Subpopulations of human peripheral granulocyes and monocytes express receptors for IgA

Nonclassical Monocytes in Health and Disease

Monocytes are innate blood cells that maintain vascular homeostasis and are early responders to pathogens in acute infections. There are three well-characterized classes of monocytes: classical (CD14+CD16−in humans and Ly6Chiin mice), intermediate (CD14+CD16+in humans and Ly6C+Treml4+in mice), and nonclassical (CD14−CD16+in humans and Ly6Cloin mice). Classical monocytes are critical for the initial inflammatory response. Classical monocytes can differentiate into macrophages in tissue and can contribute to chronic disease. Nonclassical monocytes have been widely viewed as anti-inflammatory, as they maintain vascular homeostasis. They are a first line of defense in recognition and clearance of pathogens. However, their roles in chronic disease are less clear. They have been shown to be protective as well as positively associated with disease burden. This review focuses on the state of the monocyte biology field and the functions of monocytes, particularly nonclassical monocytes, in health and disease.

Linear IgA bullous dermatosis

Aim: to present a clinical case of linear IgA bullous dermatosis.Materials and methods. A 44 years old patient complaining of skin rashes on the trunk and extremities, accompanied by severe itching was examined. We carried out a morphological investigation of biopsy samples derived from the lesion and apparently unaffected skin areas using the method of indirect immunofluorescence.Results. The patient having rashes in the form of multiple vesicles and small bubbles with a tight cover, which had been grouped into figures resembling pearl necklaces, demonstrated the presence of focal subepidermal cracks (subepidermal bubble in one location), as well as a linear deposition of IgA along the epidermal basement membrane. According to the clinical picture and following the histological and immunofluorescent investigation of skin biopsies, the patient was diagnosed with linear IgA bullous dermatosis. Lesion regression was achieved as a result of systemic therapy with prednisolone at a dose of 50 mg per day.Conclusion. The diagnosis of linear IgA bullous dermatosis should be made on the basis of skin biopsy investigation by the method of indirect immunofluorescence. Systemic glucocorticosteroids are seen as an effective approach to the treatment of such patients.

The Fc-alpha receptor is a new target antigen for immunotherapy of myeloid leukemia

Antibody-based immunotherapy of leukemia requires the targeting of specific antigens on the surface of blasts. The Fc gamma receptor (CD64) has been investigated in detail, and CD64-targeting immunotherapy has shown promising efficacy in the targeted ablation of acute myeloid leukemia (AML), acute myelomonocytic leukemia (AMML) and chronic myeloid leukemia cells (CML). Here we investigate for the first time the potential of FcαRI (CD89) as a new target antigen expressed by different myeloid leukemic cell populations. For specific targeting and killing, we generated a recombinant fusion protein comprising an anti-human CD89 single-chain Fragment variable and the well-characterized truncated version of the potent Pseudomonas aeruginosa exotoxin A (ETA'). Our novel therapeutic approach achieved in vitro EC50 values in range 0.2-3 nM depending on the applied stimuli, that is, interferon gamma or tumor necrosis factor alpha. We also observed a dose-dependent apoptosis-mediated cytotoxicity, which resulted in the elimination of up to 90% of the target cells within 72 hr. These findings were also confirmed ex vivo using leukemic primary cells from peripheral blood samples of three previously untreated patients. We conclude that CD89-specific targeting of leukemia cell lines can be achieved in vitro and that the efficient elimination of leukemic primary cells supports the potential of CD89-ETA' as a potent, novel immunotherapeutic agent.

DNA microarray analysis of transcriptional responses of rats housed on solid and grid cage flooring

We performed DNA microarray analysis on the white blood cells (WBCs) of rats housed on solid and grid cage flooring. The expression levels of 50 genes were found to increase more than 2-fold in the WBCs on grid cage flooring, including many genes encoding proteins involved in inflammatory or immune responses. It is therefore suggested that the health and welfare of laboratory rats is likely to be improved by housing rats on solid floors.

Functional expression of IgA receptor FcalphaRI on human platelets

FcalphaRI (CD89) is a human IgA FcR expressed on cells of myeloid lineage such as neutrophils, monocytes, tissue macrophages, eosinophils, and subpopulations of dendritic cells. FcalphaRI mediates cell activation through Src family kinases and downstream tyrosine-based phosphorylation pathways. However, the role of IgA and the expression and role of its cognate receptor FcalphaRI (CD89) in platelet activation are undefined. In the current study, we demonstrate that human platelets express FcalphaRI mRNAs and proteins. Furthermore, we show that the platelet FcalphaRI is associated with the FcR gamma-chain, and cross-linking of FcalphaRI leads to Syk phosphorylation. Clustering of FcalphaRI induces pre-mRNA splicing and protein production of tissue factor and IL-1beta, suggesting novel roles for human platelet FcalphaRI and serum IgA in thrombosis and inflammation.

Fc receptor genes and the systemic lupus erythematosus diathesis

Fc receptors represent a distinct group of hematopoeitic cell surface glycoproteins that have a characterized role in affecting the efficiency of the mononuclear phagocyte system to clear IgG immune complexes. Functional genetic variations in this family of receptors have been identified as heritable susceptibility factors for SLE and lupus nephritis across diverse populations. In this review, we describe the roles of the classical Fc receptors for IgG (Fc gamma) and non-classical Fc-like receptors (FCR1-FCRL6L), Fc receptors for IgE (Fc epsilon RI) and IgA and IgM (Fc alpha/mu R) in SLE diathesis. The combined effects of these genes on SLE pathogenesis, either via linkage disequilibrium or epistasis with additional genetic or environmental factors, provide a challenge for future investigations. The pursuit of a polygenic SLE-profile that includes longitudinal evaluations of SLE and markers involved in the protean clinical manifestations associated with SLE will facilitate our understanding of the cascade of inflammatory events associated with the diathesis.

