The Role of Secretory Immunoglobulin A in the Natural Sensing of Commensal Bacteria by Mouse Peyer's Patch Dendritic Cells.

The mammalian gastrointestinal (GI) tract harbors a diverse population of commensal species collectively known as the microbiota, which interact continuously with the host. From very early in life, secretory IgA (SIgA) is found in association with intestinal bacteria. It is considered that this helps to ensure self-limiting growth of the microbiota and hence participates in symbiosis. However, the importance of this association in contributing to the mechanisms ensuring natural host-microorganism communication is in need of further investigation. In the present work, we examined the possible role of SIgA in the transport of commensal bacteria across the GI epithelium. Using an intestinal loop mouse model and fluorescently labeled bacteria, we found that entry of commensal bacteria in Peyer's patches (PP) via the M cell pathway was mediated by their association with SIgA. Preassociation of bacteria with nonspecific SIgA increased their dynamics of entry and restored the reduced transport observed in germ-free mice known to have a marked reduction in intestinal SIgA production. Selective SIgA-mediated targeting of bacteria is restricted to the tolerogenic CD11c(+)CD11b(+)CD8(-) dendritic cell subset located in the subepithelial dome region of PPs, confirming that the host is not ignorant of its resident commensals. In conclusion, our work supports the concept that SIgA-mediated monitoring of commensal bacteria targeting dendritic cells in the subepithelial dome region of PPs represents a mechanism whereby the host mucosal immune system controls the continuous dialogue between the host and commensal bacteria.

Multiple facets of secretory immunoglobulin A at mucosal surfaces

Résumé : Le condylome acuminé anal (CAA), transmis par contact sexuel, résulte d'une infection par Human Papilloma Virus (HPV). Son traitement chirurgical est grevé d'un taux de récidive de 4-29%. Le but de cette étude était d'identifier une éventuelle corrélation entre type d'HPV présent dans les CAA excisés chirurgicalement et taux de récidive de la maladie, ? Cette étude rétrospective porte sur 140 patients opérés au Centre Hospitalier Universitaire Vaudois de CAA, entre 1990 et 2005. Le diagnostic lésionnel a été confirmé par un examen histomorphologique. Le(s) type(s) d'HPV présent(s) dans ces lésions a été déterminé par Polymerase Chain Reaction (PCR). Les patients ont donné leur accord à cette analyse et complété un questionnaire. Une éventuelle corrélation entre récidive de CAA, type d'HPV et status HIV a été recherchée. HPV 6 et 11 sont les virus les plus fréquemment découverts (51% et 28%, respectivement) chez les 140 patients (123H/17F). Trente-cinq (25%) d'entre eux ont présenté une récidive. HPV 11 était present chez 19 (41%) sujets. Ceci est statistiquement significatif (P<0.05), en comparaison aux autres HPVs. Il n'y a par contre pas de différence significative entre la fréquence de récidive des 33 (24%) patients HIV-positifs et le reste du collectif. HPV 11 est donc associé à un taux de récidive de CAA significativement élevé. Un suivi strict des patients atteints est nécessaire pour identifier une récidive et la traiter sans délai, notamment lorsque HPV 11 est present. Ces résultats innovateurs soulèvent la question de la nécessité de pratiquer une typisation virale systématique sur les lésions excisées. La justification d'une telle attitude demande toutefois encore d'être confirmée.

Deciphering the unusual HLA-A2/Melan-A/MART-1-specific TCR repertoire in humans.

