Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 4 uppsatser.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Title from first page of PDF file (viewed Feb. 18, 2009). Includes bibliographical references.

Orientador: Renata de Oliveira Mattos Graner / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-24T14:42:19Z (GMT). No. of bitstreams: 1 Alves_LiviaAraujo_M.pdf: 2021430 bytes, checksum: 07a84279508cd84bfef41550d34e6ca7 (MD5) Previous issue date: 2014 / Resumo: Streptococcus mutans (SM) é um patógeno oral da cárie dentária e endocardite infecciosa. Para se estabelecer no hospedeiro, SM precisa se adaptar às condições biofísicas e aos fatores de defesa do hospedeiro. Para isto, SM utiliza sistemas reguladores de transcrição de dois componentes (SDC). Dois SDCs, VicRK e CovR, são associados à virulência de SM. O objetivo deste trabalho foi investigar a participação dos reguladores de transcrição gênica VicRK e CovR na evasão de SM ao sistema complemento e fagocitose. Dessa forma, a marcação pelo complemento foi comparada entre os mutantes vicK- e covR- obtidos da cepa SM UA159 (UAvic e UAcov, respectivamente) e UA159, através da incubação com soro humano a 20% ou soro humano livre de C1q (30 min, 37 ?C, 10% CO2). A deposição de C3b sobre a superfície de SM foi analisada também nas cepas cultivadas em meio com 0,1% de sacarose. A quantidade de C3b nas superfícies bacterianas foi determinada através de reações com anticorpos IgG de cabra anti-C3 humano conjugado com FITC e análise de citometria. Bactérias incubadas com PBS foram usadas como controle negativo. O reconhecimento das cepas de SM por anticorpos séricos opsonizantes foi realizado com anticorpos anti-IgG humano conjugado com FITC e anti-IgM humano conjugado com APC. Para análise da fagocitose, as mesmas cepas coradas com FITC foram incubadas com neutrófilos (PMN) por 5 e 30 min. na presença ou ausência de soro humano a 20%; o número de PMN com bactérias fagocitadas foi determinado por citometria de fluxo. A deposição de C3b foi menor em UAcov (10,86%) e em UAvic (7,6%), comparado à UA159 (23,5%). Na presença de sacarose, a marcação por C3b caiu para 10,86% em UA159, e para os mutantes UAcov e UAvic foi reduzida a 6,6 e 3,96%, respectivamente (ANOVA p<0,001). Os mutantes UAcov e UAvic foram menos reativos contra anticorpos IgG e IgM. A fagocitose por PMN foi reduzida em UAcov e UAvic em cerca de 50 a 60% em relação à UA159 nos tempos de 5 e 30 min. (ANOVA p< 0,005). Assim, a inativação dos sistemas VicRK e CovR reduz significativamente a deposição de C3b do complemento e a frequência de fagocitose de SM, indicando que estes SDC regulam genes envolvidos no escape à opsonização pelo complemento / Abstract: Streptococcus mutans (SM) is an oral pathogen of dental caries and infective endocarditis. To get established in host sites, SM needs to adapt to biophysical conditions and host defense factors. To this purpose, SM applies transcriptional regulatory systems of two components (SDC). Two SDCs, VicRK and CovR, have been implicated in SM virulence. The aim of this study was to investigate the role of VicRK and CovR on SM evasion from complement system and phagocytosis by neutrophils (PMN). Thus, complement deposition was compared between vicK- and covR- mutants obtained strain UA159 (UAvic and UAcov, respectively) and the parent UA159 exposed to 20% human serum or human serum depleted of C1q (30 min, 37ºC, 10% CO2). Deposition of C3b on SM surfaces was also analyzed in strains cultivates in the presence of 0.1% sucrose. The amount of C3b on the bacterial surface was determined by reactivity with goat IgG antibody anti-C3 conjugated FITC and flow cytometry analysis. Bacteria incubated with PBS were used as negative control. The reactiveness of SM strains with human serum antibodies was quantified by flow citometry with anti- human IgG- FITC and anti- human IgM-APC antibodies. For analysis of phagocytosis, the strains stained with FITC were incubated with PMN during 5 and 30 min. in the presence or absence of 20% human serum; the number of internalized bacteria by PMN was determined by flow cytometry. The deposition of C3b on UAcov (10.86 %) and UAvic (7.6%) was lower, compared to UA159 (23.5%) (ANOVA p<0,001). In the presence of sucrose, C3b deposition decreased to 10.86 % in UA159, and to 6.6 and 3.96% in UAcov and UAvic , respectively (ANOVA p < 0.001). The UAcov and UAvic mutants were less reactive with IgG and IgM antibodies. The phagocytosis by PMN was 50 to 60% reduced in UAcov and UAvic compared to UA159, respectively at times 5 and 30 min. (ANOVA p < 0.005). Thus, inactivation of CovR and VicRK TCS systems significantly reduces deposition of complement C3b and phagocytosis by PMN in a serum-dependent way, indicating that these SDC regulate genes involved in the evasion of complement to opsonization / Mestrado / Microbiologia e Imunologia / Mestra em Biologia Buco-Dental

