La dermatite atopique (DA) est une maladie inflammatoire chronique de la peau caractérisée par un épaississement épidermique et un infiltrat dermique de lymphocytes T mémoire activés, macrophages, mastocytes et éosinophiles avec des phases aiguë et chronique associées respectivement à des profils cytokiniques de type Th2 et Th1. Chez la majorité des patients atteints de DA, une augmentation de production d'IgE et IgG totales et spécifiques d'allergènes et d'antigènes microbiens est observée. Les récepteurs de forte et de faible affinité pour l'IgE, FcepsilonRI et FcepsilonRII/CD23 et le récepteur de faible affinité pour l'IgG, FcgammaRIII/CD16, jouent un rôle essentiel dans les maladies allergiques. Dans la peau humaine, ces FcR sont exprimés par des cellules présentatrices d'antigène et des cellules effectrices résidentes ou recrutées au derme durant l'inflammation. Au cours de ce travail, nous avons étudié le rôle de ces FcR dans un modèle murin de DA, qui reproduit la pathologie humaine, en comparant des animaux déficients pour ces FcR aux animaux correspondants de type sauvage (WT). Les symptômes de la DA sont complètement absents chez les souris déficientes en FcRgamma et partiellement inhibés dans les souris déficientes en FcepsilonRI ou CD16. Cette inhibition est corrélée avec une augmentation de l'expression cutanée de l'IL-10 et Foxp3. Alors que FcepsilonRI régule les réponses Th1 et Th2, le recrutement des mastocytes vers les ganglions drainants et la production d'IgE, CD16 régule uniquement la réponse Th2, la prolifération lymphocytaire et la production d'IgG1. FcepsilonRI et CD16 régulent spécifiquement la production de leurs ligands en contrôlant respectivement l'expression ganglionnaire d'IL-4 et d'IL-21. D'une façon importante, l'absence de CD23 aboutit à une inhibition drastique de la pathologie cutanée et, comme celle de FcepsilonRI, à une diminution des réponses cutanées Th1 et Th2 ainsi que de la production sérique de l'IgE mais pas celle de l'IgG1. Par ailleurs, nous avons étudié le rôle régulateur du récepteur nucléaire PPAR-alpha dans ce modèle de DA. En effet, il est exprimé par plusieurs types cellulaires au sein du système immunitaire et possède des propriétés anti-inflammatoires dans d'autres pathologies. Suite à la sensibilisation cutanée, nous avons remarqué que les souris déficientes en PPAR-alpha montrent une exacerbation des réponses cutanée et pulmonaire, et de la production de l'IgE et IgG2a par rapport aux souris WT. Ce phénomène est corrélé avec une exacerbation des réponses moléculaires cutanées Th2 et surtout Th1 ainsi qu'à une augmentation d'expression de NF-kappaB. D'une façon intéressante, l'expression de PPAR-alpha a été diminuée dans les lésions cutanées de patients atteints de DA suggérant donc que cette diminution d'expression puisse contribuer à la pathologie. Enfin, l'application d'un agoniste spécifique de PPAR-alpha diminue significativement la pathologie expérimentale. Nos travaux ont donc précisé la contribution des IgE/FcepsilonR et IgG/FcgammaR à la physiopathologie de la DA. Ces derniers, comme PPAR-alpha, constituent des cibles thérapeutiques potentielles pour cette affection.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

In the age of highly active antiretroviral therapy (HAART), patients infected with Human Immunodeficiency Virus Type 1 (HIV-1) are now living significantly healthier and longer lives. However, HIV prevention and cure still remain significant challenges. Globally, women face specific barriers to using and accessing both female and male condoms, the primary method recommended by the World Health Organization (WHO) to prevent sexual transmission of HIV-1. Although HAART treatment as prevention (TasP) of HIV has shown promising preliminary results, poor economic feasibility of the method in resource poor settings has yet to be resolved. Since women carry over 50% of the disease burden, there is a significant need for the development of a female-controlled method of prevention. One such approach is the reformulation of topical vaginal microbicides. Our laboratory is developing HIV-targeted microbicide formulations that utilize highly specific, broadly neutralizing anti-HIV antibodies (bNAbs). The purpose of my research project was to characterize Fc receptor expression in epithelial cell models of the lower female genital tract with a particular focus on the neonatal Fc receptor (FcRn). Fc receptors are a large family of proteins that bind to the Fc region of immunoglobulins (Igs) and function in Ig transport and effector functions. These receptors could function in enhancing the delivery of bNAbs in microbicide formulations or potentially serve as a mechanism of delivering HIV to target cells in tissues via transport of HIV-antibody complexes. Thus, this thesis assesses Fc receptor expression in human vaginal and endocervical organotypic cultures via microarray, quantitative RT-PCR, immunohistology and preliminary functional assays. Microarray results revealed significant expression of Fc receptor family genes in the epithelial cells of the lower female reproductive tract (FRT). The polymeric immunoglobulin receptor (pIgR), a well-characterized receptor that transports secretory IgA across mucosal