Os tecidos pulpar e periodontal são frequentemente agredidos por fatores ambientais como calor, trauma mecânico e micro-organismos, sendo estes considerados o fator etiológico principal das periodontopatias e periapicopatias. Dentre as células residentes desses tecidos, especial atenção tem sido dada ao papel dos fibroblastos no desenvolvimento da resposta imune. Fibroblastos são células que respondem à estímulos microbianos e existem evidências do papel de receptores do tipo Toll (TLR) no reconhecimento desses estímulos. Dessa forma, o presente trabalho teve como objetivo principal avaliar o reconhecimento de Candida albicans por fibroblastos gengivais e pulpares. Para tal, fibroblastos isolados a partir de tecido gengival e pulpar de camundongos do grupo controle e deficientes de TLR2, CD14 e MyD88 foram avaliados quanto à expressão de TLRs e moléculas de superfície, resposta proliferativa e produção de citocinas (TGF-β, IL-1β, TNF-α, IL-13 e IL-6), após a estimulação com agonistas de TLR2, TLR4 e C. albicans. Fibroblastos gengivais e pulpares, apesar de provenientes de tecidos diferentes, apresentaram características morfológicas semelhantes. Contudo, a cinética de crescimento dos fibroblastos gengivais deficientes de MyD88 foi mais lenta, e fibroblastos pulpares demoraram mais tempo para surgir a partir dos fragmentos de tecido. A ausência de TLR2 e da molécula adaptadora MyD88 não afetaram a produção de colágeno Tipo I pelos fibroblastos gengivais. Entretanto, fibroblastos deficientes de CD14 apresentaram baixa produção de colágeno. Ademais, os fibroblastos gengivais expressaram TLR2, TLR3, TLR4, assim como as moléculas de adesão ICAM-1 e CD44. A ausência de TLR2 e CD14 interferiu na resposta proliferativa de fibroblastos gengivais e pulpares, respectivamente. O reconhecimento de C. albicans por fibroblastos gengivais e pulpares modulou a produção das citocinas. A produção de TNF-α foi dependente da sinalização via MyD88, CD14 e TLR2, enquanto que a produção de IL-1β e IL-13 foi dependente de TLR2. / Pulpal and periapical tissue are frequently injured by heat, mechanical trauma and microorganisms, which are considered the main etiological factor of periodontal and endodontic diseases. Among these tissue resident cells, special attention has been given to fibroblasts in the immune response. Fibroblasts are cells that recognize pathogens through Toll like receptors (TLR). The aim of this study was to evaluate the recognition of Candida albicans by pulpal and gingival fibroblasts from TLR2, CD14, MyD88 knockout mice and control group mice. The results were analyzed concerning the expression of TLR(s) and surface molecules, proliferative response and citokynes production (TGF-β, IL-1β, TNF-α, IL-13 e IL-6) after the cells stimulation with TLR2, TLR4 and C.albicans agonists. Gingival and Pulpal fibroblasts, even isolated from different tissue, showed morphological similarities; however, gingival fibroblast deficient of MyD88 show lower proliferative response and pulpa l fibroblasts needed more time to detach from tissue fragments. The production of Type I collagen was affected in gingival cells deficient of CD14. Gingival fibroblasts expressed TLR2, TLR3, TLR4, and the adhesion molecules (ICAM-1 and CD44). The absence of TLR2 and CD14 interfered with the proliferative response of pulpal and gingival fibroblasts, respectively. The recognition of C. albicans by gingival and pulpal fibroblasts modulated the citokynes production. TNF-α production after the recognition of C. albicans was dependent from MyD88, CD14 and TLR2 molecules, whereas the production of IL-1β and IL-13 was dependent of TLR2.

