A peculiar case of onychomycosis caused by Cladosporium halotolerans

A 49-year-old patient with changes in the nails of the hallux for 10 years was diagnosed with onychomycosis. The identity of the causative agent was confirmed as Cladosporium halotolerans from the Cladosporium sphaerospermum species complex using molecular techniques. MALDI-TOF identified the agent as C. sphaerospermum complex species. Overall, species such as onychomycosis agents should attract special attention to avoid mistakes in the identification process while considering a probable contaminant as responsible for the disease. These species deserve attention since there are rare descriptions of them as causes of onychomycosis. It is important to recognize them as causes of disease and not just as a probable contaminant.

High-Throughput Microsatellite Markers Development for Genetic Characterization of Emerging Sporothrix Species

Sporotrichosis is the main subcutaneous mycosis worldwide transmitted by animal or plant vectors and often escalates to outbreaks or epidemics. The current cat-transmitted sporotrichosis driven by Sporothrix brasiliensis has become a significant public health issue in South America. Transmission dynamics remain enigmatic due to the lack of development of polymorphic markers for molecular epidemiological analysis. This study used a high-throughput mining strategy to characterize simple sequence repeat (SSR) markers from Sporothrix genomes. A total of 118,140-143,912 SSR loci were identified (82,841-98,369 unique markers), with a 3651.55-3804.65 SSR/Mb density and a majority of dinucleotides motifs (GC/CG). We developed a panel of 15 highly polymorphic SSR markers suitable for genotyping S. brasiliensis, S. schenckii, and S. globosa. PCR amplification revealed 240 alleles in 180 Sporothrix isolates with excellent polymorphic information content (PIC = 0.9101), expected heterozygosity (H = 0.9159), and discriminating power (D = 0.7127), supporting the effectiveness of SSR markers in uncovering cryptic genetic diversity. A systematic population genetic study estimated three clusters, corresponding to S. brasiliensis (population 1, n = 97), S. schenckii (population 2, n = 49), and S. globosa (population 3, n = 34), with a weak signature of mixed ancestry between populations 1 and 2 or 3 and 2. Partitioning of genetic variation via AMOVA revealed highly structured populations (ΦPT = 0.539; Nm = 0.213; p < 0.0001), with approximately equivalent genetic variability within (46%) and between (54%) populations. Analysis of SSR diversity supports Rio de Janeiro (RJ) as the center of origin for contemporary S. brasiliensis infections. The recent emergence of cat-transmitted sporotrichosis in northeastern Brazil indicates an RJ-Northeast migration resulting in founder effects during the introduction of diseased animals into sporotrichosis-free areas. Our results demonstrated high cross-species transferability, reproducibility, and informativeness of SSR genetic markers, helping dissect deep and fine-scale genetic structures and guiding decision making to mitigate the harmful effects of the expansion of cat-transmitted sporotrichosis.

Sporothrix pathogenic clade: Molecular analysis of animal and human clinical isolates

Sporotrichosis is a subcutaneous mycosis that affects animals and humans. Varying in severity, occurrences range from local lesions to systemic involvement. It is caused by thermodimorphic and saprobic fungi from the Sporothrix pathogenic clade. This study aimed to identify the species and the sexual idiomorph distribution patterns responsible for diagnosed cases of sporotrichosis in São José do Rio Preto, Brazil. We included 188 isolates of Sporothrix sp. from feline lesions and 27 of human origin, which underwent molecular identification and genotyping for mating-type MAT1-1 and MAT1-2. The results showed that Sporothrix brasiliensis is the prevalent species in feline sporotrichosis outbreaks with the overwhelming presence of a single mating-type, MAT1-2 (P <.0001), suggesting a prevalently clonal form of spread. Morphological analyses did not discriminate among cryptic species in the genus Sporothrix, and molecular identification was essential for the correct identification of the species responsible for the observed cases of sporotrichosis. Distribution analyses of MAT1-2 isolates support the hypothesis of unidirectional migration from the current epidemics in São Paulo and Rio de Janeiro to the municipality of São José do Rio Preto.

Trends in Molecular Diagnostics and Genotyping Tools Applied for Emerging Sporothrix Species

Sporotrichosis is the most important subcutaneous mycosis that affects humans and animals worldwide. The mycosis is caused after a traumatic inoculation of fungal propagules into the host and may follow an animal or environmental transmission route. The main culprits of sporotrichosis are thermodimorphic Sporothrix species embedded in a clinical clade, including S. brasiliensis, S. schenckii, S. globosa, and S. luriei. Although sporotrichosis occurs worldwide, the etiological agents are not evenly distributed, as exemplified by ongoing outbreaks in Brazil and China, caused by S. brasiliensis and S. globosa, respectively. The gold standard for diagnosing sporotrichosis has been the isolation of the fungus in vitro. However, with the advance in molecular techniques, molecular assays have complemented and gradually replaced the classical mycological tests to quickly and accurately detect and/or differentiate molecular siblings in Sporothrix. Nearly all techniques available for molecular diagnosis of sporotrichosis involve PCR amplification, which is currently moving towards detecting Sporothrix DNA directly from clinical samples in multiplex qPCR assays. From an epidemiological perspective, genotyping is key to tracing back sources of Sporothrix infections, detecting diversity in outbreak areas, and thus uncovering finer-scale epidemiological patterns. Over the past decades, molecular epidemiological studies have provided essential information to policymakers regarding outbreak management. From high-to-low throughput genotyping methods, MLSA, AFLP, SSR, RAPD, PCR-RFLP, and WGS are available to assess the transmission dynamics and sporotrichosis expansion. This review discusses the trends in the molecular diagnosis of sporotrichosis, genotyping techniques applied in molecular epidemiological studies, and perspectives for the near future.

Toll-like receptor 3 expression and function in childhood idiopathic nephrotic syndrome

The efficacy of steroids and immunosuppressive treatments in idiopathic nephrotic syndrome (INS) hints at the implication of immune cells in the pathophysiology of the disease. Toll-like receptor (TLR) dysfunctions are involved in many kidney diseases of immune origin, but remain little described in INS. We investigated the expression and function of TLRs in peripheral blood mononuclear cells (PBMC) of INS children, including 28 in relapse, 23 in remission and 40 controls. No child had any sign of infection, but a higher Epstein-Barr virus viral load was measured in the PBMC of relapsing patients. TLR-3 expression was increased in B cells only during INS remission. There was a negative correlation between proteinuria and TLR-3 expression in total and the main subsets of PBMC from INS patients. The expression of TLR-8 was also increased in both CD4(+) T cells and B cells in INS remission. There was a negative correlation between proteinuria and TLR-8 expression in total PBMC, CD4(+) T cells and B cells of INS patients. Nevertheless, TLR-3 and TLR-8 expression was normalized in all PBMC subsets in an additional group of 15 INS patients in remission with B cell repletion after rituximab therapy. Paradoxically, interferon (IFN) regulatory factor 3 transactivation was increased in PBMC of all INS patients. In-vitro secretion of IFN-α and interleukin 6 were increased spontaneously in PBMC of INS remission patients, whereas PBMC from all INS patients displayed an impaired IFN-α secretion after TLR-3 stimulation. Thus, TLR-3 pathway dysfunctions may be closely involved in INS pathogenesis.

Natural antibodies, intravenous immunoglobulin and their role in autoimmunity, cancer and inflammation

Natural antibodies are produced by B lymphocytes in the absence of external antigen stimulation. With their ability to recognize self, altered self and foreign antigens, they comprise an important first-line defence against invading pathogens, but are also important for tissue homeostasis. By recognizing oligosaccharides expressed on tumour cells and modified cell surface structures accompanying necrosis, natural antibodies have an important anti-tumorigenic function. IVIg contains a wide spectrum of specificities presented in normal plasma including natural antibodies and has been shown to exert inhibitory effects on tumour cells through a subfraction of anti-vascular endothelial growth factor immunoglobulin (Ig)G antibodies with anti-angiogenic properties. IgA antibodies also have potent immunomodulatory properties, being able to both induce and suppress immune responses. IgA-mediated inhibitory function is able to inhibit several inflammatory diseases including asthma and glomerulonephritis. Autoantibodies of the IgM type, on the other hand, have shown promising results in the treatment of multiple sclerosis. These autoantibodies promote remyelination rather than modulating inflammation. Oxidation-specific epitopes, as found in atherosclerotic lesions and on apoptotic cells, comprise one important target of natural antibodies. By recognizing these epitopes, natural antibodies neutralize proinflammatory responses and mediate atheroprotection.

