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IntroductionSubcutaneous macroencapsulation devices circumvent disadvantages of intraportal islet therapy. However, a curative dose of islets within reasonably sized devices requires dense cell packing. We measured internal PO2 of implanted devices, mathematically modeled oxygen availability within devices and tested the predictions with implanted devices containing densely packed human islets.MethodsPartial pressure of oxygen (PO2) within implanted empty devices was measured by noninvasive 19F-MRS. A mathematical model was constructed, predicting internal PO2, viability and functionality of densely packed islets as a function of external PO2. Finally, viability was measured by oxygen consumption rate (OCR) in day 7 explants loaded at various islet densities.ResultsIn empty devices, PO2 was 12 mmHg or lower, despite successful external vascularization. Devices loaded with human islets implanted for 7 days, then explanted and assessed by OCR confirmed trends proffered by the model but viability was substantially lower than predicted. Co-localization of insulin and caspase-3 immunostaining suggested that apoptosis contributed to loss of beta cells.DiscussionMeasured PO2 within empty devices declined during the first few days post-transplant then modestly increased with neovascularization around the device. Viability of islets is inversely related to islet density within devices.

Scholars increasingly recognize that voters' attitudes about gender shape their electoral preferences. Yet previous research has not captured important nuances of the relationship between gender attitudes and electoral choice. We argue that the effects of gender attitudes are not unidirectional and interact in complex ways with voters' perceptions of candidates, depending not only on candidates' sex but also on their gender-relevant characteristics and values. We draw on an original survey of Americans during the 2016 elections that measured three gender attitudes—hostile sexism, modern sexism, and traditional gender roles—and evaluations of primary and general election candidates. Our study design increases analytical leverage by examining actual and hypothetical candidate matchups. We find that among Democrats, hostile sexists were drawn to Bernie Sanders, but gender traditionalists preferred Hillary Clinton. Our results also suggest that if Sanders had been the Democratic nominee, gender egalitarians would have strongly supported him over Donald Trump, as they did Clinton. [ABSTRACT FROM AUTHOR]

Cellular therapies are emerging as a standard approach for the treatment of several diseases. However, realizing the promise of cellular therapies across the full range of treatable disorders will require large-scale, controlled, reproducible culture methods. Bioreactor systems offer the scale-up and monitoring needed, but standard stirred bioreactor cultures do not allow for the real-time regulation of key nutrients in the medium. In this study, β-TC6 insulinoma cells were aggregated and cultured for 3 weeks as a model of manufacturing a mammalian cell product. Cell expansion rates and medium nutrient levels were compared in static, stirred suspension bioreactors (SSB), and continuously fed (CF) SSB. While SSB cultures facilitated increased culture volumes, no increase in cell yields were observed, partly due to limitations in key nutrients, which were consumed by the cultures between feedings, such as glucose. Even when glucose levels were increased to prevent depletion between feedings, dramatic fluctuations in glucose levels were observed. Continuous feeding eliminated fluctuations and improved cell expansion when compared with both static and SSB culture methods. Further improvements in growth rates were observed after adjusting the feed rate based on calculated nutrient depletion, which maintained physiological glucose levels for the duration of the expansion. Adjusting the feed rate in a continuous medium replacement system can maintain the consistent nutrient levels required for the large-scale application of many cell products. Continuously fed bioreactor systems combined with nutrient regulation can be used to improve the yield and reproducibility of mammalian cells for biological products and cellular therapies and will facilitate the translation of cell culture from the research lab to clinical applications.

The ablation of the mammalian chromatin remodeling complex, PBAF-specific subunit BAF180 in mouse embryos results in severe hypoplastic ventricle development and trophoblast placental defects, similar to those found in mice lacking nuclear receptors, RXRalpha and PPARgama. Embryonic aggregation analyses reveal that in contrast to PPARgama-deficient mice, the heart defects are likely result of BAF180 ablation, rather than an indirect consequence of trophoblast placental defects.