The Melan-A/MART-1(26-35) antigenic peptide is one of the best studied human tumor-associated antigens. It is expressed in healthy melanocytes and malignant melanoma and is recognized by CD8(+) T cells in the context of the MHC class I molecule HLA-A*0201. While an unusually large repertoire of CD8(+) T cells specific for this antigen has been documented, the reasons for its generation have remained elusive. In this issue of the European Journal of Immunology, Pinto et al. [Eur. J. Immunol. 2014. 44: 2811-2821] uncover one important mechanism by comparing the thymic expression of the Melan-A gene to that in the melanocyte lineage. This study shows that medullary thymic epithelial cells (mTECs) dominantly express a truncated Melan-A transcript, the product of misinitiation of transcription. Consequently, the protein product in mTECs lacks the immunodominant epitope spanning residues 26-35, thus precluding central tolerance to this antigen. In contrast, melanocytes and melanoma tumor cells express almost exclusively the full-length Melan-A transcript, thus providing the target antigen for efficient recognition by HLA-A2-restricted CD8(+) T cells. The frequency of these alternative gene transcription modes may be more common than previously appreciated and may represent an important factor modulating the efficiency of central tolerance induction in the thymus.

Optimal 3-T MRI for depiction of the finger A2 pulley: comparison between T1-weighted, fat-saturated T2-weighted and gadolinium-enhanced fat-saturated T1-weighted sequences

OBJECTIVE: To compare three spin-echo sequences, transverse T1-weighted (T1WI), transverse fat-saturated (FS) T2-weighted (T2WI), and transverse gadolinium-enhanced (Gd) FS T1WI, for the visualisation of normal and abnormal finger A2 pulley with magnetic resonance (MR) imaging at 3 tesla (T). MATERIALS AND METHODS: Sixty-three fingers from 21 patients were consecutively investigated. Two musculoskeletal radiologists retrospectively compared all sequences to assess the visibility of normal and abnormal A2 pulleys and the presence of motion or ghost artefacts. RESULTS: Normal and abnormal A2 pulleys were visible in 94% (59/63) and 95% (60/63) on T1WI sequences, in 63% (40/63) and 60% (38/63) on FS T2WI sequences, and in 87% (55/63) and 73% (46/63) on Gd FS T1WI sequences when read by the first and second observer, respectively. Motion and ghost artefacts were higher on FS T2WI sequences. Seven among eight abnormal A2 pulleys were detected, and were best depicted with Gd FS T1WI sequences in 71% (5/7) and 86% (6/7) by the first and the second observer, respectively. CONCLUSION: In 3-T MRI, the comparison between transverse T1WI, FS T2WI, and Gd FS T1WI sequences shows that transverse T1WI allows excellent depiction of the A2 pulley, that FS T2WI suffers from a higher rate of motion and ghost artefacts, and transverse Gd FS T1WI is the best sequence for the depiction of abnormal A2 pulley.

Secretory IgA's complex roles in immunity and mucosal homeostasis in the gut.

Secretory IgA (SIgA) serves as the first line of defense in protecting the intestinal epithelium from enteric toxins and pathogenic microorganisms. Through a process known as immune exclusion, SIgA promotes the clearance of antigens and pathogenic microorganisms from the intestinal lumen by blocking their access to epithelial receptors, entrapping them in mucus, and facilitating their removal by peristaltic and mucociliary activities. In addition, SIgA functions in mucosal immunity and intestinal homeostasis through mechanisms that have only recently been revealed. In just the past several years, SIgA has been identified as having the capacity to directly quench bacterial virulence factors, influence composition of the intestinal microbiota by Fab-dependent and Fab-independent mechanisms, promote retro-transport of antigens across the intestinal epithelium to dendritic cell subsets in gut-associated lymphoid tissue, and, finally, to downregulate proinflammatory responses normally associated with the uptake of highly pathogenic bacteria and potentially allergenic antigens. This review summarizes the intrinsic biological activities now associated with SIgA and their relationships with immunity and intestinal homeostasis.

High frequencies of functionally impaired cytokeratin 18-specific CD8+ T cells in healthy HLA-A2+ donors.

