No description available.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

BACKGROUND Inducible costimulator (ICOS) and its ligand (ICOSL) are a pair of costimulatory molecules that co-localize in germinal centers (GC). This interaction is critical for the maturation of GC B cells to affinity-matured memory B cells and long-lived plasma cells. Both ICOS and ICOSL are implicated in systemic lupus erythematosus (SLE). It is known that ICOSL sheds from the cell membrane and that the soluble form of ICOSL (sICOSL) is elevated in SLE; though the function of sICOSL is poorly understood. While it is known that binding of ICOSL on antigen-presenting cells (APC) to ICOS on T cells leads to cell signaling resulting in T cell activation and differentiation, there is also some preliminary evidence that reverse signaling may also occur through ICOSL in APCs. The binding interaction between ICOS and sICOSL has not been fully characterized and is important to understand if either molecule is to be targeted therapeutically. The hypothesis evaluated in this study was that the ICOS: ICOSL interaction is a potent and critical mediator of proinflammatory signaling and immune activation that functions both via activated T cell-mediated forward signaling and APC-mediated reverse signaling mechanisms and that ectodomain shedding of ICOSL is a protective mechanism that leads to down-regulation of the proinflammatorysignaling cascade initiated by this interaction. The aim of this thesis is to characterize the binding interaction between ICOS and ICOSL and to provide a review of the literature and discuss future work that would enhance the biological understanding of this interaction and its role in lupus and other autoimmune diseases. METHODS The binding interaction between ICOS and ICOSL was characterized using both soluble proteins and cells with expressed recombinant proteins. Purified soluble ICOSL (sICOSL) was characterized using size-exclusion chromatography multiangle light scattering (SEC-MALS). Surface plasmon resonance (SPR) was used to measure the binding affinity between sICOSL and human ICOS fused to the fragment crystallizable (Fc) portion of an immunoglobulin molecule (hICOS.Fc). The binding interaction was further characterized to account for avidity between hICOS.Fc and sICOSL and between hICOS.Fc and ICOSL expressed recombinant on the cell surface using a solution-based binding method. RESULTS Expressed recombinant and purified sICOSL dimerized over time and with increasing temperatures. The sICOSL: hICOS.Fc interaction did not follow a typical 1:1 binding interaction. In-solution binding experiments resulted in a tighter equilibrium dissociation binding constant (KD) than the surface-based results obtained by SPR. The KD for hICOS.Fc binding to human ICOSL(hICOSL) expressed on cells agreed well with the KD for hICOS.Fc to the soluble protein, indicating that the in-solution binding measurement may measure binding avidity rather than affinity and that this may be the more physiologically relevant interaction. CONCLUSIONS I show in the experimental part of this study that the interaction between ICOS and ICOSL is quite potent and that much of the binding strength is due to avidity, or the combined strength of multiple parts of the molecules interacting with one another, rather than the affinity alone. As this interaction is implicated in SLE pathogenesis, it would be useful to develop a clearer understanding of the most relevant physiological form of these molecules (soluble or transmembrane) and of the biological signaling events that are initiated via this interaction in order to determine whether targeting ICOS or ICOSL may be therapeutically viable approaches.

Superantigens (SAgs) are implicated in the initiation of many diseases, including Kawasaki disease (KD), a multi-system vasculitis that leads to persistent inflammation and damage of coronary arteries. T cells are central to the pathogenesis of SAg-mediated diseases. Lactobacillus casei cell wall extract (LCWE) induces a disease in mice that resembles human KD, and contains a novel SAg. Despite the fact that SAg-activated T cells undergo apoptosis, they persist and are necessary for coronary inflammation in this model of KD. We report rescue from apoptosis of SAg-stimulated T cells in vitro by costimulation through CD28 or 4-1BB. CD28- or 4-1BB-mediated signaling stimulated concurrently with SAg upregulated the anti-apoptotic factor Bcl-XL. In vivo, co-injection of LCWE and a 4-1BB agonist aggravated coronary disease. These findings suggest that costimulation of T cells affects extent of illness in this model of KD, and supports targeting costimulation as a therapeutic intervention in SAg-triggered diseases.

Kawasaki disease (KD) is a multisystem vasculitis with predilection for the coronary arteries. Although the cause of KD remains elusive, there is evidence to suggest a superantigenic trigger. When T-cells are activated by a superantigen (SAg) they undergo massive proliferation but eventually apoptose; however, in KD, we hypothesize that these T-cells persist and infiltrate the coronary arteries. Previous studies have shown that enhanced costimulation through CD28 or 4-1BB rescues T-cells from apoptosis and exacerbates disease in a mouse model of KD. Our results suggest that this signal needs to be initiated close in timing to that of the SAg. In addition, the two molecules can act independently of one another, but are not additive. Also, stimulation of the 4-1BB pathway in the presence of a SAg elicits a Th1 phenotype. Lastly, TRAF1 regulates this enhanced survival downstream of 4-1BB. Thus, these results provide new insights into the effects of costimulation in SAg-mediated disease, and suggest that these pathways need to be targeted early to abrogate the enhanced survival of SAg-activated T-cells.