Recent advances in adult T-cell leukemia therapy: focus on a new anti-transferrin receptor monoclonal antibody

HTLV-I is an endemic retrovirus responsible for the adult T-cell leukemia/lymphoma (ATLL). This aggressive lymphoid proliferation is associated with a bad prognosis due to the resistance of HTLV-I-infected cells to most classical chemotherapeutic agents. Here we review recent advances in ATLL immunotherapy. We particularly focus on promising data from our group, characterizing a new mouse monoclonal antibody (mAb A24) against the human transferrin receptor (TfR-1). Monoclonal antibodies to target cell differentiation markers on ATLL cells have already been proposed as therapeutic agents. However, in clinical trials acute forms of ATLL were resistant to these immunotherapies. A24 binds TfR-1 (K(d) 2.7 nM) and competes with transferrin for receptor binding. It blocks the proliferation of malignant cells (TfR-1(high)), such as HTLV-I-infected T cells but not of resting cells. A24 induces TfR-1 endocytosis in lysosomal compartments where the receptor is degraded leading to intracellular iron deprivation. In HTLV-I-infected cells, A24 targets and induces apoptosis of both chronic and acute ATLL forms, independent of antibody aggregation, antibody-dependent cellular cytotoxicity and/or complement addition. The antibody efficacy was confirmed in animal models. We are currently developing strategies to use A24 in clinical trials.

New insights in the pathogenesis of IgA nephropathy

IgA nephropathy (N) or Berger's disease is the most common form of primary glomerulonephritis worldwide and one of the first cause of end-stage renal failure. The disease is characterized by the accumulation in mesangial areas of complexes containing polymeric IgA1. The mechanisms involved in the pathogenesis of IgAN is only now emerging. We discussed here three essential points: (i) the generation of abnormal IgA1 and formation of IgA1 complexes; (ii) the generation of mesangial injury mediated by interaction of IgA1 complexes with mesangial IgA1 receptors, and (iii) the progression of IgA-mediated mesangial injury towards renal failure. In summary, our data reveal that quantitative and structural changes of IgA1 play a key role on the onset of the disease due to functional abnormalities of two IgA receptors: the Fc alphaRI (CD89) expressed by blood myeloid cells and the transferrin receptor (CD71) on mesangial cells. Abnormal IgA induces release of soluble CD89 soluble leading to the formation of circulating IgA complexes, which in turn may be trapped by CD71 that is overexpressed on mesangial cells in IgAN patients allowing formation of IgA1 deposits. The elucidation of IgA-receptor interactions may open new avenues for drug design and treatment of IgAN.

Enhanced expression of Fc alpha receptor I on blood phagocytes of patients with gram-negative bacteremia is associated with tyrosine phosphorylation of the FcR-gamma subunit

Sepsis caused by gram-negative bacteria is a common finding having high incidence and mortality. Fc alpha RI (CD89), a receptor for immunoglobulin A (IgA), has been shown to mediate bacterial phagocytosis, which might play a role in the pathogenesis of sepsis. In this study the expression and function of Fc alpha RI were analyzed on blood monocytes and neutrophils of patients with bacteremia. We found a marked increased in expression of the alpha- and gamma-subunits of the Fc alpha RI on both types of cells in patients with gram-negative bacteremia, but not in patients with gram-positive bacteremia. This increase was independent of serum IgA levels. Fc alpha RI M(r) was lower on cells from gram-negative patients than on cells from controls (50-65 kDa versus 55-75 kDa), despite a similar 32-kDa backbone, indicating altered glycosylation. Increased levels of Fc alpha RI on blood phagocytes correlated with enhanced serum IL-6 levels, but not with IFN gamma or TNF-alpha. FcR-gamma chain associated with Fc alpha RI was phosphorylated in patients neutrophils, indicating functional engagement of this receptor during gram-negative sepsis. Increased expression and activation of Fc alpha RI-gamma 2 complexes following gram-negative infections suggests its involvement in host defense against bacteria.

IgE receptor type I-dependent tyrosine phosphorylation of phospholipid scramblase

To identify new effectors of IgE receptor (FcepsilonRI) signaling, we purified proteins from FcepsilonRI-stimulated RBL-2H3 rat mast cells on anti-phosphotyrosine beads and generated mouse monoclonal antibodies (mAb) against these proteins. Two mAbs bound to a protein that was identified as a new isoform of phospholipid scramblase (PLSCR) after screening an RBL-2H3 cDNA expression library. This isoform differed from PLSCR1 by the absence of an exon 3-encoded sequence and by an insert coding six QGPY(P/A)GP repeats. The PLSCR family of proteins is responsible for a redistribution of phospholipids across the plasma membrane. Although rat PLSCR is a 37-kDa protein, anti-phosphotyrosine immunoblots revealed the presence of 37-49 kDa phosphoproteins in the material immunoprecipitated with either anti-PLSCR mAb but not with unrelated monoclonal or polyclonal antibodies. Depletion of PLSCR resulted in the absence of these phosphoproteins. Additional experiments led to the identification of these phosphoproteins as phospho-PLSCR itself. Stimulation of RBL-2H3 cells upon FcepsilonRI engagement resulted in a dramatic increase in PLSCR tyrosine phosphorylation. A comparison of the relative amounts of phospho-PLSCR and nonphosphorylated PLSCR demonstrated that only a tiny fraction was thus modified, indicating a finely targeted involvement of PLSCR in FcepsilonRI signaling. Thus, this study reports the cloning of a new isoform of PLSCR, as well as the first observation that a member of the PLSCR family is a target for tyrosine kinases and is involved in signaling by an immune receptor. These findings open new perspectives on the role of phospholipid scramblases and to the mechanisms involved in their regulation.

Colostral neutrophils express Fc alpha receptors (CD89) lacking gamma chain association and mediate noninflammatory properties of secretory IgA

Colostrum plays an important role in protecting newborn infants against acute gastrointestinal and respiratory infections. IgA antibodies have been considered the major effector component; however, the role of their receptors on colostral phagocytes, especially neutrophils, has not been studied. Here, we demonstrate that CD15+ colostrum neutrophils express IgA Fc receptors (Fc alphaR, CD89) at levels similar to those of blood neutrophils. Most colostral cells (70%) bear secretory IgA (SIgA) on their surface (and intracellularly), whereas blood cells do not. The Fc alphaR on colostral neutrophils was identified as the a.1 isoform with a similar molecular mass (55-75 kDa) as that identified for blood neutrophils. Removal of N-linked carbohydrates revealed a major protein core of 32 kDa for both cell types. In contrast, co-immunoprecipitation and immunoblot experiments using a mild detergent, digitonin, revealed a lack of gamma chain association with Fc alphaR (gamma-less) exclusively on colostral neutrophils. The functional role of these gamma-less Fc alphaR cells was evaluated by measuring superoxide release and killing of SIgA-coated enteropathogenic E. coli. No increase in superoxide release was observed in colostral cells compared with blood neutrophils, whereas optimal release was obtained with PMA stimulation. Furthermore, despite similar bacterial phagocytosis index between both cell types, IgA-mediated bacterial-killing was not detectable with colostral neutrophils, whereas killing was detectable on blood cells. These results reveal exclusive expression of gamma-less Fc alphaR on colostral neutrophils associated with receptor hyperoccupation by IgA and with low, bacterial-killing activity, which suggest that this receptor may mediate noninflammatory effects of SIgA.