<p>Intraportal transplantation of isolated islets of Langerhans is a procedure approaching clinical acceptance as a treatment for patients with type I diabetes mellitus. One major problem with this treatment is that large amounts of cells are lost at the time of infusion into the portal vein, resulting in a low level of engraftment of the islets. One likely explanation for this loss is the instant blood-mediated inflammatory reaction (IBMIR), a thrombotic/inflammatory reaction occurring when islets come in contact with blood. The IBMIR is characterized by coagulation and complement activation, leading to platelet consumption, leukocyte infiltration of the islets, and disruption of islet integrity.</p><p>In this thesis, the IBMIR is shown to be triggered by tissue factor (TF), the main initiator of blood coagulation<i> in vivo</i>. TF is expressed in two forms by the endocrine cells of the pancreas, a full-length membrane-bound and an alternatively spliced soluble form. Blocking TF <i>in vitro</i> efficiently reduces the macroscopic clotting, expression of coagulation activation markers, and leukocyte infiltration. This blockade can be achieved by adding either an active site-specific anti-TF antibody or site-inactivated FVIIa that competes with active FVIIa in the blood. TF may be secreted from the islets, since it is colocalized with insulin and glucagon in their granules. The IBMIR has also been demonstrated <i>in vivo</i> in patients transplanted with isolated islets.</p><p>There are two ways to block the IBMIR in transplantation: systemic treatment of the patients, or islet pretreatment before transplantation to reduce their thrombogenicity. In this thesis, low molecular weight dextran sulfate (LMW-DS) is shown to reduce activation of the complement and coagulation systems and decrease the cell infiltration into the islets <i>in vitro</i> and<i> in vivo</i>, in both a xenogenic and an allogenic setting. Based on these results, LMW-DS is now in clinical trials. </p>

Intraportal transplantation of isolated islets of Langerhans is a procedure approaching clinical acceptance as a treatment for patients with type I diabetes mellitus. One major problem with this treatment is that large amounts of cells are lost at the time of infusion into the portal vein, resulting in a low level of engraftment of the islets. One likely explanation for this loss is the instant blood-mediated inflammatory reaction (IBMIR), a thrombotic/inflammatory reaction occurring when islets come in contact with blood. The IBMIR is characterized by coagulation and complement activation, leading to platelet consumption, leukocyte infiltration of the islets, and disruption of islet integrity. In this thesis, the IBMIR is shown to be triggered by tissue factor (TF), the main initiator of blood coagulation in vivo. TF is expressed in two forms by the endocrine cells of the pancreas, a full-length membrane-bound and an alternatively spliced soluble form. Blocking TF in vitro efficiently reduces the macroscopic clotting, expression of coagulation activation markers, and leukocyte infiltration. This blockade can be achieved by adding either an active site-specific anti-TF antibody or site-inactivated FVIIa that competes with active FVIIa in the blood. TF may be secreted from the islets, since it is colocalized with insulin and glucagon in their granules. The IBMIR has also been demonstrated in vivo in patients transplanted with isolated islets. There are two ways to block the IBMIR in transplantation: systemic treatment of the patients, or islet pretreatment before transplantation to reduce their thrombogenicity. In this thesis, low molecular weight dextran sulfate (LMW-DS) is shown to reduce activation of the complement and coagulation systems and decrease the cell infiltration into the islets in vitro and in vivo, in both a xenogenic and an allogenic setting. Based on these results, LMW-DS is now in clinical trials.

