IgA and the IgA Fc receptor

Mucosal B cell deficiency in IgA-/- mice abrogates the development of allergic lung inflammation

We have investigated the consequence of lack of IgA on host immunity using a murine model of allergic lung inflammation. Mice with a targeted disruption of the alpha-switch region and 5' H chain gene (IgA(-/-) mice), which lack total IgA, developed significantly reduced pulmonary inflammation with fewer inflammatory cells in lung tissue and bronchoalveolar lavage fluids, as well as reduced levels of total and IgG1 OVA-specific Abs and decreased IL-4 and IL-5 in bronchoalveolar lavage fluids compared with IgA(+/+) controls, following allergen sensitization and challenge. This defect was attributable to fewer B cells in the lungs of IgA(-/-) mice. Polymeric IgR-deficient (pIgR(-/-)) mice, which lack the receptor that transports polymeric IgA across the mucosal epithelium where it is cleaved to form secretory IgA, were used to assess the contribution of secretory IgA vs total IgA in the induction of allergic lung inflammation. pIgR(-/-) and pIgR(+/+) mice had comparable levels of inflammation, demonstrating that IgA bound to secretory component is not necessary for the development of allergic lung inflammation, although this does not necessarily rule out a role for transudated IgA in lung secretions because of "mucosal leakiness" in these mice. The results indicate that Ag-specific B cells are required at mucosal surfaces for induction of inflammation and likely function as major APCs in the lung for soluble protein Ags.

Secretory immunoglobulin A in saliva of women with oral and genital HPV infection

Secretory IgA contributes towards the protection of mucosal surfaces against invading microorganisms.

OBJECTIVES

Quantify secretory IgA titers in the saliva of women with HPV in the oropharynx and/or in the genital area.

SUBJECTS AND METHODS

Seventy women with clinical genital HPV lesions and 70 women without HPV infection were tested for oral HPV DNA and the levels of total IgA in their saliva. One millilitre of saliva was collected, centrifuged and stored at -80 degrees C for the measurement of secretory IgA by nephelometry technique. A pool of oral pharyngeal cells was collected for HPV identification by polymerase chain reaction.

RESULTS

Oral HPV PCR was positive in 29 (21%) women (26 women with genital HPV and only 3 women without genital HPV). Titers of secretory IgA were extremely lower in-patients with HPV DNA in the oropharynx when compared to HPV negative women (p<0.0001). Genital HPV and smoking were also associated to low levels of total sIgA in saliva (p<0.01). After multivariable analyses only the presence of HPV in the oral cavity and/or in genital area, but not smoking, was related to low levels of total secretory IgA.

CONCLUSION

Women with low levels of total secretory IgA could be more susceptible to having their oral mucosa colonized by HPV.

Immunomodulatory properties of human serum immunoglobulin A: anti-inflammatory and pro-inflammatory activities in human monocytes and peripheral blood mononuclear cells

Our study investigated the immunomodulatory activities of human plasma-derived serum immunoglobulin (Ig)A. Previous findings seem contradictory indicating either pro- or anti-inflammatory activities. We used serum IgA purified from large plasma pools and studied the modulation of the release of cytokines and chemokines from resting and lipopolysaccharide (LPS, endotoxin)-stimulated human adherent monocytes and human peripheral blood mononuclear cells (PBMC). Our results indicate that IgA down-modulates the release of the pro-inflammatory chemokines monocyte chemoattractant protein (MCP) 1, macrophage inflammatory protein (MIP) 1alpha and MIP1beta from LPS-stimulated PBMC and the release of MCP1, MIP1alpha and MIP1beta from LPS-stimulated monocytes. Furthermore, we confirmed previous reports that plasma-derived serum IgA down-modulates the release of the pro-inflammatory cytokines, interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha, from LPS-stimulated monocytes and PBMC, and up-regulates the release of IL-1 receptor antagonist (IL-1RA) from resting and LPS-stimulated monocytes and resting PBMC. This IgA-mediated up-regulation of IL-1RA is independent of the simultaneous up-regulation of IL-1beta release, as shown by blocking the biological activity of IL-1beta with a neutralizing antibody. On the other hand, we also found an IgA-induced pro-inflammatory activity, namely IgA-mediated up-regulation of the release of pro-inflammatory IL-1beta as well as down-regulation of the anti-inflammatory cytokines IL-10 and IL-12p40 from LPS-stimulated monocytes and PBMC and a down-regulation of transforming growth factor (TGF)-beta from resting and LPS-stimulated PBMC. We conclude that human serum IgA has both an anti-inflammatory and a pro-inflammatory capacity and this dual capacity might contribute to the feedback mechanisms maintaining a balance between pro-inflammatory and anti-inflammatory activities.

Anti-infection effect of hydrolysates from conglycinin on E.coli in mice

AIM: To elucidate anti-infection effect of hydrolysates from conglycinin on E.coli in mice.

METHODS: Male KM mice were assigned randomly in five treatments. After feeding basal diet three days, E.coliO₁₃₈ was fed in five treatments from 2×10¹¹ to 2×10⁷CFU/L, diluted (in decuple) ordinally. The LD₅₀ of mice feeding E.coliO₁₃₈ after 56 h was 4.73×10¹⁰ CFU/L. Two batch of Male KM mice were randomly assigned to six treatments respectively: normal (NOR) group, feeding-E.coli control (FEC), Basal diet + physiological saline, Basal diet + Hcl-full hydrolysis of conglycinin (HCL-FHC), Basal diet + conglycinin (Conglycinin), Basal diet + pepsin-hydrolysate conglycinin (PTC), and Basal diet + purified fraction B of pepsin hydrolysates of conglycinin (P2-PTC) group. The mice were fed with a dose of 0.2 mL /g (containing equal amount of nitrogen) except the ones in NOR and FEC group. Twenty days after feeding, each mouse in FEC, HCL-FHC, Conglycinin, PTC and P2-PTC group was fed with E.coliO₁₃₈ (2×10⁹ CFU/L and 2×10¹¹ CFU/L for the two batch, respectively, 0.2 mL/g) in the 22^nd day (midday). The actions of the mice were observed until 48 h after feeding with E.coliO₁₃₈. Then all the mice were killed. The blood, spleen and the whole length of intestines were collected. The immune index was determined by radioimmunoassay.

RESULTS: The KM mice reacted differently when infected with different levels of E.coli after feeding the pepsin-hydrolysate conglycinin. In mice fed with 2×10⁹ CFU/L of E.coliO₁₃₈, the pepsin-hydrolysate conglycinin significantly increased the level of spleen IL-2 (19.2±9.6 μg/g vs 11.5±4.7 μg/g in P2-PTC and NOR group respectively, P<0.05; 19.2±9.6 μg/g vs 9.4±3.7 μg/g in P2-PTC and FEC group respectively, P<0.01), the intestinal sIgA concentration, and significantly decreased spleen IL-6 (127.1±52.8 ng/g vs 276.4±60.1 ng/g in P2-PTC and NOR respectively, P<0.01; 127.1±52.8 ng/g vs 224.5±38.9 ng/g in P2-PTC and FEC respectively, P<0.05) and TNF-α (9.1±2.0 μg/g vs 16.3±3.9 μg/g in PTC and NOR group respectively, P<0.05) level, but had no significant effect on serum IL-2. In mice fed with 2×10¹¹ CFU/L of E.coliO₁₃₈, the pepsin-hydrolysate conglycinin significantly increased the levels of spleen IL-6 (480.5±184.7 ng/g vs 206.7±72.3 ng/g in P2-PTC and NOR respectively, P<0.05) and TNF-α (43.3±5.8 μg/g vs 10.5±4.1 μg/g in P2-PTC and NOR group respectively, P<0.01; 43.3±5.8 μg/g vs 19.7±9.0 μg/g in P2-PTC and FEC group respectively, P<0.01), and decreased the serum IL-6 and TNF-α (P2-PTC group 2.8±1.0 μg/L vs FEC group 4.6±2.0 μg/L in P2-PTC and FEC group respectively, P<0.05) concentrations.

