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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Aseptic Machining of Live Bendable Osteochondral Allografts for Articular Surface Remodeling

Spack, Katherine January 2024 (has links)
Young patients diagnosed with post-traumatic osteoarthritis (PTOA) face significant hurdles to restoring pain-free joint function. While surgical interventions exist for replacing damaged cartilage, few are able to offer complete replacement of the articular surface with a bearing material that maintains the longevity and mechanical properties of native articular cartilage necessary to prevent the need for costly and painful revision procedures. Osteochondral allograft technology has begun to address this need by allowing surgeons to resurface constrained small to medium articular defects with live tissue-bank-sourced cartilage tissue explants. A primary limitation surgeons face when choosing osteochondral allotransplantation to treat large articular surface deficits is the scarcity of high-quality live explant tissue with sufficient congruence to fully restore the biomechanical function in the affected joint. This dissertation asserts that augmentation of native tissues donated to tissue banks is a promising strategy for providing more physiologically appropriate tissue replacements for patients with PTOA, providing significant symptomatic relief and allowing young patients to delay or prevent invasive total joint arthroplasty treatments.This dissertation aims to improve treatment modalities for this patient population by developing a surgical technique that enables adaptive reshaping of the articular surface of donor osteochondral tissue explants. The driving hypothesis of this dissertation is that osteochondral allografts that conform better to the opposing articular surface result in better clinical outcomes than those with lesser congruence with the native joint. The corollary hypothesis is that better conformity may be achieved by providing some measure of bending flexibility to the allograft, using streamlined tissue processing procedures to cut grooves in the bony substrate. To address these needs, we first developed, implemented, and validated the technology for milling grooves on the back of large human and canine osteochondral allografts. This resulted in the development of a process for milling grooves in patellar osteochondral samples using a computer-numerically controlled 3-axis milling machine. Sample-specific spatial information was captured within machining fixtures to generate machining paths. The curvature of human and canine osteochondral allografts was captured using a laser scanning system to fit B-Spline surfaces and generate articular curvature maps for the modified allografts. We hypothesize that due to the surface modification enabled by the bending method, bendable osteochondral allografts may provide better curvature matching for patella transplants in the patellofemoral joint. We used a cadaveric knee joint model to investigate patellofemoral joint congruence for unbent and bendable osteochondral allografts at various flexion angles. Shell and bendable allografts were machined from donor human patellae and inserted into the patellofemoral joint space of five knee joints, creating 25 femur-patella osteochondral allograft pairings. Patellofemoral joints with either shell or bendable allografts were loaded at 15-degree increments from 15 to 90 degrees flexion, and the resultant patellofemoral joint contact area was measured and compared against the native patellofemoral contact areas. On average, no significant difference in contact area was found between native patellofemoral joints and OCAs or BOCAs, indicating that both types of allografts restored native congruence. This result aligned with prior computational models of the behavior of bendable and shell allografts in the patellofemoral joint. This finding suggests that future investigations of the benefits of BOCA for allografting other joints could be initiated using computational methods, as the results of the current study suggest that the computational predictions may remain valid under the right set of conditions. Clinical studies of outcomes of osteochondral tissue transplantation indicate that maintenance of donor chondrocyte viability is crucial for the long-term success of the transplanted tissue. In order to assure that CNC machined allografts maintained appropriate chondrocyte viability and tissue sterility, we created a sterile environment for CNC milling of fresh canine patellar osteochondral allografts and quantified allograft chondrocyte viability for up to two weeks post-milling. Following machining and extended culture, bending of the allografts produced neither fracture of the samples nor resulted in loss of chondrocyte viability when compared to non-grooved controls. Therefore, these results provide basic scientific support for the clinical use of bendable osteochondral allografts. Having developed a method of bendable allografts and verifying the tissue viability and sterility, in addition to simulating joint contact in the cadaveric model, we ran a study to assess the performance of bendable osteochondral allografts and shell allografts in the contralateral stifle joints of purpose-bred dogs. This animal model was used to measure the clinical outcomes of bendable osteochondral allografts transplantation following in-vivo loading. Functional clinical outcomes were collected, including force mat kinematics, lameness scoring, range of motion, and pain scoring. At the termination of the study, allograft tissue and synovial fluid from the joint were recovered to assess the sterility, chondrocyte viability, chondrocyte morphology, and bony integration of the allograft. The allografts showed no signs of infection or rejection, and the CNC-machined shell allografts performed well in the joint. Unfortunately, the grooves machined for the bendable allograft patellae were more appropriate in width for the human patella. The removal of excess bony tissue destabilized the bendable allografts and led to fractures and fissures in the tissue. Based on the fissuring and fragmentation mode of failure noted in the canine BOCAs, the size and number of the machined grooves must be optimized for preclinical testing so the potential advantages of bendable OCAs can be realized without compromising their integrity and osteointegration during healing. Bulk mechanical properties and failure thresholds dependent on the width of allograft grooves must be established to reduce the risk of post-transplantation failure. Ongoing work aims to establish safe geometrically-based machining criteria and determine load-to-failure thresholds for osteochondral allografts to improve tissue integrity and functional viability post-transplantation. This aim will be addressed by loading canine bendable allografts with variable groove widths to assess the threshold for mechanical failure against simulated femoral trochlea. The aim of this study is to define allograft bulk mechanical properties and failure thresholds for producing bendable osteochondral allografts. The final chapter of this dissertation aims to assess the impact of sustained mechanical loading on the fluid exchange between the interfibrillar and extrafibrillar space in native articular cartilage, as the fluid load support in articular cartilage is crucial to the maintenance of the low coefficient of friction within the tissue. In our study, we developed a technique to measure water extruded from the interfibrillar space in articular cartilage by applying static compression to unconfined tissue. Preliminary results indicate that the loading and pressurization of the articular tissue can potentially make previously trapped interfibrillar water content more accessible
22