Macrophages represent long lived immune cells that are remarkably resistant to apoptosis, which allows them to perform in highly stressful environments. Apoptosis resistance is a characteristic that develops during the differentiation process from monocytes to macrophages. However, the signaling pathways that mediate the development of macrophage antiapoptotic phenotype during differentiation remain mostly unknown. Because of their decreased susceptibility to cell death, macrophages are also key viral reservoirs during HIV infection. My research aims to understand the molecular mechanisms and signaling pathways that mediate cell survival during and after monocyte to macrophage differentiation and the involvement of the main families of antiapoptotic proteins, IAPs (inhibitors of apoptosis) and Bcl2 in this process. HIV accessory protein Vpr was used as an apoptotic stimulus, due to its death inducing abilities in other cell types. My results show that survival of macrophages is distinctively regulated during and after differentiation. I have identified a signaling pathway consisting of PI3K/Akt activation of NFκB that is important in survival of differentiating macrophages by specifically sustaining antiapoptotic Bcl-xL expression. However, once differentiated, Mcl-1, but not Bcl-xL is dependent on PI3K/Akt activation. Moreover, differentiated macrophages are resistant to the effect of HIV-Vpr, which is highly apoptotic for monocytes. In contrast, resistance to HIV-Vpr induced apoptosis of human macrophages is specifically mediated by antiapoptotic IAP proteins, with no involvement of the Bcl2 family, which maintains macrophage viability in the absence of any apoptotic stimuli. In addition to their antiapoptotic properties, IAPs are also important regulators of macrophage function. By using chemical compounds (SMAC mimetics) that target IAPs for degradation, I have shown that IAPs positively modulate LPS-induced IL10, IL-27 and MIG (monokine induced by IFNγ) production in human macrophages, by promoting TRAF2, JNK and p38 signaling and NFκB activation. In addition, IAPs also contribute to LPS-induction of CD80/CD86 costimulatory molecules. Overall, my results suggest that both IAPs and Bcl2 families contribute to survival of human macrophages and that IAPs are also involved in innate immune responses. Unraveling the mechanisms that control macrophage survival and function in various settings would provide therapeutic strategies aimed at eliminating cells when their survival is no longer beneficial for the host, as in the case of HIV infection or autoimmune diseases.

Ce projet doctoral s’est déroulé dans le cadre d’une collaboration entre le laboratoire d’Imagerie par Résonance Magnétique Médicale et Multi-Modalités (IR4M) de l’Université Paris-Sud (France) et le Center for Medical Physics and Biomedical Engineering at Medical (CMPBME) de l’Université Médicale de Vienne (Autriche). L’objectif principal de ce travail était de développer un réseau d’antennes radiofréquence flexible fonctionnant en émission/réception pour l’IRM à 7T. Les réseaux d’antennes permettent de bénéficier du rapport signal sur bruit élevé des antennes de surface de petites tailles tout en accédant à un champ de vue étendu. De plus, les réseaux d’antennes permettent l’utilisation de technique d’imagerie parallèle afin d’accélérer l’acquisition des images ainsi que l’utilisation d’algorithme de transmission parallèle afin de produire un champ radiofréquence homogène, ce qui est crucial en IRM. Ce projet doctoral visait la conception, le développement, l’installation et l’évaluation d’un réseau d’antenne RF flexible basé sur le principe des résonateurs à lignes de transmission (RLT). Ces structures sont intrinsèquement monolithiques et auto-résonantes et ne nécessitent donc pas l’emploi de condensateurs discrets pour accorder l’antenne. Des simulations électromagnétiques 3D, ainsi que des caractérisations expérimentales sur table et en IRM ont été réalisées pour évaluer les performances de ce réseau, en configuration plate et courbée. / This PhD thesis was conducted in the frame of a bilateral project between the laboratoire d’Imagerie par Résonance Magnétique Médicale et Multi-Modalités (IR4M) at Université Paris-Sud (Orsay, France) and the Center for Medical Physics and Biomedical Engineering (CMPBME) at the Medical University of Vienna (Vienna, Austria). The main objective of this work was to develop a flexible transceiver RF coil array for 7 T MRI. Coil arrays benefit from the high SNR of small surface coils over an extended field of view (FOV). Furthermore, array coils enable the use of parallel imaging (PI) techniques for accelerated image acquisition and pTx algorithms that can be used to produce a homogeneous transmit field which is of importance in MRI. This project targets the design, development, implementation and evaluation of a flexible RF coil array based on the transmission line resonator (TLR) principle. TLRs are inherently monolithic and self-resonant structures, i.e. there is no need for lumped element capacitors to tune the coil. 3D electromagnetic simulation (EMS) together with bench and MRI experiments were performed to evaluate the performance of the developed array in flat and bent configuration.