FcalphaRI (CD89) alleles determine the proinflammatory potential of serum IgA

The human IgA FcR (FcalphaRI; CD89) mediates a variety of immune system functions including degranulation, endocytosis, phagocytosis, cytokine synthesis, and cytokine release. We have identified a common, nonsynonymous, single nucleotide polymorphism (SNP) in the coding region of CD89 (844A-->G) (rs16986050), which changes codon 248 from AGC (Ser(248)) to GGC (Gly(248)) in the cytoplasmic domain of the receptor. The two different alleles demonstrate significantly different FcalphaRI-mediated intracellular calcium mobilization and degranulation in rat basophilic leukemia cells and cytokine production (IL-6 and TNF-alpha) in murine macrophage P388D1 cells. In the absence of FcR gamma-chain association in P388D1 cells, the Ser(248)-FcalphaRI allele does not mediate cytokine production, but the Gly(248)-FcalphaRI allele retains the capacity to mediate a robust production of proinflammatory cytokine. This allele-dependent difference is also seen with FcalphaRI-mediated IL-6 cytokine release by human neutrophils ex vivo. These findings and the enrichment of the proinflammatory Gly(248)-FcalphaRI allele in systemic lupus erythematosus populations in two ethnic groups compared with their respective non-systemic lupus erythematosus controls suggest that FcalphaRI (CD89) alpha-chain alleles may affect receptor-mediated signaling and play an important role in the modulation of immune responses in inflammatory diseases.

IgA Fc receptors

The IgA receptor family comprises a number of surface receptors including the polymeric Ig receptor involved in epithelial transport of IgA/IgM, the myeloid specific IgA Fc receptor (FcalphaRI or CD89), the Fcalpha/muR, and at least two alternative IgA receptors. These are the asialoglycoprotein receptor and the transferrin receptor, which have been implicated in IgA catabolism, and tissue IgA deposition. In this review we focus on the biology of FcalphaRI (CD89). FcalphaRI is expressed on neutrophils, eosinophils, monocytes/macrophages, dendritic cells, and Kupffer cells. This receptor represents a heterogeneously glycosylated transmembrane protein that binds both IgA subclasses with low affinity. A single gene encoding FcalphaRI has been isolated, which is located within the leukocyte receptor cluster on chromosome 19. The FcalphaRI alpha chain lacks canonical signal transduction domains but can associate with the FcR gamma-chain that bears an activation motif (ITAM) in the cytoplasmic domain, allowing activatory functions. FcalphaRI expressed alone mediates endocytosis and recyling of IgA. No FcalphaRI homologue has been defined in the mouse, and progress in defining the in vivo role of FcalphaRI has been made using human FcalphaRI transgenic (Tg) mice. FcalphaRI-Tg mice demonstrated FcalphaRI expression on Kupffer cells and so defined a key role for the receptor in mucosal defense. The receptor functions as a second line of antibacterial defense involving serum IgA rather than secretory IgA. Studies in FcalphaRI-Tg mice, furthermore, defined an essential role for soluble FcalphaRI in the development of IgA nephropathy by formation of circulating IgA-FcalphaRI complexes. Finally, recent work points out a role for human IgA in treatment of infectious and neoplastic diseases.

Characteristics of polymeric lambda-IgA binding to leukocytes in IgA nephropathy

IgA nephropathy (IgAN) is characterized by predominant mesangial polymeric IgA1 (pIgA1) deposits, with increased plasma IgA1 levels. Plasma IgA levels are determined by the rate of IgA production, uptake by leukocytes, and removal by hepatocytes. Fc(alpha) receptor 1 (Fc(alpha)R1) is a candidate molecule for the regulation of IgA levels, but reports of its expression in leukocytes in IgAN are conflicting. Increased binding of endogenous IgA to circulating granulocytes and monocytes in IgAN was demonstrated in this study. Fc(alpha)R1 expression on leukocytes was increased, independently of plasma IgA levels. Fc(alpha)R1 was not saturated in leukocytes, because of internalization of IgA after uptake. Further binding of exogenous IgA isolated from individual subjects was observed with leukocytes from the same subjects. Compared with cells from control subjects, granulocytes but not monocytes from patients with IgAN exhibited a greater binding capacity for exogenous IgA, predominantly pIgA. To circumvent the possibility that endogenous IgA might alter Fc(alpha)R1 expression, granulocytes or monocytes derived from the HL-60 or U937 cell lines were used to explore the nature of IgA binding. A higher affinity for pIgA was demonstrated. Inhibition studies using unlabeled IgA, other serum proteins, or a specific Fc(alpha)R1-blocking antibody suggested binding mechanisms other than Fc(alpha)R1 for pIgA uptake by leukocytes. This study also suggested the migration and/or sequestration of "activated" leukocytes with predominant lambda-IgA in the mononuclear phagocytic system or inflammatory tissues, after the initial binding of lambda-pIgA. These immunologic abnormalities might contribute to the glomerulointerstitial injury in IgAN, in the presence of leukocytic infiltration.

Lung mucosal immunity: immunoglobulin-A revisited

Mucosal defence mechanisms are critical in preventing colonization of the respiratory tract by pathogens and penetration of antigens through the epithelial barrier. Recent research has now illustrated the active contribution of the respiratory epithelium to the exclusion of microbes and particles, but also to the control of the inflammatory and immune responses in the airways and in the alveoli. Epithelial cells also mediate the active transport of polymeric immunoglobulin-A from the lamina propria to the airway lumen through the polymeric immunoglobulin receptor. The role of IgA in the defence of mucosal surfaces has now expanded from a limited role of scavenger of exogenous material to a broader protective function with potential applications in immunotherapy. In addition, the recent identification of receptors for IgA on the surface of blood leukocytes and alveolar macrophages provides an additional mechanism of interaction between the cellular and humoral immune systems at the level of the respiratory tract.

IgA immunodeficiency leads to inadequate Th cell priming and increased susceptibility to influenza virus infection

IgA is considered to be the principal Ab involved in defense against pathogens in the mucosal compartment. Using mice with a targeted disruption in IgA gene expression (IgA(-/-) mice), we have examined the precise role of IgA in protective anti-influenza responses after intranasal vaccination. IgA(-/-) mice immunized intranasally with soluble hemagglutinin (hemagglutinin subtype 1) and neuraminidase (neuraminidase subtype 1) vaccine in the absence of adjuvant were found to be more susceptible to influenza virus infection than IgA(+/+) mice (13 vs 75% survival after virus challenge). Inclusion of IL-12 during immunization restored the protective efficacy of the vaccine to that seen in IgA(+/+) animals. IgA(-/-) mice had no detectable IgA expression, but displayed enhanced serum and pulmonary IgM and IgG Ab levels after IL-12 treatment. Assessment of T cell function revealed markedly depressed splenic lymphoproliferative responses to PHA in IgA(-/-) animals compared with IgA(+/+) mice. Furthermore, IgA(-/-) animals displayed impaired T cell priming to the H1N1 subunit vaccine, with concomitant reduction in recall memory responses due to a defect in APC function. Collectively, these results provide evidence that a major role of IgA is to facilitate presentation of Ag to mucosal T cells. IL-12 treatment can overcome IgA deficiency by providing adequate T cell priming during vaccination.

