Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Title from first page of PDF file (viewed Feb. 7, 2008). Includes bibliographical references.

Coral reefs are biologically and economically important ecosystems underpinned by corals that are able to flourish in oligotrophic waters due to their mutualistic association with dinoflagellate symbionts (genus Symbiodinium). Symbiodinium are strictly intracellular, residing within the gastrodermal tissues of the coral host, and contributing the majority of the coral’s energy requirements. Coral reefs are in rapid decline due to a range of threats such as local human influences, bleaching (loss of Symbiodnium and/or reduction of pigment), disease and ocean acidification, to which links to climate change have been made. The close association of corals and a diverse community of microbes led to development of the coral holobiont hypothesis, in which a range of microorganisms (e.g Bacteria) form a functionally-relevant mutualistic relationship with corals and Symbiodinium. This thesis aimed to fill knowledge gaps in the coral holobiont hypothesis and the host-microbe interactions within this system, including pathogen interactions and coral immune system functioning. This thesis revealed that host-microbe interactions in corals are complex, and that the underlying mechanisms of immunity and symbiosis may be similar. The findings corroborate the idea that corals maintain specific bacterial communities that have potential probiotic and nutritional value. In particular, a group of common coral associates were identified, and it is suggested that members of this group are globally occurring key associates. Corals affected by a disease previously described as “White Syndrome” were observed to undergo pronounced changes in their microbial community structure in comparison to healthy colonies. However, in contrast to previous findings, no single pathogen could be identified as the causative agent of the disease syndrome, and it is speculated that corals experiencing altered health status result in a breakdown of the resident associated microbial community structure. Culturable bacterial isolates from corals were shown to affect the growth of each other and in particular some species had great inhibitory properties. Hence, the presence of some bacterial species has the potential to influence the all over structure of the coral associated microbial community. It was also shown that changed environmental conditions may alter the growth conditions for coral associated bacteria in mucus. It is suggested that increased replication is needed in studies of bacterial assemblages on corals, as variability between coral species and sites were observed. In addition, studies of the role of coral microbial communities in health and disease should broaden their focus to more thoroughly consider the role of the coral holobiont, especially with regards to the coral host. This thesis identified the first functional Pattern Recognition Protein (PRP), a C-type lectin named Millectin, in scleractinian corals. Millectin was isolated by affinity chromatography and was shown to bind to bacterial pathogens as well as coral Symbiodinium symbionts. Gene expression of Millectin was upregulated in response to immune stimuli and the lectin was further abundantly expressed in the tissues of corals, suggesting a major role for this protein in system functioning and immunity. Further research into Millectin and a complement factor C3 homolog suggested that these molecules may have been co-opted into the equally important role of symbiont recruitment. Gene expression analysis of C3 also indicated this molecule may be involved in responses to tissue trauma. Millectin shows variability in the binding region, and hence, is the earliest evolutionary representative to date of a variable PRP. This finding, and the observed ancestral relation with vertebrate homologs, provided further information on the evolution of the innate immune system and gives further insight into invertebrate immunity.

INTRODUÇÃO: Indivíduos com SZ (esquizofrenia) fumam até três vezes mais que a taxa da população em geral. Constatou-se que fumantes com esquizofrenia fumam mais intensamente do que comparados com fumantes não esquizofrênicos. Adicionalmente, existem relatos não sistemáticos de que apesar de alta taxa de tabagismo, os esquizofrênicos apresentam proporcionalmente pouca lesão pulmonar comparado com tabagistas de igual consumo sem esquizofrenia. Esta diferença, se confirmada, poderia sugerir mecanismos diferentes de reação a agentes exógenos nos sistema respiratório, e entre estes mecanismos diferentes poderia estar o sistema de complemento, já evidenciado em estudos do grupo de pesquisa, porém sem controle para tabagismo. Este estudo investigou se a capacidade de difusão pulmonar em SZ é maior que em NSZ, e se o sistema complemento C3 e C4 é diferente entre SZ e NSZ e ao mesmo tempo está associado a difusão pulmonar de forma diferente em SZ e NSZ. OBJETIVOS: comparar a capacidade de difusão pulmonar e complemento C3 e C4 em pacientes fumantes com e sem esquizofrenia e analisar se existe evidência de mecanismos diferentes mediando prejuízo na capacidade de difusão em tabagistas com e sem SZ. MÉTODOS: esse é um estudo caso controle pareado, desenhado para ser multicêntrico, no momento descrevendo resultados de um centro. Recrutados 30 tabagistas sendo 15 SZ e 15 NSZ pareados por sexo, idade e tempo de tabagismo. Foram medidos complemento C3 e C4, espirometria e difusão pulmonar, dependência de nicotina pelo Teste de Fargerstrom e psicopatologia psiquiátrica nos portadores de esquizofrenia