Charles University Faculty of Pharmacy in Hradec Králové Department of Pharmacology and Toxicology Student: Kristína Hudáková Supervisor: doc. PharmDr. František Trejtnar, CSc. Title of diploma thesis: In vitro evaluation of novel Toll-like receptor ligands I Vaccination against preventable infections prevents millions of deaths each year. Their immunity enhancing activity is strengthened by the presence of vaccine adjuvants. Development of vaccine adjuvants leads to improved safety profile and also can play a vital role in the research of new vaccines against pathogens against which the vaccines currently do not exist. The main aim of this diploma thesis was to verify the ability of rationally developed small molecule ligands to influence Toll-like receptors and thus their potential to be utilized as vaccine adjuvants. The assay was carried out using modified cell lines continually expressing the human TLR4 or TLR8 whose activation leads to production of secreted embryonic alkaline phosphatase. Ten analyzed substances labelled as DM 001 - DM 010 were examined for their agonistic and also antagonistic properties while interacting with the TLRs. Immunomodulatory activity of these tested samples was then determined by quantification of secreted alkaline phosphatase with the help of a colorimetric...

Charles University Faculty of Pharmacy in Hradec Králové Department of Pharmacology & Toxicology Student: Vanda Machalová Supervisor: doc. PharmDr. František Trejtnar, CSc. Title of diploma thesis: In vitro evaluation of novel Toll-like receptor ligands II. The aim of this diploma thesis was to test the new substances at Toll-like receptors (TLR), namely TLR4 and TLR8 subtypes, as potential vaccine adjuvants. Adjuvants are required for new subunit vaccines to promote stimulation of a sufficient immune response. Stimulation of TLR receptors is safe and leads to the activation of both innate and adaptive immunity and to subsequent specific immune response. Testing was carried out on cell lines stable co-expressing the respective receptors, with colorimetric activity detection. In this work, both agonist and antagonist activity at TLR4 and TLR8 receptors was investigated and a half maximal effective concentration (EC50) of resiquimod was determined. Based on the results, the respective substances cannot be considered as potential adjuvants to the TLR8 receptor and DM014 exhibits the potential for agonist activity on the TLR4 receptor, whereas the substance DM015 can be used on further investigation of immunosuppression in autoimmune diseases and diseases associated with excessive activation of the...

Charles University Faculty of Pharmacy in Hradec Králové Department of Pharmacology and Toxicology Student: Linda Tamášiová Supervisor: doc. PharmDr. František Trejtnar, CSc. Title of diploma thesis: In vitro evaluation of novel Toll-like receptor ligands III Research on new ligands with potential immunomodulatory activity is a tool for the development of new immunological adjuvants for use in vaccines, or as separate immunomodulators in the treatment of various diseases. The aim of this thesis was to analyze the ability of new ligands to stimulate toll-like receptors 4 (TLR4) and to assess the potential for further use of these substances based on established immunomodulatory activity. The analysis was performed on modified TLR4-expressing cell lines whose activation was subsequently detected using a colorimetric-enzymatic reaction. Sixteen new substances were tested for TLR4 receptor activation in comparison with a standard agonist. The results showed a significant TLR4 agonistic activity in several of the test substances, suggesting that they are activating ligands of the receptor tested. However, due to their low solubility, some of these substances are not suitable candidates for further use and testing. Taking all parameters into consideration, among of all of the evaluated substances that...

AimsPellino1 is an evolutionally conserved immune regulator and participates in the regulation of Toll-like receptor/interleukin-1 receptor (TLR/IL-1R)-mediated signalling. Recent studies have shown that TLR/IL-1R contributes to the left ventricular (LV) remodelling after myocardial infarction (MI). However, the role of Pellino1 in LV remodelling following MI has not been investigated. This study examined the effect of Pellino1 silencing on cardiac function and LV remodelling after MI.Methods and resultsMale C57BL/6 mice were subjected to permanent ligation of left anterior descending coronary artery (LAD) to induce MI. The levels of Pellino1 were significantly increased in the myocardium 3 days and sustained for 4 weeks after MI, when compared with the sham control. Hypoxia increased Pellino1 expression in cultured cardiomyocytes and fibroblasts. To examine whether Pellino1 plays a role in MI-induced cardiac dysfunction and the LV remodelling, we suppressed the expression of Pellino1 either by intramyocardial delivery of adenovirus expressing siRNA for Pellino1 (AdsiPeli1) or by Cre-LoxP-mediated conditional deletion of Pellino1 from the myocardium. In both models, silencing of Pellino1 significantly attenuated MI-induced cardiac dysfunction, decreased scar size, and reduced collagen deposition, when compared with the control groups. Pellino1 silencing in mice also attenuated MI-induced Pellino1 E3 ligase activity, receptor-interacting protein 1 and tumor necrosis factor receptor associated factor 6 (TRAF6) ubiquitination, nuclear factor Kappa B (NF-κB) activity, cytokine production, and inflammatory cell infiltration into the myocardium when compared with the MI group.ConclusionsOur data demonstrate that Pellino1 plays an important role in the pathogenesis of MI. Targeting Pellino1 may ameliorate cardiac dysfunction and remodelling following MI.