CONCLUSION: The hydrolysates from conglycinin with pepsin can increase the immune function in mice, defend the invasion of E.coli and keep the gut healthy.

Immature Neutrophils Mediate Tumor Cell Killing via IgA but Not IgG Fc Receptors

Antitumor Abs are promising therapeutics for cancer. Currently, most Ab-based therapies focus on IgG Ab, which interact with IgG FcR (FcgammaR) on effector cells. In this study, we examined human and mouse neutrophil-mediated tumor cell lysis via targeting the IgA FcR, FcalphaRI (CD89), in more detail. FcalphaRI was the most effective FcR in triggering tumor cell killing, and initiated enhanced migration of neutrophils into tumor colonies. Importantly, immature neutrophils that are mobilized from the bone marrow upon G-CSF treatment efficiently triggered tumor cell lysis via FcalphaRI, but proved incapable of initiating tumor cell killing via FcgammaR. This may provide a rationale for the disappointing results observed in some earlier clinical trials in which patients were treated with G-CSF and antitumor Ab-targeting FcgammaR.

Identification of FcalphaRI as an inhibitory receptor that controls inflammation: dual role of FcRgamma ITAM

Serum IgA is considered a discrete housekeeper of the immune system with multiple anti-inflammatory functions, whereas IgA-immune complexes mediate inflammatory responses. Here, we identify FcalphaRI as a molecular device that determines the nature of IgA responses. In the absence of sustained aggregation, receptor targeting by serum IgA or anti-FcalphaRI Fab inhibits activating responses of heterologous FcgammaR or FcepsilonRI. The inhibitory mechanism involves recruitment of tyrosine phosphatase SHP-1 to FcalphaRI and impairment of Syk, LAT, and ERK phosphorylation induced by FcepsilonRI engagement. SHP-1 recruitment is dependent on ERK. Conversely, sustained aggregation of FcalphaRI by multimeric ligands stimulates cell activation by recruiting high amounts of Syk and aborting SHP-1 binding. Both types of signals require the FcRgamma-ITAM motif. Anti-FcalphaRI Fab treatment suppresses manifestations of allergic asthma in FcalphaRI transgenic mice. These findings redefine FcalphaRI as a bifunctional inhibitory/activating receptor of the immune system that mediates both anti- and proinflammatory functions of IgA.

The Staphylococcal Superantigen-Like Protein 7 Binds IgA and Complement C5 and Inhibits IgA-FcαRI Binding and Serum Killing of Bacteria

The staphylococcal superantigen-like proteins (SSLs) are close relatives of the superantigens but are coded for by a separate gene cluster within a 19-kb region of the pathogenicity island SaPIn2. rSSL7 (formally known as SET1) bound with high affinity (K(D), 1.1 nM) to the monomeric form of human IgA1 and IgA2 plus serum IgA from primate, pig, rat, and horse. SSL7 also bound the secretory form of IgA found in milk from human, cow, and sheep, and inhibited IgA binding to cell surface FcalphaRI (CD89) and to a soluble form of the FcalphaRI protein. In addition to IgA, SSL7 bound complement factor C5 from human (K(D), 18 nM), primate, sheep, pig, and rabbit serum, and inhibited complement-mediated hemolysis and serum killing of a Gram-negative organism Escherichia coli. SSL7 is a superantigen-like protein secreted from Staphylococcus aureus that blocks IgA-FcR interactions and inhibits complement, leading to increased survival of a sensitive bacterium in blood.

The mannose receptor is expressed by subsets of APC in non-lymphoid organs

BACKGROUND

The mannose receptor (MR) is an endocytic receptor of Mphi and endothelial cell subsets whose natural ligands include both self glycoproteins and microbial glycans. It is also expressed by immature cultured dendritic cells (DC), where it mediates high efficiency uptake of glycosylated antigens, yet its role in antigen handling in vivo is unknown. Knowledge of which APC subsets express MR will assist the design of experiments to address its immunological functions. Here the expression of MR by MHC class II positive APC in non-lymphoid organs of the mouse is described.

RESULTS

MR positive APC were identified in several peripheral organs: skin, liver, cardiac and skeletal muscle and tongue. MR positive cells in salivary gland, thyroid and pancreas coexpressed MHC class II and the myeloid markers macrosialin and sialoadhesin, but not the dendritic cell markers CD11c or DEC-205. MR and MHC class II colocalised in confocal microscope images, implying that antigen capture may be the primary role of MR in these cells. Distinct ligands of MR were found in salivary gland and pancreas tissue lysates that are candidate physiological ligands of MR positive APC in these organs.

CONCLUSIONS

The tissue and subcellular distribution of MR suggest it is appropriately located to serve as a high efficiency antigen uptake receptor of APC.

Cloning and characterization of the human FCRL2 gene

We report cloning and characterization of FCRL2, a novel human gene that belongs to the FcR family. The gene is closely linked and structurally similar to the recently identified FCRL/FREB/FcRX gene. The encoded protein is composed of three Ig-like domains and a C-terminal mucin-like domain containing a conserved alpha-helical motif with dileucine signals. Intraexonic splicing may generate two alternative transcripts, coding for isoforms with the third and fourth domains replaced by entirely different amino acid sequences. Like FCRL, the full-length isoform of FCRL2 is expressed intracellularly in transfected 293T cells. Expression analysis revealed FCRL2 mRNA only in placenta. The gene transcripts were not detected in lymphoid tissues or in the main leukocyte subsets isolated from peripheral blood. However, we found that FCRL2 is differentially expressed by transformed B cell lines. Of interest is also the finding that the gene expression may be up-regulated in the progression of melanocytic tumors.

Measurement of messenger RNA encoding the -chain, polymeric immunoglobulin receptor, and J-chain in duodenal mucosa from dogs with and without chronic diarrhea by use of quantitative real-time reverse transcription-polymerase chain reaction assays

OBJECTIVE

To examine the difference in expression of messenger RNA (mRNA) transcripts for polymeric immunoglobulin receptor (plgR), alpha-chain, and J-chain determined by use of quantitative real-time reverse transcription-polymerase chain reaction (QRT-PCR) assays in duodenal biopsy specimens obtained from dogs with and without chronic diarrhea.

SAMPLE POPULATION

Biopsy specimens of the proximal portion of the duodenum were obtained endoscopically from 39 dogs evaluated because of chronic diarrhea (12 German Shepherd Dogs and 27 non-German Shepherd Dog breeds); specimens were also obtained from a control group of 7 dogs evaluated because of other gastrointestinal tract diseases and 2 dogs that were euthanatized as a result of nongastrointestinal tract disease.