pelo Escala Breve de Avaliação Psiquiátrica (BPRS). Os pacientes foram oriundos do centro colaborador do estudo no HCPA. RESULTADOS: C3 foi significantemente maior em SZ quando comparado com controles (p=0,041), e C4 não mostrou diferença. Houve associação negativa entre o C4 e a capacidade de difusão somente no grupo controle (r=-0,692; p=0,009), sem diferença significativa no grupo de esquizofrênicos (r=0,451; p=0,141). Os grupos foram equivalentes em idade, grau de dependência de nicotina, porém foram diferentes em relação a ocupação (p=0,001). O grupo de esquizofrênicos apresenta maior proporção de desempregados e em benefício do que os controles. Desta forma, apesar de C3 mais aumentado em esquizofrênicos, este sistema aparentemente não media perda de difusão pulmonar, enquanto que aparentemente C4 mostra diferença quanto a prejuízo de difusão em esquizofrênicos tabagistas (maior C4 associado a menor capacidade de difusão somente nos tabagistas sem esquizofrenia). CONCLUSÃO: Quanto ao sistema complemento, houve maior ativação do C3 em tabagistas portadores de esquizofrenia comparados com tabagistas sem esquizofrenia, o que corrobora pesquisas anteriores que descrevem ativação do sistema complemento na SZ indicado pelo aumento dos níveis de C3. Curiosamente, somente nos controles tabagistas foi identificada associação entre aumento de C4 e redução da capacidade de difusão pulmonar. Nos pacientes com esquizofrenia não houve relação entre ativação de C4 e prejuÍzo de difusão pulmonar, o que sugere um padrão de ativação do sistema de complemento diferente dos sujeitos normais, preferencialmente pela via C3 e não pela via C4. Este fator não parece estar afetado pela diferença em escolaridade e trabalho, visto que era esperado que o aumento fosse maior nos esquizofrênicos devido a maior gravidade representada por menor índice de trabalho e menor escolaridade. Este estudo, se confirmado em amostras maiores envolvendo os outros centros colaboradores, pode confirmar existência de mecanismos diferentes de reação inflamatória em esquizofrenia. / Background: Subjects with SZ (schizophrenia) smoke up to three times the rate of the general population. It was found that smokers with schizophrenia smoke more intensely than smokers compared with non-psychiatric. Additionally, there are no systematic reports that despite high rates of smoking, people with schizophrenia have proportionately less lung injury compared with smokers without schizophrenia equal consumption. This difference, if confirmed, would suggest different mechanisms of response to exogenous agents in the respiratory system, and between these different mechanisms could be the complement system, as evidenced in studies of the research group, but not control for smoking. This study investigated whether the pulmonary diffusion capacity in SZ is higher than in non-SZ, and the complement C3 and C4 is different between SZ and NSZ and if at the same time is associated with pulmonary diffusion differently in SZ and NSZ. OBJECTIVES: To compare the pulmonary diffusion capacity and complement C3 and C4 in smokers with and without schizophrenia and examine whether there is evidence of different mechanisms mediating impaired diffusion capacity in smokers with and without SZ. METHODS: This is a matched case-control study, designed as a multicenter, when describing the results of a center. Recruited 30 smokers and 15 non-schizophrenics and 15 schizophrenics matched for sex, age and duration of smoking. We measured C3 and C4 complement, spirometry and DLCO, nicotine dependence and the test Fargerstrom psychiatric psychopathology in patients with schizophrenia by Brief Psychiatric Rating Scale (BPRS). The patients came from the study's collaborating center at HCPA. RESULTS: C3 was significantly higher in SZ compared to controls (p = 0.041), and C4 showed no difference. There was a negative association between C4 and the ability to broadcast only in the control group (r =- 0.692, p = 0.009), no significant difference in the schizophrenic group (r = 0.451, p = 0.141). The groups were equivalent in age, degree of nicotine dependence, but were different in relation to occupation (p = 0.001). The schizophrenic group has a higher proportion of unemployed and for the benefit of the controls. Thus, although most of C3 increased in schizophrenics, this system apparently did not measure loss of pulmonary diffusion, while C4 shows apparent difference in the loss of diffusion in schizophrenic smokers (greater C4 associated with a lower diffusion capacity in smokers without schizophrenia only) . CONCLUSION: As the complement system, activation of C3 was higher in smokers with schizophrenia compared with smokers without schizophrenia, which corroborates previous studies that describe activation of the complement system in SZ indicated by increased levels of C3. Interestingly, only smokers in controls been identified association between increased C4 and reduction of pulmonary diffusion capacity. In patients with schizophrenia there was no relationship between activation of C4 and prejuízo pulmonary diffusion, which suggests a pattern of activation of the complement system different from normal subjects, preferably through C3 and not via C4. This factor does not seem to be affected by the difference in schooling and work, as it was expected that the increase was greater in schizophrenics because of greater severity represented by lower rates of work and less schooling. This study, if confirmed in larger samples involving other collaborating centers, can confirm the existence of different mechanisms of inflammatory response in schizophrenia.