A subset of human dendritic cells expresses IgA Fc receptor (CD89), which mediates internalization and activation upon cross-linking by IgA complexes

Immature dendritic cells (DC) sample Ags within nonlymphoid tissues and acquire exogenous proteins/pathogens via scavenger receptors or Ig FcR such as Fc gamma R and Fc epsilon R. IgA is present in a significant proportion among serum Ig and is the main isotype in mucosae, where DC are numerous. We found that a functional Fc alpha R (CD89) was expressed in situ and in vitro on interstitial-type DC but not on Langerhans cell-type DC. Interstitial-type DC expressed CD89 as a 50- to 75-kDa glycoprotein with a 32-kDa protein core, which was down-regulated upon addition of TGF-beta 1. DC, Fc alpha R specifically, bound IgA1 and IgA2. Cross-linking of CD89 on DC triggered endocytosis in time-dependent manner. In addition, internalization of polymeric IgA complexes induced the production of IL-10 and DC activation, as reflected by up-regulation of CD86 costimulatory molecules, class II MHC expression, and increased allostimulatory activity. Therefore, interstitial-type DC may use Fc alpha R-mediated Ag sampling in the subepithelium to check tissue integrity while Langerhans cells inside epithelial layers may neglect IgA immune complexes.

Impaired expression of IgA Fc receptors (CD89) by blood phagocytic cells in ankylosing spondylitis

OBJECTIVE

Expression of IgA Fc receptors (CD89, FcalphaR) and their occupancy by endogenous IgA were studied on blood monocytes and neutrophits to determine if FcalphaR defects could account for enhanced serum IgA and IgA-IC commonly found in patients with ankylosing spondylitis (AS).

METHODS

Peripheral blood samples were obtained from 34 patients with AS, 15 patients with rheumatoid arthritis, and 34 healthy individuals. Cell surface FcalphaR was analyzed using a quantitative flow cytometry method in which blood cells were stained with anti-FcalphaR monoclonal antibodies recognizing epitopes outside the IgA binding site and with F(ab')2 fragments of anti-IgA antibodies. Modulation of cell surface FcalphaR was evaluated after incubation of blood cells at 37 degrees C in absence of plasma. Biochemical characterization of iodinated FcalphaR molecules was determined by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).

RESULTS

FcaR expression was significantly decreased on monocytes and neutrophils in patients with AS compared to control groups. FcalphaR levels were inversely correlated with serum IgA, suggesting its negative regulatory role. Modulation experiments resulted in rapid and higher FcalphaR upregulation in AS than in controls, indicating that these molecules were downregulated only at the cell surface. Moreover, analysis of the surface iodinated FcalphaR molecules by SDS-PAGE revealed higher Mr (60-90 kDa) in AS than controls (55-75 kDa), also suggesting an altered glycosylation. Analysis of receptor occupancy revealed high levels of endogenous IgA bound to monocytes and neutrophils in patients with AS, pointing to a saturation of IgA Fc receptors.

CONCLUSION

We observed impaired expression of FcalphaR in patients with AS that is characterized by a downregulation process associated with post-translational alterations and enhanced binding of endogenous IgA. These alterations might lead to a defective blood clearance by FcalphaR resulting in the enhancement of IgA and IgA-IC in AS patients. Decreased FcalphaR expression represents a new marker for this disease.

Elevation of serum IgA in spondyloarthropathies and IgA nephropathy and its pathogenic role

Ankylosing spondylitis and IgA nephropathy share some immunologic features, eg, elevated serum IgA and IgA-immune complex levels. These entities are frequently found as being associated. IgA and IgA immune complex catabolism involves asialoglycoprotein receptors and specific IgA Fc receptors (FcalphaR or CD89) on tissue and blood cells. Recent studies revealed impaired CD89 expression in both diseases. These abnormalities, which are associated with receptor saturation, might generate the increase in serum IgA and IgA immune complex levels by either altered recycling or failure of degradation. This article reviews the literature on IgA abnormalities and discusses the potential role of FcalphaR in IgA nephropathy and AS and the consequences of its similar defect in the two diseases.

Alternative endocytic pathway for immunoglobulin A Fc receptors (CD89) depends on the lack of FcRgamma association and protects against degradation of bound ligand

IgA is the most abundant immunoglobulin in mucosal areas but is only the second most common antibody isotype in serum because it is catabolized faster than IgG. IgA exists in monomeric and polymeric forms that function through receptors expressed on effector cells. Here, we show that IgA Fc receptor(s) (FcalphaR) are expressed with or without the gamma chain on monocytes and neutrophils. gamma-less FcalphaR represent a significant fraction of surface FcalphaR molecules even on cells overexpressing the gamma chain. The FcalphaR-gamma2 association is up-regulated by phorbol esters and interferon-gamma. To characterize gamma-less FcalphaR functionally, we generated mast cell transfectants expressing wild-type human FcalphaR or a receptor with a point mutation (Arg --> Leu at position 209) which was unable to associate with the gamma chain. Mutant gamma-less FcalphaR bound monomeric and polymeric human IgA1 or IgA2 but failed to induce exocytosis after receptor clustering. The two types of transfectant showed similar kinetics of FcalphaR-mediated endocytosis; however, the endocytosis pathways of the two types of receptor differed. Whereas mutant FcalphaR were localized mainly in early endosomes, those containing FcalphaR-gamma2 were found in endo-lysosomal compartments. Mutant gamma-less FcalphaR recycled the internalized IgA toward the cell surface and protected against IgA degradation. Cells expressing the two forms of FcalphaR, associated or unassociated with gamma chains, may thus have differential functions either by degrading IgA antibody complexes or by recycling serum IgA.

Overexpression of natural killer T cells protects Valpha14- Jalpha281 transgenic nonobese diabetic mice against diabetes

Progression to destructive insulitis in nonobese diabetic (NOD) mice is linked to the failure of regulatory cells, possibly involving T helper type 2 (Th2) cells. Natural killer (NK) T cells might be involved in diabetes, given their deficiency in NOD mice and the prevention of diabetes by adoptive transfer of alpha/beta double-negative thymocytes. Here, we evaluated the role of NK T cells in diabetes by using transgenic NOD mice expressing the T cell antigen receptor (TCR) alpha chain Valpha14-Jalpha281 characteristic of NK T cells. Precise identification of NK1.1(+) T cells was based on out-cross with congenic NK1.1 NOD mice. All six transgenic lines showed, to various degrees, elevated numbers of NK1.1(+) T cells, enhanced production of interleukin (IL)-4, and increased levels of serum immunoglobulin E. Only the transgenic lines with the largest numbers of NK T cells and the most vigorous burst of IL-4 production were protected from diabetes. Transfer and cotransfer experiments with transgenic splenocytes demonstrated that Valpha14-Jalpha281 transgenic NOD mice, although protected from overt diabetes, developed a diabetogenic T cell repertoire, and that NK T cells actively inhibited the pathogenic action of T cells. These results indicate that the number of NK T cells strongly influences the development of diabetes.

IgA Fc receptor (CD89) activation enables coupling to syk and Btk tyrosine kinase pathways: differential signaling after IFN-gamma or phorbol ester stimulation

IgA Fc receptors (Fc alphaR) can mediate a variety of inflammatory responses. It has been demonstrated that the FcRgamma subunit is critical in mediating signaling through Fc alphaR. We show that aggregation of Fc alphaR on U937 cells and blood neutrophils results in tyrosine phosphorylation of several intracellular proteins, including the FcR gamma subunit, p72syk, and Bruton tyrosine kinase (Btk). Syk was found to be associated with Fc alphaR and its phosphorylation was increased in phorbol myristate acetate (PMA)- and interferon-gamma (IFN-gamma)-treated U937 cells. In contrast, phosphorylation of Btk was only detected after cell treatment with PMA but not IFN-gamma. These data indicate that signaling through Fc alphaR gamma2 involves at least two subfamilies of tyrosine kinases, syk and Btk. Our results also suggest that activation of tyrosine kinase pathways through Fc alphaR depends on the activation state of the cell. This may be an important regulatory mechanism in IgA-mediated responses at inflammatory sites.