PROCEDURE

Dogs were anesthetized, and multiple mucosal biopsy specimens were obtained endoscopically at the level of the caudal duodenal flexure by use of biopsy forceps; in 2 control dogs, samples were obtained from the descending duodenum within 5 minutes of euthanasia. One-step QRT-PCR was used to quantify the level of expression of transcripts for the housekeeper gene glyceraldehyde-3-phosphate dehydrogenase, plgR, alpha-chain, and J-chain in duodenal mucosal tissue.

RESULTS

There was no significant difference in the level of expression of any transcript among non-German Shepherd Dog breeds without diarrhea (control group), non-German Shepherd Dog breeds with chronic diarrhea, and German Shepherd Dogs with chronic diarrhea. Conclusions and Clinical Relevance-Results indicated that the susceptibility of German Shepherd Dogs to chronic diarrhea is not a result of simple failure of transcription of the key genes that encode molecules involved in mucosal IgA secretion.

Phase variable desialylation of host proteins that bind to Streptococcus pneumoniae in vivo and protect the airway

Most clinical isolates of Streptococcus pneumoniae consist of heterogeneous populations of at least two colony phenotypes, opaque and transparent, selected for in the bloodstream and nasopharynx, respectively. Microarray analysis revealed 24 orfs that demonstrated differences in expression greater than twofold between variants of independent strains. Twenty-one of these showed increased expression in the transparent variants, including 11 predicted to be involved in sugar metabolism. A single genomic region contains seven of these loci including the gene that encodes the neuraminidase, NanA. In contrast to previous studies, there was no contribution of NanA to adherence of S. pneumoniae to epithelial cells or colonization in an animal model. However, we observed NanA-dependent desialylation of human airway components that bind to the organism and may mediate bacterial clearance. Targets of desialylation included human lactoferrin, secretory component, and IgA2 that were shown to be present on the surface of the pneumococcus in vivo during pneumococcal pneumonia. The efficiency of desialylation was increased in the transparent variants and enhanced for host proteins binding to the surface of S. pneumoniae. Because deglycosylation affects the function of many host proteins, NanA may contribute to a protease-independent mechanism to modify bound targets and facilitate enhanced survival of the bacterium.

Fc receptors in livestock species

Many of the receptors for the Fc domain of immunoglobulins in cattle, sheep, pigs and horses have been cloned and characterized recently. This review summarises recent developments and relates them to the current understanding of the primary structure, cellular specificity and binding properties of Fc receptors (FcRs). Although there is an obvious overall similarity to their human and mouse counterparts, some Fc receptors in domestic animals are unusual, perhaps most notably the bovine Fcgamma2R, which although related to other mammalian FcgammaRs, belongs to a novel gene family and the porcine FcgammaRIIIA, which associates with a molecule that contains significant homology to the cathelin family of antimicrobial proteins. Accumulating data suggest the possibility of a different role for the FcRn in ruminants, which may secrete IgG onto the mucosal surfaces, rather than absorbing it, as was suggested by mouse studies. These differences may be linked to the diversity of immunoglobulin classes in different mammalian species, and may contribute to different immune functions. The observations made so far emphasize the importance of elucidating and analyzing the roles of these molecules within the immune system of each host animal, rather than inferring roles from conclusions made in human and mouse studies. A better understanding of Fc receptor expression on immune effector cells should help in developing new immunization protocols, while knowledge of the Fc receptors involved in immunoglobulin transport, especially in the mammary gland, may help to develop new products which could be used not only for veterinary purposes but perhaps also for human therapy.

The Fc receptor for IgA (FcalphaRI, CD89)

Traditionally IgA has been regarded as a non-inflammatory antibody, which inhibits adhesion of micro-organisms to the mucosal wall without initiation of inflammatory responses. Recently, however, a dichotomy has been suggested between the actions of secretory IgA (SIgA), which is present at mucosal sites, and serum IgA. SIgA exerts its function as first line of defence by limiting invasion of pathogens. Serum IgA in turn may be engaged in inflammatory responses after breaching of mucosal wall integrity. Several receptors for IgA have been described. However, the-as yet-best characterized prototypic Fc receptor for IgA, FcalphaRI (CD89), is the most likely candidate for initiation of inflammatory responses, as it binds poorly to SIgA, but vigorously triggers potent effector functions upon binding to serum IgA. Here, new insights in IgA-FcalphaRI binding are described and the functional implications of these interactions are discussed.

TGF-beta receptor signaling is critical for mucosal IgA responses

TGF-beta receptor (TbetaR) signaling is important for systemic IgA production; however, its contribution to IgA secretion at mucosal sites remained uncertain. This important question was addressed using mice lacking the TbetaR in B cells (TbetaRII-B). Although reduced, IgA-secreting cells and IgA were still present in the systemic and mucosal compartments. The adaptive immune response was investigated after oral or nasal immunization using adjuvants acting on different molecular targets, namely, the cholera toxin B subunit and the macrophage-activating lipopeptide-2. Efficient Ag-specific cellular and humoral responses were triggered both in controls and TbetaRII-B mice. However, a significant reduction in Ag-specific IgG2b and increased levels of IgG3 were observed in sera from TbetaRII-B mice. Furthermore, Ag-specific IgA-secreting cells, serum IgA, and secretory IgA were undetectable in TbetaRII-B mice. These results demonstrate the critical role played by TbetaR in Ag-driven stimulation of secretory IgA responses in vivo.

Recognition of Entamoeba histolytica 115-kDa surface protein by human secretory immunoglobulin A antibodies from asymptomatic carriers

Entamoeba histolytica is a protozoan parasite that can invade the intestinal mucosa. Infection induces production of secretory immunoglobulin A (SIgA) antibodies that can diminish the adhesion between E. histolytica trophozoites and epithelial cells in vitro and reduce the rate of new infections in children. SIgA antibodies produced by asymptomatic cyst carriers could play a protective role against the damage caused by E. histolytica. To identify membrane antigens capable of inducing SIgA response in E. histolytica cyst carriers, salivary SIgA antibodies were confronted with blotted plasma membrane proteins from amebae. A surface 115-kDa ameba protein was recognized by 62% of the human SIgA antibodies tested. The 115-kDa protein is not a mannose-containing glycoprotein and has no protease activity. Rabbit anti-115-kDa protein antibodies were capable of reducing erythrophagocytosis but were unable to protect culture cells from the cytopathic damage caused by E. histolytica. However, anti-115-kDa protein antibodies induced surface receptor redistribution.

Synergistic interaction of two independent genetic loci causes extreme elevation of serum IgA in mice

Understanding the molecular regulation of immunoglobulin A (IgA) expression is important as it plays an essential role in the first-line defence through mucosal secretions. Using inbred mouse strains, we identified two independent and dominant acting genetic loci that synergistically cause a 40-fold upregulation in serum IgA levels when introduced into the murine strain C57Bl/6J (B6). The first locus on chromosome 12 appears to be mainly responsible for the natural four-fold higher IgA levels in C3HeB/FeJ (C3H) compared to B6 mice. A second independent, chemically induced mutation on chromosome 5 caused a two-fold elevation when transferred from C3H into B6 mice. Both loci in concert effect a 40-fold elevation against the B6 genetic background. We determined the chromosomal localization of the two loci simultaneously by a one-step mapping process. The chemically induced mutation was identified within the immunoglobulin joining chain (IgJ) gene on chromosome 5. The major serum IgA modifier between the C3H and B6 was located on chromosome 12. This modifier region was mapped to a 350 kb region containing several immunoglobulin heavy-chain genes and the Ig alpha germline switch gene. We speculate that by interfering with both IgA expression and distribution, synergistic regulation of IgA is achieved.

