L'efferocytose est un phénomène physiologique par lequel des millions de cellules apoptotiques sont efficacement éliminées par phagocytose sans provoquer une réaction inflammatoire. L'efficacité de ce processus nécessite une interaction rapide entre la cellule apoptotique et son phagocyte afin d'éviter l'entrée de la première dans une phase de nécrose secondaire. Cette interaction implique des motifs de la surface des 2 cellules qui peuvent interagir directement ou aussi indirectement via des molécules de pontage. Ce dernier rôle est associé à C1q, premier composant du système du complément. En effet, C1q favorise l'élimination des cellules apoptotiques et aussi la réponse tolérogène en interagissant avec des ligands présents de part et d'autre de la synapse efferocytaire. La calréticuline (CRT) de surface fait partie de ces ligands. Initialement connue comme co-récepteur, avec CD91, de la queue collagène de C1q à la surface du phagocyte, la CRT est aujourd'hui décrite comme un signal « eat-me » de la surface des cellules apoptotiques où elle peut aussi interagir avec les têtes globulaires de C1q. Des études récentes ont soulevé le potentiel immunogénique de la CRT, notamment au cours de la mort des cellules cancéreuses. Ainsi, la CRT de surface joue un rôle important dans l'efferocytose même si l'on ne sait pas exactement comment cette protéine chaperonne résidente du réticulum endoplasmique est exposée à la membrane plasmique. Dans un premier temps, j'ai démontré que la CRT augmente à la surface des cellules Jurkat rapidement après l'induction de l'apoptose, à un stade où la phosphatidylsérine, marqueur emblématique de l'apoptose, n'est pas encore détectée. D'une manière intéressante, C1q est capable d'interagir directement avec la CRT exposée à la surface des cellules à ce stade « pré-apoptotique », et de favoriser significativement leur phagocytose par les macrophages THP1. Dans un deuxième temps, j'ai mis en évidence la présence de la CRT dans le milieu extracellulaire et montré qu'elle varie avec l'évolution de l'apoptose. De plus, la CRT soluble est capable d'induire la migration des macrophages THP1, d'augmenter l'expression à leur surface de CD14, récepteur impliqué dans l'efferocytose, et de stimuler la macropinocytose, un processus utilisé par les phagocytes lors de la phagocytose des cellules apoptotiques. Cela suggère que la CRT extracellulaire peut moduler la biologie du phagocyte. Enfin, la CRT exogène peut se lier à la surface des macrophages et peut être ainsi une source externe de la CRT retrouvée à la surface des phagocytes. / Efferocytosis is a physiological phenomenon whereby millions of apoptotic cells are efficiently removed by phagocytosis without inducing an inflammatory response. The efficiency of this process requires rapid interaction between the apoptotic cell and the phagocyte in order to prevent the entry of the dying cell in a secondary necrosis phase. This interaction involves patterns of the surface of the 2 cells that can interact directly or indirectly via bridging molecules. The latter role is associated to C1q, the first component of the complement system. Indeed, C1q promotes the removal of apoptotic cells and the tolerogenic response by interacting with ligands present on either side of the efferocytic synapse. Surface exposed calreticulin (CRT) is one of these ligands. Initially known as the co-receptor, with CD91, to the collagenous tail of C1q on the phagocyte surface, CRT is now described as an “eat-me" signal of the apoptotic cell surface where it can also interact with the globular heads of C1q. Recent data have revealed the immunogenic potential of CRT, especially in the case of cancer cell death. Thus, surface exposed CRT plays an important role in efferocytosis even if it is not fully understood how this reticulum endoplasmic resident protein gets to the plasma membrane. I firstly demonstrated that CRT increases rapidly on the surface of Jurkat cells after the induction of apoptosis, at a stage where phosphatidylserine, emblematic marker of apoptosis, is not yet detected. Interestingly, C1q is capable of interacting directly with this “pre-apoptotic” cell surface exposed CRT, and promotes significantly the uptake of Jurkat cells by THP1 macrophages at this stage. Secondly, I demonstrated the presence of CRT in the extracellular medium whose content depends on the evolution of apoptosis. Furthermore, soluble CRT induces the migration of THP1 macrophages, increases their surface expression of CD14, a receptor involved in efferocytosis, and stimulates macropinocytosis, a process used by phagocytes during phagocytosis of apoptotic cells. These results suggest that the extracellular CRT can modulate the biology of the phagocyte. Finally, exogenous CRT binds to the surface of macrophages and can therefore be an external source of the CRT found on the phagocyte surface.