Down-regulation of Fc alpha receptors on blood cells of IgA nephropathy patients: evidence for a negative regulatory role of serum IgA

IgA nephropathy (IgAN) is associated with increased serum IgA1 and IgA1-immune complexes (IC). As Fc alpha receptors (Fc alpha R) are candidate molecules to regulate IgA levels, increased receptor occupation by IgA1 prompted us to study the expression of Fc alpha R on blood cells of IgAN patients. Surface and cytoplasmic Fc alpha R expression were markedly decreased on monocytes, despite normal levels of transcripts. Fc alpha R expression on patients' neutrophils was slightly decreased, exclusively at the cell surface. However, when autologous plasma was removed from the cells Fc alpha R was up-regulated. This observation led us to search for circulating regulatory factors. In vitro experiments revealed that Fc alpha R was down-regulated on normal monocytes following long-term culture with control or patient purified serum IgA at high concentrations (5 mg/ml). Moreover, polymeric myeloma IgA1 induced stronger down-regulation than monomeric IgA1. These results point to a negative regulatory role of serum IgA on surface Fc alpha R expression. This is also supported by a negative correlation between levels of Fc alpha F on blood cells and serum IgA. On the other hand, endogenous IgA bound to IgAN cells was significantly higher than IgA bound to control cells pre-incubated with patients' plasma, suggesting abnormalities in the receptor-ligand interaction. Patient Fc alpha R had a higher Mr (60 to 85 kDa) than those of controls (55 to 75 kDa) and a decreased binding to a sialic acid-specific lectin on blots, indicating post-translational modifications with impaired sialylation of surface Fc alpha R molecules that might be involved in enhanced IgA binding. Continuous Fc alpha R occupation by IgA, associated with receptor down-regulation, might contribute to the enhancement of circulating IgA1 and IgA1-IC by impairing their binding and degradation. Finally, increased receptor occupation by IgA on monocytes was linked to mesangial proliferation and glomerular sclerosis, suggesting a role for IgA-bound cells in the pathogenesis of mesangial damage.

Defective Fc gamma RII gene expression in macrophages of NOD mice: genetic linkage with up-regulation of IgG1 and IgG2b in serum

A quantitative trait locus for increased IgG serum levels in the NOD mouse strain was mapped to distal chromosome 1, close to the fcgr2 locus encoding the low-affinity type II receptor for the Fc portion of IgG (Fc gamma RII). Expression of membrane-inserted (b2) and soluble (b3) isoforms of Fc gamma RII was strongly decreased in macrophages of NOD compared with C57BL/6 (B6) mice. In contrast, B cell-specific (Fc gamma RIIb1) isoform was only slightly decreased and Fc gamma RIII was not altered. This Fc gamma RII regulatory defect was cis-encoded by fcgr2 or by a closely linked locus, occurred at the mRNA level, and was associated with multiple mutations in the fcgr2 gene promoter. In relation with this defect, binding of IgG1- and IgG2b- but not IgG2a-opsonized RBC by macrophages of NOD and congenic B6.NOD-fcgr2 mice was severely impaired, but was normal in macrophages of NOD.B6-fcgr2 congenic mice, indicating that Fc gamma RII plays a nondispensable role in binding of IgG1 and IgG2b isotypes. Likewise, serum levels of IgG1 and IgG2b but not IgG2a were up-regulated in NOD compared with NOD.B6-fcgr2 congenic mice. These findings indicate that macrophage Fc gamma RII may regulate serum IgG1 and IgG2b through their catabolism, and validate the NOD strain as a model to investigate the functions of Fc gamma RII isoforms.

Defective Fc gamma RII gene expression in macrophages of NOD mice: genetic linkage with up-regulation of IgG1 and IgG2b in serum

A quantitative trait locus for increased IgG serum levels in the NOD mouse strain was mapped to distal chromosome 1, close to the fcgr2 locus encoding the low-affinity type II receptor for the Fc portion of IgG (Fc gamma RII). Expression of membrane-inserted (b2) and soluble (b3) isoforms of Fc gamma RII was strongly decreased in macrophages of NOD compared with C57BL/6 (B6) mice. In contrast, B cell-specific (Fc gamma RIIb1) isoform was only slightly decreased and Fc gamma RIII was not altered. This Fc gamma RII regulatory defect was cis-encoded by fcgr2 or by a closely linked locus, occurred at the mRNA level, and was associated with multiple mutations in the fcgr2 gene promoter. In relation with this defect, binding of IgG1- and IgG2b- but not IgG2a-opsonized RBC by macrophages of NOD and congenic B6.NOD-fcgr2 mice was severely impaired, but was normal in macrophages of NOD.B6-fcgr2 congenic mice, indicating that Fc gamma RII plays a nondispensable role in binding of IgG1 and IgG2b isotypes. Likewise, serum levels of IgG1 and IgG2b but not IgG2a were up-regulated in NOD compared with NOD.B6-fcgr2 congenic mice. These findings indicate that macrophage Fc gamma RII may regulate serum IgG1 and IgG2b through their catabolism, and validate the NOD strain as a model to investigate the functions of Fc gamma RII isoforms.

Identification of Fc alpha receptor (CD89) isoforms generated by alternative splicing that are differentially expressed between blood monocytes and alveolar macrophages

One of the hallmarks of mucosal-host defense is the clearance of inhaled Ags by alveolar macrophages (AM) through interactions of IgA Abs and IgA Fc receptors (Fc alpha R). AM constitutively expressed Fc alpha R at lower levels than freshly isolated and in vitro-differentiated monocytes as determined by immunofluorescence using four anti-Fc alpha R mAb. SDS-PAGE analysis of iodinated cell surface proteins revealed that Fc alpha R on AM has an Mr of 50 to 65 kDa, slightly lower than that on monocytes (55-75 kDa). Treatment of AM Fc alpha R by N-glycanase gave rise to a protein core of 28 KDa, smaller than the 32-kDa backbone of blood monocytes. AM Fc alpha R molecules were unaffected by phosphatidylinositol-phospholipase C treatment. Fc alpha R transcripts were analyzed by reverse transcription-PCR using primers in the 5' and 3' regions of a U937 Fc alpha R cDNA. Three transcripts were amplified, cloned, and sequenced from AM and/or monocyte mRNA, the full length Fc alpha R and two alternatively spliced products corresponding to deletions of 66 and 288 nucleotides in the portion coding for the extracellular domain; they were named Fc alpha R a.1, a.2, and a.3, respectively. These PCR products were transcribed and translated in vitro into three proteins (Mr 32, 30, and 22 kDa, respectively), in which the 32- and 30-kDa species were immunoprecipitated by an anti-Fc alpha R mAb. The predicted size of the protein encoded by the Fc alpha R a.2 transcript without the leader peptide is Mr approximately 27,400, a value that is consistent with the Mr of AM Fc alpha R backbone. These results indicate that AM express at their surfaces a protein product of an alternatively spliced Fc alpha R transcript, the Fc alpha R a.2 isoform, that might have physiologic relevance in IgA-mediated host defense at mucosal sites.