epithelia, was abundantly expressed and hormonally regulated in epithelial cells of the vagina and endocervix. FcRn, a receptor originally characterized in the placenta and gut where it confers passive immunity from mother-to-child via bidirectional IgG transcytosis, was expressed in both tissue models. Moreover, several members of the novel FC receptor-like (FCRL) family were detected by microarray in both models. Immunohistological staining revealed pIgR protein in the endocervical mucosal epithelium, confirming current literature describing its expression in the FRT and role in local production of cervicovaginal secretions. FcRn protein expression was detected in the basal cell layer of the stratified squamous vaginal epithelium and in the columnar cells of the endocervix. Preliminary functional assays did not observe FcRn-specific transcytosis of human IgG across vaginal or endocervical epithelia by ELISA or immunohistology. VRCO1, a monoclonal antibody in development for application in microbicide formulation, crossed the epithelium, but was likely not transcytosed via FcRn because immunohistology revealed the presence of antibody between epithelial cells rather than the expected intracellular localization of IgG utilized in the FcRn mechanism. These preliminary findings indicate that Fc receptors, pIgR and Fc receptor-like proteins may play an important role in antibody-mediated immune responses in the FRT. Further research is require to determine whether FcRn functions in HIV-antibody complex-mediated HIV transmission or monoclonal antibody transcytosis.

Terminally differentiated B cells are responsible for antibody generation, a key component of adaptive immunity. IgG antibodies play an important role in defence against infection but can be pathogenic in some autoimmune diseases and in solid organ transplantation. In addition to antibody generation, there is increasing interest in the antibody-independent functions of B cells, including their ability to regulate immune responses via the production of IL10. In this thesis I firstly explored the therapeutic potential of belimumab, an anti-BLyS antibody, in an experimental medicine study in kidney transplant recipients. The rationale for this study was based on published studies showing that B cells activate alloreactive T cells and secrete human leukocyte antigen (HLA) and non-HLA antibodies that negatively affect graft function and survival, but may also play a protective role by regulating alloimmune responses promoting transplant tolerance. B-Lymphocyte Stimulator (BLyS) is a cytokine that promotes B cell activation and survival. We performed the first randomized controlled trial using belimumab as early maintenance immunosuppression in kidney transplantation. In belimumab-treated subjects, we demonstrate a reduction in naïve and activated memory B cells, plasmablasts, IgG transcripts in peripheral blood and new antibody formation as well as evidence of reduced CD4 T cell activation and of a skewing of the residual B cell compartment towards an IL10-producing regulatory phenotype. This experimental medicine study highlights the potential of belimumab as a novel therapeutic agent in transplantation. In the second part of my project I performed a preclinical study investigating the potential efficacy of bromodomain inhibitors in reducing antibody-mediated immune cell activation. Immune complexed antigen can activate mononuclear phagocytes (MNP), comprising macrophages and dendritic cells (DCs), via ligation of Fc gamma receptors (FcγR), that bind the Fc region of IgG. FcγR-dependent MNP activation results in profound changes in gene expression that mediate antibody effector function in these cells. The resulting inflammatory response can be pathological in the setting of autoimmune diseases, such as systemic lupus erythematosus and in antibody-mediated rejection in transplantation. BET proteins are a family of histone modification 'readers' that bind acetylated lysine residues within histones and function as a scaffold for the assembly of complexes that regulate gene transcription. Bromodomain inhibitors (I-BET) selectively inhibit the transcription of a subset of inflammatory genes in macrophages following toll-like receptor stimulation. Since MNPs make a key contribution to antibody-mediated pathology, we sought to determine the extent to which I-BET inhibits macrophage and DC activation by IgG. We show that I-BET delays phagolysosome maturation associated with build-up of immune complex (IC) whilst selectively inhibiting IC induced cytokine production. I-BET changed MNP morphology, resulting in a less adherent phenotype, prompting an assessment of its impact on DC migration. In vitro, in a three-dimensional collagen matrix, IgG-IC induced augmentation of DC chemotaxis to chemokine (C-C motif) ligand 19 (CCL19) was abrogated by the addition of I-BET. In vivo, two photon imaging showed that systemic I-BET treatment reduced IC-induced dermal DC mobilisation. Tissue DCs and transferred DC also had reduced migration to draining lymph nodes following I-BET treatment. These observations provide mechanistic insight into the potential therapeutic benefit of I-BET in the setting of antibody-associated inflammation.