Both Multiple Sclerosis (MS) and Guillan-Barré syndrome (GBS) are neurological inflammatory demyelinating autoimmune diseases, with a probable antibody contribution. Complement proteins in both MS and GBS does play a role in inflammation and demyelination at pathogenesis, according to earlier scientific evidence. The aim of this examination project work was to investigate systemic and intrathecal complement activation in MS and GBS, to gain further knowledge that might be useful for development of future therapeutics targeting immune responses during those diseases. An additional aim was to develop a new ELISA method for detection of complement iC3. By using sandwich ELISA, complement proteins C1q, C4, C3, fH and C3a were measured in plasma and cerebrospinal fluid (CSF) from persons within 4 different diagnostic groups; MS, other neurological diseases (OND), GBS and controls (C). An ELISA method to detect iC3 (hydrolysed C3) was also developed, including usage of SDS-PAGE. Results based on raw data and statistical analysis show significantly elevated levels of C3a (C3a/C3) in MS and decreased C3 in plasma. In CSF low levels of C4 and C3a/C3 in MS were detected, though correlation of C3a and C1q was positive. GBS reveal high levels of all complement proteins analysed in CSF except for C3, and a positive correlation of C3a and C1q as well as C3a and fH was found. These results indicate that MS patients have systemic complement activation; however the activation pathway is not determined. Complement activation in MS may also occur intrathecally, with correlation analysis indicating a possible activation via the classical pathway. MS patients suffering from a more acute relapsing-remitting (RR) MS have a more prominent systemic complement activation compared to MS patients responding to beta-interferon treatment. Systemic increased C3a/C3 ratio may be a possible biomarker to distinguish more acute RR MS in an earlier step of MS pathogenesis and should be further investigated. GBS patients have an intrathecal complement activation that seems to occur via the classical pathway.

Les efforts investis pour diminuer les risques de développer un infarctus du myocarde sont nombreux. Aujourd’hui les médecins prennent connaissance des divers facteurs de risque connus prédisposant aux syndromes coronariens aigus (SCA) dans le but de prendre en charge les patients «à risque» [1]. Bien que le suivi rigoureux et le contrôle de certains facteurs de risque modifiables aient permis une meilleure gestion des cas de SCA, les cas d’infarctus persistent de manière encore trop fréquente dans le monde. Puisque d’importantes études ont démontré que les SCA pouvaient survenir sans même la présence des facteurs de risque conventionnels [2, 3], les chercheurs se sont penchés sur un autre mécanisme potentiellement responsable de l’avènement des SCA : l’inflammation. L’inflammation joue un rôle prépondérant dans l’initiation, la progression et les complications de l’athérosclérose [4, 5] mais aussi dans les situations post-infarctus [6, 7]. Au cours des dernières années, le contrôle du processus inflammatoire est devenu une cible de choix dans la prévention et le traitement des SCA. Cependant, malgré les efforts investis, aucun de ces traitements ne s’est avéré pleinement efficace dans l’atteinte du but ultime visé par une diminution de l’inflammation : la diminution de la mortalité. Le complément est un système complexe reconnu principalement pour son rôle primordial dans l’immunité [2]. Cependant, lorsqu’il est activé de manière inappropriée ou excessive, il peut être à l’origine de nombreux dommages cellulaires caractéristiques de plusieurs pathologies inflammatoires dont font partie les complications de l’athérosclérose et des événements post-infarctus. Le travail effectué dans le cadre de mon doctorat vise à établir les rôles physiopathologiques du complément dans les interactions de l’axe thrombose-inflammation caractéristiques des SCA dans le but ultime d’identifier des cibles thérapeutiques permettant le développement de nouvelles approches pour la prévention et le traitement de ces pathologies. Les principaux résultats obtenus durant mon cursus suggèrent d’abord que la voie alterne du complément peut représenter une cible thérapeutique de choix dans les maladies coronariennes aiguës puisque l’activation terminale du complément semble y être principalement causée par l’activation du cette voie. De faibles niveaux sériques de MBL (mannan-binding lectin) et une activation terminale négligeable du complément caractérisent plutôt la maladie coronarienne stable. En comparant l’activité relative de chacune des voies du complément chez des cohortes de patients traités ou non par un anticorps spécifique à la protéine C5 du complément (pexelizumab), un second volet démontre quant à lui qu’une inhibition de l’activation du C5 n’a pas d’effet bénéfique majeur