Editorial : Function and Dysfunction of Complement Factor H

Non peer reviewe

A sedimentary basin as a cradle for biodiversity: the case of the Salado basin in the Buenos Aires province, Argentina

The sedimentary Salado basin is located in the Province of Buenos Aires, Argentina, and extends for about 150,000 km2; of which 50,000 km2 correspond to the lower estuary (or marine estuary) of the Rio de la Plata and to the adjacent sector of the Atlantic Ocean. The basin, which takes its name from the homonymous river that crosses it, is composed of blocks that allowed fluvial-lacunar environments with extended flood plains to be developed. The present configuration of the basin comes from recent sedimentary fill, and shows a broad accretion plain with a low topographic slope that extends with similar features toward the continental shelf. With a sedimentary thickness of over 6,000 m, the Salado basin is characterized by a large vertical development of Upper Paleozoic, Mesozoic and Tertiary continental sediments, with no outcrops from before the Quaternary. The origin of the basin can be related to the development of extensional fractures that took place over ancient weakness zones where the starting aperture mechanism of Gondwana began. The geographical location of the basin, together with its large extent, low elevation over sea level, geology, geomorphology and the prevalent humid climate have produced a particular hydrological behavior with strong ecological characteristics. Vertical water movements (evapotranspiration – infiltration) predominate over horizontal ones (runoff), and there is a strong connection between surface water and groundwater. Due to the low topographic gradients the regional velocity of runoff and streams are very much reduced, which results in a longer time of contact between water and the soil surface and the ensuing increase in infiltration and evapotranspiration. Local and regional seepage are identified. Local seepage refers to an active subsurface flow that outcrops in creeks or ponds, forming their base flow. Regional seepage is a very slow passive flow connected with the deep sedimentary layers in which it takes place. Because of the frequent presence of a shallow water table, surface water and groundwater are strongly related, thus allowing the existence of numerous water bodies rich in biotic resources. The study area has a high biodiversity with sectors of considerable importance for conservation purposes. It can really be considered as a cradle for biodiversity, even though sensitive to human activities. The study area periodically experiences prolonged floods and strong droughts that have frequently led to great losses in the agricultural production and in the urban and road infrastructures. However, floods prevent soil from being salinized, and control the spreading of some harmful dicotyledons in pastures. A general monitoring proposal that would be very useful for the management of natural resources is also given.Facultad de Ciencias Naturales y MuseoFacultad de Ingenierí

A sedimentary basin as a cradle for biodiversity: the case of the Salado basin in the Buenos Aires province, Argentina

The sedimentary Salado basin is located in the Province of Buenos Aires, Argentina, and extends for about 150,000 km2; of which 50,000 km2 correspond to the lower estuary (or marine estuary) of the Rio de la Plata and to the adjacent sector of the Atlantic Ocean. The basin, which takes its name from the homonymous river that crosses it, is composed of blocks that allowed fluvial-lacunar environments with extended flood plains to be developed. The present configuration of the basin comes from recent sedimentary fill, and shows a broad accretion plain with a low topographic slope that extends with similar features toward the continental shelf. With a sedimentary thickness of over 6,000 m, the Salado basin is characterized by a large vertical development of Upper Paleozoic, Mesozoic and Tertiary continental sediments, with no outcrops from before the Quaternary. The origin of the basin can be related to the development of extensional fractures that took place over ancient weakness zones where the starting aperture mechanism of Gondwana began. The geographical location of the basin, together with its large extent, low elevation over sea level, geology, geomorphology and the prevalent humid climate have produced a particular hydrological behavior with strong ecological characteristics. Vertical water movements (evapotranspiration – infiltration) predominate over horizontal ones (runoff), and there is a strong connection between surface water and groundwater. Due to the low topographic gradients the regional velocity of runoff and streams are very much reduced, which results in a longer time of contact between water and the soil surface and the ensuing increase in infiltration and evapotranspiration. Local and regional seepage are identified. Local seepage refers to an active subsurface flow that outcrops in creeks or ponds, forming their base flow. Regional seepage is a very slow passive flow connected with the deep sedimentary layers in which it takes place. Because of the frequent presence of a shallow water table, surface water and groundwater are strongly related, thus allowing the existence of numerous water bodies rich in biotic resources. The study area has a high biodiversity with sectors of considerable importance for conservation purposes. It can really be considered as a cradle for biodiversity, even though sensitive to human activities. The study area periodically experiences prolonged floods and strong droughts that have frequently led to great losses in the agricultural production and in the urban and road infrastructures. However, floods prevent soil from being salinized, and control the spreading of some harmful dicotyledons in pastures. A general monitoring proposal that would be very useful for the management of natural resources is also given.Facultad de Ciencias Naturales y MuseoFacultad de Ingenierí

A sedimentary basin as a cradle for biodiversity: the case of the Salado basin in the Buenos Aires province, Argentina