Identification of Fc alpha receptor (CD89) isoforms generated by alternative splicing that are differentially expressed between blood monocytes and alveolar macrophages

One of the hallmarks of mucosal-host defense is the clearance of inhaled Ags by alveolar macrophages (AM) through interactions of IgA Abs and IgA Fc receptors (Fc alpha R). AM constitutively expressed Fc alpha R at lower levels than freshly isolated and in vitro-differentiated monocytes as determined by immunofluorescence using four anti-Fc alpha R mAb. SDS-PAGE analysis of iodinated cell surface proteins revealed that Fc alpha R on AM has an Mr of 50 to 65 kDa, slightly lower than that on monocytes (55-75 kDa). Treatment of AM Fc alpha R by N-glycanase gave rise to a protein core of 28 KDa, smaller than the 32-kDa backbone of blood monocytes. AM Fc alpha R molecules were unaffected by phosphatidylinositol-phospholipase C treatment. Fc alpha R transcripts were analyzed by reverse transcription-PCR using primers in the 5' and 3' regions of a U937 Fc alpha R cDNA. Three transcripts were amplified, cloned, and sequenced from AM and/or monocyte mRNA, the full length Fc alpha R and two alternatively spliced products corresponding to deletions of 66 and 288 nucleotides in the portion coding for the extracellular domain; they were named Fc alpha R a.1, a.2, and a.3, respectively. These PCR products were transcribed and translated in vitro into three proteins (Mr 32, 30, and 22 kDa, respectively), in which the 32- and 30-kDa species were immunoprecipitated by an anti-Fc alpha R mAb. The predicted size of the protein encoded by the Fc alpha R a.2 transcript without the leader peptide is Mr approximately 27,400, a value that is consistent with the Mr of AM Fc alpha R backbone. These results indicate that AM express at their surfaces a protein product of an alternatively spliced Fc alpha R transcript, the Fc alpha R a.2 isoform, that might have physiologic relevance in IgA-mediated host defense at mucosal sites.

Detection of antilineage specific leucocyte antibodies by a quantitative immunocytometry method in sera from candidates for renal allografts

A sensitive and quantitative flow cytometry method for detecting antileucocyte antibodies was developed to study retrospectively samples from candidates using frozen donor cells and frozen recipient sera. This immunofluorescence method was used to compare levels of reactivities of serum antibodies before and after donor specific blood transfusion treatment and after renal transplantation. The results demonstrate that the flow cytometry crossmatch is a sensitive and accurate method which should be used prospectively before precluding transplantation in the presence of a positive B cell standard crossmatch. Antibodies detected by flow cytometry before transplantation could be responsible for an early acute rejection episode. Finally, combination of flow cytometry crossmatch and standard crossmatch assays might thus be useful before precluding transplantation in living related donors.

Fc alpha receptors mediate release of tumour necrosis factor-alpha and interleukin-6 by human monocytes following receptor aggregation

The functional capacity of the human monocyte receptor for the Fc portion of IgA (Fc alpha R) in mediating signal transduction was evaluated by cytokine release. F(ab')2 fragments of anti-Fc alpha R monoclonal antibodies (mAb) were used as specific probes to induce release of tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). Multivalent cross-linking by a secondary anti-mouse antibody [F(ab')2 fragments] induced a significant release of TNF-alpha and IL-6 by human blood mononuclear cells, indicating requirements for Fc alpha R aggregation on the cell surface to transmit signals. Both cytokines were released exclusively by adherent cells, identifying monocytes as the responding cells within the mononuclear cell population. This cytokine release could not be due to contaminating endotoxins, because it was not abolished by polymyxin B, a lipopolysaccharide (LPS) inhibitor. Moreover, purified recombinant soluble Fc alpha R inhibited the anti-Fc alpha R mAb-mediated cytokine release from blood monocytes, demonstrating that TNF-alpha and IL-6 were released in a receptor-specific manner. Our data suggest that Fc alpha R, through its capacity to mediate secretion of IL-6, may play an important role in B-cell proliferation and immunoglobulin production. On the other hand, release of TNF-alpha following stimulation of Fc alpha R molecules directly implicates these receptors in amplification and regulation of the inflammatory process occurring during IgA-mediated host defence.

Altered expression of monocyte IgA Fc receptors is associated with defective endocytosis in patients with alcoholic cirrhosis. Potential role for IFN-gamma

Expression, saturation, and endocytosis of IgA Fc receptors (Fc alpha R) were analyzed in blood phagocytic cells of patients with alcoholic liver cirrhosis (ALC). Surface Fc alpha R expression was decreased in monocytes but not in neutrophils, as evaluated by IgA binding and anti-Fc alpha R mAb. The Fc alpha R of ALC patients were saturated by IgA1 and IgA2. ALC Fc alpha R had a higher M(r) (60 to 90 kDa) than those of controls (55 to 75 kDa) with a similar 32-kDa protein core after N-glycanase treatment, suggesting the expression of Fc alpha R molecules with altered carbohydrate moieties. Treatment of U937 cells with IFN-gamma induced a decrease of surface Fc alpha R expression in a dose-dependent manner, with a similar M(r) as observed for ALC patient Fc alpha R (60 to 90 kDa). Fc alpha R endocytosis was induced by anti-Fc alpha R or IgA. Neutrophils internalized Fc alpha R molecules faster than did monocytes. Endocytosed Fc alpha R co-localized with cathepsin D, suggesting an endolysosomal compartment pathway. In ALC monocytes, Fc alpha R endocytosis was defective, with nearly 50 to 60% of receptors detected on the cell surface even after 90 min at 37 degrees C. Similarly, delayed Fc alpha R endocytosis was observed on IFN-gamma-treated U937 cells as compared with PMA-activated cells. Defective internalization of surface-bound IgA with reflux of IgA to cell surface was also observed on ALC monocytes, but not on normal cells preincubated with patients' plasma, ruling out direct effects of IgA. The inverse correlation between monocyte Fc alpha R levels and serum IgA levels associated with defective endocytosis suggest that altered Fc alpha R expression might contribute to receptor saturation and generation of increased plasma levels of IgA and IgA-immune complexes in ALC patients.

Altered expression of monocyte IgA Fc receptors is associated with defective endocytosis in patients with alcoholic cirrhosis. Potential role for IFN-gamma

Expression, saturation, and endocytosis of IgA Fc receptors (Fc alpha R) were analyzed in blood phagocytic cells of patients with alcoholic liver cirrhosis (ALC). Surface Fc alpha R expression was decreased in monocytes but not in neutrophils, as evaluated by IgA binding and anti-Fc alpha R mAb. The Fc alpha R of ALC patients were saturated by IgA1 and IgA2. ALC Fc alpha R had a higher M(r) (60 to 90 kDa) than those of controls (55 to 75 kDa) with a similar 32-kDa protein core after N-glycanase treatment, suggesting the expression of Fc alpha R molecules with altered carbohydrate moieties. Treatment of U937 cells with IFN-gamma induced a decrease of surface Fc alpha R expression in a dose-dependent manner, with a similar M(r) as observed for ALC patient Fc alpha R (60 to 90 kDa). Fc alpha R endocytosis was induced by anti-Fc alpha R or IgA. Neutrophils internalized Fc alpha R molecules faster than did monocytes. Endocytosed Fc alpha R co-localized with cathepsin D, suggesting an endolysosomal compartment pathway. In ALC monocytes, Fc alpha R endocytosis was defective, with nearly 50 to 60% of receptors detected on the cell surface even after 90 min at 37 degrees C. Similarly, delayed Fc alpha R endocytosis was observed on IFN-gamma-treated U937 cells as compared with PMA-activated cells. Defective internalization of surface-bound IgA with reflux of IgA to cell surface was also observed on ALC monocytes, but not on normal cells preincubated with patients' plasma, ruling out direct effects of IgA. The inverse correlation between monocyte Fc alpha R levels and serum IgA levels associated with defective endocytosis suggest that altered Fc alpha R expression might contribute to receptor saturation and generation of increased plasma levels of IgA and IgA-immune complexes in ALC patients.