Human embryonic stem (ES) cells, like ES cells from mice, have the potential to differentiate into many tissues in vitro, including neural, muscle, and hematopoietic cells. While the development of human ES cell lines gives us a potential source of differentiated, immunologically compatible cells and tissues for transplantation, our understanding of the regulation of these differentiation processes is limited. We have previously demonstrated a method by which pluripotent mouse ES cell lines differentiate in vitro to produce intermediate precursors that give rise to early hematopoietic cells. The ES-derived hematopoietic precursors have a differentiation potential similar to those found in embryonic yolk sac and AGM regions of the mouse, and have a limited ability to engraft the hematopoietic organs of irradiated adult mice. In an effort to understand and regulate the differentiation of human ES cells in vitro, we have documented the differentiation of neural, hematopoietic and cardiac muscle cells in the spontaneously differentiating human embryoid body using morphological analysis. In addition, we have used rtPCR to identify expression patterns of endoderm and mesoderm-specific genes in primary tissues and embryoid bodies. We have cultured ES and ES-derived cells with characteristics of endoderm and mesoderm, using cytokines and induction by feeder cells to direct differentiation. The goal of this research is to direct differentiation to endodermal and mesodermal cells, and ultimately precursors of hematopoietic cells and hepatocytes by inductive agents, or by the genetic modification of ES cells. These studies lay the groundwork for the in vitro production of hepatocytes and hematopoietic stem cells for transplantation, and for the in vitro differentiation of other tissues, such as pancreas cells for diabetes and neural cells for Parkinson's disease. This study was funded by the University of California BioSTAR Project and Geron Corporation.

Abstract: Factor H is an important regulator of complement activation in plasma and on cell surfaces in both humans and mice. If FH function is compromised, inappropriate complement activation on self‐surfaces can have disastrous effects as seen in the kidney diseases atypical haemolytic uremic syndrome (aHUS) and C3 glomerulopathy. As FH constructs have been proposed to be used in treatment for these diseases, we studied the distribution of exogenous FH fragments in mice. Full‐length mFH, mFH1‐5 and mFH18‐20 fragments were radiolabelled, and their distribution was examined in WT, FH−/− and FH−/−C3−/− mice in vivo. Whole body scintigraphy revealed accumulation of radioactivity in the abdominal part of the mice, but also to the thyroid gland and urinary bladder. At organ level in WT mice, some full‐length FH accumulated in internal organs, but most of it remained in the circulation. Both of the mFH fragments accumulated in the kidneys and were excreted in urine. For mFH1‐5, urinary secretion is the likely cause for the accumulation. Concentration of mFH18‐20 to kidneys was slower, and at tissue level, mFH18‐20 was localized at the proximal tubuli in WT and FH−/−C3−/− mice. No C3‐independent binding to glomeruli was detected. In conclusion, these results show that glomerular glycosaminoglycans and sialic acids alone do not collect FH in kidneys. Deposition of C3 fragments is also needed, which implies that in aHUS, the problem is in simultaneous recognition of C3 fragments and glycosaminoglycans or sialic acids by FH, not just the inability of FH to recognize glomerular endothelium as such. [ABSTRACT FROM AUTHOR]

This study uncovers strong evidence that polarization has developed in presidential candidate trait evaluations. Unlike for ideology or policy preferences, the distribution of trait evaluations has become increasingly bimodal and clustered toward the poles. This change stems in part from a more polarized choice set, but perceptions of candidate extremeness are asymmetric, with partisans perceiving the other party's candidate, but not their own, as extreme. In addition, the increased salience of racial and moral issues helps explain trait polarization. Racial attitudes among Republicans have become both more conservative over time and more potent in explaining trait evaluations; among Democrats, racial attitudes have neither changed over time nor become more potent. Moral values among Democrats have grown more liberal over time and more potent in explaining trait evaluations. Among Republicans, however, moral values have not become more conservative, but have become a more potent predictor of trait evaluations. We discuss the implications of the emergence of trait polarization for understanding problematic features of contemporary American politics. [ABSTRACT FROM AUTHOR]