Functional analysis of IgA antibodies specific for a conserved epitope within the M protein of group A streptococci from Australian Aboriginal endemic communities

The mucosa is one of the initial sites of group A streptococcal (GAS) infection and salivary IgA (sIgA) is thought to be critical to immunity. However, the target epitopes of sIgA and the function of sIgA in GAS immunity, in particular the role of accessory cells and complement, is largely unknown. We studied the aquisition and the function of sIgA specific for a conserved region epitope, p145 (sequence: LRRDLDASREAKKQVEKALE) of the M protein. Peptide 145-specific sIgA is highly prevalent within an Aboriginal population living in an area endemic for GAS and acquisition of p145-specific sIgA increases with age, consistent with a role for such antibodies in immunity to GAS. Human sIgA and IgG specific for p145 were affinity purified and shown to opsonize M5 GAS in vitro. Opsonization could be specifically inhibited by the addition of free p145 to the antibodies during assay. Opsonization of GAS was totally dependent on the presence of both complement and polymorphonuclear leukocytes, and, moreover, affinity-purified p145-specific sIgA was shown to fix complement in the presence of M5 GAS. These data show that mucosal IgA to this conserved region peptide within the M protein has an important role in human immunity against GAS and may be useful in a broad-based cross-protective anti-streptococcal vaccine.

Size-dependent effect of IgA on the IgA Fc receptor (CD89)

The IgA Fc receptor (FcR; CD89) is expressed on several types of cells of the myeloid cell lineage. We investigated whether different sizes of heat-aggregated IgA (aIgA) bind to CD89 and subsequently induce cellular activation. As a model we used the murine B cell line IIA1.6 transfected with CD89 or IIA1.6 cells transfected with CD89 as well as with the FcR gamma chain to study the binding of IgA to CD89. When these cells expressing CD89 were incubated with monomeric IgA, no significant binding of IgA to the cells was detectable by fluorescence-activated cell sorter analysis; however, incubation of the cells with aggregated IgA resulted in 93 +/- 2% positive cells. Incubation of the cells with different sizes of IgA-containing aggregates revealed optimal binding with aggregates containing five to six molecules of IgA per aggregate. No difference was observed between the binding to CD89 of both IgA1- or IgA2-containing aggregates. Furthermore, the binding of aIgA was found to be CD89-specific, since the binding of IgA was completely inhibited by the CD89-specific monoclonal antibody My43 and no detectable binding occurred to the IIA1.6 parent cell line. Activation studies using interleukin-2 (IL-2) production as a marker, showed that the FcR gamma chain is necessary to induce cellular activation. Only cells transfected with both CD89 and the FcR gamma chain (CD89+/gamma +) enhance the IL-2 production 10-12-fold upon stimulation with aggregates of IgA. Furthermore, triggering of CD89 only results in increase of intracellular calcium concentration ([Ca2+]i) in cells co-expressing FcR gamma chain. Mutation of the tyrosine residues in the FcR gamma chain immunoreceptor tyrosine-based activation motif of the FcR gamma chain abolishes this increase in [Ca2+]i, indicating association and involvement of the FcR gamma chain in CD89-mediated signaling.

Immunoglobulins and their receptors on epidermal Langerhans cells in atopic dermatitis

To elucidate the etiological role of immunoglobulin molecules on Langerhans cells (LCs) in atopic dermatitis, we conducted immuno-histochemical studies on the localization of immunoglobulin G1 (IgG1), IgG2, IgG3, IgG4, IgA and IgM on epidermal LCs from 30 patients with atopic dermatitis (AD) and five non-atopic healthy volunteers. We also investigated the types of receptors for the immunoglobulins (Fc epsilon RI, Fc epsilon RII, Fc gamma RI, Fc gamma RII, and Fc gamma RIII) on epidermal LCs in the patients. IgE positive epidermal LCs were observed in 28 of 30 AD patients, and 46.7% of the epidermal LCs were positive for IgE. Both IgG1- and IgG2-positive epidermal LCs were observed in 70% of AD patients, and 21.8% and 28.7% of the total epidermal LCs were positive for IgG1 and IgG2, respectively. IgG3- or IgG4-positive LCs were present in only small proportions of AD patients. IgA-positive LCs were observed in 8 AD patients; our study suggested that the IgA bound on LCs was secretory IgA (S-IgA). These surface immunoglobulins were observed significantly more frequently on epidermal LCs in the involved skin of AD than in clinically uninvolved skin. No IgM-positive epidermal LCs were observed in the AD patients or healthy volunteers. In non-atopic healthy controls, no immunoglobulin-binding LCs were observed. In receptors for immunoglobulins, Fc epsilon RI and Fc gamma RII were exclusively expressed on nearly all epidermal LCs from all AD patients and all non-atopic controls. These results suggested that not only IgE but also IgG and IgA may play some etiological role in the pathogenesis of AD.

IgA autoantibodies against human eye muscle antigen detected by western blotting and immunohistochemical methods in Graves' disease

The presence of IgA autoantibodies against human eye muscle was investigated in 40 patients with Graves' disease (33 had ophthalmopathy). IgA anti-eye muscle antibodies could be demonstrated in sera of patients using western blotting and immunohistochemical methods. For the detection of sera possessing autoantibodies against eye muscle antigen the indirect immunosorbent assay had been used. IgA anti-eye muscle antibodies could be demonstrated in 25 cases and IgG types in 16 cases out of 40 patients. These anti-muscle autoantibodies were associated with eye muscle rather than skeletal muscle, the number of positive cases with the latter being 5/40 for IgG and 2/40 for IgA. Immunoreactive bands of IgA autoantibodies against eye cytosol were found at 84, 64, 45, 40 and 25-23 kDa in 22, 2, 16, 2 and 18 cases, respectively. A difference was observed in the staining of IgG and IgA types of autoantibodies by immunohistochemical analysis of eye muscle tissue. The IgA anti-eye muscle antibodies reacted with muscle fibers and the IgG types showed staining on endomysium. No sera of Graves' disease patients gave staining on skeletal muscle tissue. The results supported the presence of IgA anti-human eye muscle antibodies in patients with Graves' ophthalmopathy, which might play a relevant role in the development of eye disease.

