Superantigens are exotoxins produced by Staphylococcus aureus and induce extensive T cell proliferation and proinflammatory cytokines, leading to toxic shock syndrome at high concentrations. However, the role of superantigens produced at relatively low concentrations during asymptomatic colonization or chronic infection has not been well established. In this dissertation, we demonstrated that stimulation of human PBMCs with staphylococcal enterotoxin C1 (SEC1) at the dose inducing a half maximal T cell proliferation (suboptimal stimulation) induced immunosuppressive CD4+CD25+FOXP3+ and CD8+CD25+FOXP3+ T cells. The suppression of these cells was mainly mediated by the galectin-1. We found that suboptimal stimulation with SEC1 induced differential activation of PI3K-mTOR-Akt pathway, leading to expression of FOXP3 isoforms preferably localized to the nucleus and induction of PTEN that contributes to maintain stability and suppressive activity of regulatory T cells. Taken together, these results demonstrate the important role of superantigen produced at low concentration during asymptomatic colonization that induce immunosuppressive CD4+ and CD8+ regulatory T cells to promote survival, propagation, and colonization for S. aureus in the host.

In der vorliegenden Arbeit wurde die Präsentationsfunktion der LEW-Ratten-MHC-Klasse-II-Moleküle RT1B und RT1D für verschiedene Super- und Peptidantigene sowie die Generierung gemischter MHC-Klasse-II-Isotypen in der LEW-Ratte untersucht. Sag sind Proteine bakterieller und viraler Herkunft und führen nach Bindung an MHC-Klasse-II-Moleküle durch Interaktion mit dem TZR-Vb-Teil zu einer von der TZR-Spezifität unabhängigen Aktivierung von T-Zellen, die bis zu 30 % der Gesamt-T-Zellpopulation eines Organismus erfassen kann. Die dadurch bedingte Mediatorenfreisetzung aus T- oder konsekutiv aktivierten Zellen ist einerseits für die Entwicklung bestimmter akuter Krankheitsbilder wie des toxischen Schocksyndroms, Gastroenteritiden u. a. verantwortlich, kann aber auch potentiell zu einer Aktivierung autoreaktiver T-Zellen und der Entstehung von Autoimmunkrankheiten beitragen. Zur Untersuchung der LEW-MHC-Klasse-II-Charakteristika wurden zunächst mittels retroviralen Gentransfers RT1B- und RT1D-Gene in L929-Zellen übertragen und die Oberflächenexpression durch die mAK Ox6 und 14-4-4S nachgewiesen. Anschließend erfolgte der Nachweis einer Sag-Präsentation durch Stimulation des LEW-Vb8.2-TZH 53/4 durch die bakteriellen Sag SEB, SEC1-3, MAS und YPM und von aus Lymphknoten isolierten LEW-T-Zellen durch SEC1, MAS und YPM, die beide mit der durch eine HLA-DR1-positive Zelllinie getragenen Aktivierung verglichen wurden. Beide Experimente ergaben für die Sag des primär humanpathogen Staph. aureus eine weitaus stärkere Reaktivität in Anwesenheit humaner gegenüber LEW-MHC-Klasse-II-Molekülen bei RT1B-dominierter Antwort innerhalb der präsentatorischen Rattenmoleküle. Für SEB ergaben sich zusätzlich Hinweise auf eine MHC-Klasse-II-unabhängige Aktivierung. Das von Yersinia pseudotuberculosis produzierte Sag YPM wurde ebenfalls wesentlich besser von humanen als LEW-MHC-Klasse-II-Molekülen präsentiert, zeigte allerdings nur geringe Unterschiede zwischen RT1B und RT1D. Für das aus Nagern isolierte Sag von Mykoplasma arthritidis MAS konnte eine präferentielle Bindung an RT1D mit HLA-DR1-ähnlicher Stimulationskapazität nachgewiesen werden. Darüber hinaus wurden die generierten Zelllinien auf Präsentation der definierten Antigene L.casein und gpMBP gegenüber reaktiven TZH getestet. Dabei konnte die RT1D-restringierte Antwort von Klon19 auf L.casein und die RT1B-restringierte Antwort von 53/4 auf gpMBP bestätigt werden. Ebenfalls wurden die erstellten Transfektanten mit einem viralen Sag der Maus, dem vSag7-Gen des mtv7, transfiziert und auf Stimulation des TZH RG17 und von LEW-Lymphozyten getestet. Dabei zeigte sich eine geringe Reaktivität gegenüber den erstellten Transfektanten, die RT1B-dominiert