La mort cellulaire par apoptose est un processus biologique fondamental, nécessitant des interactions fines avec le système immunitaire pour une reconnaissance et une élimination efficace des cellules mortes. C'est ainsi que C1q, une molécule du complément, essentielle dans le système immunitaire inné, a été mise en évidence comme fortement impliquée dans le mécanisme de reconnaissance et d'élimination des cellules apoptotiques, notamment via sa région globulaire (C1qGR). Récemment, la translocation de la calréticuline (CRT) au niveau externe de la membrane plasmique des cellules cancéreuses a été identifiée comme un signal « eat-me » pouvant être immunogène. Initialement, l'interaction entre la CRT et C1q a été caractérisée à la surface des phagocytes et la CRT a été considérée comme un récepteur pour les queues collagènes de C1q (C1qCLF). L'ensemble de ces observations est en faveur d'un double rôle de la CRT, à la surface des phagocytes et des cellules apoptotiques. Dans un premier temps, l'élaboration d'une stratégie de FRET a permis de détecter une interaction directe entre la CRT et C1qGR à la surface de la cellule HeLa en apoptose précoce. Dans un second temps, la mise en place de tests de phagocytose a permis de montrer que la calréticuline exposée à la surface des cellules apoptotiques peut moduler la phagocytose : des effets opposés ont été observés selon le modèle cellulaire utilisé (HeLa traitées par des ARNi ou MEF CRT-/-) et dans certaines conditions, une modulation combinée de la calréticuline et de C1q a été observée sur la réponse inflammatoire (production de cytokines). / Cell death by apoptosis is a fundamental biological process, requiring fine interactions with the immune system for the effective recognition and removal of the apoptotic cells. C1q, a complement molecule, essential in the innate immune system, has been shown to be strongly involved in the mechanism of recognition and elimination of apoptotic cells, mainly through its globular region (C1qGR). Recently, the translocation of calreticulin (CRT) at the surface of cancer cells has been identified as an eat-me signal, which can be immunogenic. Initially, the interaction between CRT and C1q was characterized on phagocytes surface and CRT was described as a receptor for the collagenous tails of C1q (C1qCLF). All these observations support a dual role of CRT at the surface of phagocytes and their targets. At first, using a FRET strategy we achieve to detect a direct interaction between CRT and C1qGR at the surface of early apoptotic HeLa cells. Second, the establishment of phagocytosis assays showed that calreticulin exposed at the surface of apoptotic cells could modulate phagocytosis: opposite effects were observed depending on the cellular model used (RNAi treated HeLa or MEF CRT-/-) and under certain conditions, a combined modulation of calreticulin and C1q was observed on the inflammatory response (cytokine production).