In-vitro study of the cryopreserved intervertebral disc

Chan, Chun-wai., 陳春慧. January 2008 (has links)
published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy
23

Fabrication of Tissue Engineered Osteochondral Allografts for Clinical Translation

Nover, Adam Bruce January 2015 (has links)
Damage to articular cartilage, whether through degeneration (i.e. osteoarthritis) or acute injury, is particularly debilitating due to the tissue's limited regenerative capacity. These impairments are common: nearly 27 million Americans suffer from osteoarthritis and 36% of athletes suffer from traumatic cartilage defects. Allografts are the preferred treatment for large cartilage defects, but demand for these tissues outweighs their supply. To generate additional replacement tissues, tissue engineering strategies have been studied as a cell-based alternative therapy. Our laboratory has had great success repeatedly achieving native or near-native mechanical and biochemical properties in grafts engineered from chondrocyte-seeded agarose hydrogels. The most common iteration of this technique yields a disk of ~4 mm diameter and ~2.3 mm thickness. However, much work is still needed to increase the potential for clinical translation of this product. Our laboratory operates under the premise that in vivo success is predicated on replicating native graft properties in vitro. Compared to these engineered grafts, native grafts are larger in size. They consist of cartilage, which has properties varying in a depth-specific manner, anchored to a porous subchondral bone base. They are able to be stored between harvest and transplantation. This dissertation presents strategies to address a subset of the remaining challenges of reproducing these aspects in engineered grafts. First, graft macrostructure was addressed by incorporating a porous base to generate biomimetic osteochondral grafts. Previous studies have shown advantages to using porous metals as the bony base. Likewise, we confirmed that osteochondral constructs can be cultured to robust tissue properties using porous titanium bases. The titanium manufacturing method, selective laser melting, offers precise control, allowing for tailoring of base shape and pore geometry for optimal cartilage growth and osteointegration. In addition to viability studies, we investigated the influence of the porous base on the measured mechanical properties of the construct's gel region. Through measurements and correlation analysis, we linked a decrease in measured mechanical properties to pore area. We promote characterization of such parameters as an important consideration for the generation of functional grafts using any porous base. Next, we investigated a high intensity focused ultrasound (HIFU) denaturation of gel-incorporated albumin as a strategy for inducing local tissue property changes in constructs during in vitro growth. HIFU is a low cost, non-contact, non-invasive ultrasound modality that is used clinically and in the laboratory for such applications as ablation of uterine fibroids and soft tissue tumors. Denaturing such proteins has been shown to increase local stiffness. We displayed the ability incorporate albumin into tissue engineering relevant hydrogels, alter transport properties, and visualize treatment with its denaturation. HIFU treatment is aided by the porous metal base, allowing for augmented heating. Though heating cartilage is used in the clinic, it is associated with cell death. We investigated this effect, finding that the associated loss of viability remains localized to the treatment zone over time. This promotes the option of balancing desired changes in tissue properties against the concomitant cell viability loss. In order to match clinically utilized allografts, engineered constructs must be scaled up in size. This process is limited by diffusional transport of nutrients and other chemical factors, leading to preferential extracellular matrix deposition in the construct periphery. Many methods are being investigated for overcoming this limitation in fixed-size constructs. In this chapter, we investigated a novel strategy in which small constructs are cultured for future assembly. This modular assembly offers coverage of variable sized defects with more consistent growth with more uniform distribution of biochemical constituents than large constructs cultured on their own. Physiologic failure testing showed that integration of these tissues may be strengthened by increased subunit strength or assembled culture. It is expected that bioadhesive caulking and/or the incorporation of osteochondral bases would further increase integration of the assembled large graft. Finally, we sought to provide a preservation/storage protocol for engineered cartilage constructs. Such a technique is critical for clinical translation, providing the engineered graft with a “shelf-life.” We adopted and evaluated the Missouri Osteochondral Allograft Preservation System (MOPS), which had been shown to maintain cell viability in native grafts for at least 63 days at room temperature without serum or growth factors. Within the current clinical of 28 days, MOPS maintained chondrocyte viability and 75% of the pre-preservation Young's modulus without significant decline in biochemical content, however it did not extend the clinical window as it had with native grafts. Refrigeration with MOPS did not show any benefit at day 28, but proved better with longer preservation times. These results are the first evaluating engineered cartilage storage. Further optimization is necessary to extend storage tissue property maintenance in storage. Overall, this dissertation presents four strategies for increasing the translation potential of engineered articular cartilage grafts by better matching the clinically utilized native allograft system. Combining these techniques, one could ideally engineer small, interlocking ostechondral constructs with HIFU modified interface properties, which could be stored from maturity to implantation. Future optimization is required to better understand and utilize these methods to engineer fully functional, clinically relevant grafts.
24