war. Gleichzeitig ergaben sich in der Auswertung Hinweise für einen vSag7-Transfer von MHC-Klasse-II-negativen Produzenten auf MHC-Klasse-II-positive Rattenzellen, die durch weitere Experimente inklusive eines In-vivo-Tests bestätigt werden konnten. In der Generierung gemischter Isotypen aus MHC-Klasse-II-Einzelkettengenen der LEW-Ratte konnte gezeigt werde, dass die Übertragung der RT1DaBb-Genkombination mit Hilfe eines retroviralen Gentransfers auf P80- und L929-Zellen nicht zu einer sicher detektierbaren Oberflächenexpression führte, auch nicht bei Koübertragung der invarianten Kette der Maus. Durch einen Western Blot unter reduzierenden Bedingungen konnte eine bezüglich Molekulargewicht und Quantität zu einem regulären RT1B-Molekül differente RT1Bb-Einzelkette in der Kombination RT1DaBb nachgewiesen werden. / In the work at hand the presenting function of LEW rat MHC class II molecules RT1B and RT1D for various superantigens and antigens as well as the generation of mixed MHC class II isotypes in the LEW rat have been investigated. Superantigens are proteins of bacterial and viral origin, which lead to a TCR-specificity-independent activation of up to 30 % of the individual's T-cell population by interacting with the Vb part of the T-cell receptor after having bound to an MHC class II molecule. The release of mediators by T- and consecutively activated cells causes on the one hand development of acute diseases like toxic shock syndrome, gastroenteritis and other, but can also potentially activate autoreactive T-cells and lead to autoimmune diseases. In order to examine characteristics of LEW MHC class II molecules, first RT1B and RT1D chain genes were transferred into L929 cells via a retroviral transfection system and surface expression was demonstrated by using the monoclonal antibodies Ox6 and 14-4-4S. Successively, superantigen presentation was verified by stimulation of the LEW Vb8.2+ T-cell hybridoma 53/4 by bacterial superantigens SEB, SEC1-3, MAS and YPM and of LEW T-cells isolated from lymph nodes by SEC1, MAS and YPM. Both results were compared to activation in context of an HLA-DR1+ cell line. Experiments showed a much higher reactivity for the superantigens of human pathogen staph. aureus in presence of human versus LEW MHC class II molecules and an RT1B dominated answer amongst LEW presentatory molecules. Additionally, clues for MHC class II independent activation were found in case of SEB. The superantigen of yersinia pseudotuberculosis YPM was also much better presented by human than LEW MHC class II molecules while showing little differences between RT1B and RT1D. MAS bound preferentially to RT1D and equal stimulative capacity compared to HLA-DR1 could be detected. Accessorily, generated cell lines were analysed for presentation of peptide antigens L.casein and gpMBP towards reactive T-cell hybridomas, in which RT1D-restricted answer of Klon19 to L.casein and RT1B-restricted answer of 53/4 to gpMBP could be confirmed. Also generated cell lines were transfected with a viral mouse superantigen, the vsag7 gene of mtv7, and tested for stimulation of the RG17 T-cell hybridoma and LEW lymphocytes. Low reactivity towards transfected cell lines was detected, which was dominated by RT1B. Additionally, evidence for a transfer of vsag7 from MHC class II- producers to MHC class II+ rat cells could be found, which was enhanced by additional experiments including in vivo testing. Attempting to create mixed isotypes consisting of LEW rat MHC class II chains, it was demonstrated, that transferring the gene combination RT1DaBb via retroviral gene transfer into P80 and L929 cell lines resulted in no certain surface expression, also not under cotransfection of these cells with mouse invariant chain. Using western blot method under reducing conditions, a RT1Bb single chain different to the one of the regular RT1B molecule concerning molecular weight and quantitiy could be detected in the combination RT1DaBb.