INTRODUÇÃO: Indivíduos com SZ (esquizofrenia) fumam até três vezes mais que a taxa da população em geral. Constatou-se que fumantes com esquizofrenia fumam mais intensamente do que comparados com fumantes não esquizofrênicos. Adicionalmente, existem relatos não sistemáticos de que apesar de alta taxa de tabagismo, os esquizofrênicos apresentam proporcionalmente pouca lesão pulmonar comparado com tabagistas de igual consumo sem esquizofrenia. Esta diferença, se confirmada, poderia sugerir mecanismos diferentes de reação a agentes exógenos nos sistema respiratório, e entre estes mecanismos diferentes poderia estar o sistema de complemento, já evidenciado em estudos do grupo de pesquisa, porém sem controle para tabagismo. Este estudo investigou se a capacidade de difusão pulmonar em SZ é maior que em NSZ, e se o sistema complemento C3 e C4 é diferente entre SZ e NSZ e ao mesmo tempo está associado a difusão pulmonar de forma diferente em SZ e NSZ. OBJETIVOS: comparar a capacidade de difusão pulmonar e complemento C3 e C4 em pacientes fumantes com e sem esquizofrenia e analisar se existe evidência de mecanismos diferentes mediando prejuízo na capacidade de difusão em tabagistas com e sem SZ. MÉTODOS: esse é um estudo caso controle pareado, desenhado para ser multicêntrico, no momento descrevendo resultados de um centro. Recrutados 30 tabagistas sendo 15 SZ e 15 NSZ pareados por sexo, idade e tempo de tabagismo. Foram medidos complemento C3 e C4, espirometria e difusão pulmonar, dependência de nicotina pelo Teste de Fargerstrom e psicopatologia psiquiátrica nos portadores de esquizofrenia pelo Escala Breve de Avaliação Psiquiátrica (BPRS). Os pacientes foram oriundos do centro colaborador do estudo no HCPA. RESULTADOS: C3 foi significantemente maior em SZ quando comparado com controles (p=0,041), e C4 não mostrou diferença. Houve associação negativa entre o C4 e a capacidade de difusão somente no grupo controle (r=-0,692; p=0,009), sem diferença significativa no grupo de esquizofrênicos (r=0,451; p=0,141). Os grupos foram equivalentes em idade, grau de dependência de nicotina, porém foram diferentes em relação a ocupação (p=0,001). O grupo de esquizofrênicos apresenta maior proporção de desempregados e em benefício do que os controles. Desta forma, apesar de C3 mais aumentado em esquizofrênicos, este sistema aparentemente não media perda de difusão pulmonar, enquanto que aparentemente C4 mostra diferença quanto a prejuízo de difusão em esquizofrênicos tabagistas (maior C4 associado a menor capacidade de difusão somente nos tabagistas sem esquizofrenia). CONCLUSÃO: Quanto ao sistema complemento, houve maior ativação do C3 em tabagistas portadores de esquizofrenia comparados com tabagistas sem esquizofrenia, o que corrobora pesquisas anteriores que descrevem ativação do sistema complemento na SZ indicado pelo aumento dos níveis de C3. Curiosamente, somente nos controles tabagistas foi identificada associação entre aumento de C4 e redução da capacidade de difusão pulmonar. Nos pacientes com esquizofrenia não houve relação entre ativação de C4 e prejuÍzo de difusão pulmonar, o que sugere um padrão de ativação do sistema de complemento diferente dos sujeitos normais, preferencialmente pela via C3 e não pela via C4. Este fator não parece estar afetado pela diferença em escolaridade e trabalho, visto que era esperado que o aumento fosse maior nos esquizofrênicos devido a maior gravidade representada por menor índice de trabalho e menor escolaridade. Este estudo, se confirmado em amostras maiores envolvendo os outros centros colaboradores, pode confirmar existência de mecanismos diferentes