Articular Cartilage Contact Mechanics and Development of a Bendable Osteochondral Allograft

Jones, Brian Kelsie January 2017 (has links)
Articular cartilage is a hydrated soft tissue with a fibrous solid matrix characterized by high porosity and low permeability. It is the bearing material of diarthrodial joints, permitting motion and transmitting loads with extraordinarily low friction. This function may be disrupted pathologically by osteoarthritis, a disease where cartilage becomes weakened and eroded. Osteoarthritis creates pain during normal activities like walking or grasping, thus diminishing quality of life. The disease affects nine percent of Americans and is one of the leading causes of disability worldwide. There is presently no cure or prevention for osteoarthritis, only palliative treatments designed to help patients manage pain and regain mobility. New such treatments are developed in part by advancing the science of cartilage mechanics, structure and function, and this dissertation presents novel contributions toward this effort: Chapters 2, 3, and 4 enhance our knowledge of the structure-function relationships critical to our understanding of cartilage friction and load support. Whereas most prior theoretical and experimental studies have focused on the analysis of small cylindrical explants, or idealized joint geometries such as cylindrical or spherical articular layers, these chapters describe novel investigations performed on whole articular layers of the shoulder and knee joints. Insights from these investigations have a direct impact on our formulation of design objectives in cartilage tissue engineering, whose purpose is to grow constructs that reproduce the functional properties of native cartilage. The studies presented in this chapter are critical to ongoing tissue engineering studies in our laboratory, which has pioneered the development of anatomically sized cartilage constructs. Finally, Chapter 5 describes the development of a novel clinical treatment for thumb osteoarthritis that uses bent osteochondral allografts (living bone and cartilage from human donors) to replace the eroded thumb trapezial articular layer with a healthy and thick articular layer from another joint such as the knee. This highly promising treatment strategy overcomes the limitation of size mismatch between donor and recipient which had relegated osteochondral allograft surgery to a niche treatment. Like other fibrous tissues, cartilage exhibits tension-compression nonlinearity, meaning it can be 100 times stiffer in tension than in compression. Tension-compression nonlinearity allows compressive physiologic joint loads to be supported by tensile stress within the collagen fibers and elevated fluid pressure, effectively shielding the solid matrix from compressive load. According to theory, fluid load support derives directly from tension-compression nonlinearity. Fluid load support is also a dominant mechanism of cartilage lubrication. Because cartilage is 80 to 90% water, most of the contact traction on the porous cartilage surface takes the form of hydrostatic fluid pressure. Friction forces only occur upon solid-on-solid contact, so cartilage friction is nearly negligible, even for joint contact forces that may routinely exceed three or four times the body’s total weight. The dependence of friction on fluid load support is demonstrated by experiments that simultaneously measure interstitial fluid pressure and friction - a transient rise in friction occurs as pressure subsides and fluid drains from the tissue. These structure-function relationships have been identified over decades of research, mostly through small cartilage explant studies, which have supported hypothesized mechanisms under non-physiologic conditions. Therefore, in situ studies utilizing intact, naturally-congruent articular surfaces under physiologic loading conditions would significantly extend and validate these principles. For example, friction may rise nearly 100-fold after only 1 hour in cartilage explant experiments, yet there is no evidence that normal daily activities spanning 16 hours or more lead to cartilage damage. Can fluid