The chicken BG system is a highly polymorphic and polygenic multigene family encoding type I transmembrane proteins, with butryophilins as homologues in mammals, some of which are crucial in T cell regulation. There are three genomic locations where BG genes are found: one singleton BG gene (BG0) on chromosome 2, another singleton gene (BG1) in BF-BL region (the so-called minimal essential chicken MHC) on chromosome 16, and many BG genes arranged tandemly in the BG region just outside the MHC. BG genes in BG region have copy number variation between different chicken haplotypes, so it has been unclear which BG genes are alleles, as very little sequence information has been available for haplotypes other than B12, the best characterized one. Also, the functions of chicken BG genes have been a mystery for half a century, although there is evidence for cytoskeletal regulation and for viral disease resistance. Therefore, the aim of the research was to develop new procedures and reagents to understand the BG system. A novel PCR protocol was established to overcome the difficulty of amplifying full length polymorphic BG transcripts, and then was applied to systematically examine the BG cDNA sequences from T cells and B cells of four different chicken haplotypes. In total 23 BG genes were found, most with alternative splicing isoforms; most strikingly, the transcripts potentially encoding soluble BG proteins were only seen in B cells, indicating functional differences of the same gene in T and B cells. By comparing the dominantly expressed BG genes as 'functional alleles' in these cells, only the cytoplasmic tail region is clearly seen to be under selection, based on the overwhelming preponderance of non-synonymous changes. With many other unexpected findings discovered in this project, a clearer picture of chicken BG genes is presented, and more questions were raised for future study. In order to explore BG functions and further characterize BG proteins, fourteen stable cell lines were developed expressing fusion proteins of the Ig-V domains of the 14 BG genes from the B12 haplotype chicken with the human IgG1 Fc fragment. These BG-Fc fusion proteins were used in sandwich enzyme-linked immunosorbent assays (ELISAs) to screen 290 BG monoclonal antibody (mAb) tissue culture supernatants, and these BG mAbs were further characterized for specificity by western blot using BG-Fc fusion proteins. These solid tools (BG-Fc fusion proteins and BG mAbs) provide the basis to further understand chicken BG functions and answer other interesting questions.