Staphylococcus aureus causes significant illnesses throughout the world, including toxic shock syndrome (TSS), pneumonia, and infective endocarditis. Major contributors to S. aureus illnesses are secreted virulence factors it produces, including superantigens and cytolysins. Rabbit cardiac physiology is considered similar to humans, and rabbits exhibit susceptibility to S. aureus superantigens and cytolysins. As such, rabbits are an excellent model for studying pneumonia, infective endocarditis, and sepsis, We examined the ability of USA200, USA300 and USA400 strains to cause vegetations and lethal sepsis in rabbits. USA200, TSST-1+ strains that produce only low amounts of Α-toxin, exhibited modest LD50 in sepsis (1x108-5x108) colony-forming units (CFUs), and 3/4 caused significant IE. USA200 strain MNPE, which produces high levels of Α-toxin, was both highly lethal (LD50 5x106 CFUs) and effective in causing IE. In contrast, USA300 strains were highly effective in causing lethal sepsis (LD50s 1 x 106 and 5 x 107 CFUs) but were minimally capable of causing IE. USA400 strains were both highly lethal (LD50s of 1 x 107 and 5 x 107 CFUs) and highly effective causes of IE. Additional studies investigated the role of phenol soluble modulins in infection. We showed that PSMs are important for the ability of S. aureus to cause sepsis but not infective endocarditis. Additionally, immunization against PSMs did not protect rabbits from lethal infection. Our studies show that clonal groups of S. aureus differ in abilities to cause infective endocarditis and lethal sepsis and suggest that secreted virulence factors, including superantigens and cytolysins, account for some of these differences. This thesis also investigates the use of superantigens and cytolysins as staphylococcal vaccine candidates. We generated three TSST-1 mutants; G31S/S32P, H135A, and Q136A. All rabbits administered these TSST-1 toxoids generated strong antibody responses (titers>10,000) that neutralized native TSST-1 in TSS models, both in vitro and in vivo. These TSST-1 mutants lacked detectable residual toxicity. Additionally, the TSST-1 mutants exhibited intrinsic adjuvant activity, increasing antibody responses to a second staphylococcal antigen (Β-toxin). This effect may be due to TSST-1 mutants binding to the immune co-stimulatory molecule CD40. The superantigens TSST-1 and SEC and the cytolysin Α-toxin are known to contribute to staphylococcal pneumonia. Immunization of rabbits against these secreted toxins provided complete protection from highly lethal challenge with a USA200 S. aureus strain producing all three exotoxins; USA200 strains are common causes of staphylococcal infections. The same three exotoxins plus the cytolysins Β-toxin and Γ-toxin contribute to infective endocarditis and sepsis caused by USA200 strains. Immunization against these five exotoxins protected rabbits from infective endocarditis and lethal sepsis. Additionally, a heptavalent vaccine composed of the pentavalent units plus SEB and SE-l X protected rabbits from lethal pneumonia caused by USA100 strain 209. Passive immunization using pooled sera protects previously non-immunized rabbits from lethal pneumonia due to MNPE. These data suggest that immunization against toxoid proteins of S. aureus exotoxins protects from serious illnesses, and concurrently superantigen toxoid mutants provide endogenous adjuvant activity.

Kawasaki Disease (KD) is a childhood disease leading to coronary arteritis. Elevated numbers of CD40L+ platelets in circulation is correlated with risk of heart damage. CD40L is a tumor necrosis family member that binds to CD40 and αIIbβ3, receptors which are also expressed on platelets. A single injection of Lactobacillus casei Cell Wall Extract (LCWE) induces a disease similar to KD in mice, where LCWE superantigen (SAg) reactive T-cells persist in the coronary artery. This phenotype is inconsistent with the fate of SAg-stimulated cells and is likely mediated by co-stimulation. This work shows that stimulation with a SAg induces platelet activation and CD40L expression in vitro. Furthermore, enhanced survival of SAg-reactive T-cells is demonstrated following antibody-mediated CD40L cross-linking. This effect is mediated via inhibition of the extrinsic apoptosis pathway. In addition, CD40 cross-linking is also reported to enhance SAg-reactive T-cell survival by enhancing CD86 expression on APCs and CD28 co-stimulation.

Kawasaki Disease (KD) is a childhood disease leading to coronary arteritis. Elevated numbers of CD40L+ platelets in circulation is correlated with risk of heart damage. CD40L is a tumor necrosis family member that binds to CD40 and αIIbβ3, receptors which are also expressed on platelets. A single injection of Lactobacillus casei Cell Wall Extract (LCWE) induces a disease similar to KD in mice, where LCWE superantigen (SAg) reactive T-cells persist in the coronary artery. This phenotype is inconsistent with the fate of SAg-stimulated cells and is likely mediated by co-stimulation. This work shows that stimulation with a SAg induces platelet activation and CD40L expression in vitro. Furthermore, enhanced survival of SAg-reactive T-cells is demonstrated following antibody-mediated CD40L cross-linking. This effect is mediated via inhibition of the extrinsic apoptosis pathway. In addition, CD40 cross-linking is also reported to enhance SAg-reactive T-cell survival by enhancing CD86 expression on APCs and CD28 co-stimulation.