de reação inflamatória em esquizofrenia. / Background: Subjects with SZ (schizophrenia) smoke up to three times the rate of the general population. It was found that smokers with schizophrenia smoke more intensely than smokers compared with non-psychiatric. Additionally, there are no systematic reports that despite high rates of smoking, people with schizophrenia have proportionately less lung injury compared with smokers without schizophrenia equal consumption. This difference, if confirmed, would suggest different mechanisms of response to exogenous agents in the respiratory system, and between these different mechanisms could be the complement system, as evidenced in studies of the research group, but not control for smoking. This study investigated whether the pulmonary diffusion capacity in SZ is higher than in non-SZ, and the complement C3 and C4 is different between SZ and NSZ and if at the same time is associated with pulmonary diffusion differently in SZ and NSZ. OBJECTIVES: To compare the pulmonary diffusion capacity and complement C3 and C4 in smokers with and without schizophrenia and examine whether there is evidence of different mechanisms mediating impaired diffusion capacity in smokers with and without SZ. METHODS: This is a matched case-control study, designed as a multicenter, when describing the results of a center. Recruited 30 smokers and 15 non-schizophrenics and 15 schizophrenics matched for sex, age and duration of smoking. We measured C3 and C4 complement, spirometry and DLCO, nicotine dependence and the test Fargerstrom psychiatric psychopathology in patients with schizophrenia by Brief Psychiatric Rating Scale (BPRS). The patients came from the study's collaborating center at HCPA. RESULTS: C3 was significantly higher in SZ compared to controls (p = 0.041), and C4 showed no difference. There was a negative association between C4 and the ability to broadcast only in the control group (r =- 0.692, p = 0.009), no significant difference in the schizophrenic group (r = 0.451, p = 0.141). The groups were equivalent in age, degree of nicotine dependence, but were different in relation to occupation (p = 0.001). The schizophrenic group has a higher proportion of unemployed and for the benefit of the controls. Thus, although most of C3 increased in schizophrenics, this system apparently did not measure loss of pulmonary diffusion, while C4 shows apparent difference in the loss of diffusion in schizophrenic smokers (greater C4 associated with a lower diffusion capacity in smokers without schizophrenia only) . CONCLUSION: As the complement system, activation of C3 was higher in smokers with schizophrenia compared with smokers without schizophrenia, which corroborates previous studies that describe activation of the complement system in SZ indicated by increased levels of C3. Interestingly, only smokers in controls been identified association between increased C4 and reduction of pulmonary diffusion capacity. In patients with schizophrenia there was no relationship between activation of C4 and prejuízo pulmonary diffusion, which suggests a pattern of activation of the complement system different from normal subjects, preferably through C3 and not via C4. This factor does not seem to be affected by the difference in schooling and work, as it was expected that the increase was greater in schizophrenics because of greater severity represented by lower rates of work and less schooling. This study, if confirmed in larger samples involving other collaborating centers, can confirm the existence of different mechanisms of inflammatory response in schizophrenia.