T cell activation through Thy-1 is associated with the expression of a surface protein (p100) on a subset of CD4 cells

Thy-1 molecules, which lack a transmembrane domain, can nonetheless induce T cell activation; it has thus been suggested that a separate transmembrane molecule associated with Thy-1 is required for signal transduction. We have previously characterized a transmembrane protein with an Mr of 100,000 (p100), which is non-covalently bound to two glycosyl-phosphatidylinositol (GPI)-linked molecules, Thy-1 and ThB. p100 is selectively expressed on the T cell surface and divides peripheral CD4 cells into two subpopulations. This differential expression on CD4 cells allowed us to investigate the role of p100 in signal transduction through Thy-1 molecules. Here we report that only p100+ CD4 cells proliferate and release cytokines in response to cross-linkage of Thy-1, although both p100+ and p100- CD4 cells strongly express Thy-1 on their surfaces. Control stimulation by anti-CD3 antibodies or concanavalin A induces identical thymidine uptake by the two CD4 cell populations. Interestingly, these two populations of CD4 cells had different cytokine release profiles after activation through CD3: only p100+ CD4 cells released high amounts of IL-2 and IFN-gamma, whereas both populations released IL-4. p100 expression correlates with the induction of homotypic aggregation of T cells after Thy-1 triggering. p100 is associated with kinase activity (fyn and lck), and phosphorylated proteins of 90, 59, 57 and 33 kDa co-precipitate with Thy-1 only in p100+ CD4 cells. Altogether, these data suggest that p100 is involved in signal transduction through Thy-1. p100 expression by activated CD4 cells in vivo may be relevant to the proposed function of Thy-1 as an accessory signaling molecule in cell activation.

Impaired Fc alpha receptor expression is linked to increased immunoglobulin A levels and disease progression in HIV-1-infected patients

OBJECTIVES

Expression of immunoglobulin (Ig) A Fc receptors (Fc alpha R) and their saturation by endogenous IgA were studied on blood monocytes and neutrophils to evaluate the role of Fc alpha R in the formation of increased serum levels of IgA and IgA-immune complexes (IgA-IC) observed during HIV-1 infection.

METHODS

Peripheral blood samples were obtained from 45 patients at different stages of HIV-1 infection and from 22 healthy volunteers. This study was performed using a quantitative flow cytometry method in which blood cells were stained with anti-Fc alpha R monoclonal antibodies (MAb) recognizing epitopes outside the IgA-binding site and with F(ab')2 fragments of anti-IgA antibodies. Immunoprecipitations of radiolabelled surface Fc alpha R molecules were analysed by sodium dodecylsulphate-polyacrylamide gel electrophoresis under glycosylated and deglycosylated conditions.

RESULTS

This study reveals a diminished surface expression of Fc alpha R on blood monocytes of HIV-1-infected patients, which follows disease progression. Fc alpha R molecules on patients' neutrophils have a higher apparent molecular mass (60-90 kD) with normal protein core, suggesting expression of receptors with altered carbohydrate moieties. Increased levels of serum IgA significantly correlate with decreased levels of Fc alpha R in HIV-1-infected patients. Surface Fc alpha R molecules are saturated by endogenous IgA1 in both cell types.

CONCLUSION

These findings suggest that defective expression and/or altered glycosylation of Fc alpha R may result in receptor saturation, impairment of IgA catabolism and diminished clearance of IgA-IC in HIV-1-infected patients. Fc alpha R expression represents a new marker for disease progression.

Definition of immunoglobulin A receptors on eosinophils and their enhanced expression in allergic individuals

Fc alpha receptors (Fc alpha R), detected by the binding of IgA and by anti-Fc alpha R antibodies, were found to be differentially expressed on eosinophils and neutrophils. Neutrophils were the major granulocyte population expressing Fc alpha R, and they expressed much higher levels of Fc alpha R than eosinophils. The expression of Fc alpha R by eosinophils could be upregulated approximately threefold by Ca2+ ionophore treatment in a dose- and time-dependent manner. This effect, which was blocked by a chelating agent, was not duplicated by other cellular stimuli. Eosinophils in allergic individuals displayed enhanced Fc alpha R expression, whereas neutrophils did not. The Fc alpha R on eosinophils had a higher molecular mass (70-100 kD) than those identified on neutrophils (55-75 kD). However, removal of N-linked carbohydrates from Fc alpha R of eosinophils and neutrophils revealed a major protein core of 32 kD for both cell types. The data indicate that expression of Fc alpha R molecules with a characteristic glycosylation pattern is upregulated on eosinophils in allergic individuals.

Expression of surrogate light chain receptors is restricted to a late stage in pre-B cell differentiation

Surrogate light chain (psi LC) genes are transcriptionally active in progenitor B (pro-B) cells before immunoglobulin genes are rearranged. Current hypothetical models suggest that the psi LC proteins may couple with surrogate or conventional heavy chain proteins to form cell surface receptors that signal the progressive differentiation of pro-B, precursor B (pre-B), and immature B cells. Monoclonal antibodies were produced and used to examine the synthesis, expression, intermolecular interaction, and function of psi LC during B cell differentiation. The results indicate that, while psi LC production spans several developmental stages, cell surface expression is confined to a relatively late stage in normal pre-B cell differentiation, during which receptor cross-linkage does not impede cell growth or B cell differentiation.

Recombinant soluble IgA Fc receptor: generation, biochemical characterization, and functional analysis of the recombinant protein

We previously described the cloning of a human myeloid cell surface receptor for the Fc region of immunoglobulin A (Fc alpha R). In the present study, a soluble version of the Fc alpha R (solFc alpha R) was generated by removing the transmembrane and cytoplasmic coding regions from full-length Fc alpha R cDNA and ligating into a mammalian expression vector. COS-7 cells transfected with the solFc alpha R plasmid secreted a protein that inhibited both immunoglobulin A (IgA) and anti-Fc alpha R monoclonal antibody (mAb) binding to Fc alpha R+ U937 cells. Furthermore, the solFc alpha R bound specifically to and could be eluted from an anti-Fc alpha R mAb-immunoaffinity column, retaining biological activity. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that the recombinant full-length Fc alpha R migrates over a molecular mass range of approximately 40-60 kd, consistent with the reported size and heterogeneity of the naturally occurring myeloid cell surface Fc alpha R. The solFc alpha R ran on SDS-PAGE as a smaller band (37-55 kd) that reduced to two bands of 23 and 25 kd following N-glycanase treatment, indicating that the Fc alpha R is a heavily glycosylated protein. The biochemical data, coupled with flow cytometry studies showing that the recombinant Fc alpha Rs bind to five different anti-Fc alpha R mAbs, clearly demonstrate that the cloned Fc alpha R corresponds directly to the major Fc alpha R species expressed on human monocytes, neutrophils, and myeloid cell lines. The generation of soluble receptor protein will permit investigations of the role of Fc alpha R in IgA-mediated immunoregulation, effector functions, and disease.

Identification of a surface protein (p100) associated with two glycosyl-phosphatidylinositol-linked molecules (Thy-1 and ThB) by natural anti-lymphocyte autoantibodies

Our previous study of natural autoantibodies showed that anti-lymphocyte antibodies are frequently produced by perinatal B cells from normal strains of mice. One-third of these monoclonal antibodies (mAb) recognized similar epitopes on the surface of thymocytes. In the present report, we have characterized the molecule recognized by three of these mAb (D10, G7, 22). These mAb identified a 100-kDa protein (p100) on the surface of thymocytes. This protein resolved into 70-kDa polypeptide chains under reducing conditions. Inhibition experiments as well as antibody immunoprecipitations in the presence of mild detergents revealed non-covalent association of the p100 with Thy-1 and ThB. A similar multimolecular complex was identified following chemical cross-linking of thymocyte surface proteins. Analysis of several Thy-1-defective mutant cells lines, and thymocytes treated with phosphatidylinositol-specific phospholipase C (PI-PLC) showed that the expression of p100 was strongly influenced by Thy-1 molecule. The p100 was resistant to PI-PLC treatment and was not released into the supernatant as was the case for Thy-1 and ThB molecules. These data lead us to propose that the p100 is a transmembrane protein, the expression of which in the plasma membrane is dependent on the association or presence of Thy-1 molecule.