Activation of innate immune surveillance mechanisms during the development of cancer is well-documented. However, knowledge of how these innate immune proteins, when added exogenously, independent of tumour microenvironment, affect tumour cells is limited. In Chapter 3, the effects of human C1q and its individual globular domains (ghA, ghB and ghC) on an ovarian cancer cell line, SKOV3, have been examined. C1q and globular head modules induced apoptosis in approximately 55% of cells, which involved upregulation of TNF-α and Fas and activation of the caspase cascade. This occurred in parallel to the downregulation of mTOR, RICTOR and RAPTOR survival pathways, which are often over-expressed in the majority of the cancers. Thus, this study provided evidence for another complement-independent role of C1q. The second part of this thesis was to investigate the effect of Human Surfactant Protein-D (SP-D), which is known to modulate secretion of a range of cytokines and chemokines by effector immune cells, such as TNF-a and TGF-β, at mucosal surfaces during infection and inflammation. Our hypothesis was that SP-D can influence these soluble factors as a part of its putative role in the immune surveillance against pancreatic cancer, where the inflammatory tumour microenvironment contributes to the epithelial-to-mesenchymal transition (EMT) invasion and metastases. In this study, a recombinant fragment of human SP-D (rfhSP-D) inhibited TGF-β expression in a range of pancreatic cancer cell lines, thereby reducing their invasive potential by downregulating Smad2/3 expression that may have interrupted signal transduction negatively, which affected the transcription of key mesenchymal genes such as Vimentin, Zeb1 and Snail. Furthermore, prolonged treatment with rfhSP-D induced apoptosis in the pancreatic cancer cell lines via activation of the caspase cascade. Thus, this study added another layer to the well-known protective role of SP-D.

Immune molecules, including complement proteins, C1q and C3, have emerged as critical mediators of synaptic refinement and plasticity. Complement proteins localize to synapses and refine the developing retinogeniculate system via C3-dependent microglial phagocytosis of synapses. Retinal ganglion cells (RGCs) express C1q, the initiating protein of the classical complement cascade, during retinogeniculate refinement; however, the signals controlling C1q expression and function remain elusive. RGCs grown in the presence of astrocytes significantly upregulated C1q compared to controls, implicating an astrocyte-derived factor in neuronal C1q expression. A major goal of my dissertation research was to identify the signals that regulate C1q expression and function in the developing visual system. In this study, I have identified transforming growth factor beta \((TGF-\beta)\), an astrocyte-secreted cytokine, as both necessary and sufficient for C1q expression in RGCs through an activity-dependent mechanism. Specific disruption of retinal \(TGF-\beta\) signaling resulted in a significant reduction in the deposition of C1q and downstream C3 at retinogeniculate synapses and significant synaptic refinement defects in the retinogeniculate system. Microglia engulfment of RGC inputs in the lateral geniculate nucleus (LGN) was also significantly reduced in retinal \(TGF\beta\)RII KOs, phenocopying the engulfment defects observed in C1q KOs, C3 KOs, and CR3 KOs. Interestingly, in C1q KOs and retinal \(TGF\beta\)RII KOs, microglia also failed to preferentially engulf less active inputs when retinal activity was manipulated, suggesting that retinal activity and \(TGF-\beta\) signaling cooperatively regulate complement mediated synaptic refinement. In support of this hypothesis, blocking spontaneous activity in RGC cultures significantly reduced C1q upregulation by \(TGF-\beta\). Moreover, manipulating spontaneous retinal activity in vivo modulated C1q expression levels in RGCs and C1q deposition in the LGN. Together these findings support a model in which retinal activity and \(TGF-\beta\) signaling control expression and local release of C1q in the LGN to regulate microglia-mediated, complement-dependent synaptic pruning. These results provide mechanistic insight into synaptic refinement and, potentially, pathological synapse loss which occurs in the early stages of neurodegenerative diseases concurrently with aberrant complement expression and reactive gliosis.