load support sustain low friction under these relatively harsh conditions? To date, no study has examined this question, so Chapter 2 of this work addresses the hypothesis that the friction coefficient of diarthrodial joints can remain low over a full day of loading at physiologic speeds and load magnitudes. Another question that may be uniquely addressed by an in situ analysis is: What is the complete state of stress within naturally-congruent cartilage layers? A primary hypothesis for the initiation and progression of osteoarthritis is that the state of stress within articular cartilage may exceed a threshold beyond which the tissue is unable to repair itself. Since the complete stress tensor within a material is immeasurable, techniques such as finite element analysis must be used to examine the state of stress. Additionally, a theoretical framework such as mixture theory may be used to examine the stresses in the fluid and solid constituents of the tissue separately, making it possible to test theories of solid matrix damage. Chapter 3 of this work uses this strategy to examine the hypothesis that physiologic solid matrix stresses within anatomically-shaped, biphasic, tension-compression nonlinear cartilage layers are primarily tensile, despite the fact that the articular layers are loaded in compression. The proteoglycan content of articular cartilage gives the tissue an osmotic swelling pressure that is resisted by tensile stresses in the collagen fibrils, even in the absence of external loads. This charge effect may be additionally incorporated into a mixture theory finite element analysis to examine the role of osmotic swelling on the solid matrix stresses in a physiologic, in situ analysis. This capability has only been developed recently and is explored for the first time in Chapter 4. The final part of this work translates basic cartilage science into a clinical therapy for thumb joint osteoarthritis, a common site for this disease. The current gold-standard treatment for thumb joint osteoarthritis replaces the trapezium bone with a soft-tissue tendon autograft, relieving pain but significantly weakening hand strength. Living osteochondral allograft transplantation may provide a relatively straightforward treatment alternative, though this procedure has not been used for the thumb due to the inadequate availability of suitable allografts. The ideal allograft would have a relatively thick articular layer to provide sufficient compliance for promoting joint congruence with the mating metacarpal surface, and surface curvatures that match the saddle-shaped anatomy of the distal trapezial articular surface to reproduce the normal joint motions. A potential solution that would provide suitable trapezium osteochondral allografts for patients involves precisely machining and bending allografts from a lower extremity joint with thicker cartilage, such as the distal femoral surface of the knee, to match the shape and curvature of the trapezium. Such bent osteochondral allografts would provide all the desired benefits of the ideal arthroplasty. Chapter 5 outlines the development of this novel technology, including proof of concept and feasibility demonstrations, business strategy and market analysis.
25

Factors influencing cryopreserved allograft heart valve degeneration /

Yap, Cheng-Hon. January 2006 (has links)
Thesis (M.S.)--University of Melbourne, Dept. of Surgery (St.Vincent's Hospital),Faculty of Medicine, Dentistry and Health Sciences, 2006. / Typescript. Includes bibliographical references (leaves 118-141).
26

Stabilization of irradiated allografts via crosslinking and free radical scavenging

Seto, Aaron U. January 2007 (has links)
Thesis (M.S.)--Rutgers University, 2007. / "Graduate Program in Biomedical Engineering." Includes bibliographical references (p. 80-85).
27

A study of the effects of warm ischaemic times on harvested homografts

Bester, Dreyer 03 1900 (has links)
Thesis (M. Tech.) -- Central University of Technology, Free State, 2009
28

Comportamento biomecânico do reparo ósseo nos biomateriais de origem bovina / Biomechanical behavior of bone healing in biomaterials of bovine matter