Asthma Bronchiale (AB) ist eine chronisch- obstruktive, teilweise reversible Entzündung der Atemwege, deren klinisches Korellat die bronchiale Hyperreagibilität (BHR) ist. Es lassen sich aufgrund ethiologischer Faktoren extrinsiches und intrinsisches AB unterscheiden, wobei ersteres auf einer allergischen Sensibilisierung und letzteres auf irritativen oder infektbedingten entzündlichen Prozessen beruht. In der vorliegenden Arbeit wurde der Einfluß von bakteriellem Superantigen auf die Entzündungsreaktion und die bronchiale Hyperreagibilität untersucht. Stapylococcal enterotoxin B (SEB) wurde hierbei als Modellsubstanz in einem Mausmodell eingesetzt, da SEB produzierende Staphylokokken im Nasenrachenraum von Asthmatikern nachgewiesen werden konnten. Nasale Applikation von SEB induzierte in C57BL/6 Mäusen eine Entzündungsreaktion mit Influx von Lymphozyen und eosinophilen Granulozyten sowie gesteigerte Produktion von IL-4, IL-5 und TNF-alpha in der Lunge, welches in der Histologie und Bronchiallavage nachgewiesen wurde. Desweiteren führt SEB allergenunabhängig zur Ausbildung von BHR. SEB Applikation in einem Mausmodell der allergischen Sensibilisierung (gegen Ovalbumin in C57BL/6 Mäusen) verstärkt die allergische Entzündung in der Lunge und die BHR. CD23 (Low-Affinity IgE Rezeptor) Knock out Tiere zeigen nach allergischer Sensibilisierung und SEB Behandlung keinen Anstieg der TNF-alpha Produktion und keine Hyperreagibilität. Aus diesen Ergebnisse läßt sich schlußfolgern: I. Bakterielles Superantigen induziert das Vollbild des intrinsischen AB im Tiermodell. II. Bakterielles Superantigen kann das extrinsische, allergische AB verstärken. III. Der CD23 Rezeptor ist essentiell für die TNF-alpha Produktion und die Induktion von BHR. Diese Resultate sollten in klinischen Studien am Patienten überprüft werden, da aufgrund der hier vorliegenden Daten zu erwarten ist, daß Antibiotikatherapie, und damit Elimination superantigenproduzierender Bakterien im Nasenrachenraum, die klinische Symptomatik des AB reduzieren kann. / Asthma bronchiale (AB) is an obstructive, partially reversible chronic inflammatatory disease of the small airways, which clinical correlate is represented by airway hyperreactivity. Based on etiological factors, AB can be divided in extrinsic and intrinsic AB, where the first depends on an allergic sensitization and the latter on airway irritation by environmental factors or airway inflammation due to viral or bacterial infection. In this thesis, the role of bacterial superantigens in airway inflammation and -hyperreactivity is analyzed. Staphylococcal enterotoxin B (SEB) was used as a prototypic substance, since SEB producing Staphylo-coccal aureus can be found in the nose and pharynx of asthmatic patients. Nasal application of SEB in C57BL/6 mice resulted in airway inflammation characterized by an influx of lymphocytes and eosinophil granulocytes and increased production of IL-4, IL-5, and TNF-alpha, which was analyzed by histology and bronchiolalveolar lavage. Furthermore, SEB induced independent of aller-gens airway hyperreactivity. SEB application in a mouse-model of allergic sensitization (to ovalbumin in C57BL/6 mice) boosts the allergen-induced allergic inflammation and airway hyperreactivity. CD23 (low-affinity IgE receptor) knock out mice showed no increased TNF-alpha production and no air-way hyperreactivity after allergic sensitization and SEB treatment. These results demonstrate: I. Bacterial superantigen can induce intrinsic AB in a mouse model. II. Bacte-rial superantigen can significantly boost the allergic, extrinsic AB. III. The CD23 receptor is essential for TNF-alpha production and for the induction of airway hyperreactivity. Based on these findings, clinical surveys should be performed, since one could expect, that eradication of nasal bacterial carriage and therefore local superantigen sezernation should improve the AB- symptoms in affected patients.