INTRODUÇÃO: Indivíduos com SZ (esquizofrenia) fumam até três vezes mais que a taxa da população em geral. Constatou-se que fumantes com esquizofrenia fumam mais intensamente do que comparados com fumantes não esquizofrênicos. Adicionalmente, existem relatos não sistemáticos de que apesar de alta taxa de tabagismo, os esquizofrênicos apresentam proporcionalmente pouca lesão pulmonar comparado com tabagistas de igual consumo sem esquizofrenia. Esta diferença, se confirmada, poderia sugerir mecanismos diferentes de reação a agentes exógenos nos sistema respiratório, e entre estes mecanismos diferentes poderia estar o sistema de complemento, já evidenciado em estudos do grupo de pesquisa, porém sem controle para tabagismo. Este estudo investigou se a capacidade de difusão pulmonar em SZ é maior que em NSZ, e se o sistema complemento C3 e C4 é diferente entre SZ e NSZ e ao mesmo tempo está associado a difusão pulmonar de forma diferente em SZ e NSZ. OBJETIVOS: comparar a capacidade de difusão pulmonar e complemento C3 e C4 em pacientes fumantes com e sem esquizofrenia e analisar se existe evidência de mecanismos diferentes mediando prejuízo na capacidade de difusão em tabagistas com e sem SZ. MÉTODOS: esse é um estudo caso controle pareado, desenhado para ser multicêntrico, no momento descrevendo resultados de um centro. Recrutados 30 tabagistas sendo 15 SZ e 15 NSZ pareados por sexo, idade e tempo de tabagismo. Foram medidos complemento C3 e C4, espirometria e difusão pulmonar, dependência de nicotina pelo Teste de Fargerstrom e psicopatologia psiquiátrica nos portadores de esquizofrenia pelo Escala Breve de Avaliação Psiquiátrica (BPRS). Os pacientes foram oriundos do centro colaborador do estudo no HCPA. RESULTADOS: C3 foi significantemente maior em SZ quando comparado com controles (p=0,041), e C4 não mostrou diferença. Houve associação negativa entre o C4 e a capacidade de difusão somente no grupo controle (r=-0,692; p=0,009), sem diferença significativa no grupo de esquizofrênicos (r=0,451; p=0,141). Os grupos foram equivalentes em idade, grau de dependência de nicotina, porém foram diferentes em relação a ocupação (p=0,001). O grupo de esquizofrênicos apresenta maior proporção de desempregados e em benefício do que os controles. Desta forma, apesar de C3 mais aumentado em esquizofrênicos, este sistema aparentemente não media perda de difusão pulmonar, enquanto que aparentemente C4 mostra diferença quanto a prejuízo de difusão em esquizofrênicos tabagistas (maior C4 associado a menor capacidade de difusão somente nos tabagistas sem esquizofrenia). CONCLUSÃO: Quanto ao sistema complemento, houve maior ativação do C3 em tabagistas portadores de esquizofrenia comparados com tabagistas sem esquizofrenia, o que corrobora pesquisas anteriores que descrevem ativação do sistema complemento na SZ indicado pelo aumento dos níveis de C3. Curiosamente, somente nos controles tabagistas foi identificada associação entre aumento de C4 e redução da capacidade de difusão pulmonar. Nos pacientes com esquizofrenia não houve relação entre ativação de C4 e prejuÍzo de difusão pulmonar, o que sugere um padrão de ativação do sistema de complemento diferente dos sujeitos normais, preferencialmente pela via C3 e não pela via C4. Este fator não parece estar afetado pela diferença em escolaridade e trabalho, visto que era esperado que o aumento fosse maior nos esquizofrênicos devido a maior gravidade representada por menor índice de trabalho e menor escolaridade. Este estudo, se confirmado em amostras maiores envolvendo os outros centros colaboradores, pode confirmar existência de mecanismos diferentes de reação inflamatória em esquizofrenia. / Background: Subjects with SZ (schizophrenia) smoke up to three times the rate of the general population. It was found that smokers with schizophrenia smoke more intensely than smokers compared with non-psychiatric. Additionally, there are no systematic reports that despite high rates of smoking, people with schizophrenia have proportionately less lung injury compared with smokers without schizophrenia equal consumption. This difference, if confirmed, would suggest different mechanisms of response to exogenous agents in the respiratory system, and between these different mechanisms could be the complement system, as evidenced in studies of the research group, but not control for smoking. This study investigated whether the pulmonary diffusion capacity in SZ is higher than in non-SZ, and the complement C3 and C4 is different between SZ and NSZ and if at the same time is associated with pulmonary diffusion differently in SZ and NSZ. OBJECTIVES: To compare the pulmonary diffusion capacity and complement C3 and C4 in smokers with and without schizophrenia and examine whether there is evidence of different mechanisms mediating impaired diffusion capacity in smokers with and without SZ. METHODS: This is a matched case-control study, designed as a multicenter, when describing the results of a center. Recruited 30 smokers and 15 non-schizophrenics and 15 schizophrenics matched for sex, age and duration of smoking. We measured C3 and C4 complement, spirometry and