Cellular therapies are emerging as a standard approach for the treatment of several diseases. However, realizing the promise of cellular therapies across the full range of treatable disorders will require large-scale, controlled, reproducible culture methods. Bioreactor systems offer the scale-up and monitoring needed, but standard stirred bioreactor cultures do not allow for the real-time regulation of key nutrients in the medium. In this study, β-TC6 insulinoma cells were aggregated and cultured for 3 weeks as a model of manufacturing a mammalian cell product. Cell expansion rates and medium nutrient levels were compared in static, stirred suspension bioreactors (SSB), and continuously fed (CF) SSB. While SSB cultures facilitated increased culture volumes, no increase in cell yields were observed, partly due to limitations in key nutrients, which were consumed by the cultures between feedings, such as glucose. Even when glucose levels were increased to prevent depletion between feedings, dramatic fluctuations in glucose levels were observed. Continuous feeding eliminated fluctuations and improved cell expansion when compared with both static and SSB culture methods. Further improvements in growth rates were observed after adjusting the feed rate based on calculated nutrient depletion, which maintained physiological glucose levels for the duration of the expansion. Adjusting the feed rate in a continuous medium replacement system can maintain the consistent nutrient levels required for the large-scale application of many cell products. Continuously fed bioreactor systems combined with nutrient regulation can be used to improve the yield and reproducibility of mammalian cells for biological products and cellular therapies and will facilitate the translation of cell culture from the research lab to clinical applications. [ABSTRACT FROM AUTHOR]

To cause infections microbes need to evade host defense systems, one of these being the evolutionarily old and important arm of innate immunity, the alternative pathway of complement. It can attack all kinds of targets and is tightly controlled in plasma and on host cells by plasma complement regulator factor H (FH). FH binds simultaneously to host cell surface structures such as heparin or glycosaminoglycans via domain 20 and to the main complement opsonin C3b via domain 19. Many pathogenic microbes protect themselves from complement by recruiting host FH. We analyzed how and why different microbes bind FH via domains 19-20 (FH19-20). We used a selection of FH19-20 point mutants to reveal the binding sites of several microbial proteins and whole microbes (Haemophilus influenzae, Bordetella pertussis, Pseudomonas aeruginosa, Streptococcus pneumonia, Candida albicans, Borrelia burgdorferi, and Borrelia hermsii). We show that all studied microbes use the same binding region located on one side of domain 20. Binding of FH to the microbial proteins was inhibited with heparin showing that the common microbial binding site overlaps with the heparin site needed for efficient binding of FH to host cells. Surprisingly, the microbial proteins enhanced binding of FH19-20 to C3b and down-regulation of complement activation. We show that this is caused by formation of a tripartite complex between the microbial protein, FH, and C3b. In this study we reveal that seven microbes representing different phyla utilize a common binding site on the domain 20 of FH for complement evasion. Binding via this site not only mimics the glycosaminoglycans of the host cells, but also enhances function of FH on the microbial surfaces via the novel mechanism of tripartite complex formation. This is a unique example of convergent evolution resulting in enhanced immune evasion of important pathogens via utilization of a "superevasion site." [ABSTRACT FROM AUTHOR]

Objectives: Limited lower trunk rotation, which includes rotation of the lumbar spine, may hinder or even prevent functional activities. Currently, due to the lack of reliable, valid, and clinically useful tests, there is no standard objective measure of lower trunk rotation that can be easily performed in the clinic. The purpose of this study was to establish a standard protocol and to determine inter-rater and intra-rater reliability for a goniometric measurement developed to measure lower trunk rotation. Methods: Lower trunk rotation was measured using a specific, goniometric method in 41 subjects. Each subject was measured 6 times by 2 different examiners for a total of 12 measurements. Results: Pearson correlation coefficients indicate good intra-rater reliability ranging from 0.59 to 0.82 for right rotation (P< 0.001) and 0.76 to 0.82 for left rotation (P< 0.001), as well as good inter-rater reliability ranging from 0.62 to 0.83 with right rotation (P< 0.001) and 0.75 to 0.77 for left rotation (P< 0.001). Conclusion: This measure of trunk rotation may be useful for objectively documenting lower trunk rotation. [ABSTRACT FROM AUTHOR]