Human eosinophils express a receptor for secretory component. Role in secretory IgA-dependent activation

The existence of a functional receptor for secretory component (SC) on the eosinophil membrane might explain the preferential degranulation induced by secretory IgA (sIgA) when compared to serum IgA. Indeed, flow cytometry analysis revealed that purified human SC could bind to a subpopulation (4-59%) of blood eosinophils purified from 19 patients with eosinophilia. Binding of radiolabeled human SC could be competitively inhibited using unlabeled SC or secretory IgA but not with serum IgA or IgG. Immunoprecipitation and immunosorbent chromatography using human SC revealed the presence of a major component at 15 kDa in eosinophil extracts as well as in culture supernatants but not in neutrophils. The 15-kDa protein eluted from the human SC immunosorbent was able to bind to SC or to sIgA but not to serum IgA. Eosinophils preincubated with human SC or sIgA released eosinophil cationic protein (ECP) and eosinophil peroxidase (EPO) after addition of anti-SC or anti-IgA monoclonal antibody as respective cross-linking reagents. These results indicated that binding of free or complexed SC to human eosinophils could induce eosinophil degranulation. Furthermore, the dose-dependent inhibition by SC of mediator release induced by sIgA but not by serum IgA, suggested that the receptor for SC could be involved in the preferential degranulation mediated by sIgA. These results indicate a novel pathway of eosinophil activation and its potential involvement in mucosal immunity, particularly in inflammatory diseases associated with infiltration of eosinophils and the enhanced production of sIgA.

Influence of tumour necrosis factor-alpha on the expression of Fc IgG and IgA receptors, and other markers by cultured human blood monocytes and U937 cells

The expression of Fc receptors for IgG (Fc gamma R) and IgA (Fc alpha R) and of various other antigens on the human monocytic cell line U937 and peripheral blood monocytes, under stimulation with human recombinant tumour necrosis factor-alpha (TNF-alpha) and other cytokines, was investigated by flow cytometry. TNF-alpha, as well as interferon-gamma (IFN-gamma) or interleukin-6 (IL-6) had a significant up-regulating effect on U937 expression of Fc gamma RI/CD64. Furthermore, the action of TNF-alpha was augmented by IL-6, and more evidently by IFN-gamma. IFN-alpha alone had only a marginal effect, but was able to increase the TNF-alpha-driven Fc gamma RI expression. In contrast to U937 cells, TNF-alpha did not enhance significantly Fc gamma RI expression on human monocytes. Interestingly, on both U937 cells and monocytes, Fc alpha R was augmented markedly by TNF-alpha. Furthermore, TNF-alpha induced the expression of HLA-DR and HLA-DP antigens on monocytes and U937 cells. The expression of Fc gamma RII/CD32, FC gamma RIII/CD16, CD14, complement receptor type 1 (CR1/CD35), CR4 (CD11c/CD18), and MHC class-I antigens, was not influenced significantly by TNF-alpha. The results of this study show that TNF-alpha may act on human mononuclear phagocytes, alone or in combination with other cytokines, by modulating the expression of various cell-surface antigens.

Cross-linking of monocyte plasma membrane Fc alpha, Fc gamma or mannose receptors induces TNF production

We have studied and compared the effects of IgA and IgG immune complexes and concanavalin A (Con A) on human monocyte tumour necrosis factor (TNF) production. The presence of IgA-containing immune complexes in monocyte monolayers resulted in a dose-dependent increase of TNF production. Similar results were obtained with IgG-containing immune complexes and Con A. The presence of monomeric IgA or IgG did not increase TNF secretion. Both IgA and IgG immune complexes also increased monocyte interleukin-1 beta (IL-1 beta) production. Galactose inhibited the effect of IgA but not IgG immune complexes, while mannose inhibited the effect of Con A. Prednisolone abrogated TNF production, while indomethacin enhanced TNF production in all instances where cross-linking of plasma membrane receptors was achieved. These results indicate that activation of Fc alpha receptors (Fc alpha R), Fc gamma R or mannose receptors of the human monocyte plasma membrane by cross-linking results in increased TNF and IL-1 beta secretion. These findings may be of particular relevance in the pathogenesis of IgA immune complex-mediated disease.

Effects of recombinant GM-CSF and IgA opsonisation on neutrophil phagocytosis of latex beads coated with P6 outer membrane protein from Haemophilus influenzae

BACKGROUND

IgA is the major antibody class in mucosal secretions, yet its biological functions remain poorly understood and its role as an opsonin for neutrophils has been the subject of controversy. It has been reported that treatment of neutrophils with granulocyte-macrophage colony stimulating factor (GM-CSF) induces the cells to phagocytose particles opsonised with IgA. A study was performed to investigate the effects of GM-CSF and IgA opsonisation on the ability of human neutrophils to recognise and phagocytose latex beads coated with the P6 outer membrane protein of Haemophilus influenzae.

METHODS

Human neutrophils with and without preincubation with 100 pmol/l GM-CSF, were incubated with non-opsonised P6-coated latex beads or beads opsonised with IgA purified from the blood of a bronchiectatic patient with high titres of IgA anti-P6. Phagocytosis was measured by counting internalised beads during microscopic examination.

RESULTS

The phagocytosis of IgA opsonised beads by untreated neutrophils (mean (SE) 2.1 (0.43) beads/cell) was significantly greater than that of non-opsonised beads (mean (SE) 1.3 (0.30) beads/cell). Treatment of neutrophils with GM-CSF resulted in increased phagocytosis of non-opsonised beads (mean (SE) 2.1 (0.39) beads/cell) but opsonisation with IgA increased this further (mean (SE) 3.4 (0.53) beads/cell).

CONCLUSIONS

Human neutrophils recognise and phagocytose non-opsonised particles coated with bacterial antigen. Antibodies of the IgA isotype opsonise for neutrophil phagocytosis of particles coated with bacterial antigen but this behaviour is enhanced, in an additive fashion, by treatment of the cells with GM-CSF. The results suggest that IgA and GM-CSF are important cofactors for neutrophil recognition and elimination of bacterial pathogens.