Fc Receptor γ Chain Residues at the Interface of the Cytoplasmic and Transmembrane Domains Affect Association with FcαRI, Surface Expression, and Function

The assembly of multiple subunit immunoreceptors is dependent on transmembrane interactions. The Fc receptor gamma (FcR-gamma) chain is a ubiquitous immune receptor tyrosine-based activation motif-containing dimeric subunit, gamma(2), which in humans associates with both the activating members of the leukocyte receptor cluster, including the IgA receptor FcalphaRI, and the classical Fc receptors, including the IgE receptor FcepsilonRI. This study identifies a new site in the transmembrane region of FcR-gamma that affects receptor assembly and surface expression with FcalphaRI but not with FcepsilonRI. The wild type complex, FcalphaRI-gamma(2)WT, remains robustly associated in both Brij-96 and Thesit detergent conditions. However, mutation of either Tyr(25) or Cys(26) of FcR-gamma, near the interface of the transmembrane and cytoplasmic regions, resulted in impaired FcR-gamma association with FcalphaRI. This association was disrupted in the presence of the detergent Brij-96 but was preserved in milder conditions using the detergent Thesit. Ligand-mediated cross-linking of the FcalphaRI-gamma(2)Y25F mutant receptor resulted in diminished signal transduction, including an abnormal calcium response, compared with the FcalphaRI-gamma(2)WT receptor. Furthermore, the FcalphaRI-gamma(2)Y25F mutant receptor was expressed at the cell surface at approximately 10% of that of the wild type, whereas the surface expression of FcepsilonRI-gamma(2)Y25F was not significantly different from the wild type. In contrast, although the FcalphaRI-gamma(2)C26S mutant was also less stably associated, it was not reduced in surface expression or function. Thus, these TM residues of FcR-gamma are important for association with FcalphaRI and probably other activating LRC members but not with the classical FcR, FcepsilonRI.

Solution Structure Determination of Monomeric Human IgA2 by X-ray and Neutron Scattering, Analytical Ultracentrifugation and Constrained Modelling: A Comparison with Monomeric Human IgA1

Immunoglobulin A (IgA), the most abundant human immunoglobulin, mediates immune protection at mucosal surfaces as well as in plasma. It exists as two subclasses IgA1 and IgA2, and IgA2 is found in at least two allotypic forms, IgA2m(1) or IgA2m(2). Compared to IgA1, IgA2 has a much shorter hinge region, which joins the two Fab and one Fc fragments. In order to assess its solution structure, monomeric recombinant IgA2m(1) was studied by X-ray and neutron scattering. Its Guinier X-ray radius of gyration R(G) is 5.18 nm and its neutron R(G) is 5.03 nm, both of which are significantly smaller than those for monomeric IgA1 at 6.1-6.2 nm. The distance distribution function P(r)for IgA2m(1) showed a broad peak with a subpeak and gave a maximum dimension of 17 nm, in contrast to the P(r) curve for IgA1, which showed two distinct peaks and a maximum dimension of 21 nm. The sedimentation coefficients of IgA1 and IgA2m(1) were 6.2S and 6.4S, respectively. These data show that the solution structure of IgA2m(1) is significantly more compact than IgA1. The complete monomeric IgA2m(1) structure was modelled using molecular dynamics to generate random IgA2 hinge structures, to which homology models for the Fab and Fc fragments were connected to generate 10,000 full models. A total of 104 compact best-fit IgA2m(1) models gave good curve fits. These best-fit models were modified by linking the two Fab light chains with a disulphide bridge that is found in IgA2m(1), and subjecting these to energy refinement to optimise this linkage. The averaged solution structure of the arrangement of the Fab and Fc fragments in IgA2m(1) was found to be predominantly T-shaped and flexible, but also included Y-shaped structures. The IgA2 models show full steric access to the two FcalphaRI-binding sites at the Calpha2-Calpha3 interdomain region in the Fc fragment. Since previous scattering modelling had shown that IgA1 also possessed a flexible T-shaped solution structure, such a T-shape may be common to both IgA1 and IgA2. The final models suggest that the combination of the more compact IgA2m(1) and the more extended IgA1 structures will enable human IgA to access a broader range of antigens than either acting alone. The hinges of both IgA subclasses appear to show reduced flexibility when compared to their equivalents in IgG, and this may be important for maintaining an extended IgA structure.

A novel polymorphism in the cytoplasmic region of the human immunoglobulin A Fc receptor gene*

The Fc receptor for immunoglobulin A (IgA), FcalphaRI, is expressed on several types of myeloid cells, and activates them upon ligand binding. However, binding of IgA to the extracellular domain of the receptor requires previous stimulation of the cell by cytokines, and the cytoplasmic tail of FcalphaRI has been shown to play a role in this. Therefore, polymorphism in this region might affect this process. However, no changes in the amino acid sequence in this region of the FcalphaRI have so far been reported. Here, we describe for the first time a single nucleotide polymorphism in exon 5 of the immunoglobulin A Fc receptor (FCAR) gene leading to a Ser-->Gly substitution at position 248 of the mature FcalphaRI protein. Prediction of structural features suggests some changes that may affect the function of the protein to some extent. However, the Gly248 variant is quite common (4% homozygotes and 38% heterozygotes) in healthy population, suggesting a weak effect, if any, on function, at least in heterozygotes.

Role of transforming growth factor-beta in breast milk for initiation of IgA production in newborn infants

BACKGROUND

Transforming growth factor (TGF)-beta has a crucial effect on IgA production, which is the major humoral effector of mucosal immunity. Breast milk contains the abundant amount of TGF-beta in the early period of lactation. AIM-STUDY DESIGN: To verify the notion that TGF-beta in breast milk might contribute to the development of IgA production in newborns, we investigated the association of TGF-beta in maternal colostrum with an increase of serum IgA in newborns during the first month of life.

SUBJECTS AND METHODS

The concentrations of TGF-beta1 and TGF-beta2, including IL-6 and IL-10, in colostrum samples from 55 healthy mothers were determined by ELISA. The levels of IgA and IgM in serum samples collected from corresponding newborn babies at birth and at 1 month of age were measured by ELISA.

RESULTS

TGF-beta1 and TGF-beta2 were detected in substantial quantities in all colostrum samples, but IL-6 and IL-10 were present only in a proportion of samples. An increase of serum IgA in newborn during the first month of life was significantly higher than that of serum IgM (p<0.001). Notably, an increase of serum IgA in newborns during 1 month of life was well correlated with levels of both TGF-beta1 (r=0.38, p=0.005) and TGF-beta2 (r=0.45, p=0.0005) in colostrum, while that of IgM was marginally correlated with colostral TGF-beta2 (r=0.28, p=0.04). The association of increase of serum IgA in newborns with IL-6 and IL-10 in colostrum was not evident.

CONCLUSION

Our findings suggest that TGF-beta in colostrum might serve as the starter of IgA production in newborn infants.