Transforming growth factor {beta} (TGF{beta}) plays an important role in development and maintenance of murine yolk sac vascular development. Targeted deletions of Tgfb1 and other components of this signaling pathway, such as Acvrl1, Tgfbr1 and Tgfbr2, result in abnormal vascular development especially of the yolk sac, leading to embryonic lethality. There are significant differences between murine and primate development that limit interpretation of studies from mouse models. Thus, to examine the role of TGF{beta} in early human vascular development we used the model of differentiating human embryonic stem cell-derived embryoid bodies to recapitulate early stages of embryonic development. TGF{beta} was applied for different time frames after initiation of embryoid body cultures to assess its effect on differentiation. TGF{beta} inhibited the expression of endodermal, endothelial and hematopoietic markers, which contrasts with findings in the mouse in which TGF{beta} reduced the level of endodermal markers but increased endothelial marker expression. The inhibition observed was not due to changes in proliferation or apoptosis. This marked contrast between the two species may reflect the different origins of the yolk sac hemangiogenic lineages in mouse and human. TGF{beta} effects on the hypoblast, from which these cell lineages are derived in human, would decrease subsequent differentiation of hematopoietic, endothelial and endodermal cells. By contrast, TGF{beta} action on murine hypoblast, while affecting endoderm would not affect the hemangiogenic lineages that are epiblast-derived in the mouse. This study highlights important differences between early human and mouse embryonic development and suggests a role of TGF{beta} in human hypoblast differentiation. [ABSTRACT FROM AUTHOR]

Introduction: Subcutaneous macroencapsulation devices circumvent disadvantages of intraportal islet therapy. However, a curative dose of islets within reasonably sized devices requires dense cell packing. We measured internal PO2 of implanted devices, mathematically modeled oxygen availability within devices and tested the predictions with implanted devices containing densely packed human islets., Methods: Partial pressure of oxygen (PO2) within implanted empty devices was measured by noninvasive 19 F-MRS. A mathematical model was constructed, predicting internal PO2, viability and functionality of densely packed islets as a function of external PO2. Finally, viability was measured by oxygen consumption rate (OCR) in day 7 explants loaded at various islet densities., Results: In empty devices, PO2 was 12 mmHg or lower, despite successful external vascularization. Devices loaded with human islets implanted for 7 days, then explanted and assessed by OCR confirmed trends proffered by the model but viability was substantially lower than predicted. Co-localization of insulin and caspase-3 immunostaining suggested that apoptosis contributed to loss of beta cells., Discussion: Measured PO2 within empty devices declined during the first few days post-transplant then modestly increased with neovascularization around the device. Viability of islets is inversely related to islet density within devices., Competing Interests: KP is the co-founder and CEO of Procyon Technologies, LLC, a startup company focused on the development of oxygenated cell encapsulation devices. BW, who was a graduate student at the time of this study, is now employed by Sylvatica Biotech Inc. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The author MG declared that he was an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision., (© 2023 Einstein, Steyn, Weegman, Suszynski, Sambanis, O'Brien, Avgoustiniatos, Firpo, Graham, Janecek, Eberly, Garwood, Putnam and Papas.)

Background: Many studies use similar methods to measure skin turgor, but there is no gold standard method that is being followed in clinics or hospitals., Purpose: The purpose of this systematic review was to determine if there is any consistent method to measure skin turgor in humans that is valid and reliable., Methods: Topics of interest for turgor assessment included dehydration; skin integrity, including wounds and skin flaps; and fluid/electrolyte balance for adults 18 years and older. PubMed, ProQuest Medical, SPORTDiscus, PEDro, Web of Science Core Collection, and Cumulative Index of Nursing and Allied Health Literature complete databases were utilized. Levels of evidence were established with 2011 Oxford Centre for Evidence-Based Medicine scale. Methodological rigor was assessed with Quality Assessment of Diagnostic Accuracy Studies checklist. Two researchers graded rigor and level of evidence with a third researcher serving as a tie-breaker., Results: Thirteen articles were included in the final analysis. Some researchers used skin turgor as a measure but did not give details regarding specifically how this measure was used. The pinch test was the most commonly used measure of skin turgor. There were 4 articles ranked as evidence level 2, 1 article as evidence level 3, and 8 articles as evidence level 4. Rigor scores ranged from 3 to 13/14., Conclusion: Skin turgor may not be the best assessment tool for some conditions or purposes in adults, such as dehydration, which could lead to a medical emergency.