Inhibition of neutrophil adherence to antibody by dapsone: a possible therapeutic mechanism of dapsone in the treatment of IgA dermatoses

Dapsone is frequently effective in cutaneous diseases characterized by antibody deposition and accumulation of neutrophils. We hypothesized that this mechanism of action of dapsone may involve the inhibition of neutrophil adherence to antibody. The neutrophil adherence assay, which measures the binding of neutrophils to basement membrane zone-bound antibody on skin sections, was used to evaluate the effect of dapsone on neutrophil adherence to immunoglobulin A and immunoglobulin G. We evaluated the effect of dapsone on adherence of normal neutrophils to immunoglobulin A and immunoglobulin G from sera of linear immunoglobulin A bullous dermatosis and bullous pemphigoid patients, respectively. Linear immunoglobulin A bullous dermatosis or bullous pemphigoid antibody were bound to the basement membrane zone of normal skin sections as a substrate for the neutrophil adherence assay. Dapsone was added directly to the neutrophils or to the antibody source in concentrations of 0-50 micrograms/ml (pharmacologic range). Addition of dapsone to neutrophils produced an incremental inhibition of neutrophil adherence up to 75% at 50 micrograms/ml. Dapsone produced similar inhibition when added directly to the antibody itself, despite washing prior to usage in the neutrophil-adherence assay. Control specimens including irrelevant fractions of patient sera failed to demonstrate binding. Serum from a patient on dapsone therapy also showed inhibition of neutrophil adherence compared to the same patient on no therapy. We conclude that dapsone inhibits the adherence of neutrophils to basement membrane zone antibody in a dose-dependent manner. This may be related to an effect directly on antibody. This inhibition may contribute to the clinical efficacy of dapsone in antibody-mediated diseases.

Receptors for IgA on phagocytic cells

IgA receptors have been detected on monocytes, polymorphonuclear neutrophils (PMNs) and eosinophils, and on phagocytic cells at mucosal sites. These receptors bind both secretory and serum forms of immunoglobulin A (IgA) and require the Ca2 region of the IgA molecule for ligand recognition. Monocytes and PMNs modulate their expression of the IgA receptor upon treatment with cytokines, such as granulocyto-macrophage colony-stimulating factor, and lipopolysaccharide. Purified IgA receptors appear as heavily glycosylated molecules with an average molecular weight of 60 kD, dropping to 32 and 36 kD upon treatment with N-glycanase. The cDNA sequence encoding the IgA receptor has been determined by expression cloning, and predicts that the receptor consists of two Ig-like extracellular domaines, a transmembrane region and a cytoplasmic tail of 41 residues. Ligation of IgA receptors on phagocytic cells by multivalent IgA complexes induces a variety of responses, including superoxide generation, release of inflammatory mediators, phagocytosis, and killing of various pathogenic microorganisms. Thus the apparent role of these receptors is to amplify the protective effects of the IgA antibody, a function of potential importance to mucosal defense.

Antibacterial properties of breast milk: requirements for surface phagocytosis and chemiluminescence

The opsonic components of breast milk responsible for phagocytosis of surface-adherent Staphylococcus aureus by human polymorphonuclear leukocytes were investigated. There was significantly greater phagocytosis of bacteria pre-opsonized with 100% breast milk than of unopsonized bacteria (p less than 0.001). Heat inactivation of breast milk had no effect on surface phagocytosis, indicating that phagocytosis is independent of complement. The predominant immunoglobulin in breast milk, secretory immunoglobulin A (IgA), did not promote phagocytosis. In contrast, IgG, which is present in very low amounts in breast milk (0.05 mg/ml), was as opsonic as 100% breast milk, suggesting that this is the major opsonin. An oxidative burst as measured by chemiluminescence was observed during phagocytosis of bacteria pre-opsonized with 100% breast milk. Heat inactivation of breast milk reduced the chemiluminescence response to the level of control. Neither secretory IgA nor IgG stimulated a polymorphonuclear leukocyte chemiluminescence response to surface-adherent bacteria. These experiments indicate that IgG is the principal component of breast milk responsible for surface phagocytosis but that complement is required for the generation of chemiluminescence and thus may be essential for intracellular killing of bacteria. Secretory IgA, despite its abundance in breast milk, has no effect on surface phagocytosis or neutrophil chemiluminescence.

IgA-mediated inhibition of human leucocyte function by interference with Fc gamma and C3b receptors

The inhibitory effects of IgA from human colostrum, and IgA1 and IgA2 from human serum on the chemiluminescence (CL) response and phagocytosis of polymorphonuclear leucocytes (PML) to Staphylococcus epidermidis and the CL response to formylmethionyl-leucyl-phenylalanine (FMLP) were studied. The dose-dependent inhibition of the luminol-mediated CL response of human PML to the bacteria was observed in the presence of more than 0.1 mg/ml IgA from both colostrum and serum. The preincubation of PML with a solution of IgA enhanced the suppressive effect of IgA on the cells. Removal of IgA from the reaction mixture after preincubation resulted in recovery, with time, of the response of PML to the bacteria. The bacteria treated with IgA did not give rise to any inhibition of the response. The CL response of PML to FMLP was not affected by the presence of IgA in the reaction mixture. The decrease of phagocytic activity of PML in the presence of IgA resulted in a decrease of NADPH oxidase activity of PML after stimulation with the bacteria as compared with the absence of IgA. The effect of IgA on the receptors of Fc and C3b (CR1) on the surface of PML was measured by monitoring erythrocyte-antibody (EA) or erythrocyte-antibody-complement (EAC) rosette formation and by direct and indirect immunofluorescence techniques using anti-CR1 antibody and Fc-specific antibodies. The presence of IgA in the reaction mixture led to a quantitative decrease in CR1 and the ability to bind IgG to the surface of PML.

Activation of human monocytes via their sIgA receptors

We have studied the interaction of secretory immunoglobulin A (sIgA) derived from human breast milk with human monocytes. The presence of specific sIgA receptors on the monocyte membrane was confirmed by dose-dependent inhibition of E-sIgA rosette formation and by the binding of iodinated sIgA to monocyte monolayers. Binding was dependent on both the number of monocytes, as well as the amount of [125I]sIgA, and could be inhibited by unlabelled sIgA. Incubation of monocyte monolayers in the presence of increasing concentrations of secretory IgA and F(ab')2 anti-IgA resulted in a dose-dependent increase of the oxidative burst, as measured by H2O2 production. Neither sIgA or anti-IgA alone, nor incubation of IgG with anti-IgA, had any effect on the oxidative burst. These studies indicate that human monocytes have a receptor for sIgA and that specific activation of the monocytes occurs via these receptors.