Induction of HIV-specific antibody response and protection against vaginal SHIV transmission by intranasal immunization with inactivated SHIV-capturing nanospheres in macaques

We have previously reported that concanavalin A-immobilized polystyrene nanospheres (Con A-NS) could efficiently capture HIV-1 particles and that intranasal immunization with inactivated HIV-1-capturing nanospheres (HIV-NS) induced vaginal anti-HIV-1 IgA antibody response in mice. In this study, to evaluate the protective effect of immunization, each three macaques was intranasally immunized with Con A-NS or inactivated simian/human immunodeficiency virus KU-2-capturing nanospheres (SHIV-NS) and then intravaginally challenged with a pathogenic virus, SHIV KU-2. After a series of six immunizations, vaginal anti-HIV-1 gp120 IgA and IgG antibodies were detected in all SHIV-NS-immunized macaques. After intravaginal challenge, one of the three macaques in each of the Con A-NS- and SHIV-NS-immunized groups was infected. Plasma viral RNA load of infected macaque in SHIV-NS-immunized macaques was substantially less than that in unimmunized control macaque and reached below the detectable level. However, it could not be determined whether intranasal immunization with SHIV-NS is effective in giving complete protection against intravaginal challenge. To explore the effect of the SHIV-NS vaccine, the remaining non-infected macaques were rechallenged intravenously with SHIV KU-2. After intravenous challenge, all macaques became infected. However, SHIV-NS-immunized macaques had lower viral RNA loads and higher CD4(+) T cell counts than unimmunized control macaques. Plasma anti-HIV-1 gp120 IgA and IgG antibodies were induced more rapidly in the SHIV-NS-immunized macaques than in the controls. The rapid antibody responses having neutralizing activity might contribute to the clearance of the challenge virus. Thus, SHIV-NS-immunized macaques exhibited partial protection to vaginal and systemic challenges with SHIV KU-2.

Assessment of the Opsonic Activity of Purified Bovine sIgA Following Intramammary Immunization of Cows with Staphylococcus aureus

The phagocytosis of Staphylococcus aureus by bovine polymorphonuclear neutrophils (PMN) requires the presence of antibodies. Among the major isotypes of bovine antibodies, IgG2 and IgM are considered opsonic for bovine PMN. However, the role of purified bovine secretory IgA (sIgA) as an opsonin has not been assessed. In the present study, IgG2 were obtained from serum and sIgA, IgG1, and IgM were purified from the colostrums of three cows intramammarily immunized with heat-killed Staphylococcus aureus. The Ig preparations were assayed for specific antibodies, and the opsonic capacity of every isotype was investigated. Despite the presence of antibodies, we observed no distinct chemiluminescence response of PMN stimulated with sIgA- or IgG1-opsonized S. aureus, whereas IgM or IgG2 bound to bacteria induced a marked chemiluminescence response. Moreover, the counting of internalized bacteria per PMN after phagocytosis revealed a low uptake of S. aureus opsonized with sIgA or IgG1, in contrast to IgM or IgG2, which triggered efficient ingestion of bacteria. Priming of neutrophils by TNF-alpha, IFN-gamma, or C5adesArg did not promote an oxidative burst or uptake of sIgA-opsonized S. aureus to a greater extent than with IgG1-opsonized bacteria. Furthermore, analysis of uningested bacteria by flow cytometry after incubation with PMN showed a preferential uptake of IgM-opsonized S. aureus by PMN and only few sIgA-positive stained bacteria were PMN-associated. These experiments indicate that sIgA, like IgG1 and unlike IgM or IgG2, could not be considered as a major opsonin for phagocytosis of S. aureus by bovine blood PMN.

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.

Class and subclass selection in parasite-specific antibody responses

Antibodies are characteristically induced in many parasitic infection processes. The class and subclass of the antibody response is instrumental because each isotype has a distinct biological function. It is thus crucially important for an infected individual to mount the most appropriate secondary antibody response--that is the response that has the best chance of clearing the infection and/or controlling disease. This represents a fundamental of vaccine strategies. Immuno-epidemiological surveys and in vitro models of antibody production have helped to understand some of the goals which should be achieved when designing antiparasitic vaccines.

Expression and functional activity of isotype and subclass switched human monoclonal antibody reactive with the base of the V3 loop of HIV-1 gp120

Immunoglobulins undergo isotype switching in response to antigenic stimulation. The C(H) domains, in particular the hinge region, impose structural constraints on the interaction of antibody with antigen, especially multivalent antigens such as HIV. We previously showed that switching the IgG1 anti-HIV human monoclonal antibody (HMAb) F105 to an IgG3 resulted in significantly enhanced neutralization of HIV. To further investigate the influence of isotype, including the functional activity of HMAbs switched to IgA, which may be important in mucosal defenses, isotype switched antibodies have been generated for the anti-V3 loop base IgG2 HMAb F425B4e8. Reactivity of the IgG1 antibody was greater than the parental IgG2 antibody for SF2 infected cells but less for primary isolate virions. In contrast, there was less reactivity of the IgG3 with either infected cells or virions. IgA reacted significantly more with infected cells and virions as compared to the IgG subclasses. In contrast to previous studies whereby IgG3 enhanced neutralization, comparable neutralization of primary isolate virus was observed for IgG subclasses (IgG1, IgG2, IgG3) and IgA. This may reflect differences in the exposure of epitopes recognized by the HMAb with antibody flexibility being important to neutralization by antibodies reactive with obscured epitopes (e.g., CD4 binding site). Further analysis of the in vitro activity of isotype or subclass switched antibodies, IgA in particular, alone and in combination with other HMAbs, will provide important information on the role of IgG subclass and IgA antibodies on protective immunity to HIV.

Expression and modulation of the human immunoglobulin A Fc receptor (CD89) and the FcR gamma chain on myeloid cells in blood and tissue

CD89, the human immunoglobulin A (IgA) Fc receptor (FcR), is a potential target for antibody-based therapeutics, but little is known about its expression and modulation in vivo. In this study, we examined the expression pattern of CD89 and its signalling subunit, the FcR gamma chain, on circulating myeloid cells and in various tissues. Our results showed a wide tissue distribution of CD89+ cells. Thus, CD89+ cells were evident as clusters in tonsils and appendix and scattered in varying numbers in lymph nodes, kidney, liver, intestinal mucosa, bronchoalveolar lavage and peritoneal fluid. Most CD89+ cells were identified as neutrophils with high levels of CD89. A few recently emigrated macrophages (CD14low), weakly positive for CD89, were occasionally found in the tissues and more often in the peritoneal fluid. The level of CD89 on neutrophils in tissues and peripheral blood was similar, whereas on monocytes it was much lower in the tissues than in blood, and it was absent on CD14-/CD68+ intestinal lamina propria macrophages. Conversely, we detected much higher levels of the FcR gamma chain in monocytes than in neutrophils, but the FcR gamma chain was also downregulated in tissue macrophages as well as in in vitro-differentiated monocyte-derived macrophages and dendritic cells. The implications of our current findings on the biological functioning of CD89 are discussed.

Secretory IgA N- and O-glycans provide a link between the innate and adaptive immune systems

Secretory IgA (SIgA) is a multi-polypeptide complex consisting of a secretory component (SC) covalently attached to dimeric IgA containing one joining (J) chain. We present the analysis of both the N- and O-glycans on the individual peptides from this complex. Based on these data, we have constructed a molecular model of SIgA1 with all its glycans, in which the Fab arms form a T shape and the SC is wrapped around the heavy chains. The O-glycan regions on the heavy (H) chains and the SC N-glycans have adhesin-binding glycan epitopes including galactose-linked beta1-4 and beta1-3 to GlcNAc, fucose-linked alpha1-3 and alpha1-4 to GlcNAc and alpha1-2 to galactose, and alpha2-3 and alpha2-6-linked sialic acids. These glycan epitopes provide SIgA with further bacteria-binding sites in addition to the four Fab-binding sites, thus enabling SIgA to participate in both innate and adaptive immunity. We also show that the N-glycans on the H chains of both SIgA1 and SIgA2 present terminal GlcNAc and mannose residues that are normally masked by SC, but that can be unmasked and recognized by mannose-binding lectin, by disrupting the SC-H chain noncovalent interactions.