La polyarthrite rhumatoïde (PR) est une maladie auto-immune inflammatoire. La PR touche les articulations jusqu'à les détruire. Elle est caractérisée par la présence d’anticorps anti protéines citrullinées (ACPA) mais l’auto-antigène n’est toujours pas connu. Dans cette maladie, l’implication de l’immunité adaptative ne fait donc aucun doute mais le rôle de l’immunité innée reste encore flou. Le système du complément joue un rôle important dans l’immunité innée tout comme les récepteurs de type Toll (TLR) qui sont des récepteurs de celle-ci. C1q, par la reconnaissance des ses ligands, active une des voies du complément, la voie classique. Chez les patients atteints de PR, le complément est activé et un dépôt de C1q est retrouvé dans l’articulation. Le TLR9 reconnaît des ADN dérivés de bactéries ou de virus mais une expression à la surface des cellules pourrait conduire à la reconnaissance d’autres motifs comme les signaux de danger (DAMP). D’ailleurs, nous avons montré récemment qu’il existait un TLR9 exprimé à la surface des polynucléaires neutrophiles (PNN). Enfin, il a été mis en évidence récemment un nouveau mécanisme bactéricide effectué par les PNN : la formation de NET (neutrophil extracellular traps). Mais en dehors de leur rôle bactéricide, les NET ont été montrés comme pathogènes dans certaines maladies comme le lupus. Dans ce travail de thèse, je me suis intéressé à l’implication de ces acteurs, NET, C1q et TLR9 dans la PR. Nous avons montré que C1q est indispensable au développement de l’arthrite dans un modèle animal. De plus, l’expression des récepteurs au C1q par les PNN et les monocytes est corrélée à l’activité de la maladie et à l’inflammation. Nous avons montré que les NET représentent une cible pour les ACPA (ce qui en fait des auto-antigènes potentiels dans la PR) et que ces NET sont immunogènes. L’immunogénicité des NET est modulée par C1q. Enfin, il semblerait que le TLR9 ait moins d’importance dans l’arthrite. Par ce travail, nous avons montré l’importance du rôle joué par l’immunité innée dans la PR et ses modèles. / Rheumatoid artthritis (RA) is the most frequent rheumatic disease. This auto-immune disease causes pain and joint destruction. RA has been characterized by adaptative immunity involvement and anti-citrullinated protein antibodies (ACPA) production. Involvement of innate immunity is less investigated. Complement system, part of innate immunity, is activated in RA. C1q activates classical complement pathway by binding its ligands. C1q is found in joint of RA patients. On the other hand Toll-like-receptor (TLR), innate receptors could play a role in RA upon recognition of pathogen-derived DNA (TLR9). Cell surface expression of TLR9 has been reported as potentially pathological, and we describe that polymorphonuclear neutrophils (PMN) express a cell surface TLR9 wich could recognize damage associated molecular pattern (DAMP). Finally, neutrophil extracellular traps (NET) wich are expelled chromatin fiber and represent a physiological response to bacteria, have been reported as pathological in certain circumstances. We investigated the role of those three innate actors in RA. We have shown that C1q is mandatory to develop experimental arthritis and expression of their receptors on RA patient PMN and monocytes is correlated with disease activity and inflammation. We have also shown that NET are immunogenic and this immunogenicity is partly modulated and mediated by C1q. NET might trigger ACPA production in RA. Finally, it seems that involvement of TLR9 is less important in RA. With those experiments we have shown that the involvement of innate immunity in RA is more important than that has been reported so far.