sur l’inhibition de la formation du complexe sC5b-9 ou sur les événements cliniques subséquents. Par conséquent, nous avons exploré, à l’aide d’un modèle in vitro, les raisons de l’inefficacité du traitement. Les résultats révèlent que le blocage du C5 avec le pexelizumab inhibe la production de l’anaphylatoxine pro-inflammatoire C5a et du complexe terminal du complément sans toutefois avoir d’effet sur l’apoptose des cellules endothéliales produites induite par le sérum des patients atteints de STEMI. Finalement, une autre section stipule que l’atorvastatine diminue l’activation du complément induite par les plaquettes sanguines chez des patients hypercholestérolémiques, mettant en évidence l’importance du rôle de cette statine dans la réduction des effets délétères de l’activation du système du complément médié par les plaquettes. Ensemble, l’étude du rôle spécifique des différentes voies d’activation du complément dans des contextes pathologiques variés, l’analyse des effets d’une inhibition spécifique de la protéine C5 du complément dans la progression des SCA et la mise en évidence des interactions entre l’activation du complément et les plaquettes activées ont contribué au développement d’une meilleure connaissance des rôles physiopathologiques du complément dans la progression de la maladie coronarienne. / Many efforts have been made in lowering the risk of myocardial infarction in the general population. Most clinicians are knowledgeable of the several identified risk factors leading to the development of acute coronary syndromes (ACS), and in turn, insure a better follow-up for “at risk” patients [1]. Despite the fact that intensive efforts in controlling modifiable risk factors have led to a better management of new cases of ACS, myocardial infarction and its deleterious consequences are still a world plague. Because it as been shown that ACS can occur without the presence of traditional risk factors [3, 4], researchers have been interested in modifying new ACS biological pathways such as inflammation. Inflammation plays a key role in the initiation, progression, and complications of atherosclerosis [5, 6], but also in post-infarction situations [7, 8]. In the past years, inflammation markers have become important targets for the prevention and treatment of ACS. Despite intensive efforts, none of the yet tested drug was found to be effective in decreasing mortality. The complement system is mainly known for its fundamental role in innate and adaptive immunity [2]. However, excessive activation of the complement can lead to a significant number of deleterious effects such as inflammation, apoptosis, necrosis and cell lysis. Earlier findings have shown that complement is extensively activated in atherosclerotic lesions, particularly in vulnerable and ruptured plaques. The objective of my doctoral project was to establish the pathophysiological roles of complement in the axis inflammation-thrombosis of ACS with the ultimate goal of identifying new therapeutic targets leading to the development of new drugs for the prevention and treatment of these diseases. The main results obtained first suggest that the complement alternative pathway represents a potential therapeutic target in acute coronary disease since terminal complement activation occurs mainly by this specific pathway. Low MBL levels (mannan-binding lectin) in serum and negligible terminal complement activation rather characterize stable coronary artery disease. By comparing the relative activity of each pathway of the complement in patients treated or not by an antibody specific to the C5 protein of the complement (pexelizumab), other results show that an inhibition of C5 activation does not have a major beneficial effect on the inhibition of the sC5b-9 complex expression or on the subsequent clinical events. Consequently, we explored, using an in vitro model of endothelial cells, the reasons of this inefficiency. This work reveals that C5 inhibition by pexelizumab inhibits the production of the pro-inflammatory anaphylatoxin C5a and of the terminal complement complex without, however, effecting endothelial cell apoptosis induced by the serum of patients with STEMI. Finally, another section stipulates that atorvastatin decreases platelet-induced complement activation in hypercholesterolemic patients, highlighting the importance of statins in the reduction of the deleterious effects of platelets-induced complement activation. All together, the study of the specific role of the various pathways of complement activation in different pathological contexts, the analysis of the effects of a specific inhibition of the C5 complement protein in the progression of ACS and the highlighting of the interactions between complement and platelet activation contribute to the development of a better knowledge of the pathophysiological roles of the complement system in ACS.