Secretory antibodies do not affect the composition of the bacterial microbiota in the terminal ileum of 10-week-old mice

Terminal restriction fragment length polymorphism (T-RFLP) analysis was conducted on the 16S rRNA genes of the bacterial communities colonizing the epithelial surfaces of the terminal ilea of open conventionally housed mice in an institutional small-animal facility. Polymeric-immunoglobulin-receptor-deficient (pIgR(-/-)) mice that were unable to secrete antibodies across mucosal surfaces were cohoused with normal and otherwise genetically identical wild-type (C57BL/6) mice for 4 weeks. If secretory antibodies played a role in modeling the gastrointestinal microbiota, C57BL/6 mice would have had a more distinct and uniform microbiota than their pIgR(-/-) cage mates. The T-RFLP profiles of the bacterial communities were compared by using Sorensen's pairwise similarity coefficient, a newly developed weighted pairwise similarity coefficient, and on the basis of Shannon's and Simpson's diversity indices. No systematic differences were observed between the dominant components of the mucosa-associated bacterial communities of the terminal ileal walls of the two types of mice, indicating that secretory antibodies do not control the composition of this microbiota. Similar analyses of experiments conducted at two different times, between which the bacterial community composition of the mouse colony in the small-animal facility appeared to have changed, showed that differences could have been detected, had they existed.

C/EBP alpha and Ets protein family members regulate the human myeloid IgA Fc receptor (Fc alpha R, CD89) promoter

Fc alpha R (CD89), the FcR for IgA, is expressed exclusively in myeloid cells, including monocytes/macrophages, neutrophils, and eosinophils, and is thought to mediate IgA-triggered cellular functions in immunity. Here we demonstrate that the Fc alpha R 5'-flanking region from -102 to -64 relative to the ATG translation initiation codon is essential for promoter activity and contains two functional binding motifs for C/EBP and Ets family members at -74 and -92, respectively. EMSAs and cotransfection experiments show that C/EBP alpha acts as a major activator of the Fc alpha R promoter at least in immature myeloid cells. In addition, we found two additional functional targets of C/EBP alpha at -139 and -127. On the other hand, the Fc alpha R Ets binding motif could bind Elf-1 and mediate the trans-activation by cotransfected Elf-1, but a major component of the complex forming on this site appears to be an unidentified Ets-like nuclear protein that is preferentially detected in cells of hemopoietic origin. Furthermore, separation of the C/EBP and Ets binding sites reduces Fc alpha R promoter activity, suggesting some functional interaction between these factors. As the in vivo role of Fc alpha R is still incompletely defined, these findings reveal the features controlling the Fc alpha R promoter in myeloid lineage and provide a foundation for clarifying regulatory mechanisms of Fc alpha R gene expression associated with its potential roles.

Mucosal immunization with inactivated HIV-1-capturing nanospheres induces a significant HIV-1-specific vaginal antibody response in mice

Mucosal secretory IgA is considered to have an important role in the prevention of human immunodeficiency virus type 1 (HIV-1) transmission through sexual intercourse. Therefore, substances that induce HIV-1-specific IgA antibody in the genital tract may become promising candidates for prophylactic vaccine against HIV-1 infection. We have previously reported that concanavalin A-immobilized polystyrene nanospheres (Con A-NS) could efficiently capture HIV-1 particles and gp120 antigens on their surface and that intravaginal immunization with inactivated HIV-1-capturing nanospheres (HIV-NS) induced vaginal anti-HIV-1 IgA antibody in mice. In this study, various strategies for immunization with HIV-NS were undertaken to induce HIV-1-specific IgA response in the mouse genital tract. HIV-NS were administered intravaginally, orally, intranasally or intraperitoneally to mice. Progesterone treatment enhanced the anti-HIV-1 IgA response to intravaginal immunization significantly, but intranasal immunization with HIV-NS was more effective compared with other immunization routes in terms of vaginal IgA response. In addition, vaginal washes from intranasally immunized mice were capable of neutralizing HIV-1(IIIB). Thus, application of HIV-NS is a practical approach to promote HIV-1-specific IgA response by the vaginal mucosa in the mouse and intranasal appears to be an effective immunization route in this animal model. Intranasal immunization with HIV-NS should be further pursued for its potential as an HIV-1 prophylactic vaccine.

Alternative splicing of myeloid IgA Fc receptor (Fc alpha R, CD89) transcripts in inflammatory responses

More than 10 splice variants of the Fc receptor for IgA (Fc alpha R, CD89) have been identified in human myeloid cells. In this study, we quantified Fc alpha R splice transcripts Delta EC2 and Delta 66 EC2, which lack the entire and a part of the homologous immunoglobulin-like extracellular domain 2 (EC2), respectively. Tumor necrosis factor-alpha was found to specifically increase the ratio of Delta EC2 to the wild type CD89 in neutrophils and conversely decrease the Delta EC2 ratio in monocytes. We also observed a significant decrease in the neutrophil Delta EC2/CD89 ratio in pneumonia patients. These results suggest that Delta EC2 is differentially regulated and could be involved in immunoregulation of IgA-mediated host defense.

Humoral and cellular responses to gliadin in wheat-dependent, exercise-induced anaphylaxis

BACKGROUND

Wheat-dependent, exercise-induced anaphylaxis (WDEIA) is a severe allergy where wheat ingestion together with physical exercise induces anaphylaxis. We have previously shown that patients with WDEIA have IgE antibodies against gliadin proteins and identified omega-5 gliadin (Tri a 19) as a major allergen.

OBJECTIVE

The aim of this study was to examine gliadin-specific IgG subclass, IgA and IgE antibodies, basophil histamine release and cell-mediated responses in WDEIA.

METHODS

Sera and peripheral blood mononuclear cells (PBMC) were obtained from patients with WDEIA and from controls without wheat allergy. Serum antibodies to crude gliadin extract (CGE) and purified omega-5 gliadin were measured by ELISA and basophil reactivity by histamine-release test. Gliadin-induced cell-mediated responses were assessed by lymphocyte proliferation assay, and cytokine mRNA expression with real-time quantitative PCR.

RESULTS

All patients with WDEIA, but none of the controls, had IgE antibodies to CGE and omega-5 gliadin. Both allergens released high levels of histamine from the basophils of patients with WDEIA. Levels of IgA antibodies to CGE and omega-5 gliadin were significantly elevated in the patients, but the distribution of IgG subclass antibodies showed no statistically significant differences between the two groups. Proliferative responses of PBMC to CGE were increased in patients with WDEIA, and stimulation of PBMC with CGE caused, both in patients and in controls, a clear induction of IL-10 mRNA. Compared with the controls, induction of IL-10 mRNA expression in patients with WDEIA was significantly (P < 0.01) suppressed.

CONCLUSION

These results suggest that, in addition to IgE antibodies against omega-5 gliadin, specific IgA antibodies may be involved in the pathogenesis of WDEIA. Decreased expression of IL-10 mRNA in PBMC during gliadin stimulation may facilitate the development of gliadin-specific T cell responses.