Martins, Cesar Antonio de Quadros 21 December 2001 (has links)
Made available in DSpace on 2016-12-06T17:07:09Z (GMT). No. of bitstreams: 1 CesarMartins.pdf: 970860 bytes, checksum: 6ad6b24dacadddaad307316c6a4edb43 (MD5) Previous issue date: 2001-12-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The purpose of this study was to analyze the ultimate strength and displacement behavior of healed 3.5-mm segmental radius defects in seventeen adult male rabbits in a fourty-two days follow-up. The defect was filled out with biomaterials (ten radius) such as bone morphogenetic protein, inorganic bovine bone matrix, organic bovine bone matrix and bovine collagen in one group (group I). Group II (seven radius) received fresh-frozen allograft bone obtained from a rabbit bone-banking created for this study. The opposite limbs were the control group (group III) with seventeen radius. The three point bending and the displacement were recorded in all specimens studied. The one-way analysis of variance (p£ 0.05) and the variation coefficient in the whole three groups. Significant difference in the ultimate strengh were found between group I and III (p= 0.0009). The variable ultimate strength of group I has presented a coefficient of variation of 87%, group II has presented a oefficient of variation of 66% and the control group a coefficient of variation of 31%. Group I in the variable displacement has presented a coefficient do variation of 70%, group II has presented a coefficient of variation of 60% and group III 33%. Beetwen groups I and II the least variated group was group II in both variables. However, four in ten non-unions were recorded in the biomaterial group. All allograft group specimens have shown bone healing in the follow-up period. This study do not demonstrate the effectiveness of bovine origin biomaterials as suitable on bone formation. Clinical Relevance: Segmental Bone loss due to trauma, tumor resection or other causes are one of the most challenging problems in orthopaedic surgery. Several materials have been used as bone regenerator, even thou bone tissue has a very known potential of healing. Allograft bone tissue is very attractive possibility but presents a high disease transmission risk. Although autograft tissue has a short stock tissue for some situations in the daily orthopaedic activity, it remains the gold standard for most surgeons. In some cases, bovine origin biomaterials are the only choice available to solve the bone loss situations. / O presente estudo tem como objetivo identificar a resistência mecânica óssea e o deslocamento do osso neoformado utilizando-se biomateriais de origem bovina e enxerto homólogo no preenchimento de uma falha de 3,5 mm no rádio em 17 dos 19 coelhos adultos machos da raça nova zelândia, com massa de 3,5 a 5,0 Kg. Os biomateriais são substâncias biologicamente ativas, que apresentam efeito osteogênico, isto é, ativam a formação de osso novo nos organismos vivos. Neste estudo foram utilizados três grupos: grupo I com enxerto ósseo orgânico e inorgânico bovino, pool de proteína morfogenética bovina e colágeno bovino, como biomateriais em dez animais. Dois animais foram submetidos à retirada das asas ilíacas para posterior congelamento e implantação em sete animais formando o grupo II, ou enxerto homólogo. O grupo III ou controle consistiu nos rádios não operados dos 17 animais. Após 42 dias, os animais foram sacrificados e os rádios foram submetidos ao teste de flexão em três pontos, com a aplicação da carga no sítio da regeneração, sendo avaliados a carga máxima e o deslocamento neste ensaio mecânico. O teste estatístico realizado foi ANOVA - um caminho, com p£0,05 para três amostras, post-hoc de Scheffé e o coeficiente de variação. Quanto à carga máxima para a ruptura, o grupo I (biomateriais) apresentou uma média de 77,1 N ± 67,2N e um CV (coeficiente de variação) de 87%, o grupo II (enxerto homólogo) apresentou uma média de 154,8 N ±103,2 N, com um CV de 66%, já o grupo controle obteve uma média de 201,8 N ± 63,0N e um CV de 31%, que caracterizou uma diferença estatisticamente significante entre o grupo I com o grupo controle (p=0,0009). Quanto a variável deslocamento, o grupo I apresentou uma média de 1,0 mm ± 0,7mm com um CV de 70%, o grupo do II apresentou uma média de 1,0 mm ± 0,6 mm com um CV de 60% e o grupo III uma média de 0,9 mm ± 0,3 mm e CV de 33%, não demonstrando diferença estatisticamente significante (p=0,49). Quatro espécimes do grupo dos biomateriais que fizeram parte do estudo estatístico apresentaram não consolidação na falha criada, por outro lado os espécimes preenchidos com enxerto homólogo consolidaram em todos os casos. Em conclusão, os enxertos homólogos apresentaram consolidação satisfatória demonstrando um pico de carga máxima com valores próximos aos do grupo controle. Porém, os biomateriais demonstraram uma variação intragrupo muito alta devido às não consolidações, com média de carga máxima muito baixa.
29