Combining cell surface phenotyping with functional analysis, human CD8+ T cells have been divided into several subsets which are being studied extensively in diverse physiological situations, such as viral infection, cancer and ageing. In particular, so-called terminally differentiated effector cells possess a CD45RA+ CCR7- CD27- CD28- phenotype, contain perforin and, in different models, have been shown to exert direct ex vivo killing and to release interleukins upon both antigen-nonspecific and -specific stimulation. Using HLA class I multimers, we have identified a high frequency of peripheral CD8+ T cells that recognize a peptide derived from the self protein cytokeratin 18 presented by the HLA-A*0201 molecule. These cells can be detected in approximately 15% of the HLA-A2-positive healthy donors tested. A detailed analysis revealed that they must have divided extensively in vivo, have an effector cell phenotype and express various natural killer cell-associated receptors. Interestingly, however, they remained unresponsive to antigen-specific stimulation in vitro in terms of cytotoxicity and cytokine secretion. Thus, cytokeratin 18-specific cells constitute a frequently encountered, new CD8+ T lymphocyte subpopulation without classical effector status and with so far unknown function.

Secretory IgA-mediated neutralization of Shigella flexneri prevents intestinal tissue destruction by down-regulating inflammatory circuits.

Shigella, a Gram-negative invasive enteropathogenic bacterium responsible for bacillary dysentery, causes the rupture, invasion, and inflammatory destruction of the human colonic mucosa. We explored the mechanisms of protection mediated by Shigella LPS-specific secretory IgA (SIgA), the major mucosal Ab induced upon natural infection. Bacteria, SIgA, or SIgA-S. flexneri immune complexes were administered into rabbit ligated intestinal loops containing a Peyer's patch. After 8 h, localizations of bacteria, SIgA, and SIgA-S. flexneri immune complexes were examined by immunohistochemistry and confocal microscopy imaging. We found that anti-Shigella LPS SIgA, mainly via immune exclusion, prevented Shigella-induced inflammation responsible for the destruction of the intestinal barrier. Besides this luminal trapping, a small proportion of SIgA-S. flexneri immune complexes were shown to enter the rabbit Peyer's patch and were internalized by dendritic cells of the subepithelial dome region. Local inflammatory status was analyzed by quantitative RT-PCR using newly designed primers for rabbit pro- and anti-inflammatory mediator genes. In Peyer's patches exposed to immune complexes, limited up-regulation of the expression of proinflammatory genes, including TNF-alpha, IL-6, Cox-2, and IFN-gamma, was observed, consistent with preserved morphology. In contrast, in Peyer's patches exposed to Shigella alone, high expression of the same mediators was measured, indicating that neutralizing SIgA dampens the proinflammatory properties of Shigella. These results show that in the form of immune complexes, SIgA guarantees both immune exclusion and neutralization of translocated bacteria, thus preserving the intestinal barrier integrity by preventing bacterial-induced inflammation. These findings add to the multiple facets of the noninflammatory properties of SIgA.

Lacrimal secretory IgA in active posterior uveitis induced by Toxoplasma gondii

It is quite difficult to diagnose active toxoplasmosis in patients with ocular toxoplasmosis. Active posterior uveitis presumably due to Toxoplasma gondii infection (APUPT) is seldom produced during a prime-infection; hence most patients do not show high IgM antibodies. High levels of IgA have been described in active toxoplasmosis. The purpose of this study was to investigate possible association between APUPT and the specific anti-parasite sIgA in tears. The study was carried out as case-control. Tears of 25 clinically confirmed APUPT patients and 50 healthy control subjects were analyzed. All were IgG seropositive. Specific sIgA was determined by ELISA assay using T. gondii RH strain crude extract. Anti-T. gondii sIgA was found in 84% of the cases and in 22% of the control subjects. The intensity of the reaction was higher in APUPT cases (P = 0.007). There was strong association between APUPT patients and lacrimal sIgA (odds-ratio 18.61, P = 0.0001). ELISA test sensitivity was 84% and specificity 78% . Our data suggest that anti-T.gondii secretory IgA found in tears may become an important marker for active ocular toxoplasmosis.

Role of secretory IgA in infection and maintenance of homeostasis.