The sedimentary Salado basin is located in the Province of Buenos Aires, Argentina, and extends for about 150,000 km2; of which 50,000 km2 correspond to the lower estuary (or marine estuary) of the Rio de la Plata and to the adjacent sector of the Atlantic Ocean. The basin, which takes its name from the homonymous river that crosses it, is composed of blocks that allowed fluvial-lacunar environments with extended flood plains to be developed. The present configuration of the basin comes from recent sedimentary fill, and shows a broad accretion plain with a low topographic slope that extends with similar features toward the continental shelf. With a sedimentary thickness of over 6,000 m, the Salado basin is characterized by a large vertical development of Upper Paleozoic, Mesozoic and Tertiary continental sediments, with no outcrops from before the Quaternary. The origin of the basin can be related to the development of extensional fractures that took place over ancient weakness zones where the starting aperture mechanism of Gondwana began. The geographical location of the basin, together with its large extent, low elevation over sea level, geology, geomorphology and the prevalent humid climate have produced a particular hydrological behavior with strong ecological characteristics. Vertical water movements (evapotranspiration – infiltration) predominate over horizontal ones (runoff), and there is a strong connection between surface water and groundwater. Due to the low topographic gradients the regional velocity of runoff and streams are very much reduced, which results in a longer time of contact between water and the soil surface and the ensuing increase in infiltration and evapotranspiration. Local and regional seepage are identified. Local seepage refers to an active subsurface flow that outcrops in creeks or ponds, forming their base flow. Regional seepage is a very slow passive flow connected with the deep sedimentary layers in which it takes place. Because of the frequent presence of a shallow water table, surface water and groundwater are strongly related, thus allowing the existence of numerous water bodies rich in biotic resources. The study area has a high biodiversity with sectors of considerable importance for conservation purposes. It can really be considered as a cradle for biodiversity, even though sensitive to human activities. The study area periodically experiences prolonged floods and strong droughts that have frequently led to great losses in the agricultural production and in the urban and road infrastructures. However, floods prevent soil from being salinized, and control the spreading of some harmful dicotyledons in pastures. A general monitoring proposal that would be very useful for the management of natural resources is also given.Facultad de Ciencias Naturales y MuseoFacultad de Ingenierí

FHR4-based immunoconjugates direct complement-dependent cytotoxicity and phagocytosis towards HER2-positive cancer cells

Directing selective complement activation towards tumour cells is an attractive strategy to promote their elimination. In the present work, we have generated heteromultimeric immunoconjugates that selectively activate the complement alternative pathway (AP) on tumour cells. We used the C4b-binding protein C-terminal-alpha-/beta-chain scaffold for multimerisation to generate heteromultimeric immunoconjugates displaying (a) a multivalent-positive regulator of the AP, the human factor H-related protein 4 (FHR4) with; (b) a multivalent targeting function directed against erbB2 (HER2); and (c) a monovalent enhanced GFP tracking function. Two distinct VHH targeting two different epitopes against HER2 and competing either with trastuzumab or with pertuzumab-recognising epitopes [VHH(T) or VHH(P)], respectively, were used as HER2 anchoring moieties. Optimised high-FHR4 valence heteromultimeric immunoconjugates [FHR4/VHH(T) or FHR4/VHH(P)] were selected by sequential cell cloning and a selective multistep His-Trap purification. Optimised FHR4-heteromultimeric immunoconjugates successfully overcame FH-mediated complement inhibition threshold, causing increased C3b deposition on SK-OV-3, BT474 and SK-BR3 tumour cells, and increased formation of lytic membrane attack complex densities and complement-dependent cytotoxicity (CDC). CDC varies according to the pattern expression and densities of membrane-anchored complement regulatory proteins on tumour cell surfaces. In addition, opsonised BT474 tumour cells were efficiently phagocytosed by macrophages through complement-dependent cell-mediated cytotoxicity. We showed that the degree of FHR4-multivalency within the multimeric immunoconjugates was the key element to efficiently compete and deregulate FH and FH-mediated convertase decay locally on tumour cell surface. FHR4 can thus represent a novel therapeutic molecule, when expressed as a multimeric entity and associated with an anchoring system, to locally shift the complement steady-state towards activation on tumour cell surface

Autoantibodies Against the Complement Regulator Factor H in the Serum of Patients With Neuromyelitis Optica Spectrum Disorder