Therapeutische Erfolge von IVIG sind gut dokumentiert, aber die zu Grunde liegenden molekularen Mechanismen sind noch nicht vollständig erforscht. Molekulare Analysen unseres Labors über die Interaktion von IVIG mit Fabs von Patienten, die an einer autoimmunen Thrombozytopenie (ITP) leiden zeigten, dass die am häufigsten selektierten Fab von den V3-23 und V3-30 VH-Keimbahngenen abstammten. Eine weitere Studie mit IgG und IgM Phagen-Display Bibliotheken von einem gesunden Spender zeigten ebenfalls eine bevorzugte Reaktivierung von IVIG mit Fabs vom Ursprung der V3-23 und V3-30 Gene. Es konnte gefolgert werden, dass diese Interaktion von IVIG mit Fabs von diesen zwei VH-Genen weder alleine auf den Gesundheitsstatus des Spenders zurückzuführen war, noch auf eine zuvor erfolgte Behandlung mit IVIG. Diese Dissertation wurde unter Verwendung der Phagen-Display Technologie unternommen, um die molekulare Interaktion von IVIG mit Antikörpern zu erforschen, die von einem Patienten kloniert wurden, der an einem systemischen Lupus erythematodes und rheumatischem Fieber leidet. Die Resultate waren mit den früheren Studien zu vergleichen, insbesondere mit den Daten eines Patienten, der zu der ITP einen Lupus entwickelte. 23 Fabs, welche 7 unabhängige Klone repräsentierten, wurden isoliert. Im Gegensatz zu von Patienten mit ITP abstammenden Klonen reagierte keines von den in dieser Studie selektierten Fabs mit Thrombozyten. Die über IVIG gebundene Fab-Phagen stammten hierbei ausschließlich von den V3-23 und V3-30 VH-Genen ab. Darüber hinaus wurde beobachtet, dass von diesen Fabs verschiedene CDR3 Regionen einschließlich verschiedenen D- und JH-Gensegmenten benutzt wurden. Die Ergebnisse zeigten weiterhing, dass die Bindung von IVIG an die Fabs unabhängig von der Leichten Kette war. Ihrem Keimbahngen-Ursprung entsprechend hatten die Fabs Aminosäuren an Positionen in den FR1, FR3 und im 3'-Ende von CDR2, die dafür bekannt sind, dass sie für die Bindung des B-Zell-Superantigens Staphylococcus Protein A (SpA) essentiell sind. Es wurde gezeigt, dass sich zwar einige von den Fabs stark an SpA banden, aber keine Korrelation in der Intensität zur Bindung mit IVIG vorlag. Einige Fabs zeigten eine schwache Bindung an HIV gp120, einem anderen B-Zell-Superantigen. Zusammenfassend lässt sich aus der vorliegenden Studie und den vorherigen Ergebnissen schließen, dass ein Anteil von IVIG wie ein B-Zellen Superantigen funktionieren könnte, das für die Bildung und Regulation des normalen B-Zellen Repertoires wichtig ist. Der Bindungsmechanismus scheint ähnlich, aber nicht identisch mit dem der anderen getesteten B-Zellen-Superantigene zu sein. / The beneficial therapeutic effects of IVIG are well documented, but the underlying molecular mechanisms are not fully understood. Recent investigations from our laboratory into the molecular analysis of Fabs bound by IVIG from patients suffering from autoimmune thrombocytopenia revealed that the most frequently selected Fabs originated from the V3-23 and V3-30 VH germline genes. A subsequent study with IgG and IgM phage display libraries from a healthy donor also demonstrated a preferential reactivity of IVIG to Fabs of V3-23 and V3-30 origin. That study revealed that the unique reactivity of IVIG to Fabs of these two VH gene loci was not restricted to the autoimmune nature of the donors, neither to previous treatment with IVIG. One of the thrombocytopenia patients developed lupus. This study was undertaken to study the molecular interaction of IVIG with antibodies selected from a patient suffering from systemic lupus erythematosus and rheumatic fever using phage display technology, and to compare the results with the previous studies. Twenty-three Fabs representing seven independent clones were isolated. In contrast to ITP-derived clones, none of the Fabs selected in this study reacted with platelets. The Fab phages bound by IVIG were sequenced in order to determine their VH gene usage and clonal relatedness. V3-23 and V3-30 VH genes were found to be exclusively utilized by the Fab phages bound by IVIG. Moreover, different CDR3 regions including different D and JH gene segments were observed to be used by these Fabs. The results further showed that the binding of IVIG to the Fabs was independent of the light chain since different light chains were observed to be associated with the VH3 immunoglobulins. Detailed sequence analysis of the Fabs revealed the presence of amino acid residues at positions within FR1, FR3, and the 3' end of CDR2 that are known to be contacted by the B cell superantigen Staphylococcus protein A (SpA). Some of the Fabs were shown to bind strongly to SpA, but there was no correlation with the binding-intensity to IVIG. Some bound very weakly to HIV gp120, another B cell superantigen. This study, together with previous results, suggests that a subset of IVIG may function as a B cell superantigen that may significantly shape the B cell repertoire. The binding mechanism appears to be similar but not identical to the other tested B cell superantigens.