<p>Prostasomes are extracellularly occurring organelles which are secreted in human semen by the prostate gland. Prostasomes have several known biological activities, but their physiological function is still unclear. In this thesis some new aspects were studied on the biological role of the prostasomes. </p><p>The motility-stimulatory effect of prostasomes on cryopreserved spermatozoa was further studied by supplementing the swim-up medium with seminal prostasomes, and with prostasomes purified from a PC-3 prostate cancer cell line (PC-3 prostasomes), on fresh spermatozoa. The recovery of motile spermatozoa after swim-up increased by 50% when the swim-up medium was supplemented with prostasomes. The PC-3 prostasomes bore a functional resemblance to seminal prostasomes as regards various expressions of sperm motility promotion. </p><p>Prostasomes proved to have potent antibacterial effects. The effects were not strictly confined to Bacillus megaterium since a few other bacteria were also sensitive. The high percentage of patients with anti-prostasome antibodies showed that prostasomes could be one of the major targets for antisperm antibodies (ASA). The results demonstrate that ASA in serum of infertile men and women recognise prostasomes as antigens, and that polyclonal antibodies raised against prostasomes agglutinate human spermatozoa. This suggests that prostasomes contribute at least partly to immunological infertility. Three types of prostasomes (seminal-, native- and metastasis-derived prostasomes) demonstrated similarities regarding a high cholesterol/phospholipid ratio and some marker enzymes. The conclusion is that prostasomes have a common and exclusive prostatic origin in man and that they are internalised in storage vesicles of the secretory cells and released in toto by an ordinary exocytotic event.</p>

Prostasomes are extracellularly occurring organelles which are secreted in human semen by the prostate gland. Prostasomes have several known biological activities, but their physiological function is still unclear. In this thesis some new aspects were studied on the biological role of the prostasomes. The motility-stimulatory effect of prostasomes on cryopreserved spermatozoa was further studied by supplementing the swim-up medium with seminal prostasomes, and with prostasomes purified from a PC-3 prostate cancer cell line (PC-3 prostasomes), on fresh spermatozoa. The recovery of motile spermatozoa after swim-up increased by 50% when the swim-up medium was supplemented with prostasomes. The PC-3 prostasomes bore a functional resemblance to seminal prostasomes as regards various expressions of sperm motility promotion. Prostasomes proved to have potent antibacterial effects. The effects were not strictly confined to Bacillus megaterium since a few other bacteria were also sensitive. The high percentage of patients with anti-prostasome antibodies showed that prostasomes could be one of the major targets for antisperm antibodies (ASA). The results demonstrate that ASA in serum of infertile men and women recognise prostasomes as antigens, and that polyclonal antibodies raised against prostasomes agglutinate human spermatozoa. This suggests that prostasomes contribute at least partly to immunological infertility. Three types of prostasomes (seminal-, native- and metastasis-derived prostasomes) demonstrated similarities regarding a high cholesterol/phospholipid ratio and some marker enzymes. The conclusion is that prostasomes have a common and exclusive prostatic origin in man and that they are internalised in storage vesicles of the secretory cells and released in toto by an ordinary exocytotic event.

Les efforts investis pour diminuer les risques de développer un infarctus du myocarde sont nombreux. Aujourd’hui les médecins prennent connaissance des divers facteurs de risque connus prédisposant aux syndromes coronariens aigus (SCA) dans le but de prendre en charge les patients «à risque» [1]. Bien que le suivi rigoureux et le contrôle de certains facteurs de risque modifiables aient permis une meilleure gestion des cas de SCA, les cas d’infarctus persistent de manière encore trop fréquente dans le monde. Puisque d’importantes études ont démontré que les SCA pouvaient survenir sans même la présence des facteurs de risque conventionnels [2, 3], les chercheurs se sont penchés sur un autre mécanisme potentiellement responsable de l’avènement des SCA : l’inflammation. L’inflammation joue un rôle prépondérant dans l’initiation, la progression et les complications de l’athérosclérose [4, 5] mais aussi dans les situations post-infarctus [6, 7]. Au cours des dernières années, le contrôle du processus inflammatoire est devenu une cible de choix dans la prévention et le traitement des SCA. Cependant, malgré les efforts investis, aucun de ces traitements ne s’est avéré pleinement efficace dans l’atteinte du but ultime visé par une diminution de l’inflammation : la diminution de la mortalité. Le complément est un système complexe reconnu principalement pour son rôle primordial dans l’immunité [2]. Cependant, lorsqu’il est activé de manière inappropriée ou excessive, il peut être à l’origine de nombreux dommages cellulaires caractéristiques de plusieurs pathologies inflammatoires dont font partie les complications de l’athérosclérose et des événements post-infarctus. Le travail effectué dans le cadre de mon doctorat vise à établir les rôles physiopathologiques du complément dans les interactions de l’axe thrombose-inflammation caractéristiques des SCA dans le but ultime d’identifier des cibles thérapeutiques permettant le développement de nouvelles approches pour la prévention et le traitement