Heterotrimeric Gi proteins play a role in lipopolysaccharide (LPS) and Staphylococcus aureus (SA) activated signaling leading to inflammatory mediator production. We hypothesized that genetic deletion of Gi proteins would alter cytokine and chemokine production induced by LPS and SA. LPS- and heat killed SA-induced cytokine and chemokine production in splenocytes from wild type (WT), Gαi2 (-/-) or Gαi1/3 (-/-) mice were investigated. LPS- or SA-induced production of TNFα, IL-6, IFNγ, IL-12, IL-17, GM-CSF, MIP-1α, MCP-1, MIG and IP-10 were significantly increased (1.2 to 33 fold, p < 0.05) in splenocytes harvested from Gαi2(-/-) mice compared with WT mice. The effect of Gαi protein depletion was remarkably isoform specific. In splenocytes from Gαi1/3 (-/-) mice relative to WT mice, SA-induced IL-6, IFNγ, GM-CSF, and IP-10 levels were decreased (59% to 86%, p < 0.05), whereas other LPS- or SA-stimulated cytokines and chemokines were not different relative to WT mice. LPS- and SA-induced production of KC were unchanged in both groups of the genetic deficient mice. Splenocytes from both Gαi2 (-/-) and Gαi1/3 (-/-) mice did not exhibit changes in TLR2 and TLR4 expression. Also analysis of splenic cellular composition by flow cytometry demonstrated an increase in splenic macrophages and reduced CD4 T cells in both Gαi2 (-/-) and Gαi1/3 (-/-) mice relative to WT mice. The disparate response of splenocytes from the Gαi2 (-/-) relative to Gαi1/3 (-/-) mice therefore cannot be attributed to major differences in spleen cellular composition. These data demonstrate that Gi2 and Gi1/3 proteins are both involved and differentially regulate splenocyte inflammatory cytokine and chemokine production in a highly Gi isoform specific manner in response to LPS and Gram-positive microbial stimuli.

Toll-Like Rezeptoren (TLR) erkennen Motive von diversen Komponenten (Proteine, Lipoproteine, Lipopolysaccharide, Nukleinsäuren) von Mikroorganismen, Viren und wirtseigenen Zellen, die als Agonisten eine Signalkaskade induzieren. Diese Agonisten werden als PAMPs (Pathogen-Associated Molecular Patterns), MAMPs (Microbe-Associated Molecular Patterns) oder DAMPs (Damage-Associated Molecular Patterns) bezeichnet. Werden TLRs stimuliert, kommt es zur Aktivierung von Signalkaskaden, die in einer agonistenspezifischen Freisetzung charakteristischer Muster von proinflammatorischen und antiinflammatorischen Zytokinen münden. Infektionserreger haben unterschiedliche Strategien entwickelt, um mittels Pathogenitätsfaktoren die Erkennung durch Immunzellen und damit der Wirtsimmunantwort zu umgehen. Yersinien, Salmonellen und Shigellen injizieren über Typ 3 Sekretionssysteme (T3SS) Effektorproteine in Wirtszellen und modifizieren die Aktivität von Rho GTPasen. Bisher wurden diese T3SS-Effektoren hinsichtlich Phagozytoseaktivierung bzw. -inhibition untersucht. In der vorliegenden Arbeit wurde die Frage untersucht, welche Rolle die Rho GTPasen von primären murinen Makrophagen für die TLR-Signalkaskade und Zytokinantwort haben könnten. Für diesen Zweck wurden erstmalig M-CSF differenzierte Knochenmarkmakrophagen (M-MΦ) sowie GM-CSF differenzierte