Intestinal IgA synthesis: regulation of front-line body defences

Immunoglobulin A is the most abundant immunoglobulin isotype in mucosal secretions. In this review, we summarize recent advances in our understanding of the sites, mechanisms and functions of intestinal IgA synthesis in mice. On the basis of these recent findings, we propose an updated model for the induction and regulation of IgA responses in the gut. In addition, we discuss new insights into the role of IgA in the maintenance of gut homeostasis and into the reciprocal interactions between gut B cells and the bacterial flora.

Chimeric IgA antibodies against HLA class II effectively trigger lymphoma cell killing

Antibodies against human leukocyte antigen (HLA) class II, such as 1D10 or Lym-1, are currently being evaluated for the treatment of B-cell lymphomas. Previous studies have demonstrated that, in addition to IgG Fc receptors, the human myeloid IgA receptor (Fc(alpha)RI, CD89) also effectively triggered tumor cell killing. Therefore, we used the variable light and heavy chain sequences from another murine anti-HLA class II hybridoma, F3.3, to generate a panel of chimeric human/mouse antibodies, including human immunoglobulin A1 (IgA1), IgA2, IgG1, IgG2, IgG3, and IgG4. Antibody production was accomplished by stable transfection of baby hamster kidney cells, and binding activity and specificity were confirmed by enzyme-linked immunosorbent assay (ELISA) and Western blotting. All constructs demonstrated similar binding to HLA class II. Functional studies revealed that chimeric IgG1, IgA1, and IgA2 triggered similar levels of tumor cell lysis. Analyses of effector populations, however, demonstrated that killing by chimeric IgG1 constructs was triggered mainly by human mononuclear cells and complement, while IgA1 and IgA2 mediated effective lysis by polymorphonuclear neutrophils. Importantly, IgG1 and both IgA isotypes were equally effective at killing freshly isolated human chronic lymphocytic leukemia cells. Chimeric IgA antibodies against HLA class II may constitute attractive reagents for lymphoma therapy.

Pathogenic significance of IgA receptor interactions in IgA nephropathy

IgA nephropathy (IgAN), the most common primary glomerulonephritis worldwide, frequently progresses to renal failure. The pathogenesis of this disease involves the deposition of undergalactosylated IgA1 complexes in the glomerular mesangium. How the IgA1 complexes are generated and why they are deposited in the mesangium remains unclear. We propose a model wherein two types of IgA receptors participate in sequential steps to promote the development of IgAN, with FcalphaRI (CD89) being initially involved in the formation of circulating IgA-containing complexes and, subsequently, transferrin receptor (CD71) in mediating mesangial deposition of IgA1 complexes.

Mac-1 (CD11b/CD18) as Accessory Molecule for FcαR (CD89) Binding of IgA

IgA, the principal ligand for FcalphaRI, exists in serum as monomeric IgA and at mucosal sites as secretory IgA (SIgA). SIgA consists of dimeric IgA linked by joining chain and secretory components. Human polymorphonuclear leukocytes (PMN) and mouse PMN transgenic for human FcalphaRI exhibited spreading and elicited respiratory burst activity upon interaction with either serum or SIgA. However, PMN devoid of the beta(2) integrin Mac-1 (Mac-1(-/-)) were unable to bind SIgA, despite expression of FcalphaRI. Consistent with this, serum IgA stimulated Mac-1(-/-) PMN oxygen radical production, in contrast to SIgA. Binding studies showed the secretory component, by itself, to interact with Mac-1-expressing PMN, but not with Mac-1(-/-) PMN. These data demonstrate an essential role for Mac-1 in establishing SIgA-FcalphaRI interactions.

Up-regulation of polymeric immunoglobulin receptor mRNA in mammary epithelial cells by IFN-gamma

As shown in previous in vivo experiment, the amount of polymeric immunoglobulin receptor (pIgR), which mediates the transcytosis of pIgA across epithelial cells, is regulated by lactogenic hormones (PRL and cortisol) during the development of the mammary gland. In the present in vitro study, it appeared that these hormones were insufficient to induce the strong expression of the gene that we observed in vivo. Several papers have shown that IFN-gamma is a strong stimulator of pIgR gene expression in different models. In contrast, nothing is known of the effects of IFN-gamma on pIgR gene expression in the mammary gland. We report here that IFN-gamma strongly increased pIgR mRNA levels through a direct effect on mammary epithelial cells. We show that IFN-gamma activated not only Stat1 but also Stat5 and that expression of the pIgR and IRF-1 genes was strongly correlated following IFN-gamma stimulation in mammary epithelial cells. In conclusion, these experiments enabled the analysis of different types of regulation of pIgR gene expression in the mammary gland and suggest possible co-operation between circulating hormones and locally produced cytokines, leading to pIgR gene expression in the mammary gland.

Isolation and detection of human IgA using a streptococcal IgA-binding peptide

Bacterial proteins that bind to the Fc part of IgG have found widespread use in immunology. A similar protein suitable for the isolation and detection of human IgA has not been described. Here, we show that a 50-residue synthetic peptide, designated streptococcal IgA-binding peptide (Sap) and derived from a streptococcal M protein, can be used for single-step affinity purification of human IgA. High affinity binding of IgA required the presence in Sap of a C-terminal cysteine residue, not present in the intact M protein. Passage of human serum through a Sap column caused depletion of >99% of the IgA, and elution of the column allowed quantitative recovery of highly purified IgA, for which the proportions of the IgA1 and IgA2 subclasses were the same as in whole serum. Moreover, immobilized Sap could be used for single-step purification of secretory IgA of both subclasses from human saliva, with a recovery of approximately 45%. The Sap peptide could also be used to specifically detect IgA bound to Ag. Together, these data indicate that Sap is a versatile Fc-binding reagent that may open new possibilities for the characterization of human IgA.

Interaction sites on human IgG-Fc for FcgammaR: current models

Recombinant monoclonal antibodies have entered the clinic as effective in vivo therapeutic. A majority of the therapeutics antibodies employed are intact IgG molecules. IgG-antibody/antigen complexes can activate a wide range of biological responses that result in elimination and destruction of immune complexes. Principle ligands for the activation of clearance (inflammatory) mechanisms are the three types of cellular Fc receptors (FcgammaR) expressed on leucocytes. The effector functions activated by FcgammaR in vivo can be 'orchestrated', in part, through choice of the IgG subclass employed, however, there is potential to customize antibody therapeutics for optimal biological efficacy, in a particular clinical setting, i.e. with respect to the specific disease and the patient response. In order to engineer IgG antibodies and customize their abilities to activate FcgammaR it is necessary to elucidate the molecular specificity of their mutual interactions. This mini-review summarizes our current understanding of interactions of FcgammaRI, FcgammaRII and FcgammaRIII with human IgG antibodies. Particular emphasis is given to the influence of IgG-Fc glycosylation.

CR3 (CD11b/CD18) and CR4 (CD11c/CD18) are involved in complement-independent antibody-mediated phagocytosis of Cryptococcus neoformans

IgM and IgA to the Cryptococcus neoformans capsular glucuronoxylomannan (GXM) promote complement-independent phagocytosis by macrophages with efficiency comparable to that of IgG1. IgM- and IgA-mediated phagocytosis of C. neoformans was proportional to CR3 expression, inhibited by Abs to CR3 (CD11b/CD18) and CR4 (CD11c/CD18), and dramatically reduced with macrophages of CD18-deficient mice. IgM and IgA promoted ingestion of yeast cells by CHO cells expressing CR3 and CR4. In contrast, IgG1-mediated phagocytosis was only partially inhibited by Abs to CR3 and CR4. Phagocytosis by IgM and IgA but not IgG1 was inhibited by soluble GXM, which binds CD18. Involvement of CR in antibody-mediated complement-independent phagocytosis indicates a new link between innate and adaptive immune systems.