Expression cloning of a human Fc receptor for IgA

IgA, the predominant isotype in secretions, mediates the neutralization and removal of environmental antigens from mucosal sites. Although cell surface receptors for the Fc region of IgA (Fc alpha R) have been implicated in a variety of immune effector mechanisms, the molecular features of Fc alpha R remain only marginally characterized. In this report, we describe the isolation of a clone from a myeloid cell line cDNA library that directs the expression of a cell surface molecule with IgA binding specificity. The cDNA encodes a peptide of Mr 30,000 including a putative transmembrane region with features atypical of conventional membrane-anchored proteins. Databank searches indicate that the human myeloid cell Fc alpha R sequence is unique, is a member of the immunoglobulin gene superfamily, and is related to Fc receptors for IgG (Fc gamma RI, II, and III) and IgE (Fc epsilon RI).

The specificity of the IgA receptor purified from human neutrophils

A receptor for IgA was purified from human polymorphonuclear neutrophils (PMN) by affinity chromatography on human serum IgA-Sepharose. The receptor appeared on SDS/polyacrylamide gels as a diffuse band with an apparent molecular mass of 50-70 kDa, whether reduced or non-reduced. During purification, the protein showed remarkable stability to proteolytic digestion by endogenous PMN proteinases. Purified radioiodinated receptor re-bound to IgA-Sepharose, but not to IgG-Sepharose or BSA-Sepharose. The binding of the receptor to IgA-Sepharose was inhibited in a dose-dependent manner by human serum IgA1 or IgA2 or secretory IgA1 or IgA2, but not by IgG or IgM. Binding of receptor to IgA-Sepharose was also inhibited by the Fc fragment of IgA, but not by the Fab fragment. An IgA fragment produced by digestion with pepsin which lacks the CH3 domain also inhibited binding, but to a more limited extent than did the whole IgA molecule.

The specificity of the human neutrophil IgA receptor (Fc alpha R) determined by measurement of chemiluminescence induced by serum or secretory IgA1 or IgA2

Heat or chemically aggregated IgA or IgG stimulated degranulation of neutrophils with comparable efficiency. The same aggregates induced a neutrophil respiratory burst which could be measured by lucigenin-enhanced chemiluminescence. Serum IgA1 or IgA2 coated onto microtitre plates were both capable of inducing a respiratory burst in neutrophils, as was secretory IgA1 or secretory IgA2. All bursts were of similar size for a given concentration of IgA and were greater than the burst elicited by an equivalent concentration of IgG. For each subclass of IgA the respiratory bursts were dependent on their density on the opsonized surface. Since monomeric and dimeric forms present in secretory IgA preparations both elicit a respiratory burst in neutrophils, secretory component and J chain cannot block the receptor binding site on the Fc region. The potential of secretory IgA to act as an opsonin might have important consequences on mucosal surfaces where the availability of complement components is limited.

The clinical and histopathological spectrum of IgA-pemphigus--report of two cases

Two new cases of neutrophilic bullous disease exhibiting bound and circulating intercellular IgA in vivo in both direct and indirect immunofluorescence (IF), for which the term IgA-pemphigus was recently proposed, are presented. The first case showed a unique constellation of clinical and histopathological features not previously described for IgA-pemphigus, resembling both dermatitis herpetiformis and pemphigus, for which the designation IgA-herpetiform pemphigus seems most appropriate. The second case showed clinical and histopathological features mimicking subcorneal pustular dermatosis for which the previously used term IgA-pemphigus foliaceus seems most appropriate. The previously reported 11 cases showing similar direct IF findings, as well as our two patients, illustrate the main differences between IgA-pemphigus and classic forms of this condition: (a) different clinical manifestations with the absence of Nikolsky's sign; (b) scanty acantholysis; an abundance of neutrophils, with occasional neutrophilic spongiosis; (c) absence of C3 on direct IF; (d) the lower sensitivity of indirect IF and low levels of circulating antibodies; (e) the relatively benign course of the disease; (f) the apparent responsiveness to sulphones in many cases. It is suggested that IgA pemphigus should be considered as an entity separate from, but closely related to, classic pemphigus.

Cutaneous IgA deposits in bullous diseases function as ligands to mediate adherence of activated neutrophils

Linear IgA bullous dermatosis and dermatitis herpetiformis are inflammatory subepidermal blistering diseases characterized by IgA deposits at the cutaneous epithelial basement membrane and in dermal papillae, respectively. Inflammation in both disorders localizes to sites of IgA deposition and is characterized by a predominance of neutrophils. From these observations we postulate that IgA deposits in both diseases may contribute to the recruitment and/or localization of neutrophils. In this study we examined the ability of in vitro and in vivo bound IgA anti-basement membrane autoantibodies from patients with linear IgA bullous dermatosis and in vivo bound IgA deposits in dermal papillae from patients with dermatitis herpetiformis to mediate adherence of neutrophils stimulated by granulocyte macrophage colony-stimulating factor. The study showed that stimulated neutrophils adhered to basement membranes and dermal papillae containing IgA deposits. Adherence was IgA anti-basement membrane antibody concentration dependent and correlated with the immunofluorescence staining intensity of IgA deposits in dermal papillae. Adherence to IgA deposits but not IgG deposits could be inhibited by purified exogenous secretory IgA but not IgG and adherence to IgG deposits could be inhibited by purified exogenous IgG but not secretory IgA. These results provide direct experimental evidence that cutaneous IgA deposits in linear IgA bullous dermatosis and dermatitis herpetiformis can function as ligands for neutrophil adherence and have a role in the localization of inflammation in these disorders.