Streptococcus pneumoniae est un pathogène humain majeur causant des pneumonies, méningites et septicémies. Pour assurer sa survie et sa dissémination le pneumocoque déploie un ensemble de facteurs de virulence favorisant l'invasion des tissus et l'évasion du système immunitaire. Une classe particulière de protéines dites « moonlighting », ne sont associées à aucun système d'export connu et pourtant se trouvent localisées en surface du pneumocoque. Les protéines « moonlighting » sont des protéines cytoplasmiques conservées, localisées dans divers compartiments cellulaires et présentant des fonctions additionnelles. La glycéraldéhyde-3-phosphate déshydrogénase (GAPDH) est retrouvée en surface de nombreuses cellules et exerce divers rôles dans les processus de virulence d'organismes pathogènes. La GAPDH de surface du pneumocoque agit comme un facteur de virulence en recrutant le plasminogène / la plasmine de l'hôte, ce qui facilite l'invasion bactérienne à travers la matrice extracellulaire et les barrières endothéliales et épithéliales. Cependant, les mécanismes permettant l'export et la fixation de la GAPDH à la surface de la bactérie n'avaient pas encore été découverts. Ce travail démontre que la GAPDH est relarguée par lyse cellulaire et s'associe au peptidoglycane. C1q, un composant clé de la voie classique du complément, est un acteur majeur dans la réponse aux infections microbiennes et peut également détecter des éléments nocifs du soi-altéré comme les cellules apoptotiques. L'usage d'approches expérimentales complémentaires a permis d'identifier la GAPDH comme un partenaire de C1q quand elle est exposée en surface de S. pneumoniae et de cellules apoptotiques humaines. Néanmoins et de manière plutôt inattendue, seule la GAPDH du pneumocoque active la cascade du complément à la différence de la protéine homologue humaine. Ces résultats encouragent la poursuite d'études afin de comprendre comment la reconnaissance par C1q de deux protéines très proches peut conduire à de telles différences sur ses propriétés d'activation du complément. / Streptococcus pneumoniae is a major human pathogen, which causes pneumonia, meningitis and septicemia. To insure its survival and dissemination, the pneumococcus deploys an array of virulence factors promoting invasion of tissues and evasion from the immune system. A particular class of proteins not associated with any known export system, the moonlighting proteins, is found at the pneumococcal surface. Moonlighting proteins are conserved cytoplasmic metabolic enzymes or molecular chaperones localized in various cellular compartments and exhibiting additional functions. The glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is found at the surface of numerous eukaryotic and prokaryotic cells, and display diverse roles in the virulence processes of pathogenic organisms. The pneumococcal surface GAPDH acts as a virulence factor by binding to host plasminogen/plasmin, which facilitates the bacterial invasion through the extracellular matrix and the endothelial and epithelial cell barriers. However, the mechanisms leading to the GAPDH export and binding to the bacterial surface had not been deciphered yet. This work demonstrates that the GAPDH is released upon cell lysis and associates with the peptidoglycan. C1q, a key component of the classical complement pathway, is a major player in the response to microbial infection and has been shown to detect noxious altered-self substances such as apoptotic cells. The use of complementary experimental approaches allowed the identification of the GAPDH as a C1q partner when exposed at the surface of S. pneumoniae and human apoptotic cells. However, and rather unexpectedly, the pneumococcal GAPDH activates the complement cascade unlike the human one. Those results encourage further studies in order to understand how C1q recognition of two closely related proteins can lead to such striking differences on its complement activation properties.

Les collagènes de défense (C1q, MBL, ficolines) sont capables de reconnaître de nombreux motifs à la surface des éléments du non soi ou du soi altéré, via leurs domaines globulaires C-terminaux. Ils peuvent également interagir avec certains récepteurs présents à la surface des cellules humaines ou de pathogènes. Nous nous sommes intéressés dans un premier temps à la calréticuline de Trypanosoma Cruzi (TcCRT), une protéine qui interviendrait dans les mécanismes d'évasion de ce parasite. Dans le but de réaliser des études fonctionnelles et structurales de la TcCRT, nous avons produit différents fragments recombinants. Nous ne sommes cependant pas parvenus à obtenir un échantillon nous permettant d'accomplir nos objectifs, nous conduisant à reporter nos efforts sur l'étude d'un autre récepteur, CR1/CD35. Il a été montré précédemment que CR1/CD35 pouvait interagir avec C1q et la MBL, probablement par ses modules CCP 22-30. Cette interaction pourrait être impliquée dans l'élimination des complexes immuns, la phagocytose ou encore des mécanismes de signalisation cellulaire. A l'aide d'un fragment recombinant comprenant les modules CCP 22-30 de CR1, nous avons confirmé par SPR l'interaction avec C1q et la MBL. Nous avons également montré pour la première fois que CR1 pouvait interagir avec les ficolines L, H et M par ce même