Humoral immune responses to microbial infections in the genital tract

Human reproductive tracts represent components of the mucosal immune system with unique features. Although secretory IgA is present, IgG is more abundant, and typical mucosa-associated lymphoid tissue for generating common mucosal immune responses is absent. Antibody responses to genital infections or to locally applied vaccines are usually modest, but alternative strategies for eliciting genital tract antibodies are being developed.

Some immunological aspects of patients with rhinitis in Lebanon

BACKGROUND

Hitherto immunological determinates in Lebanese patients with rhinitis have not been investigated.

OBJECTIVE

To identify causative allergens in Lebanese patients with allergic rhinitis and determine possible correlation's among serum allergen specific antibody, polyclonal IgE, IL-4, IL-5 and peripheral eosinophil levels.

METHODS

One hundred and thirteen patients with a long lasting history of nasal obstruction, rhinorrhea, sneezing and nasal itching were investigated. Serum allergen specific antibodies using a panel of 10 potential allergens, IL-4 and IL-5 levels were determined by enzyme immunoassays. Polyclonal IgE levels were estimated by an immunochromatographic assay and eosinophil counts by a Coulter STKS counter.

RESULTS

Based on the presence of serum allergen-specific IgE antibodies, 74 patients were considered to have an allergic etiology. Polyclonal IgE levels were elevated in 41 of the 74 allergic rhinitis patients while the other 33 patients had normal serum levels. In the remaining 39 specific IgE antibody-negative patients, 32 had normal, and 7 had elevated, polyclonal IgE levels. IgE specific antibodies to more than one allergen were detected in 59 of 74 patients. The most common causative allergens were mite, Dermatophagoides pteronyssinus, Dpt (83.8%) and Dermatophagoides farinae, Df (78.4%). Analysis of the data indicated that elevated polyclonal IgE levels correlated with the concentration of serum specific IgE antibodies and the number of the detected causative allergens per patient. Fifty-nine of 74 allergic rhinitis patients had elevated IL-4 levels and 44 had elevated IL-5 levels. The number of allergic patients with both elevated IL-4 and IL-5 levels was 24. Finally, only 9 allergic rhinitis patients had peripheral eosinophilia.

CONCLUSION

Mite Dpt and Df were the most common causative agents of allergic rhinitis in the Lebanese group studied. A prerequisite for Specific Immunotherapy is the identification of the causative allergen. Determinations of polyclonal IgE level and peripheral eosinophil count alone, as an aid to diagnosis are insufficient and may be misleading. On the other hand, determination of all the parameters studied in conjunction appears to be of diagnostic value.

IgA autoreactivity: a feature common to inflammatory bowel and connective tissue diseases

The immunopathogenic mechanisms in inflammatory bowel disease (IBD) are not yet fully established. The aim of this study was to determine the profile and magnitude of IgA and IgG autoantibodies in IBD patients. The autoantigen profile defined by IgA and IgG antibodies from 24 IBD (14 Crohn's disease CD], 10 ulcerative colitis UC]), three coeliac, 12 connective tissue disease (CTD) patients and 10 healthy individuals was studied in human cellular extracts by Western blotting. The magnitude of the IgA and IgG1-4 subclass responses was measured by ELISA. IBD patients could not be distinguished from healthy individuals on the basis of IgG autoantibodies to Western blotted proteins. IgG subclass analysis indicated no clear bias towards Th1 or Th2 immune responses in IBD or CTD. In accordance with previous work, we found that IgA autoreactivity was strongest in coeliac disease patients. Unexpectedly, IBD as well as CTD patients exhibited strong IgA autoantibody reactivities to components of similar molecular weights (16-80 kD) in intestinal and non-intestinal epithelial cell lines. Our data indicate immunopathogenic similarities between IBD and CTD.

Human immature dendritic cells efficiently bind and take up secretory IgA without the induction of maturation

Immature dendritic cells (DC) reside in peripheral tissues, where they pick up and process incoming pathogens via scavenger receptors or FcR such as FcgammaR and FcepsilonR. At mucosal surfaces, IgA is the main Ig to protect the body from incoming pathogens. In addition, DC are present in high numbers at these sites. We detected expression of FcalphaR (CD89) on the CD14+ population of CD34+ progenitor-derived DC and on monocyte-derived DC (MoDC). However, CD89 expression was strongly decreased upon differentiation from monocyte to DC. We found only minimal binding of serum IgA to MoDC but strong binding of secretory IgA (SIgA). The SIgA binding to MoDC could not be blocked by anti-CD89 blocking Abs. DC efficiently internalized SIgA, but not serum IgA, and uptake of SIgA could be blocked by specific sugars or partially by Ab reactive with mannose receptor. Importantly, binding and uptake of SIgA was not accompanied by signs of DC maturation, such as increased expression of CD86 and CD83 or induction of cytokine secretion. These data indicate that SIgA can interact with DC not via CD89, but via carbohydrate-recognizing receptors like mannose receptor and suggest that uptake of SIgA-containing immune complexes by immature DC may be a mechanism to modulate mucosal immune responses.

FCRL, a novel member of the leukocyte Fc receptor family possesses unique structural features

A novel conserved member of the leukocyte Fc receptor (FcR) family was identified in human and mouse. The presumably secreted protein, designated FCRL (FcR-like) is comprised of four domains. The three N-terminal domains are related to the extracellular region of FcgammaRI, with the second (35-37% residue identity) and the third (46-52%) domains showing highest similarity. The C-terminal domain is a unique sequence enriched with proline residues. In humans, alternative transcripts for six FCRL isoforms were revealed. Spleen and tonsils were found to be the major sources of FCRL mRNA in human tissues. Western blotting of tonsil cell lysate using FCRL-specific antibodies recognized a 44-kDa protein produced as a monomer containing free sulfhydryl groups. The monomer, however, was able to form disulfide-linked homo-oligomer upon oxidation. In COS-7 cells transiently transfected with two human FCRL isoforms, both resided intracellularly. Immunohistochemical staining of tonsil sections demonstrated the FCRL expression in germinal centers, suggesting that the protein may be implicated in germinal center-specific stages of B cell development. The phylogenetic analysis of the FCRL relationships with the leukocyte FcR supports a view that the three-domain structure was primordial in the evolution of the family.

Progress in molecular and genetic studies of IgA nephropathy

Several new findings emerged recently from biochemical, genetic, and molecular studies of patients with IgA nephropathy. It appears that immunoglobulin A1-secreting cells of IgA nephropathy patients produce increased amounts of aberrantly glycosylated IgA1 in which the O-linked glycans in the hinge region are deficient in the content of galactose. The galactose-deficient IgA1 in the circulation is recognized by naturally occurring antibodies with anti-glycan specificity, and immune complexes are formed. These circulating immune complexes escape hepatic degradation and eventually are deposited in the kidney mesangium. Resident mesangial cells bind the IgA-containing immune complexes with the involvement of a novel IgA receptor and become activated. A familial form of IgA nephropathy has been linked to chromosome 6q22-23. Recent progress in molecular analyses of IgA nephropathy thus defines this disease as an autoimmune process with a novel IgA mesangial receptor and certain genetically determined traits.