Superantigens (SAgs) are implicated in the initiation of many diseases, including Kawasaki disease (KD), a multi-system vasculitis that leads to persistent inflammation and damage of coronary arteries. T cells are central to the pathogenesis of SAg-mediated diseases. Lactobacillus casei cell wall extract (LCWE) induces a disease in mice that resembles human KD, and contains a novel SAg. Despite the fact that SAg-activated T cells undergo apoptosis, they persist and are necessary for coronary inflammation in this model of KD. We report rescue from apoptosis of SAg-stimulated T cells in vitro by costimulation through CD28 or 4-1BB. CD28- or 4-1BB-mediated signaling stimulated concurrently with SAg upregulated the anti-apoptotic factor Bcl-XL. In vivo, co-injection of LCWE and a 4-1BB agonist aggravated coronary disease. These findings suggest that costimulation of T cells affects extent of illness in this model of KD, and supports targeting costimulation as a therapeutic intervention in SAg-triggered diseases.

Kawasaki disease (KD) is a multisystem vasculitis with predilection for the coronary arteries. Although the cause of KD remains elusive, there is evidence to suggest a superantigenic trigger. When T-cells are activated by a superantigen (SAg) they undergo massive proliferation but eventually apoptose; however, in KD, we hypothesize that these T-cells persist and infiltrate the coronary arteries. Previous studies have shown that enhanced costimulation through CD28 or 4-1BB rescues T-cells from apoptosis and exacerbates disease in a mouse model of KD. Our results suggest that this signal needs to be initiated close in timing to that of the SAg. In addition, the two molecules can act independently of one another, but are not additive. Also, stimulation of the 4-1BB pathway in the presence of a SAg elicits a Th1 phenotype. Lastly, TRAF1 regulates this enhanced survival downstream of 4-1BB. Thus, these results provide new insights into the effects of costimulation in SAg-mediated disease, and suggest that these pathways need to be targeted early to abrogate the enhanced survival of SAg-activated T-cells.

No description available.

MUC1, a protein of epithelial and carcinoma cells, has recently been shown on activated T cells where it inhibits CD3-stimulated proliferation. Two immunoregulatory domains similar to ITAM and ITIMs are present on its cytoplasmic tail, suggesting that MUC1 can act as both a costimulatory and coinhibitory molecule of T cells. In my work, I have examined immunoregulatory function of MUC1 on human T cells. We first showed that MUC1, when ligated in a population of unpurified T cells with an anti-CD3 and a crosslinking antibody, enhances proliferative and cytokine responses in a NF-AT-dependent manner by recruiting the AP-1 transcription factor and translocating it into the nucleus. With purified CD3+ T cells, we instead observed inhibition after MUC1/CD3 coligation and crosslinking. Reconstituting with irradiated CD3- cells, we discovered that MUC1 costimulation is dependent on the amount of accessory cells. These data imply a novel role for MUC1 in T cell immunoregulation. / Experimental Surgery

Transplantation is the treatment of choice for end stage organ failure however current immunosuppressive therapies whilst effective at preventing acute allograft rejection, fail to prevent late graft loss due to chronic rejection and are associated with an increased risk of infection and malignancy. Therefore there is a clear unmet clinical need for improved strategies to prevent allograft rejection. OX40 is a member of the TNFR superfamily that has potent costimulatory properties. Although the impact of blockade of the OX40-OX40L pathway has been well documented in models of autoimmune disease, its effect on the rejection of allografts is less well defined. Therefore the aim of this thesis was to determine the impact of OX40 blockade on conventional and regulatory T cell responses to allografts. We found that activation of CD4+ and CD8+ naïve and memory T cells resulted in the induction of OX40 expression and that blockade of OX40-OX40L interactions partially inhibited the response of alloreactive T cells in vitro and prevented skin allograft rejection but did not result in the induction of tolerance. OX40 blockade was found to have no effect on the activation and proliferation of T cells but rather effector T cells failed to accumulate and migrate to skin allografts. This was shown to be the result of an enhanced degree of cell death amongst proliferating effector cells. In addition, blockade of OX40-OX40L interactions at a time of exposure to alloantigen resulted in a pool of Treg with an enhanced ability to suppress T cell responses to alloantigen in vitro and in vivo. Counter-intuitively, OX40 blockade was found to increase the potency of alloreactive Treg by promoting survival following re-activation. Finally, although OX40 blockade impacted both conventional and regulatory T cell responses, anti-OX40 administration did not promote skin or heart allograft survival in immunocompetent recipients and failed to synergise with blockade of other costimulatory molecules to prevent allograft rejection. In conclusion, these data demonstrate that blockade of OX40-OX40L interactions can attenuate naïve and memory T cell responses to alloantigen whilst promoting the survival of alloreactive Treg. Therefore, we propose that anti-OX40 would be a worthwhile adjunct to pre-existing strategies to induce tolerance.