Immune evasion facilitates survival of Borrelia, leading to infections like relapsing fever and Lyme disease. Important mechanism for complement evasion is acquisition of the main host complement inhibitor, factor H (FH). By determining the 2.2 Å crystal structure of Factor H binding protein A (FhbA) from Borrelia hermsii in complex with FH domains 19-20, combined with extensive mutagenesis, we identified the structural mechanism by which B. hermsii utilizes FhbA in immune evasion. Moreover, structure-guided sequence database analysis identified a new family of FhbA-related immune evasion molecules from Lyme disease and relapsing fever Borrelia. Conserved FH-binding mechanism within the FhbA-family was verified by analysis of a novel FH-binding protein from B. duttonii. By sequence analysis, we were able to group FH-binding proteins of Borrelia into four distinct phyletic types and identified novel putative FH-binding proteins. The conserved FH-binding mechanism of the FhbA-related proteins could aid in developing new approaches to inhibit virulence and complement resistance in Borrelia., Competing Interests: The authors have declared that no competing interests exist.

While most of the spontaneous mutations in the viral genome have no functional, diagnostic, or clinical consequences, some have. In February 2021, we noticed in Southern Finland coronavirus disease 2019 cases where two commercial polymerase chain reaction (PCR) analyses failed to recognize the used N gene target but recognized the other target gene of severe acute respiratory syndrome coronavirus 2. Complete viral genome sequence analysis of the strains revealed several mutations that were not found at that time in public databases. A short 3 bp deletion and three subsequent single nucleotide polymorphisms in the N gene were found exactly at the site where an early published and widely used N gene-based PCR primer is located, explaining the negative results in the N gene PCR. Later the variant strain was identified as a member of the B.1.1.318 Pango lineage that had first been found from Nigerian samples collected in January 2021. This strain shares with the Beta variant the S gene E484K mutation linked to impaired vaccine protection, but differs from this variant in several other ways, for example by deletions in the N gene region. Mutations in the N gene causing diagnostic resistance and on the other hand E484K mutation in the causing altered infectivity warrants careful inspection on virus variants that might get underdiagnosed., (© 2021 Wiley Periodicals LLC.)

BackgroundDespite the global distribution of the intestinal protozoan Dientamoeba fragilis, its clinical picture remains unclear. This results from underdiagnosis: microscopic screening methods either lack sensitivity (wet preparation) or fail to reveal Dientamoeba (formalin-fixed sample).AimIn a retrospective study setting, we characterised the clinical picture of dientamoebiasis and compared it with giardiasis. In addition, we evaluated an improved approach to formalin-fixed samples for suitability in Dientamoeba diagnostics.MethodsThis study comprised four parts: (i) a descriptive part scrutinising rates of Dientamoeba findings; (ii) a methodological part analysing an approach to detect Dientamoeba -like structures in formalin samples; (iii) a clinical part comparing demographics and symptoms between patients with dientamoebiasis (n = 352) and giardiasis (n = 272), and (iv) a therapeutic part (n = 89 patients) investigating correlation between faecal eradication and clinical improvement.ResultsThe rate of Dientamoeba findings increased 20-fold after introducing criteria for Dientamoeba -like structures in formalin-fixed samples (88.9% sensitivity and 83.3% specificity). A further increase was seen after implementing faecal PCR. Compared with patients with giardiasis, the symptoms in the Dientamoeba group lasted longer and more often included abdominal pain, cramping, faecal urgency and loose rather than watery stools. Resolved symptoms correlated with successful faecal eradication (p < 0.001).ConclusionsPreviously underdiagnosed, Dientamoeba has become the most frequently recorded pathogenic enteroparasite in Finland. This presumably results from improved diagnostics with either PCR or detection of Dientamoeba -like structures in formalin-fixed samples, an approach applicable also in resource-poor settings. Symptoms of dientamoebiasis differ slightly from those of giardiasis; patients with distressing symptoms require treatment.

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.