Group A streptococcus (GAS) is a strictly human pathogen that causes infections ranging from asymptomatic carriage to the highly lethal streptococcal toxic shock syndrome (STSS). GAS are classified according to the sequence of the variable 5’ end of the emm-gene that encodes the surface associated M-protein. In the late 1980s, outbreaks of GAS infections with high rates of STSS were reported in several parts of the world, including Sweden. Superantigens (SAgs), a group of exotoxins, have been described as key mediators of STSS due to their capacity to polyclonally activate T-cells and induce a massive release of inflammatory cytokines. Previous reports have revealed that sera from STSS patients have lower capacity to neutralize this SAg-mediated immune stimulation and a higher prevalence of GAS isolates with specific emm-genotypes during disease outbreaks. The aims of this thesis were to analyse the protective antibody response mounted by the host against SAgs produced by the infecting GAS isolate and to characterise the isolates emm-genotypes and SAg gene profiles. The clinical material examined was collected from patients with STSS, sepsis, erysipelas, or tonsillitis in Sweden between 1986 and 2001. Both acute- and convalescence-phase sera were analyzed, along with the infecting GAS isolates. The 92 clinical GAS isolates examined were found to exhibit a high degree of genetic diversity in terms of the number and identity of their SAg genes. Isolates with a given emm-genotype could be divided into subgroups on the basis of their SAg gene profiles. Ten different SAg gene profiles were identified in the 45 emm1 isolates examined; one of these ten was highly persistent, being observed in 22 isolates collected over 14 years. Two of the 11 known SAg genes in GAS, smeZ-1 and speA, were more prevalent in the emm1 associated profiles than in the SAg gene profiles of isolates with other emm-genotypes. Patients infected by GAS with the emm1-genotype were less likely to produce acute-phase sera that could effectively neutralize the T-cell mitogenicity induced by the infecting isolate’s extracellular products (EP). Sepsis patients whose sera exhibited this lack of neutralizing ability were more prone to developing STSS. Most patients whose acute-phase sera did not effectively neutralize the EP from the infecting isolate lacked protective antibodies in their convalescent-phase sera despite having elevated ELISA titers. The results reported herein show that combining SAg gene profiling with emm-genotyping may be useful for tracking the spread of GAS clones in the community. It was also shown that a lack of neutralizing activity in convalescence-phase sera might be due to an inability of those patients to mount a protective immune response against SAgs produced by the infecting GAS isolate.

Introdução: O tratamento da Rinossinusite Crônica (RSC) tem sofrido poucos avanços nas últimas décadas. Uma das barreiras na aquisição de novas terapias é a falta de conhecimento pleno sobre sua fisiopatogenia. A carência de avanço decorre principalmente da complexa e provável multifatorialidade da RSC, associada à inexistência de um bom modelo animal que possa mimetizar os fenômenos biológicos que ocorrem em humanos. A maioria dos modelos animais de RSC descrita na literatura mimetiza uma infecção aguda ou promove bloqueio das vias de drenagem que, na maioria das vezes, não corresponde aos mecanismos encontrados nas RSC em humanos. Por outro lado, diversas evidências indicam que as bactérias exercem importante papel na fisiopatogenia da RSC, possivelmente pela presença de biofilmes ou indução de inflamação crônica promovida por endo e exotoxinas. Objetivo: Neste estudo avaliou-se a viabilidade de um modelo experimental de RSC em coelhos, utilizando-se a exposição crônica de toxinas bacterianas em animais previamente sensibilizados à ovalbumina (OVA), analisando seus efeitos histopatológicos sobre a mucosa nasossinusal. Material e Métodos: Após indução de sensibilização com injeção subcutânea de OVA 2,5% e 0,4% de hidróxido de alumínio por duas semanas, os coelhos foram submetidos à implantação de cateter de longa duração em seio maxilar direito. Após, foram submetidos à irrigação nasossinusal com OVA 2,5% três vezes por semana, por duas semanas, e em seguida, irrigação de soluções contendo diferentes toxinas bacterianas (enterotoxina estaflocócica B (SEB) 1 ?g/mL, lipopolissacáride (LPS) 100 ng/mL e ácido lipotecóico (LTA) 100 ng/mL) por quatro semanas. Os animais foram sacrificados 24 horas após a última irrigação e a mucosa do seio maxilar direito (teste) e esquerdo (controle interno) foi coletada para avaliação histopatológica. Resultados: A exposição nasossinusal ao SEB causou espessamento