Knochenmarkmakrophagen (GM MΦ) mit gendeletierten Rho GTPasen Rac1, RhoA, Rac1/RhoA sowie Cdc42 auf ihre Zytokinantwort nach PAMP (LPS, Pam3CSK4 und CpG) -Stimulierung untersucht. Für die konditionale Gendeletion wurden Mäuse mit „gefloxten“ Rho GTPase-Genen mit LysMCre Mäusen zur zellspezifischen Gendeletion gekreuzt. Die Aktivität des LysM-Promotors wurde in M-MΦ und GM-MΦ aus LysM-eGFP knockin Mäusen überprüft. Dabei wurde nachgewiesen, dass eine LysMCre abhängige Gendeletion mit nachfolgender Depletion von Rho GTPasen sowohl in M-MΦ als auch in GM-MΦ mit sehr hoher Effizienz entsteht. Interessanterweise zeigten GM-MΦ, die in der Literatur auch als DCs bezeichnet und damit keinen aktiven LysM Promotor haben sollten (Clarke and Gordon, 1998), ein starkes LysM-eGFP Signal und wiesen auch Rho GTPase-Gendeletionen auf. Bei den GM-MΦ handelt es sich wahrscheinlich um eine Mischpopulation unterschiedlich differenzierter MΦ-Subpopulationen, die keine klare PAMP/TLR-Signalantwort erwarten lassen. Neben der Verwendung von primären Knochenmarkzellen sollte geprüft werden, ob HoxB8 immortalisierte Knochenmarkzellen (Wang et al., 2006) von konditionalen Rho GTPase-knockout Mäusen ebenso für die TLR Fragestellung verwendet werden können. Das Wachstumsverhalten sowie die Oberflächenmarker der immortalisierten GM-iMΦ ähneln dem der primären GM-MΦ (Rosas et al., 2011), jedoch nicht das Zytokinsekretionsmuster nach TLR-Stimulierung. Da auch die immortalisierten GM-iMΦ heterogene Populationen bilden, wurde auf eine weitere Analyse hinsichtlich der PAMP-Zytokinantwort verzichtet und die Analyse auf primäre M-MΦ fokussiert. In M MΦ(Rac1-/-) und M-MΦ(RhoA-/-) konnten eindeutige Unterschiede zu M-MΦ (wt) und damit eine wichtige Rolle der Rho GTPasen bei der TLR-Signalkaskade und Zytokinantwort in M-MΦ nachgewiesen werden. Die 6 h-Stimulierung mit den spezifischen TLR2-, TLR4- bzw. TLR9-Agonisten Pam3CSK4, LPS bzw. CpG führte in M-MΦ(Rac1-/-) zu verstärkter IL-10 Sekretion (exkl. TLR2), in M MΦ(RhoA-/-) dagegen zu verstärkter IL-12 Sekretion. Nach 24 h-Stimulierung mit den verschiedenen TLR-Agonisten sind die Zytokinmuster für die M-MΦ(wt) und Rho GTPase-deletierten M-MΦ ähnlich (exkl. für IL-10 nach TLR2- und TLR9-Stimulierung). Yersinien injizieren mittels T3SS-Injektisome den Rac1-Inhibitor YopE (Rac-GAP) und den Rho GTPasen-Inhibitor YopT (proteolytische Spaltung des C-terminalen prenylierten Cystein-Membranankers, bevorzugt von RhoA), was zur Inhibition der Rho GTPasen der kontaktierten Phagozyten führt. Es wurden deshalb auch die Zytokinmuster nach TLR-Stimulierung von M-MΦ (Rac1-/-/RhoA-/-) bestimmt. Im Vergleich zu M-MΦ(wt) war die IL-12 Antwort praktisch unverändert, während die TNFα und die IL-6 Antwort der M-MΦ (Rac1-/-/RhoA-/-) erhöht waren. Mit diesen Ergebnissen der Rac1- und RhoA-abhängigen Freisetzung von proinflammatorischen und antiinflammatorischen Zytokinen durch M-MΦ können jetzt gezielte infektionsbiologische Untersuchungen z.B. mit Yersinien durchgeführt werden, um die pathogenetische Bedeutung der mikrobiellen Modulation der Rho GTPasen auf die Wirtsabwehr bzw. Zytokinantwort zu analysieren.