Identification of an IgA inhibitor of neutrophil chemotaxis and its membrane target for the metabolic burst

Affinity-purified IgA from the serum of an 8-year-old boy with a 5-year history of recurrent facial nodules, intermittent neutropenia and elevated immunoglobulin levels, inhibited the chemotaxis of polymorphonuclear neutrophils (PMN) from both patient and normal adults. Preincubation of normal PMN with IgA from the patient's serum (0.5 mg/ml) inhibited chemotaxis to C5a and to the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (FMLP) by 80%, while IgA or IgG from pooled human serum and IgG from the patient were without effect. Normal PMN chemotaxis was restored after IgA depletion of the patient's serum by affinity chromatography. The patient's IgA, but not IgA from pooled human serum, bound specifically to normal PMN by its antigen-binding sites and recognized a 62,000 MW membrane protein on normal neutrophils, which was distinct from the FMLP receptor, the C5a receptor, or the Fca receptor. Attachment of the patient's IgA to the 62,000 MW protein activated intracellular oxidative metabolism on a parity with phorbol myristate acetate (PMA) and resulted in a significant up-regulation of membrane receptors for FMLP. After the binding of patient (Pt) IgA, normal neutrophils were rendered significantly less responsive to subsequent stimulation with phorbol esters. These results characterize a novel mechanism of chemotactic inhibition by serum IgA and also identify a neutrophil membrane protein that is linked to intracellular oxidative metabolism.

Macrophages and polymorphonuclear neutrophils in lung defense and injury

Phagocytes, in particular macrophages and PMN, are now recognized as major components of inflammatory and immunologic reactions in the lung. Normally, macrophages represent the majority of phagocytes in the lower respiratory tract. These lung macrophages are morphologically and functionally heterogenous and include alveolar, interstitial, intravascular, and airway macrophages, each with characteristic morphologic and functional features. Through the presence of surface receptors for numerous ligands and through their large number of secretory products, lung macrophages can respond to environmental factors and account for most of the clearance of microparticles and microorganisms in the distal airways and the alveolar spaces. In addition, macrophages also play an important role in inflammatory processes through the release of oxygen radicals and proteolytic enzymes. Through the release of several cytokines, i.e., growth-promoting and inhibiting factors, lung macrophages may also influence both matrix damage and repair processes. Macrophages can also contribute to the alveolitis by recruitment of inflammatory and immune cells. This latter contribution is best demonstrated in migration movement of PMN. The normal distal airways generally contain a small number of PMN, but the pulmonary vascular bed represents a large reservoir of PMN. Some of them are in intimate contact with the endothelium, forming the so-called marginating pool of PMN. Because the capillary lumen is separated only from the alveolar space by a monolayer of endothelial and epithelial cells on each side of a thin interstitial matrix, it is likely that some inhibitory mechanism exists to prevent PMN from migrating towards the alveolar space. Such inhibitors of PMN migration are present both in serum and in the alveolar space, some being released by alveolar macrophages. However, alveolar macrophages can also secrete factors called chemotaxins that attract PMN to the airways, and this supports a central role for alveolar macrophages in the regulation of PMN traffic in the lungs. Thus, secretory products of alveolar macrophages are part of the regulatory mechanisms of PMN mobility and adherence that appears to be crucial in the initiation of some inflammatory reactions. The contribution of phagocytes to the defense against infection and tumor has been documented mostly in vitro. Thus, both oxygen radicals, in particular hydroxyl radicals and proteases such as lysozyme, are potent bactericidal agents. That phagocytes are also important defenders of the lungs in vivo is best supported by the observations in immunodeficient patients and animal models.(ABSTRACT TRUNCATED AT 400 WORDS)

Monocyte superoxide secretion triggered by human IgA

While there is much evidence for a key role of IgA in mucosal defence, its mode of action is incompletely understood. The finding of Fc receptors for IgA on various phagocytic cells has led to examination of the ability of IgA to mediate the protective functions of these cells. We studied the ability of human peripheral monocytes to secrete superoxide upon interaction with human IgA, IgG or IgM bound to a solid phase. Both secretory and serum IgA triggered the superoxide response, producing superoxide levels comparable to those induced by IgG, whereas IgM and mouse IgA were inactive. A combination of monomeric IgG and a monoclonal anti-IgG Fc receptor antibody inhibited superoxide secretion mediated through IgG but failed to block the IgA-triggered response, demonstrating that IgA was recognized through specific receptors. In addition IgA was capable of mediating phagocytosis when attached to erythrocytes.

Clearance kinetics and tissue distribution of aggregated human serum IgA in rats

In the present study the clearance kinetics and tissue distribution of human polyclonal heat-aggregated serum IgA (AIgA) of different sizes in rats was studied after intravenous administration of 125I-AIgA. The 125I-AIgA of different sizes disappeared from the circulation in a biphasic manner with an initial rapid half-life (T1/2) and a second slower T1/2. The first T1/2 was related to the size of the 125I-AIgA: high molecular weight (MW) 125I-AIgA was cleared much faster than 125I-AIgA with a low MW. Relatively more degradation products were observed in blood when high MW 125I-AIgA were injected as compared to low MW 125I-AIgA. The AIgA were mainly taken up by the liver. Eight minutes after injection of high MW 125I-AIgA, 90% of the injected dose was found in the liver, whereas less than 2% was detected in the spleen. Very little activity was detectable in other organs, such as lungs, heart and kidneys. In the present study 1-3% of the injected 125I-AIgA were found in the bile. Analysis of this material revealed that low MW 125I-AIgA were transported more efficiently to the bile than high MW 125I-AIgA. To obtain more insight into the receptors involved in the clearance of 125I-AIgA, rats were pretreated with ovalbumin or asialofetuin. The clearance of 125I-AIgA of different sizes was inhibited when rats were pretreated with asialofetuin. Pretreatment with ovalbumin had no effect on the clearance rates of 125I-AIgA. These results suggest a role for carbohydrate receptors, which recognize glycoprotein-containing galactose terminal residues on Kupffer cells, in the clearance of 125I-AIgA.

Spontaneous expression of a low affinity Fc receptor for IgA (Fc alpha R) on human B cell lines

Expression of receptors for IgA (Fc alpha Rs) was investigated on a panel of 35 human B cell lines by labelling with human secretory IgA (0.5 mg/ml) and flow cytometry analysis after staining with fluoresceinated goat anti-human secretory component and/or anti-alpha chain F(ab')2 fragments. Receptors for IgA could be demonstrated on one out of nine Burkitt's lymphoma cell lines, three out of five myeloma cell lines and five out of 21 lymphoblastoid cell lines. The percentage of Fc alpha R-positive cells within the same B cell line varied upon repeated examination. Human dimeric IgA1 lambda myeloma protein revealed the same number of IgA receptor positive cells as did secretory IgA, whereas monomeric IgA did not bind to Fc alpha R. Detection of Fc alpha R was not inhibited when the tests were carried out in the presence of human dimeric IgG, IgM, asialo-orosomucoid, and secretory component but it was abrogated by pre-treatment of the cells with trypsin. The binding characteristics of Fc alpha Rs were studied on the myeloma cell line Esteve, using 125I-labelled human dimeric IgA and secretory IgA. The binding was dose-dependent with rapid kinetics and specific inhibition by unlabelled secretory IgA. Scatchard plot analysis resulted in an equilibrium constant K ranging from 3.2 to 4.7 x 10(6) M/l. No correlation was observed between Fc alpha R expression and differentiation stage, monoclonality, polyclonality of the cell lines, or Ig class produced by the B cells.