epitelial, infiltração celular, eosinofilia e neutrofilia tecidual, além de redução do epitélio ciliado. A exposição ao LPS causou espessamento epitelial e subepitelial, infiltração celular, eosinofilia epitelial e subepitelial e aumento da fibrose subepitelial. O LTA causou espessamento epitelial e subepitelial, infiltração celular e eosinofílica subepitelial e aumento da fibrose subepitelial. Conclusão: A exposição crônica de toxinas bacterianas na mucosa nasossinusal promoveu alterações histológicas, como espessamento da mucosa e infiltração celular, semelhantes às encontradas em pacientes com RSC. O presente estudo demonstrou que este é um modelo animal viável de RSC. Mais estudos serão necessários para elucidar se os mecanismos patogênicos deste modelo são semelhantes aos observados em humanos. / Background: The treatment of chronic rhinosinusitis (CRS) has had little evolvement in the last decades. One of the barriers to the development of new therapies is the lack of knowledge about CRS pathophysiology. The complexity and multifactoriality of this disease, together with the inexistence of a proper animal model of CRS, are probably the causes for the few advances in CRS therapy. Most of the animal models of CRS resemble acute infection or promote sinonasal obstructions, which are not a very common etiologies in CRS patients. However, there has been a lot of evidence that bacteria play an important role in the pathophysiology of CRS, probably due to the presence of biofilms, or the chronic inflammation induced by endo e exotoxins. Objective: This study aims to evaluate the viability of an experimental model of CRS in rabbits through the use of bacterial toxins in previously sensitized animals with ovalbumin, analyzing its histopathological effects onto the sinonasal mucosa. Materials and Methods: After inducing ovalbumin (OVA) sensitization by intradermic injection of OVA 2,5% and 0,4% aluminum hydroxide for 2 weeks, rabbits underwent maxillary sinus instillation of OVA 2,5% three times a week for 2 weeks followed by sinus lavage with either one bacterial toxin (Staphylococcus aureus enterotoxin B (SEB) 1 ?g/mL, lipopolysaccharide (LPS) 100 ng/mL, lipoteichoic acid (LTA), 100 ng/mL) for 4 weeks. Rabbits were euthanised 24 hours after the last sinus lavage and the mucosa of right maxillary sinus (tested side) and left side (control) were collected for histopathological evaluation. Results: The sinonasal exposure to SEB resulted in epithelial thickening, inflammatory cells infiltration (tissue eosinophilia and neutrophilia) and reduction of ciliated cells. The exposure to LPS resulted in epithelial and subepithelial thickening, inflammatory cells infiltration, epithelial and subepithelial eosinophilia and increased subepithelial fibrosis. The exposure to LTA resulted in epithelial and subepithelial thickening, subepithelial inflammatory cells infiltration and eosinophilia and increased subepithelial fibrosis. Conclusion: This study reported the effects of bacterial toxins on the the sinonasal mucosa of ovalbumin-sensitized rabbits, demonstrating similar changes that are observed in CRS patients. Our results show that this is a viable animal model of CRS. Further studies are need to elucidate whether the pathomechanisms in this model are similar to what are observed in humans.

MHCII molecules expose a weave of antigens, which send survival or activation signals to T lymphocytes. The ongoing process of peptide binding to the MHC class II groove implicates three accessory molecules: the invariant chain, DM and DO. The invariant chain folds and directs the MHCII molecules to the endosomal pathway. Then, DM exchanges the CLIP peptide, which is a remnant of the degraded invariant chain, for peptides of better affinity. Expressed in highly specialized antigen presenting cells, DO competes with MHCII molecules for DM binding and favors the presentation of receptor-internalized antigens. Altogether, these molecules exhibit potential immunomodulatory properties that can be exploited to increase the potency of peptide vaccines. DO requires DM for maturation and to exit the ER. Interestingly, it is possible to monitor this interaction through a conformation change on DOβ that is recognized by the Mags.DO5 monoclonal antibody. Using Mags.DO5, we showed that DM stabilizes the interactions between the DO α1 and β1 chains and that DM influences DO folding in the ER. Thus, the Mags.DO5+ conformation correlates with DO egress from the ER. To further evaluate this conformation change, directed evolution was applied to DO. Of the 41 unique mutants obtained, 25% were localized at the DM-DO binding interface and 12% are at the solvent-exposed β1 domain, which is thought to be the Mags.DO5 epitope. In