Staphyloccus aureus is a major human pathogen leading frequently to sepsis and soft tissue infections with abscesses. Multiple virulence factors including several immune modulating molecules contribute to its survival in the host. When S. aureus invades the human body, one of the first line defenses is the complement system, which opsonizes the bacteria with C3b and attract neutrophils by release of chemotactic peptides. Neutrophils express Complement receptor-1 [CR1, CD35) that interacts with the C3b-opsonized particles and thereby plays an important role in pathogen recognition by phagocytic cells. In this study we observed that a fraction of S. aureus culture supernatant prevented binding of C3b to neutrophils. This fraction consisted of S. aureus leukocidins and Efb. The C-terminus of Efb is known to bind C3b and shares significant sequence homology to the extracellular complement binding protein [Ecb). Here we show that S. aureus Ecb displays various mechanisms to block bacterial recognition by neutrophils. The presence of Ecb blocked direct interaction between soluble CR1 and C3b and reduced the cofactor activity of CR1 in proteolytic inactivation of C3b. Furthermore, Ecb could dose-dependently prevent recognition of C3b by cell-bound CR1 that lead to impaired phagocytosis of NHS-opsonized S. aureus. Phagocytosis was furthermore reduced in the presence of soluble CR1 [sCR1). These data indicate that the staphylococcal protein Ecb prevents recognition of C3b opsonized bacteria by neutrophil CR1 leading to impaired killing by phagocytosis and thereby contribute to immune evasion of S. aureus.

Embryonic stem cells (ESCs) represent a mainstay for pluripotent stem cell research and development (R&D) and provide tangible opportunities for clinical translation including cell therapies and drug discovery. Moreover, in spite of the discovery of induced pluripotent stem cells (iPSCs), ESCs are an essential reference point, against which other pluripotent cells are compared. Hence, there is an ongoing need to derive and bank quality-controlled research-grade and clinical-grade ESC lines using established and standardized methods. Here, we provide a concise, step-by-step protocol for the derivation of ESCs from human embryos. While largely based on previously reported method for clinical-grade human ESC (hESC) line derivation, the protocol is suitable for routine application, although adaptable for clinical-compliance.

In this demonstration, spheroids formed from the β-TC6 insulinoma cell line were cultured as a model of manufacturing a mammalian islet cell product to demonstrate how regulating nutrient levels can improve cell yields. In previous studies, bioreactors facilitated increased culture volumes over static cultures, but no increase in cell yields were observed. Limitations in key nutrients such as glucose, which were consumed between batch feedings, can lead to limitations in cell expansion. Large fluctuations in glucose levels were observed, despite the increase in glucose concentrations in the media. The use of continuous feeding systems eliminated fluctuations in glucose levels, and improved cell growth rates when compared with batch fed static and SSB culture methods. Additional increases in growth rates were observed by adjusting the feed rate based on calculated nutrient consumption, which allowed the maintenance of physiological glucose over three weeks in culture. This method can also be adapted for other cell types.

Staphylococcus aureus is a major human pathogen causing more than a tenth of all septicemia cases and often superficial and deep infections in various tissues. One of the immune evasion strategies of S. aureus is to secrete proteins that bind to the central complement opsonin C3b. One of these, extracellular complement binding protein (Ecb), is known to interfere directly with functions of C3b. Because C3b is also the target of the physiological plasma complement regulator, factor H (FH), we studied the effect of Ecb on the complement regulatory functions of FH. We show that Ecb enhances acquisition of FH from serum onto staphylococcal surfaces. Ecb and FH enhance mutual binding to C3b and also the function of each other in downregulating complement activation. Both Ecb and the C-terminal domains 19-20 of FH bind to the C3d part of C3b. We show that the mutual enhancing effect of Ecb and FH on binding to C3b depends on binding of the FH domain 19 to the C3d part of C3b next to the binding site of Ecb on C3d. Our results show that Ecb, FH, and C3b form a tripartite complex. Upon exposure of serum-sensitive Haemophilus influenzae to human serum, Ecb protected the bacteria, and this effect was enhanced by the addition of the C-terminal domains 19-20 of FH. This finding indicates that the tripartite complex formation could give additional protection to bacteria and that S. aureus is thereby able to use host FH and bacterial Ecb in a concerted action to eliminate C3b at the site of infection.