Molecular heterogeneity of Fc alpha receptors detected by receptor-specific monoclonal antibodies

Fc alpha receptors (Fc alpha R) were isolated from a human monocytic cell line and used to raise four mAb with receptor specificity. The antibodies were used to identify the types of white blood cells that express Fc alpha R and the molecular heterogeneity of the receptor molecules. Nonpolymorphic epitopes, outside of the Fc alpha-binding site, were recognized only on blood cells of granulocyte and monocyte/macrophage lineages. The molecules identified, both by the antibodies and by the IgA ligand, were glycoproteins ranging in relative molecular mass from 55 to 75 kDa. However, one antibody detected a subpopulation of Fc alpha R molecules characterized by relatively restricted size heterogeneity. A complex glycosylation pattern was revealed by the resolution of discrete 32- and 36-kDa molecular species after removal of N-linked oligosaccharides and by evidence for O-linked carbohydrate moieties on at least a portion of the Fc alpha R molecules. In biosynthetic studies, all four anti-Fc alpha R antibodies and the IgA ligand bound a single 32-kDa core protein present in tunicamycin-treated cells, and the exceptional antibody again recognized molecules with relatively restricted glycosylation in the nontreated cells. These antibodies and native IgA ligands thus provide complementary reagents for definition of the complex structure and function of Fc alpha R in systemic IgA antibody responses.

Molecular heterogeneity of Fc alpha receptors detected by receptor-specific monoclonal antibodies

Fc alpha receptors (Fc alpha R) were isolated from a human monocytic cell line and used to raise four mAb with receptor specificity. The antibodies were used to identify the types of white blood cells that express Fc alpha R and the molecular heterogeneity of the receptor molecules. Nonpolymorphic epitopes, outside of the Fc alpha-binding site, were recognized only on blood cells of granulocyte and monocyte/macrophage lineages. The molecules identified, both by the antibodies and by the IgA ligand, were glycoproteins ranging in relative molecular mass from 55 to 75 kDa. However, one antibody detected a subpopulation of Fc alpha R molecules characterized by relatively restricted size heterogeneity. A complex glycosylation pattern was revealed by the resolution of discrete 32- and 36-kDa molecular species after removal of N-linked oligosaccharides and by evidence for O-linked carbohydrate moieties on at least a portion of the Fc alpha R molecules. In biosynthetic studies, all four anti-Fc alpha R antibodies and the IgA ligand bound a single 32-kDa core protein present in tunicamycin-treated cells, and the exceptional antibody again recognized molecules with relatively restricted glycosylation in the nontreated cells. These antibodies and native IgA ligands thus provide complementary reagents for definition of the complex structure and function of Fc alpha R in systemic IgA antibody responses.

Immune complex-mediated glomerulopathy in experimental Chagas' disease

To investigate the development of glomerulopathy during the chronic phase of experimental Chagas' disease, C3H-Hej mice were infected with Trypanosoma cruzi trypomastigotes. Deposits of IgG, IgM, and C3 in renal mesangium were observed by immunofluorescence (IF) to increase in size as a function of time after infection (4-6 months). T. cruzi antigens were codeposited in glomeruli with Ig and C3. Electron-dense deposits were visualized in mesangial and paramesangial areas by electron microscopy. Anti-T. cruzi and rheumatoid factor (RF) antibodies (of IgG isotypes) were detected both in serum and in renal eluates. In serum, the titers of both antibodies progressively decreased as a function of time after infection. In renal eluates, titers of anti-T. cruzi antibodies appeared to be stable during the three time periods after infection. By contrast, titers of RF antibodies in renal eluates were shown to increase progressively during these same time periods, paralleling the increase in size of mesangial Ig deposits observed by IF. Several T. cruzi proteins were immunoprecipitated from radiolabeled renal eluates by a control anti-T. cruzi antibody. In addition, antibodies from renal eluates specifically precipitated a 85-kDa protein from radiolabeled T. cruzi lysates, whereas serum antibodies precipitated a broad pattern of T. cruzi proteins. These results demonstrate that mice experimentally infected with T. cruzi can develop a mesangial glomerulopathy during the chronic phase of the disease, which appears to be mediated through immune complexes containing parasite antigens associated with secondary deposition of RF.

Cellular distribution, regulation, and biochemical nature of an Fc alpha receptor in humans

In these studies, we characterize an Fc receptor (FcR) for IgA that is present on human granulocytes, monocyte/macrophages, and their corresponding cell lines. Receptor expression appears to be constitutive but can be selectively upregulated on monocyte cell lines by stimulation with a phorbol ester and polymeric IgA. Both the induction requirements and ligand specificity of the IgA receptor differ from the IgG receptors, Fc gamma R I, II, and III, that are also expressed on monocytes and granulocytes. IgA binding to the cell surface receptor is mediated via the Fc alpha region. The Fc alpha R is a heterogenously charged, approximately 60-kD molecule with an isoelectric point of 4.5-5.6 that binds monomeric or polymeric IgA1 and IgA2 molecules. This transmembrane glycoprotein appears to be composed of 32- and 36-kD protein cores with multiple N-linked carbohydrate moieties. We conclude that this Fc alpha R represents a novel member of the FcR family that may have a distinctive role in host defense.

Glomerular and serum immunoglobulin G subclasses in IgA nephropathy

The distribution of human IgG subclasses among mesangial glomerular deposits of 11 patients with IgA nephropathy (IgA-N) was examined by indirect immunofluorescence with subclass-specific mouse monoclonal antibodies (mAb). A subclass restriction was observed with mesangial deposits containing almost exclusively IgG1 (81% of the studied biopsies) and IgG3 (64%). IgG2 was present in only 1 out of the 11 cases studied and IgG4 was never found to be present, although seven different anti-IgG4 mAb were used. In addition, serum levels of total IgA and IgG, as well as serum IgG subclass levels, were measured in 27 patients with IgA nephropathy by an indirect competitive immunoenzymatic assay using mAb. It was noted in IgA-N patients, but not in normal individuals, that there was significant positive correlation between total IgA and IgG serum levels which was entirely due to a positive correlation between total serum IgA and IgG2 levels. This study provides no explanation for the subclass restrictions observed but suggests that (i) the presence of IgA-IgG1-IgG3 in mesangial deposits may be secondary to an antigenic stimulation, possibly viral, and (ii) the positive correlation between IgA and IgG2 serum levels may result from an increased T helper function.

Immunofluorescence analysis of IgA binding by human mononuclear cells in blood and lymphoid tissue

The nature of IgA-binding cells and their tissue distribution was examined by an indirect immunofluorescence assay with the use of IgA1 and IgA2 paraproteins and fluorochrome- or biotin-labeled F(ab')2 fragments of idiotype-specific antibodies. The frequency of IgA-binding mononuclear cells was approximately 13% in blood and spleen samples but less than 1% in tonsil samples. IgA binding could be visualized by flow immunocytometry on monocyte/macrophages, but not on T and B cells. IgA polymers were bound better than IgA dimers and monomers. Nonhomologous IgA myelomas of both IgA1 and IgA2 subclasses inhibited the IgA-binding to monocytes, whereas aggregated normal serum IgG, IgM paraproteins, and an IgG myeloma did not. IgA binding was relatively insensitive to changes in temperature or cation concentration. IgA-binding monocytes were found in IgA-deficient patients at the same frequency as in normal individuals. The results indicate that monocytes constitutively express class-specific binding sites for both IgA1 and IgA2 molecules.

Immunofluorescence analysis of IgA binding by human mononuclear cells in blood and lymphoid tissue

The nature of IgA-binding cells and their tissue distribution was examined by an indirect immunofluorescence assay with the use of IgA1 and IgA2 paraproteins and fluorochrome- or biotin-labeled F(ab')2 fragments of idiotype-specific antibodies. The frequency of IgA-binding mononuclear cells was approximately 13% in blood and spleen samples but less than 1% in tonsil samples. IgA binding could be visualized by flow immunocytometry on monocyte/macrophages, but not on T and B cells. IgA polymers were bound better than IgA dimers and monomers. Nonhomologous IgA myelomas of both IgA1 and IgA2 subclasses inhibited the IgA-binding to monocytes, whereas aggregated normal serum IgG, IgM paraproteins, and an IgG myeloma did not. IgA binding was relatively insensitive to changes in temperature or cation concentration. IgA-binding monocytes were found in IgA-deficient patients at the same frequency as in normal individuals. The results indicate that monocytes constitutively express class-specific binding sites for both IgA1 and IgA2 molecules.