domaine. Nos résultats indiquent que cette interaction prendrait majoritairement place dans la région collagène de C1q, de la MBL et de la ficoline L, probablement à proximité du site de fixation des protéases. L'utilisation de fragments tronqués de CR1 CCP 22-30, nous permet de proposer l'hypothèse que les modules CCP 24 et 25 de CR1 seraient le site majoritaire de fixation des collagènes de défense. Ces données ouvrent la voie à des études structurales et fonctionnelles visant à approfondir notre connaissance des interactions CR1 – collagène de défense et de leur rôle physiologique. / The defence collagens (C1q, MBL, ficolins) are able to recognize various patterns on non-self or altered-self surfaces through their globular domains. They can also interact with receptors at the surface of human cells or pathogens. First, we were interested in the calreticulin from Trypanosoma cruzi, a protein which may be involved in the evasion mechanisms of that parasite. To achieve structural and functional studies, we produced recombinant fragments from TcCRT. Unfortunately, we couldn't obtain any sample suitable for our studies, so we decided to focus on another receptor, CR1/CD35. It has been shown previously by other teams that C1q and MBL bind to CR1/CD35, probably through CCP modules 22 to 30, close to the cell membrane. This interaction could be involved in several biologic mechanisms: elimination of immune complexes, phagocytosis, cell signaling. We produced a recombinant fragment including the CCP modules 22 to 30 of CR1 and confirmed its interaction with C1q and MBL using SPR. We also showed for the first time that L-, H- and M-ficolins bind to CR1 through CCP modules 22 to 30. Our results point out that the CR1 binding site of C1q, MBL and L-ficolin is located in the collagen stalks, most probably at or in close proximity to the serine protease interaction site. By using CR1 CCP 22-30 truncated fragments, we suggest that CCP modules 24 to 25 could be the main binding site for the defence collagens. These data open the way for structural and functional studies aiming at improving our knowledge of the CR1 – defense collagen interactions and of their physiological role.

Octapharma tillverkar Octagam, en lösning innehållande humant immunglobulin för intravenös administrering, vars huvudkomponent är immunglobulin G (IgG). Aggregerade IgG förknippas med aktivering av komplementsystemet i frånvaro av antigen. Denna ospecifika aktivering av komplement har tidigare rapporterats orsaka biverkningar hos patienter. För att undvika detta använder Octapharmas laboratorium för kvalitetskontroll en metod som kallas test av antikomplementär aktivitet, för kontroll av batcher av Octagam innan de släpps ut på marknaden. Denna metod har flera problem, t.ex. låg tillgänglighet av viktiga reagens. Syftet med detta projekt var därför att undersöka om en alternativ metod, CIC-C1q ELISA, kunde mäta aktiveringen av komplementsystemet på immunglobuliner genom att testa olika batcher av IgG och värmebehandlade IgG-prover för att bedöma om det fanns en korrelation mellan resultaten från de två metoderna. Resultaten visade att det inte fanns någon korrelation mellan ACA-testet och CIC-C1q ELISA. Varken normala IgG-batcher eller värmebehandlade prover uppvisade någon tydlig korrelation. Den enda fördelen som C1q kan ha är att den gav ett högt resultat för en batch som tidigare har rapporterats orsaka biverkningar hos patienter, medan svaret i ACA-testet var relativt normalt. CIC-C1q ELISA metoden har dock visat sig ha sina egna problem eftersom standardprover ger inkonsekventa värden och mer tester behöver utföras för att hitta spädnings-linjäritet. / Octapharma manufactures Octagam, a liquid preparation of highly purified human immunoglobulin for intravenous administration, the main component of which is immunoglobulin G (IgG). Aggregated IgG is associated with activation of the complement system in the absence of antigen. This non-specific activation of complement has been reported to cause adverse reactions in patients. To avoid this, Octapharma's quality control laboratory uses a method called the determination of anti-complementary activity (ACA) in Immunoglobulin, for control of all batches of Octagam before release. This method has several problems, such as low availability of critical reagents. Therefore, the aim of this project was to investigate whether an alternative method, CIC-C1q ELISA, could measure the activation of the complement system on immunoglobulins by testing different batches of IgG and heat-treated IgG samples to assess whether there is a correlation between the results of the two methods. The results showed that there was no correlation between the ACA test and the CIC-C1q ELISA. Neither normal IgG batches nor heat-treated samples showed a clear correlation. The only advantage the C1q may have is that it gives a high response for a batch that has been reported to cause adverse reactions in patients, while the response in the ACA test was relatively normal. If this can be demonstrated by testing similar batches, it may be beneficial to continue testing the C1q ELISA. However, this method has also been shown to have its own problems, such as the standard sample giving inconsistent values, and more work is needed to find the linearity of the dilution.