An important activity of mucosal surfaces is the production of antibodies (Abs) referred to as secretory immunoglobulin A (SIgA) that serve as a first line of defense to repel pathogenic microorganisms and provide a finely tuned balance to guarantee controlled survival of essential commensal bacteria. By excluding bacteria from the epithelial cell, SIgA participates in the cross-talk between the host and its intestinal content, ensuring appropriate homeostasis under normal conditions. Besides the classical view of immune exclusion function, SIgA Abs exhibit the striking feature to adhere to gastrointestinal M cells residing in the follicle-associated epithelium in organized structures called Peyer's patches. Selective binding of SIgA results in transport across the microfold (M) cells, a process that facilitates the association of the Ab with dendritic cells (DCs) located in the underlying subepithelial dome region of Peyer's patches. Limited entry of free SIgA and SIgA-coated bacteria via this pathway is crucial to the modulation of local immune responses in an environment that limits the onset of pro-inflammatory circuits. Such a mechanism would ensure homeostasis by allowing antigen recognition under neutralized conditions and by avoiding tissue dissemination, two features that endow SIgA with non-inflammatory properties in the mucosal environment.

Preliminary study of the presence of antibodies against excretory-secretory antigens from protoscoleces of Echinococcus granulosus in dogs with intestinal echinococcosis

The aim of the present study was to analyze the antibody response against excretory-secretory antigens (ES-Ag) from Echinococcus granulosus protoscoleces, using sera from dogs infected with E. granulosus and other helminths. ES-Ag were obtained from the first 50 h maintenance of protoscoleces in vitro. Immunochemical characterization was performed by immunoblotting with sera from dogs naturally infected with E. granulosus (n = 12), sera from dogs infected with helminths other than E. granulosus (n = 30), and helminth-free dog sera (n = 20). These findings were compared to those obtained from a somatic extract of protoscoleces (S-Ag). ES-Ag only showed four cross-reacting proteins of 65, 61, 54, and 45-46 kDa. Antigens with apparent masses of 89 and 50 kDa in ES-Ag and of 130 and 67 kDa in S-Ag were identified by sera of dogs infected with E. granulosus only, whereas a protein of 41-43 kDa was recognised by the majority of the sera from dogs with non-echinococcal infection. Employing ELISA to study the same sera, S-Ag revealed higher immunoreactivity than ES-Ag, but also showed higher cross-reactivity levels when sera from dogs with non-echinococcal infection were assayed in immunoblotting.

Novel soluble HLA-A2/MELAN-A complexes selectively stain a differentiation defective subpopulation of CD8+ T cells in patients with melanoma.

Multimeric MHC I-peptide complexes containing phycoerythrin-streptavidin are widely used to detect and investigate antigen-specific CD8+ (and CD4+) T cells. Because such reagents are heterogeneous, we compared their binding characteristics with those of monodisperse dimeric, tetrameric and octameric complexes containing linkers of variable length and flexibility on Melan-A-specific CD8+ T cell clones and peripheral blood mononuclear cells (PBMC) from HLA-A*0201(+) melanoma patients. Striking binding differences were observed for different defined A2/Melan-A(26-35) complexes on T cells depending on their differentiation stage. In particular, short dimeric but not octameric A2/Melan-A(26-35) complexes selectively and avidly stained incompletely differentiated effector-memory T cells clones and populations expressing CD27 and CD28 and low levels of cytolytic mediators (granzymes and perforin). This subpopulation was found in PBMC from all six melanoma patients analyzed and proliferated on peptide stimulation with only modest phenotypic changes. By contrast influenza matrix(58-66) -specific CD8+ PBMC from nine HLA-A*0201(+) healthy donors were efficiently stained by A2/Flu matrix(58-61) multimers, but not dimer and upon peptide stimulation proliferated and differentiated from memory into effector T cells. Thus PBMC from melanoma patients contain a differentiation defective sub-population of Melan-A-specific CD8+ T cells that can be selectively and efficiently stained by short dimeric A2/Melan- A(26-35) complexes, which makes them directly accessible for longitudinal monitoring and further investigation.

