ig. Evidence is presented that soluble rCD4 and CD4 peptide (p)21–49 were capable of specific agglutination of polystyrene particles coated with polyclonal Ig of either human or sheep origin. Agglutination could be blocked by soluble human polyclonal IgG or F(ab′) 2 fragments. Both heparin and sulfated dextrans also inhibit agglutination, suggesting that charged residues on rCD4 played an important role in agglutination mediated by rCD4 or CD4 peptide. Similarly, aurintricarboxylic acid (ATA) also blocked agglutination of Ig-coated particles by rCD4. Agglutination mapping studies performed using truncated peptides revealed the existence of two discrete, closely related Ig binding sites (residues 25–28 and 35–38).

Monocyte Fc gamma receptor cross-linking induces IL-8 production.

In response to bacterial cell wall products such as LPS, monocytes produce IL-8, a powerful neutrophil chemotaxin. However, in the absence of bacterial pathogens, immune complex-mediated diseases such as rheumatoid arthritis are associated with high levels of IL-8 in monocyte-rich compartments. Since it is known that IgG-containing immune complexes can recruit neutrophils via an Fc gamma R-dependent process, we hypothesized that cross-linking of monocyte Fc gamma receptors may induce IL-8. To test this hypothesis, peripheral blood mononuclear cells were evaluated for IL-8 induction in response to immobilized LPS-free pooled human IgG. Immobilized IgG, but not soluble IgG, induced IL-8 in a dose-dependent manner (p < 0.05, r = 0.99). This induction corresponded with an up-regulation in IL-8 steady state mRNA levels that peaked at 4 h. The released IL-8 was functional, since supernatants induced concentration-dependent neutrophil migration that was inhibited by a monoclonal anti-IL-8 Ab. Evaluation of purified monocytes for IL-8 production, as well as FACS analysis of IgG-stimulated PBMC preparations, demonstrated that monocytes are the principal IL-8 producer cell. Thus, monocyte Fc gamma R cross-linking induces biologically active IL-8, which may participate in the pathogenesis of immune complex-mediated diseases.

Use of peroxidase:anti-peroxidase immune complexes as markers for Fcγ receptors in vitro

In species for which monoclonal antibodies are not yet available, the demonstration of Fc receptors has relied on a variety of ligand-based assays including the binding of antibody-coated erythrocytes, radiolabeled monomeric immunoglobulin, and non-physiologic aggregates of immunoglobulin. In order to study the binding of small immune complexes to Fc receptors on canine monocytes, a new method was developed using an enzyme-linked immune complex. The ability of rabbit polyclonal peroxidase:anti-peroxidase (PAP) immune complexes to bind to freshly isolated canine peripheral blood monocytes was characterized using standard ELISA techniques. The binding of rabbit polyclonal PAP to monocytes was time and concentration dependent and reversible. This binding was saturable with increasing concentrations of PAP and could be blocked by soluble rabbit IgG or rabbit Fc fragments. The blocking and saturation curves for canine monocytes were suggestive of multiple classes of Fcγ binding sites. In contrast to intact PAP complexes, the binding of F(ab) PAP preparations or free horseradish peroxidase was minimal. The use of commercially available PAP preparations provides a reproducible, inexpensive, and non-radioactive measure of Fcγ receptor binding on canine cells. In addition, these findings suggest caution in using heterologous PAP as a histochemical reagent in tissues expressing Fcγ receptors.

The membrane distal half of gp130 is responsible for the formation of a ternary complex with IL-6 and the IL-6 receptor

Gp130 is the signal transducing subunit of the interleukin-6 receptor. Signaling is initiated by the complex formation of gp130 with IL-6 bound to the IL-6 receptor (IL-6R). We have subdivided the extracellular domain of gp130 in two parts and expressed the mutant proteins as soluble IgG fusion proteins in COS-7 cells. By studying the formation of the ternary complex we show that the membrane distal half of gp130 which contains a cytokine receptor domain is responsible for the interaction with the IL-6/IL-6R complex. Interestingly this is the same region which is believed to be involved in specific recognition of the related cytokines LIF, OM, and probably also of CNTF and IL-11.