Mycobacterium tuberculosis (Mtb), one of the major pathogens of mankind, kills approximately 2 million people each year. Mtb induces inflammation at the site of infection, leading to leakage of serum proteins, which in turn, are likely to come in contact with the pathogen, thus modulate the pathogenesis of tuberculosis. We studied some of these proteins such as surfactant protein D (SP-D), complement protein C1q and fibronectin, which are either produced locally or they leak-out from serum during inflammation, for their interaction with M.smegmatis and BCG. These non-pathogenic mycobacteria were used as model for Mtb. In this study, the recombinant form of truncated human surfactant protein D (rhSP-D) and three globular heads of human C1q (ghA, ghB, and ghC) were expressed in E.coli. The interaction of each of these proteins with mycobacteria and human monocytic cell line THP-1, was examined via ELISA. We demonstrated that rhSP-D, C1q, three globular heads of C1q and fibronectin bind with both mycobacteria and THP-1 cells. Moreover, using rhSP-D and globular heads of C1q, the binding of SP-D and C1q was localised to C-terminal globular regions. The direct effect for each of these proteins on mycobacterial growth, their effect on the uptake and intracellular fate of mycobacteria inside THP-1 cells were also investigated. Direct interaction of rhSP-D and C1q inhibited mycobacterial growth, whereas fibronectin interaction with the mycobacteria increased their growth. RhSP-D inhibited the uptake and growth of mycobacteria inside THP-1 cells, whereas C1q and each individual globular heads of C1q enhanced the uptake of mycobacteria by THP-1 cells. However, C1q protein inhibited BCG growth but enhanced M.smegmatis growth inside these cells and the later activity was localised to ghA. Fibronectin increased the uptake and growth of mycobacteria inside THP-1 cells. Examining the gene expression of inducible nitric oxide synthase, pro-inflammatory and anti-inflammatory cytokines produced by THP-1 cells infected with the proteins treated and untreated mycobacteria, along with cytokine neutralization experiments, suggest that the nitric oxide components and cytokines could be responsible for mycobacterial growth control inside THP-1 cells. These novel and interesting functions of SP-D, C1q, and fibronectin on mycobacteria provide an insight into the modulatory function of these proteins on Mtb infection, and, therefore, in the pathogenesis of tuberculosis.

As the largest endocrine organ, adipose tissue secretes many bioactive molecules that circulate in blood, collectively termed adipokines. Efforts to identify such metabolic regulators have led to the discovery of a family of secreted proteins, designated as C1q tumor necrosis factor (TNF)-related proteins (CTRPs). The CTRP proteins, adiponectin, TNF-alpha, as well as other proteins with the distinct C1q domain are collectively grouped together as the C1q/TNF superfamily. Reflecting profound biological potency, the initial characterization of these adipose tissue-derived CTRP factors finds wide-ranging effects upon metabolism, inflammation, and survival-signaling in multiple tissue types. CTRP3 (also known as CORS26, cartducin, or cartonectin) is a unique member of this adipokine family. In this review we provide a comprehensive overview of the research concerning the expression, regulation, and physiological function of CTRP3. © 2017 American Physiological Society. Compr Physiol 7:863-878, 2017.