Neuromyelitis optica spectrum disorder (NMOSD) is an autoimmune inflammatory disease of the central nervous system (CNS), characterized by pathogenic, complement-activating autoantibodies against the main water channel in the CNS, aquaporin 4 (AQP4). NMOSD is frequently associated with additional autoantibodies and antibody-mediated diseases. Because the alternative pathway amplifies complement activation, our aim was to evaluate the presence of autoantibodies against the alternative pathway C3 convertase, its components C3b and factor B, and the complement regulator factor H (FH) in NMOSD. Four out of 45 AQP4-seropositive NMOSD patients (similar to 9%) had FH autoantibodies in serum and none had antibodies to C3b, factor B and C3bBb. The FH autoantibody titers were low in three and high in one of the patients, and the avidity indexes were low. FH-IgG complexes were detected in the purified IgG fractions by Western blot. The autoantibodies bound to FH domains 19-20, and also recognized the homologous FH-related protein 1 (FHR-1), similar to FH autoantibodies associated with atypical hemolytic uremic syndrome (aHUS). However, in contrast to the majority of autoantibody-positive aHUS patients, these four NMOSD patients did not lack FHR-1. Analysis of autoantibody binding to FH19-20 mutants and linear synthetic peptides of the C-terminal FH and FHR-1 domains, as well as reduced FH, revealed differences in the exact binding sites of the autoantibodies. Importantly, all four autoantibodies inhibited C3b binding to FH. In conclusion, our results demonstrate that FH autoantibodies are not uncommon in NMOSD and suggest that generation of antibodies against complement regulating factors among other autoantibodies may contribute to the complement-mediated damage in NMOSD.Peer reviewe

Crystal structure of a tripartite complex between C3dg, C-terminal domains of factor H and OspE of Borrelia burgdorferi

Complement is an important part of innate immunity. The alternative pathway of complement is activated when the main opsonin, C3b coats non-protected surfaces leading to opsonisation, phagocytosis and cell lysis. The alternative pathway is tightly controlled to prevent autoactivation towards host cells. The main regulator of the alternative pathway is factor H (FH), a soluble glycoprotein that terminates complement activation in multiple ways. FH recognizes host cell surfaces via domains 19–20 (FH19-20). All microbes including Borrelia burgdorferi, the causative agent of Lyme borreliosis, must evade complement activation to allow the infectious agent to survive in its host. One major mechanism that Borrelia uses is to recruit FH from host. Several outer surface proteins (Osp) have been described to bind FH via the C-terminus, and OspE is one of them. Here we report the structure of the tripartite complex formed by OspE, FH19-20 and C3dg at 3.18 Å, showing that OspE and C3dg can bind simultaneously to FH19-20. This verifies that FH19-20 interacts via the “common microbial binding site” on domain 20 with OspE and simultaneously and independently via domain 19 with C3dg. The spatial organization of the tripartite complex explains how OspE on the bacterial surface binds FH19-20, leaving FH fully available to protect the bacteria against complement. Additionally, formation of tripartite complex between FH, microbial protein and C3dg might enable enhanced protection, particularly on those regions on the bacteria where previous complement activation led to deposition of C3d. This might be especially important for slow-growing bacteria that cause chronic disease like Borrelia burgdorferi.Peer reviewe

Analysis of Linear Antibody Epitopes on Factor H and CFHR1 Using Sera of Patients with Autoimmune Atypical Hemolytic Uremic Syndrome

Introduction: In autoimmune atypical hemolytic uremic syndrome (aHUS), the complement regulator factor H (FH) is blocked by FH autoantibodies, while 90% of the patients carry a homozygous deletion of its homolog complement FH-related protein 1 (CFHR1). The functional consequence of FH-blockade is widely established; however, the molecular basis of autoantibody binding and the role of CFHR1 deficiency in disease pathogenesis are still unknown. We performed epitope mapping of FH to provide structural insight in the autoantibody recruitment on FH and potentially CFHR1. Methods: Eight anti-FH positive aHUS patients were enrolled in this study. With overlapping synthetic FH and CFHR1 peptides, we located the amino acids (aa) involved in binding of acute and convalescence stage autoantibodies. We confirmed the location of the mapped epitopes using recombinant FH domains 19-20 that carried single-aa substitutions at the suspected antibody binding sites in three of our patients. Location of the linear epitopes and the introduced point mutations was visualized using crystal structures of the corresponding domains of FH and CFHR1. Results: We identified three linear epitopes on FH (aa1157-1171; aa1177-1191; and aa1207-1226) and one on CFHR1 (aa276-290) that are recognized both in the acute and convalescence stages of aHUS. We observed a similar extent of autoantibody binding to the aHUS-specific epitope aa1177-1191 on FH and aa276-290 on CFHR1, despite seven of our patients being deficient for CFHR1. Epitope mapping with the domain constructs validated the location of the linear epitopes on FH with a distinct autoantibody binding motif within aa1183-1198 in line with published observations. Summary: According to the results, the linear epitopes we identified are located close to each other on the crystal structure of FH domains 19-20. This tertiary configuration contains the amino acids reported to be involved in C3b and sialic acid binding on the regulator, which may explain the functional deficiency of FH in the presence of auto antibodies. The data we provide identify the exact structures involved in autoantibody recruitment on FH and confirm the presence of an autoantibody binding epitope on CFHR1.Peer reviewe