Serum IgA preferentially binds to cationic polypeptides in IgA nephropathy

The observation of negatively charged IgA in the mesangium of patients with primary IgA nephropathy (IgA-GN) prompted us to study the charge of serum IgA in IgA-GN, Henoch Schönlein purpura (HSP), alcoholic liver cirrhosis (ALC), membranous nephropathy (MGN) and systemic lupus erythematosus (SLE). Since no abnormal distribution of IgA isoelectric points was detected by isoelectric focusing studies, we developed a sensitive charge-dependent assay using plates coated with either cationized BSA (cBSA) or poly-L-lysine. In 15 IgA-GN sera, the amount of IgA reacting specifically with cBSA (cBSA-IgA) was almost linearly correlated with the poly-L-lysine-binding IgA (r = 0.97, P = 0.0006), suggesting that both assays detect charge-dependent interactions and thus probably measure anionic IgA. Significantly high serum levels of cBSA-IgA were observed in 56% of IgA-GN patients and in 40% of ALC patients. In contrast, normal serum levels of cBSA-IgA were detected in HSP, MGN and SLE. Both, the mono- or polymeric IgA bound to cBSA in a patient's serum studied. Contrasting with the presence of anionic IgA, no increase of cBSA-IgG was observed in IgA-GN. IgA rheumatoid factor (IgA-RF) assay showed high levels in IgA-GN (39%) and in ALC (25%). IgA-RF levels did not correlate with the amount of cBSA-IgA. When 18 patients with IgA-GN were tested after kidney transplantation, increased levels of cBSA-IgA and/or IgA-RF were found to be associated with the recurrence of mesangial IgA deposits in the graft. This suggests that both negatively charged IgA and IgA-RF may play a role in the recurrence of mesangial IgA deposits.

Glomerular and serum immunoglobulin G subclasses in membranous nephropathy and anti-glomerular basement membrane nephritis

The distribution of human IgG subclasses among the glomerular deposits of 53 patients with glomerulonephritis was examined by immunofluorescence (IF) with subclass-specific monoclonal antibodies (Mab). A subclass restriction was observed in idiopathic membranous nephropathy (MN) with glomerular deposits predominantly containing IgG4 (81% of the studied biopsies) and IgG1 (75%). In de novo MN, occurring after transplantation, the restriction was markedly different, with a predominance of IgG1 (100%) and IgG2 (69%). In anti-glomerular basement membrane (a-GBM) nephritis the restriction was considerable with deposits containing almost exclusively IgG1 (91%) and IgG4 (73%). The same restriction was observed for circulating anti-GBM antibodies detected by indirect IF assay. By contrast IgG1, IgG2, and IgG3 deposits were identified in lupus proliferative glomerulonephritis. Serum IgG subclass levels were measured in 29 patients with idiopathic MN and a-GBM nephritis by an indirect competitive immunoenzymatic assay using Mab. Mean percentage of IgG2 serum level was significantly lower in patients. In spite of high variations from patient to patient, a serum IgG subclass imbalance was clearly present in 10 cases with low IgG2 and high IgG1 and IgG3 levels. The imbalance in these patients was not due to urinary loss since it was observed with a similar frequency in hypo- and normoimmunoglobulinemic patients. In 5 out of these 10 patients IgG2 levels were very low, analogous to those observed in selective IgG2 deficiency. Whether the important subclass restriction of glomerular IgG (in which patterns differed according to the type of glomerulonephritis) and the serum subclass imbalances were due to a clonally restricted antibody response to a particular antigen or to a host immune response defect, or both, remains to be elucidated.

Altered cell-surface protein(s), crossreactive with DNA, on spleen cells of autoimmune lupic mice

A murine monoclonal anti-DNA antibody, PME77, with specificity for double-stranded DNA, has previously been shown to react with a protein(s) present at the surface of such cells involved in lupus pathogenesis as human glomeruli, T and B lymphocytes, erythrocytes, and platelets. Mild elastase treatment of lymphoid cells from non-autoimmune (CBA/ca or BALB/c) mice releases a series of crossreactive polypeptides (34, 33, 17, 16, and 14 kDa) recognized by PME77. These polypeptides are not formed after treatment of the same cells with papain or trypsin. When lymphoid cells from autoimmune [MRL-lpr/lpr or (NZB X NZW)F1 B/W] mice are treated with elastase, trypsin, or papain, PME77 detects, in all supernatants, a single polypeptide of about 55 kDa. Antibodies present in the sera of autoimmune MRL-lpr/lpr and B/W mice and IgG eluted from kidneys of MRL-lpr/lpr mice react with the same polypeptides. Neither sera nor eluted IgG of normal BALB/c mice react with these polypeptides. These results suggest that an altered cell-surface protein(s), which we call LAMP [for lupus-associated membrane protein(s)], may be involved in lupus pathogenesis.

Induction of Fc receptors for IgA on murine T cell hybridoma by human monoclonal IgA and by high molecular weight IgA in IgA nephropathy

A reproducible immunocyto-adherence assay has been developed to study the modulation of Fc receptors for IgA (Fc alpha R), using a murine T cell hybridoma (T2D4), which expresses Fc receptors for all known isotypes of secreted immunoglobulins. By using sheep red blood cells coated with the hapten 2-4-6 trinitrophenyl (TNP), as indicator cells, and a murine monoclonal IgA (MOPC 315) antibody with anti-TNP activity, we were able to study the Fc alpha R on T2D4 cells. We found that: (a) murine Fc alpha R can bind human monoclonal IgA, and this binding is isotype specific since it was inhibited by human monoclonal IgA but not by human monoclonal IgG or IgM; (b) the expression of murine Fc alpha R is unducible by human monoclonal IgA, and this effect is isotype specific since it is not observed with human monoclonal IgM or IgG (c) sera from patients with IgA nephropathy can also induce Fc alpha R expression; by contrast, no induction was observed with normal human sera, (d) in one serum from an IgA-nephropathy patient, the inducer factor was characterized by affinity chromatography on anti-IgA-Sepharose and by gel filtration: high molecular weight IgA, probably IgA aggregates or immune complexes were recognized to be responsible for the induction of murine Fc alpha R expression.

Charge and size of mesangial IgA in IgA nephropathy

To characterize the physicochemical properties of the mesangial IgA in primary IgA nephropathy, acid-eluates from percutaneous renal biopsies of 20 patients were examined. The acid-eluates were obtained from 1287 +/- 498 glomerular sections. The IgA content (mean 15 +/- 10 ng) represented 0.4% of the total eluted proteins. To analyze the molecular weight and the charge of eluted IgA, 11 eluates were subjected to high pressure liquid chromatography (at pH 6.8 and/or pH 3.5) and five eluates to isoelectric focusing on agarose. IgA was detected in the fractions by an IgA-RIA. Comparison of the elution profiles at different pH showed a statistically significant decrease of the excluded IgA peak (greater than or equal to 1,000,000 daltons), and a significant increase of polymeric IgA peaks (1,000,000-320,000 and 320,000 daltons) in acidic chromatography, as compared to non-dissociating conditions. Under acidic conditions, polymeric IgA represent 64% of total eluted IgA. Secretory component binding to polymeric IgA was demonstrated in four out of eight eluates tested. The isoelectric point (pI) of eluted IgA ranged from 4.5 to 5.6, contrasting with the broader and more neutral pI of normal serum IgA (4.5 to 6.8). This study shows that the multimeric nature of IgA, the formation of IgA complexes, and the anionic charge of IgA are likely to be involved in the mesangial IgA deposition in idiopathic IgA nephropathy.