DLCO, nicotine dependence and the test Fargerstrom psychiatric psychopathology in patients with schizophrenia by Brief Psychiatric Rating Scale (BPRS). The patients came from the study's collaborating center at HCPA. RESULTS: C3 was significantly higher in SZ compared to controls (p = 0.041), and C4 showed no difference. There was a negative association between C4 and the ability to broadcast only in the control group (r =- 0.692, p = 0.009), no significant difference in the schizophrenic group (r = 0.451, p = 0.141). The groups were equivalent in age, degree of nicotine dependence, but were different in relation to occupation (p = 0.001). The schizophrenic group has a higher proportion of unemployed and for the benefit of the controls. Thus, although most of C3 increased in schizophrenics, this system apparently did not measure loss of pulmonary diffusion, while C4 shows apparent difference in the loss of diffusion in schizophrenic smokers (greater C4 associated with a lower diffusion capacity in smokers without schizophrenia only) . CONCLUSION: As the complement system, activation of C3 was higher in smokers with schizophrenia compared with smokers without schizophrenia, which corroborates previous studies that describe activation of the complement system in SZ indicated by increased levels of C3. Interestingly, only smokers in controls been identified association between increased C4 and reduction of pulmonary diffusion capacity. In patients with schizophrenia there was no relationship between activation of C4 and prejuízo pulmonary diffusion, which suggests a pattern of activation of the complement system different from normal subjects, preferably through C3 and not via C4. This factor does not seem to be affected by the difference in schooling and work, as it was expected that the increase was greater in schizophrenics because of greater severity represented by lower rates of work and less schooling. This study, if confirmed in larger samples involving other collaborating centers, can confirm the existence of different mechanisms of inflammatory response in schizophrenia.

L’allogreffe de cellules hématopoïétiques est une stratégie thérapeutique importante dans les hémopathies malignes. La maladie du greffon contre l’hôte (GvH) en est une complication majeure menaçant le pronostic vital. Elle est due à la reconnaissance des antigènes du receveur par les lymphocytes T du donneur et à l’activation de ceux-ci, à l’origine de dommages tissulaires. L’altération de la barrière intestinale joue un rôle critique dans la GvH. La famille des protéines de choc thermique (HSP)90 comporte cinq membres dont trois cytosoliques dénommés HSP90, et un localisé dans le réticulum endoplasmique (RE), Gp96, qui peut être sécrété en cas de stress. Nous montrons dans nos travaux de thèse que la 17AAG, un inhibiteur des HSP90, réduit la mortalité liée à la GvH dans un modèle murin. Cet effet est associé à une augmentation de la réponse au stress du RE dans les cellules épithéliales intestinales comme en atteste l’augmentation de l’épissage du facteur de transcription XBP-1, corrélée à une diminution du dommage tissulaire intestinal. Ces résultats permettent d’envisager une place pour la 17AAG ou d’autres inhibiteurs de HSP90 dans la prévention de la GvH chez l’homme. D’autre part, nous montrons que Gp96 est sécrétée dans le sérum de patients développant une GvH aiguë sévère avec atteinte intestinale. Nous suggérons de valider la pertinence de Gp96 comme biomarqueur de GvH intestinale dans une étude de plus grande ampleur. Enfin, nous trouvons que Gp96 s’associe avec le composant 3 du complément, une protéine impliquée dans l’immunité innée et adaptative, et inhibe certaines de ses fonctions. Les conséquences fonctionnelles de cette association sont discutées. / Allogeneic hematopoietic cell transplantation is a treatment for certain disorders including hematologic malignancies. Graft-versus-host-disease (GvHD) is a major, life-threatening complication. It is due to the recognition of recipient antigens by donor T cells, which activate and damage tissues. Intestinal barrier alteration plays a critical role in GvHD. Heat shock proteins (HSP)90 include five members, three cytosolic members named HSP90, and one member localized in endoplasmic reticulum (ER) called Gp96 and able to gain extracellular level in case of stress. We show in our thesis that 17AAG, a HSP90 inhibitor, reduces GvHD mortality in a mouse model. This effect is associated with an increase in ER stress pathway in intestinal epithelial cells as figured by transcription factor XBP-1 splicing, correlated to a decrease in intestinal tissue damage. These results suggest that 17AAG could be considered in GvHD prevention in human. Moreover, we show that Gp96 is secreted in serum of patients developing an acute GvHD with intestinal involvement. We propose to validate the relevance of Gp96 as an intestinal GvHD biomarker is a larger study. Finally, we find that Gp96 associate with complement component 3, a protein involved in innate and adaptive immunity, and inhibit some of its functions. Functional consequences of this association are discussed.