<p>Induction of collagen-induced arthritis (CIA), an animal model for human rheumatoid arthritis, is dependent on anti-collagen type II (CII) antibodies. The effector mechanism by which autoantibodies contribute to inflammatory reactions in autoimmune diseases is not well understood. In this thesis I have studied the effector pathways used by IgG anti-CII antibodies to initiate arthritis, namely the IgG Fc receptors (FcγRs) and the complement system. We have found that FcγRIII is crucial for development of CIA, as CII-immunized mice lacking this receptor do not develop arthritis and IgG1 and IgG2b anti-CII antibodies require FcγRIII to trigger arthritis when transferred to naïve mice. The antibody-mediated arthritis was further enhanced in mice deficient in the inhibitory FcγRIIB, indicating that FcγRIIB regulates the activation of FcγRIII. Furthermore, we demonstrate that FcγRIII exist as three distinct haplotypes in mice, FcγRIII:H, FcγRIII:V and FcγRIII:T. Mice expressing the FcγRIII:H haplotype are more susceptible to CIA than mice expressing the FcγRIII:V haplotype, indicating that certain FcγRIII haplotype predisposes for CIA. We also show that the most likely FcγRIII-expressing effector cell in CIA is the macrophage, since FcγRIII-expressing macrophages exclusively can induce arthritis in FcγRIII-deficient mice challenged for CIA.</p><p>The complement system was also investigated in development of CIA. We found that this effector pathway is also necessary for onset of arthritis, as CIA was inhibited by treatment with anti-complement factor 5 (C5) antibodies. C5-deficient mice could neither develop CIA unless provided with C5-containing sera. </p><p>Taken together, the work presented in this thesis indicates that FcγRs and the complement system are crucial for the induction of experimental arthritis. These findings are important for understanding the mechanisms behind rheumatoid arthritis and blocking of these effector pathways may in the future be used as treatment of rheumatoid arthritis. </p>

<p>Antibodies have the ability to influence their own production in a process called antibody feedback regulation. Depending on the type of antigen and the subclass of the antibody, the outcome of feedback regulation can be complete suppression or several hundred-fold enhancement of the antibody response.</p><p>IgE and IgG3 enhance responses to soluble protein antigens. Previous results suggest that IgG3-mediated enhancement of antibody responses is dependent on complement and not Fc receptors for IgG. However, the Fc receptor-deficient animals used did not completely lack the IgG3-binding FcγRI. We re-examined the role of this receptor in a new mouse strain completely lacking FcγRI and found that IgG3-mediated enhancement was unperturbed, thus confirming a role for complement. </p><p>To investigate the early responses resulting in IgE-mediated enhancement of antibody responses we used biotinylated antigen and found that mature follicular B cells and to a lesser extent transitional type 2 B cells capture IgE/antigen complexes. Adoptive transfer of CD4+ T cells expressing a transgenic TCR specific for ovalbumin demonstrated that these T cells localize near the B-cell follicle after 6-12 hours and that IgE, in contrast to IgG3, significantly increased specific T cell proliferation. After 3 days the T cells had gone through several rounds of divisions and showed an activated phenotype. Additional cell transfer studies identified CD23+ B cells as the responsible effector cells. These results indicate that the mechanism underlying IgE-mediated enhancement is rapid transport of IgE/antigen complexes by follicular B cells into B-cell follicles, followed by antigen presentation by CD23+ B cells to naïve CD4+ T cells. IgG3, inducing poor T cell responses, is more likely to depend on lowering the threshold for B-cell activation by co-ligating the B-cell receptor with the complement receptor 2/CD19 complex on the surface of the B cell.</p>

Induction of collagen-induced arthritis (CIA), an animal model for human rheumatoid arthritis, is dependent on anti-collagen type II (CII) antibodies. The effector mechanism by which autoantibodies contribute to inflammatory reactions in autoimmune diseases is not well understood. In this thesis I have studied the effector pathways used by IgG anti-CII antibodies to initiate arthritis, namely the IgG Fc receptors (FcγRs) and the complement system. We have found that FcγRIII is crucial for development of CIA, as CII-immunized mice lacking this receptor do not develop arthritis and IgG1 and IgG2b anti-CII antibodies require FcγRIII to trigger arthritis when transferred to naïve mice. The antibody-mediated arthritis was further enhanced in mice deficient in the inhibitory FcγRIIB, indicating that FcγRIIB regulates the activation of FcγRIII. Furthermore, we demonstrate that FcγRIII exist as three distinct haplotypes in mice, FcγRIII:H, FcγRIII:V and FcγRIII:T. Mice expressing the FcγRIII:H haplotype are more susceptible to CIA than mice expressing the FcγRIII:V haplotype, indicating that certain FcγRIII haplotype predisposes for CIA. We also show that the most likely FcγRIII-expressing effector cell in CIA is the macrophage, since FcγRIII-expressing macrophages exclusively can induce arthritis in FcγRIII-deficient mice challenged for CIA. The complement system was also investigated in development of CIA. We found that this effector pathway is also necessary for onset of arthritis, as CIA was inhibited by treatment with anti-complement factor 5 (C5) antibodies. C5-deficient mice could neither develop CIA unless provided with C5-containing sera. Taken together, the work presented in this thesis indicates that FcγRs and the complement system are crucial for the induction of experimental arthritis. These findings are important for understanding the mechanisms behind rheumatoid arthritis and blocking of these effector pathways may in the future be used as treatment of rheumatoid arthritis.