de ces pathologies. Les principaux résultats obtenus durant mon cursus suggèrent d’abord que la voie alterne du complément peut représenter une cible thérapeutique de choix dans les maladies coronariennes aiguës puisque l’activation terminale du complément semble y être principalement causée par l’activation du cette voie. De faibles niveaux sériques de MBL (mannan-binding lectin) et une activation terminale négligeable du complément caractérisent plutôt la maladie coronarienne stable. En comparant l’activité relative de chacune des voies du complément chez des cohortes de patients traités ou non par un anticorps spécifique à la protéine C5 du complément (pexelizumab), un second volet démontre quant à lui qu’une inhibition de l’activation du C5 n’a pas d’effet bénéfique majeur sur l’inhibition de la formation du complexe sC5b-9 ou sur les événements cliniques subséquents. Par conséquent, nous avons exploré, à l’aide d’un modèle in vitro, les raisons de l’inefficacité du traitement. Les résultats révèlent que le blocage du C5 avec le pexelizumab inhibe la production de l’anaphylatoxine pro-inflammatoire C5a et du complexe terminal du complément sans toutefois avoir d’effet sur l’apoptose des cellules endothéliales produites induite par le sérum des patients atteints de STEMI. Finalement, une autre section stipule que l’atorvastatine diminue l’activation du complément induite par les plaquettes sanguines chez des patients hypercholestérolémiques, mettant en évidence l’importance du rôle de cette statine dans la réduction des effets délétères de l’activation du système du complément médié par les plaquettes. Ensemble, l’étude du rôle spécifique des différentes voies d’activation du complément dans des contextes pathologiques variés, l’analyse des effets d’une inhibition spécifique de la protéine C5 du complément dans la progression des SCA et la mise en évidence des interactions entre l’activation du complément et les plaquettes activées ont contribué au développement d’une meilleure connaissance des rôles physiopathologiques du complément dans la progression de la maladie coronarienne. / Many efforts have been made in lowering the risk of myocardial infarction in the general population. Most clinicians are knowledgeable of the several identified risk factors leading to the development of acute coronary syndromes (ACS), and in turn, insure a better follow-up for “at risk” patients [1]. Despite the fact that intensive efforts in controlling modifiable risk factors have led to a better management of new cases of ACS, myocardial infarction and its deleterious consequences are still a world plague. Because it as been shown that ACS can occur without the presence of traditional risk factors [3, 4], researchers have been interested in modifying new ACS biological pathways such as inflammation. Inflammation plays a key role in the initiation, progression, and complications of atherosclerosis [5, 6], but also in post-infarction situations [7, 8]. In the past years, inflammation markers have become important targets for the prevention and treatment of ACS. Despite intensive efforts, none of the yet tested drug was found to be effective in decreasing mortality. The complement system is mainly known for its fundamental role in innate and adaptive immunity [2]. However, excessive activation of the complement can lead to a significant number of deleterious effects such as inflammation, apoptosis, necrosis and cell lysis. Earlier findings have shown that complement is extensively activated in atherosclerotic lesions, particularly in vulnerable and ruptured plaques. The objective of my doctoral project was to establish the pathophysiological roles of complement in the axis inflammation-thrombosis of ACS with the ultimate goal of identifying new therapeutic targets leading to the development of new drugs for the prevention and treatment of these diseases. The main results obtained first suggest that the complement alternative pathway represents a potential therapeutic target in acute coronary disease since terminal complement activation occurs mainly by this specific pathway. Low MBL levels (mannan-binding lectin) in serum and negligible terminal complement activation rather characterize stable coronary artery disease. By comparing the relative activity of each pathway of the complement in patients treated or not by an antibody specific to the C5 protein of the complement (pexelizumab), other results show that an inhibition of C5 activation does not have a major beneficial effect on the inhibition of the sC5b-9 complex expression or on the subsequent clinical events. Consequently, we explored, using an in vitro model of endothelial cells, the reasons of this inefficiency. This work reveals that C5 inhibition by pexelizumab inhibits the production of the pro-inflammatory anaphylatoxin C5a and of the terminal complement complex without, however, effecting endothelial cell apoptosis induced by the serum of patients with STEMI. Finally, another section stipulates that atorvastatin decreases platelet-induced complement activation in hypercholesterolemic patients, highlighting the importance of statins in the reduction of the deleterious effects of platelets-induced complement activation. All together, the study of the specific role of the various pathways of complement activation in different pathological contexts, the analysis of the effects of a specific inhibition of the C5 complement protein in the progression of ACS and the highlighting of the interactions between complement and platelet activation contribute to the development of a better knowledge of the pathophysiological roles of the complement system in ACS.