Granulocyte isolation from whole blood of goat, sheep, cattle, horse, dog, pig, and man

A simple two step procedure for the isolation of caprine, ovine, bovine, equine, canine, porcine and human peripheral blood granulocytes is described. After enrichment of granulocytes by centrifugation, contaminating erythrocytes are lysed hypotonically. Recovery, purity, and viability of the granulocyte suspensions are determined. FACScan analysis of the cell suspensions measuring cellular size by forward and sideward light scatter is compared with the corresponding analysis of whole blood leukocytes. Constituencies of the isolated cell suspensions and loss of granulocyte subpopulations through isolation procedure is discussed with regard to granulocyte function assays.

Chemotactic properties of rat immunoglobulins and immune complexes

The effect of rat immunoglobulins and immune complexes on the locomotor function of rat polymorphonuclear leukocytes (PMN) was investigated in vitro. Rat immunoglobulin G1 (IgG1), IgG2a, IgG2b, and IgA monoclonal antibodies specific for the dinitrophenyl hapten were used. Both monomeric and polymeric IgA showed chemotactic activity in a dose-dependent manner. IgG1 and IgG2b also induced a dose-dependent locomotor response of PMN, but the nature of the induced migration was chemokinetic (enhancing random migration). IgG2a was chemotactic and induced maximal migration at a relatively low concentration. IgG1- and IgG2b-immune complexes induced stronger migration than antibody alone; however, IgA- and IgG2a-immune complexes did not. IgA was shown to modify the chemotactic movement of PMN induced by N-formylmethionyl-leucyl-phenylalanine (FMLP). In the presence of both IgA and FMLP in the lower chamber, the migration towards suboptimal concentrations of FMLP was enhanced. By contrast, IgA in the upper chamber decreased migration towards the optimal or higher concentrations of FMLP. These findings suggest that IgA may work synergistically with luminal chemoattractants to mobilize PMN to the locus of infection on the mucosal surface. In addition, the intense activity of IgG2a alone and IgG1- or IgG2b-immune complexes in inducing PMN migration may play an important role in inflammatory processes. The data indicate that immunoglobulins have a direct effect on PMN mobility.

In vitro and in vivo activity of polyclonal and monoclonal human immunoglobulins G, M, and A against Pseudomonas aeruginosa lipopolysaccharide

We evaluated the in vitro opsonophagocytic killing activity of monoclonal human immunoglobulin G (IgG), IgM, and IgA specific for Pseudomonas aeruginosa lipopolysaccharide and the in vivo protective capacity in neutropenic mice of both monoclonal and purified polyclonal IgG, IgM, and IgA. Monoclonal IgM was efficacious in mediating opsonophagocytic killing only in conjunction with complement, whereas monoclonal IgG opsonic killing was potentiated by complement, and monoclonal IgA opsonic killing was independent of complement. These findings are similar to those previously reported for purified polyclonal IgM, IgG, and IgA. The monoclonal and polyclonal immunoglobulins had comparable 50% protective doses in neutropenic mice (range, 0.28 to 0.46 microgram per mouse). The protective activity of IgM in neutropenic mice was abolished by cobra venom factor treatment, whereas IgG and IgA maintained efficacy in cobra venom factor-treated mice. These data indicate that all three major human serum immunoglobulin isotypes have opsonophagocytic and protective activities against P. aeruginosa, with a critical role for complement in the function of IgM.

IgA pemphigus foliaceus. Report of two cases and a review of the literature

The cases of two patients with vesiculobullous lesions were diagnosed clinically and histopathologically as pemphigus foliaceus; unexpectedly, both revealed intercellular IgA, but not IgG, in the upper epidermis by direct immunofluorescence. Such histologic and immunofluorescence findings have been reported in eight other cases. In our cases no circulating IgA or IgG intercellular antibodies could be detected; in four of eight other reported cases IgA antibodies showed intercellular staining like that of pemphigus antibodies. Subcorneal acantholytic lesions occurred in both our cases; of the other cases reported, five had essentially identical histopathologic findings. The clinical and histopathologic features of pemphigus, as well as the recent findings of circulating IgA intercellular antibodies alone or with IgG antibodies, appear to place this disease into the spectrum of pemphigus. The 10 IgA pemphigus cases reported to date fall into one of two groups, the IgA pemphigus foliaceus (including our two cases) and IgA pemphigus of the intraepidermal neutrophilic type, which seems to be less common.

Binding, internalization and degradation of soluble aggregates of human secretory IgA by resident rat peritoneal macrophages

In the present study the in vitro binding, internalization and degradation of IgA immune complexes (IC) by phagocytes was studied. As a model for IgA IC, heat-aggregated human secretory IgA (AsIgA) was prepared and resident rat peritoneal macrophages (PM phi) were used as a source of phagocytes. First, binding of 125I-AsIgA to rat PM phi was investigated. Binding of 125I-AsIgA to PM phi at 4 degrees was saturable and reached plateau values after 2 hr. At 37 degrees, degradation of membrane-bound 125I-AsIgA into trichloroacetic acid (TCA)-soluble fragments occurred. Parallel experiments with unlabelled AsIgA and 125I-labelled anti-human IgA revealed that degradation of AsIgA was preceded by internalization of AsIgA. The specificity of binding of 125I-AsIgA to PM phi was investigated using human IgG, human serum IgA, human myeloma IgA1, human sIgA and the glycoproteins asialofetuin and ovalbumin. The binding of 125I-AsIgA to rat PM phi was inhibited in the presence of sIgA and asialofetuin. In contrast IgG and ovalbumin had no effect. These results suggest that receptors with a specificity for galactose on the rat PM phi are involved in the binding of AsIgA.