Antibodies have the ability to influence their own production in a process called antibody feedback regulation. Depending on the type of antigen and the subclass of the antibody, the outcome of feedback regulation can be complete suppression or several hundred-fold enhancement of the antibody response. IgE and IgG3 enhance responses to soluble protein antigens. Previous results suggest that IgG3-mediated enhancement of antibody responses is dependent on complement and not Fc receptors for IgG. However, the Fc receptor-deficient animals used did not completely lack the IgG3-binding FcγRI. We re-examined the role of this receptor in a new mouse strain completely lacking FcγRI and found that IgG3-mediated enhancement was unperturbed, thus confirming a role for complement. To investigate the early responses resulting in IgE-mediated enhancement of antibody responses we used biotinylated antigen and found that mature follicular B cells and to a lesser extent transitional type 2 B cells capture IgE/antigen complexes. Adoptive transfer of CD4+ T cells expressing a transgenic TCR specific for ovalbumin demonstrated that these T cells localize near the B-cell follicle after 6-12 hours and that IgE, in contrast to IgG3, significantly increased specific T cell proliferation. After 3 days the T cells had gone through several rounds of divisions and showed an activated phenotype. Additional cell transfer studies identified CD23+ B cells as the responsible effector cells. These results indicate that the mechanism underlying IgE-mediated enhancement is rapid transport of IgE/antigen complexes by follicular B cells into B-cell follicles, followed by antigen presentation by CD23+ B cells to naïve CD4+ T cells. IgG3, inducing poor T cell responses, is more likely to depend on lowering the threshold for B-cell activation by co-ligating the B-cell receptor with the complement receptor 2/CD19 complex on the surface of the B cell.

B cells are normally regulated to prevent activation against self-proteins through tolerance mechanisms.  However, occasionally there is a break in tolerance and B cells can become self-reactive, which might lead to the development of autoimmune disease. The activation of self-reactive B cells is regulated by receptors on the B cell surface, such as Fc gamma receptor IIb (FcγRIIb), complement receptor type 1 (CR1), and CR type 2 (CR2). In this thesis I have studied the role of FcγRIIb, CR1 and CR2 on B cells in autoimmune arthritis. By using a model for rheumatoid arthritis, I discovered that the initial self-reactive B cell response in arthritis was associated with the splenic marginal zone B cell population. Marginal zone B cells express high levels of CR1/CR2 and FcγRIIb, suggesting that they normally require high regulation. Further, female mice deficient in CR1/CR2 displayed increased susceptibility to arthritis compared to CR1/CR2-sufficient female mice. When investigating whether sex hormones affected arthritis susceptibility, we found that ovariectomy, of the otherwise fairly resistant CR1/CR2-sufficient mice, reduced the expression of CR1 on B cells and rendered the mice more susceptible to arthritis. In humans, a significantly reduced CR1 and FcγRIIb expression was found on B cells in aging women, but not in men. This may contribute to the increased risk for women to develop autoimmune disease as reduced receptor expression may lead to the activation of self-reactive B cells. In agreement, lower CR1, CR2 and FcγRIIb expression was seen in patients with rheumatoid arthritis.   Finally, a soluble form of FcγRIIb was used to investigate FcγRIIb’s ability to bind self-reactive IgG in an attempt to treat autoimmune arthritis. Treatment of mice with established arthritis was associated with less self-reactive IgG antibodies and consequently less disease, suggesting that soluble FcγRIIb may be used as a novel treatment in arthritis.