Implantació en SAP R/3 de la fusió per absorció impròpia en les societats 'A1' i 'A2'

En el context actual sovint tenen lloc operacions juridicofinanceres de gran envergadura entre empreses del mateix grup, especialment en determinats sectors de l'economia. Aquestes operacions comporten la integració dels sistemes d'informació de les societats que s'hi troben afectades. El cas que ens ocupa fa referència a una operació de fusió per absorció de dues societats que pertanyen al mateix grup. Totes dues gestionen la seva activitat fent servir el sistema d'informació SAP/R3.

Secretory IgA Induces Tolerogenic Dendritic Cells through SIGNR1 Dampening Autoimmunity in Mice.

IgA plays ambivalent roles in the immune system. The balance between inhibitory and activating responses relies on the multimerization status of IgA and interaction with their cognate receptors. In mucosal sites, secretory IgA (SIgA) protects the host through immune-exclusion mechanisms, but its function in the bloodstream remains unknown. Using bone marrow-derived dendritic cells, we found that both human and mouse SIgA induce tolerogenic dendritic cells (DCs) following binding to specific ICAM-3 grabbing nonintegrin receptor 1. This interaction was dependent on Ca(2+) and mannose residues. SIgA-primed DCs (SIgA-DCs) are resistant to TLR-dependent maturation. Although SIgA-DCs fail to induce efficient proliferation and Th1 differentiation of naive responder T cells, they generate the expansion of regulatory T cells through IL-10 production. SIgA-DCs are highly potent in inhibiting autoimmune responses in mouse models of type 1 diabetes and multiple sclerosis. This discovery may offer new insights about mucosal-derived DC immunoregulation through SIgA opening new therapeutic approaches to autoimmune diseases.

Equine secretory IgA and secretory component.

A complete secretory immunologie system has been identified in the equine species. It is characterised by the presence of a secretory component either bound to secretory IgA (SigA) or remaining in the free form (FSC). The mean molecular weights of SigA, serum lgA and FSC have been estimated. The homology of the equine and human IgA classes have been demonstrated by cross-reaction with anti-human lgA antisera. A quantit ative study of equine immunoglobulins in various fluids have shown that SlgA is predominant in saliva, mature milk, nasal and lacrimal secretions, but not in colostrum. In vitro binding of human and bovine FSC is found to occur mostly with the polymerie form of equine serum lgA.

Reconstituted human polyclonal plasma-derived secretory-like IgM and IgA maintain the barrier function of epithelial cells infected with an enteropathogen.

Intravenous administration of polyclonal and monoclonal antibodies has proven to be a clinically valid approach in the treatment, or at least relief, of many acute and chronic pathologies, such as infection, immunodeficiency, and a broad range of autoimmune conditions. Plasma-derived IgG or recombinant IgG are most frequently used for intravenous or subcutaneous administration, whereas a few IgM-based products are available as well. We have established recently that secretory-like IgA and IgM can be produced upon association of plasma-derived polymeric IgA and IgM with a recombinant secretory component. As a next step toward potential future mucosal administration, we sought to unravel the mechanisms by which these secretory Igs protect epithelial cells located at the interface between the environment and the inside of the body. By using polarized epithelial Caco-2 cell monolayers and Shigella flexneri as a model enteropathogen, we found that polyspecific plasma-derived SIgA and SIgM fulfill many protective functions, including dose-dependent recognition of the antigen via formation of aggregated immune complexes, reduction of bacterial infectivity, maintenance of epithelial cell integrity, and inhibition of proinflammatory cytokine/chemokine production by epithelial cells. In this in vitro model devoid of other cellular or molecular interfering partners, IgM and secretory IgM showed stronger bacterial neutralization than secretory IgA. Together, these data suggest that mucosally delivered antibody preparations may be most effective when combining both secretory-like IgA and IgM, which, together, play a crucial role in preserving several levels of epithelial cell integrity.