Investigation on the risk of viral infection in musculoskeletal grafts

Yao, Felix Caspar January 2010 (has links)
[Truncated abstract] Around 50,000 hip and knee replacements are performed every year in Australia and this number has been increasing by around 13% annually since 1998 (Transplantation Society 2006). The incidence and number of revision surgery has increased by a similar proportion. Autogenous bone or allograft is still the gold standard grafting material and is currently used in a variety of reconstructive surgical procedures. The use of any allograft material carries with it the risk of transfer of disease from donor to recipient. These tissues can transmit the same viral and bacterial infections as blood, and the products of a single donation may be transplanted to several recipients. In contrast to blood, musculoskeletal tissues may come from surgical and cadaveric donation. Overall, the prevention of infection relies on the maintenance of rigid protocols for procurement, donor and allograft testing, secondary sterilisation, and the adherence to internal safety standards within the tissue banks. This thesis aims to determine the risk of viral infection among musculoskeletal tissue donors in Australia. We retrieved and analysed data retrospectively from three large tissue banks in Australia (Perth, Queensland, Victoria). This includes 12,415 musculoskeletal tissue donors, 10,937 of which are surgical donors and 1,478 of which are deceased donors, for the period of 1993 -2004. This data was analysed to determine the prevalence and incidence of viral infections such as human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV) and human T-lymphotropic virus (HTLV) in musculoskeletal allografts. The results indicate that the risk of viral infection from musculoskeletal tissue transplantation in Australia is low. ... The results indicate that the overall prevalence of screened transfusion-transmitted viral infections did not vary significantly for musculoskeletal donors over the study period, despite falling in the general population and first-time blood donors. In tissue donors, HIV incidence significantly decreased over time, and HBV decreased significantly during 1999-2001; however, there was an apparent increase in the estimated incidence of HCV in 2002-2004 compared with earlier years. Furthermore the residual risk estimate of HIV in the period 2002-2004 has declined 5-fold compared to estimates in the period 1993-1995. This is perhaps due to greater awareness of high risk behaviours among donors, improvement in donor recruitment and an overall decrease in infection levels in the general population. Musculoskeletal tissue is second only to blood as the most frequent transplanted human tissue. Viral infection is a potential complication of tissue transplantation. In this thesis the rates of HIV, HBV, HCV and HTV infection in musculoskeletal donors in Australia were identified and then compared with results in published data from Canada, Scotland and the United States. The study also compared that result with first-time blood donors because they have satisfied similar donor selection criteria (Galea et al. 2006). The results indicate that prevalence and incidence estimates for viral infection in Australian tissue donors are higher than those in blood donors. This was also reported in studies from other countries. Accordingly, it is crucial that viral prevalence and incidence be monitored to evaluate the safety of tissue supply and to improve donor selection processes.
30

Role of Th2 cytokines and polymorphonuclear cells in allograft rejection in mice

Surquin, Murielle 08 October 2007 (has links)
Acute allograft rejection remains a major problem in solid organ transplantation, because rejection may lead to acute or chronic loss of graft function. The failure of certain anti-rejection prophylactic treatments suggests that several unexpected pathways might be involved in the rejection process.<p>The aim of our experiments was to investigate the effector mechanisms responsible for skin graft rejection in mice. To adress this question, we took advantage of the possibility to restrict the alloimmune response to isolated allogeneic MHC class II molecules or to isolated minor transplantation antigens, combined with the possibility to study separately the response of CD4+ or CD8+ T cells in mice deficient for Th1 or Th2 cytokines or cytotoxic molecules. We used the bm12 skin graft combination (C57BL/6 H2Kbm12 grafted on C57BL/6 H2Kb) as a model of single MHC class II disparity and the b2microglobulin skin graft model (C57BL/6 b2m+/+ grafted on C57BL/6 b2m-/-) as a model of minor transplantation antigen disparity. Our goal was to engage a limited number of effectors, trying in a second time to block each rejection pathway selectively. <p>We showed that Fas/FasL-mediated CD4+ T cells cytotoxicity, eosinophil recruitment, activation and degranulation induced by Th2 derived cytokines, and CD4-derived IFN-g production are involved in the rejection of grafts bearing either a single MHC class II disparity or b2m-derived minor histocompatibilty antigens. In addition, rejection of MHC class II disparate skin grafts also includes the participation of neutrophils, in particular conditions where the occurrence of the Th2/eosinophil pathway was prevented. <p>Altogether, our data show a multiplicity and a redundancy of the effector pathways participating in allograft rejection. Among the different effectors pathways identified, including effectors from both innate and adaptive immune systems, some act synergistically, whereas others act as alternative pathways, depending of the degree of donor-recipient mismatch. / Doctorat en Sciences médicales / info:eu-repo/semantics/nonPublished

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