Detection of Lewis, P1, and some MNS blood group system antibodies by a solid phase assay

Abstract Some solid phase red cell adherence (SPRCA) assays arc designed to detect IgG antibodies to red blood cell (RBC) antigens. These assays use anti-IgG-coated red cells as the indicator. It is reported that most antibodies to Lea, Leb, P1, M, and N fail to react by solid phase (SP), presumably because they are IgM antibodies. Those detected are assumed to be IgG. In one year, during routine testing using SPRCA to screen patients for intended RBC transfusion, 28 of 59 such examples were found to react: anti-Lea(9), -Leb(1), -M(14), -N(1), and -P1(3). A study was undertaken to determine if reactivity was due to crosslinking by IgM antibodies of antigen-positive indicator RBCs to antigen-positive reagent RBC monolayers, or due to detection of IgG antibodies. Antibodies were tested according to standard SP protocols, except where IgG-neutralized indicator RBCs were substituted for anti-IgG-active indicator cells. The 59 samples were retested with antigen-positive and antigen-negative indicator RBCs. Only 5 of 59 reacted optimally when antigen-positive indicator cells were used: anti-Lea(2), -Leb(1), -M(1), and -N(1). The reactions of all antibodies were abolished when the anti-IgG component of the indicator was neutralized by soluble IgG. These findings show that detection of most Lewis, P1, M, and N antibodies by SPRCA is dependent on the presence of an IgG antibody in the serum. Immunohematology 1995;11:78–80.

Effects of Co-Expressing Chaperone BiP on Functional Antibody Production in the Baculovirus System

The assembly pathway of the insect cell Spodoptera frugiperda (Sf-9) was engineered to include expression of the murine chaperone immunoglobulin heavy chain binding protein (BiP) using the baculovirus vector. The impact of BiP coexpression on the production and secretion of functional and soluble recombinant immunoglobulin IgG levels was evaluated. Recombinant BiP was found to associate specifically with immunoglobulins in immunoprecipitation studies. Coinfection of insect cells with a BiP-containing baculovirus and baculoviruses coding for two different murine IgG proteins increased intracellular functional antibody activity levels substantially above the levels observed in the absence of BiP. Soluble intracellular immunoglobulin levels were found to increase as well. However, secreted functional antibody levels did not increase significantly. Also, degradation of heavy chain immunoglobulin in insect cells was indicated by the accumulation of lower molecular weight immunoglobulins at 4 days postinfection. Coexpression of light chains reduced the level of these lower molecular weight immunoglobulins while BiP coexpression led to enhanced levels. These findings suggest that coexpressed BiP can increase intracellular soluble and functional antibody yields but that secretion in the baculovirus-insect cell system must be limited at some post-translational step.

Soluble IgA and IgG aggregates are catabolized by cultured rat mesangial cells and induce production of TNF-alpha and IL-6, and proliferation.

IgA nephropathy, a primary glomerulonephritis, is principally characterized by mesangial deposits of IgA immune complexes. Recently, it has been demonstrated that cultured glomerular mesangial cells (MC) express Fc alpha and Fc gamma receptors. In this work, we studied whether the interaction of soluble aggregates of IgA and IgG (AIgA and AIgG) with MC triggers a number of responses, including generation and release of inflammatory mediators, cell proliferation, and catabolism of the complexes. Aggregates bound to MC and were catabolized in a time-dependent manner. The percentage of cell-associated or -degraded proteins decreased in the presence of Fc, but not with Fab fragments. Both AIgA and AIgG elicited the synthesis and release of TNF-alpha and IL-6 in a dose-dependent manner, reaching a maximum between 6 and 12 h, respectively. Northern blot analysis showed that both aggregates induced the expression of mRNA encoding TNF-alpha and IL-6. Because MC proliferation is a morphologic feature commonly observed in patients with IgA nephropathy, we examined whether immune aggregates could be involved in this phenomenon. Both AIgA and AIgG induced an increase in MC number, assessed by [3H]thymidine and methylene blue uptake. The presence of anti-TNF-alpha or anti-IL-6 Abs in the medium decreased the proliferative effect triggered by aggregates. These results show that Fc alpha and Fc gamma receptor occupancy of MC induces the synthesis and release of inflammatory cytokines and proliferation, as well as the phagocytosis of stimulatory proteins. These findings could have implications for the understanding of inflammation and repair in IgA nephropathy.