Tableau d'honneur de la Faculté des études supérieures et postdorales, 2014-2015 / La maladie d’Alzheimer (MA) est la plus fréquente cause de démence mondialement et son incidence augmente en parallèle au vieillissement de la population. La pathogenèse de cette maladie neurodégénérative, actuellement sans traitement curatif, est associée à l’accumulation de bêta-amyloïde (Aβ) dans le parenchyme et la vasculature du cerveau en réponse à l’élimination déficiente de ce peptide neurotoxique. Des évidences épidémiologiques et expérimentales soulignent le rôle crucial du système immunitaire inné dans la MA. Plus précisément, plusieurs études suggèrent que les phagocytes mononucléaires (microglies, monocytes et macrophages cérébraux) constituent des cellules pivots pour combattre l’accumulation d’Aβ. Les études incluses dans cette thèse de doctorat avaient comme objectif d’accroitre les connaissances concernant le rôle des phagocytes mononucléaires dans la pathologie du modèle murin APP/PS1 de la MA. Un nombre croissant d’études indique que les Toll-like receptors (TLRs) seraient critiques pour la clairance d’Aβ par les phagocytes mononucléaires. Nous avons donc étudié le rôle de la protéine adaptatrice myeloid differentiation factor 88 (MyD88), qui permet la transduction du signal intracellulaire de la plupart des TLRs. Nous avons observé une augmentation des niveaux d’Aβ solubles et une aggravation des déficits cognitifs dans les souris APP/PS1 avec une signalisation MyD88 défectueuse, vraisemblablement suite à une réduction de la phagocytose des phagocytes mononucléaires et une coordination défaillante de la réponse immunitaire innée. La stimulation des TLRs pourrait ainsi avoir un grand potentiel thérapeutique pour la MA. Nous avons démontré que des injections systémiques répétées du ligand TLR4 monophosphoryl lipid A (MPL) dans les souris APP/PS1 ont mené à une réduction significative des niveaux d’Aβ et une amélioration des fonctions cognitives. Le MPL induit une forte réponse phagocytique des phagocytes mononucléaires tout en générant une réaction inflammatoire modérée. Finalement, en utilisant la microscopie intravitale biphotonique, nous avons dévoilé que les monocytes patrouilleurs en état basal sont attirés et rampent sur la face luminale de veines contenant de l’Aβ, capturent l’Aβ et ont la capacité de regagner à nouveau la circulation sanguine. L’ablation sélective des monocytes patrouilleurs dans les souris APP/PS1 a induit une augmentation significative des niveaux d’Aβ dans le cortex et l’hippocampe. Ensemble, ces données démontrent que les phagocytes mononucléaires sains et fonctionnels peuvent promouvoir l’élimination d’Aβ et constituent une cible thérapeutique prometteuse pour la MA. / Alzheimer’s disease (AD) is the most common cause of dementia worldwide and its incidence is rising in parallel with the aging population. The pathogenesis of this neurodegenerative disease, currently without curative treatment, is associated with the accumulation of amyloid-β (Aβ) in the brain parenchyma and cerebral vasculature in response to the impaired clearance of this neurotoxic peptide. Epidemiological and experimental evidence underline the crucial role of the innate immune system in AD. More precisely, several studies suggest that mononuclear phagocytes (microglia, monocytes and cerebral macrophages) constitute pivotal cells to fight the accumulation of Aβ. The studies enclosed in this doctoral thesis intended to better understand the role of mononuclear phagocytes on the pathology of the APP/PS1 mouse model of AD. Accumulating evidence indicates a critical role of Toll-like receptors (TLRs) in the clearance of Aβ by mononuclear phagocytes. We thus investigated the role of the myeloid differentiation factor 88 (MyD88), which is the adaptor protein for most of these innate immune receptors, transducing the intracellular signal from TLRs to the nucleus. We observed increased soluble levels of A oligomers and enhanced cognitive deficits in APP/PS1 mice with impaired MyD88 signalling, likely through reduced phagocytosis of mononuclear phagocytes and an impaired coordination of the innate immune response. Compounds that stimulate TLRs to clear Aβ may therefore have great therapeutic potential in AD patients. We demonstrated that repeated systemic injections of the TLR4 ligand monophosphoryl lipid A (MPL) in APP/PS1 mice led to a significant reduction in Aβ load and improved cognitive function. MPL induced a potent phagocytic response by mononuclear phagocytes while triggering a moderate inflammatory reaction. Finally, using live intravital two-photon microscopy, we discovered that patrolling monocytes in steady state are attracted and crawl onto the luminal walls of Aβ-positive veins, uptake Aβ and are able to circulate back into the bloodstream. Selective removal of patrolling monocytes in APP/PS1 mice induced a significant increase of Aβ load in the cortex and hippocampus. Overall, these studies demonstrate that healthy and functional mononuclear phagocytes can promote the elimination of Aβ and constitute a promising therapeutic target for AD.