addition, I used the library to test the ability of HLA-DO to inhibit HLA-DM and sorted for the amount of CLIP. Interestingly, most of the mutants showed a decrease inhibitory effect, supporting the notion that the intrinsic instability of DO is a required for its function. Finally, these results support the model in which DO competes against classical MHCII molecules by sequestering DM chaperone’s function. MHCII molecules are also characterized by their ability to present superantigens, a group of bacterial or viral toxins that coerces MHCII-TCR binding in a less promiscuous fashion than what is observed in a canonical setting. While the mechanism of how bacterial superantigens form trimeric complexes with TCR and MHCII is well understood, the mouse mammary tumor virus superantigens (vSAG) are poorly defined. In the absence of a crystal structure, I chose a functional approach to examine the relation between vSAG, MHCII and TCR with the goal of uncovering the overall trimolecular architecture. I showed that TCR concomitantly binds both the MHCII α chain and the vSAG and that TCR-MHCII docking is almost canonical when coerced by vSAGs. Because many peptides may be tolerated in the MHCII groove, the pressure exerted by vSAG seems to tweak conventional TCR-MHCII interactions. Furthermore, my results demonstrate that vSAG binding to MHCII molecules is conformation-dependent and abrogated by the CLIP amino-terminal residues extending outside the peptide-binding groove. In addition, they also suggest that vSAGs cross-link adjacent MHCIIs and activate T cells via a TGXY motif. / Les molécules du CMH présentent une panoplie d'antigènes qui, lorsque reconnus par un lymphocyte T spécifique, indique à ce dernier de survivre ou de s'activer. Le processus menant à la liaison d'un peptide à la poche du CMH de classe II, implique trois molécules accessoires, soit la chaine invariante, DM et DO. La chaine invariante replie et dirige les molécules du CMHII jusqu'à la voie endosomale. Ensuite, DM échange CLIP, peptide découlant de la dégradation de la chaine invariante, pour d'autres ayant une meilleure affinité. Exprimé seulement chez certaines cellules présentatrices, DO compétitionne avec les molécules du CMHII pour la liaison à DM et ainsi favorise la présentation d'antigènes internalisés par des récepteurs membranaires. Ensemble, ces protéines ont un potentiel immunomodulatoire pouvant être exploité afin d'augmenter l'efficacité de vaccin peptidique. DO requiert DM pour arriver à maturité et sortir du RE. Cette interaction, qui induit un changement de conformation dans la chaine β de DO, peut être sondée à l'aide de l'anticorps monoclonal Mags.DO5. En utilisant cet anticorps, nous avons montré que DM stabilise l'interaction entre les domaines α1 et β1 de DO et influence son repliement dans le RE. Donc, la conformation qui révèle l’épitope Mags.DO5 corrèle avec la migration de DO hors du RE. Afin d'étudier plus précisément ce changement de conformation, DO fut contraint à une ronde d’évolution dirigée. Des 41 mutants obtenus, 25% se retrouvent à l'interface DO- DM et 12% se retrouvent à la surface exposée au solvant du domain β1, région hypothétique de l'épitope Mags.DO5. De plus, la bibliothèque de mutants a été testée pour son habileté à inhiber l'activité de DM. La plupart des mutants montre une activité inhibitrice diminuée, ce qui supporte le model où DO compétionne les molécules du CMHII en séquestrant le rôle chaperon de DM. Les molécules du CMHII ont l'unique habileté de présenter les superantigènes, une famille de toxines virales et bactériennes qui force l'interaction CMHII-TCR de façon beaucoup moins spécifique qu'en contexte canonique. Alors que la façon dont les superantigènes bactériens s'assemblent avec le CMHII et le TCR soit bien comprise, la nature du complexe trimoléculaire découlant des superantigènes du virus de la tumeur mammaire de la souris (vSAG) reste mal définie. En l'absence d'une structure cristalline, une approche fonctionnelle a été choisie pour examiner la relation des vSAGs avec le CMHII et le TCR avec le but de dévoiler l'architecture de ce multi-complexe protéique. Je montre que le TCR lie parallèlement la chaine α du CMHII et vSAG, ce qui résulte en une interaction presque canonique. Puisque différents peptides peuvent être tolérés lors de cet ancrage, il semble que vSAG ajuste les interactions CMHII-TCR conventionnelles. En outre, mes résultats montrent que vSAG reconnait un épitope conformationnel et que cette liaison peut être abrogée par l'extension amino-terminale du peptide CLIP, laquelle s'étend en deçà de la niche. Finalement, mes résultats suggèrent que vSAG peut réticuler plusieurs CMHII adjacents et active les cellules T via son motif TGXY.