Activation of the endothelium by IL-1 alpha and glucocorticoids results in major increase of complement C3 and factor B production and generation of C3a

Experimentally elevated corticosterone does not affect bacteria killing ability of breeding female tree swallows (Tachycineta bicolor)

The immune system can be modulated when organisms are exposed to acute or chronic stressors. Glucocorticoids (GCs), the primary hormonal mediators of the physiological stress response, are suspected to play a crucial role in immune modulation. However, most evidence of stress-associated immunomodulation does not separate the effects of glucocorticoid-dependent pathways from those of glucocorticoid-independent mechanisms on immune function. In this study, we experimentally elevated circulating corticosterone, the main avian glucocorticoid, in free-living female tree swallows (Tachycineta bicolor) for one to two weeks to test its effects on immune modulation. Natural variation in bacteria killing ability (BKA), a measure of innate constitutive immunity, was predicted by the interaction between timing of breeding and corticosterone levels. However, experimental elevation of corticosterone had no effect on BKA. Therefore, even when BKA is correlated with natural variation in glucocorticoid levels, this relationship may not be causal. Experiments are necessary to uncover the causal mechanisms of immunomodulation and the consequences of acute and chronic stress on disease vulnerability. Findings in other species indicate that acute increases in GCs can suppress BKA; but our results support the hypothesis that this effect does not persist over longer timescales, during chronic elevations in GCs. Direct comparisons of the effects of acute vs. chronic elevation of GCs on BKA will be important for testing this hypothesis.

The complement alternative pathway and hemostasis

The complement and hemostatic systems are complex systems, and both involve enzymatic cascades, regulators, and cell components-platelets, endothelial cells, and immune cells. The two systems are ancestrally related and are defense mechanisms that limit infection by pathogens and halt bleeding at the site of vascular injury. Recent research has uncovered multiple functional interactions between complement and hemostasis. On one side, there are proteins considered as complement factors that activate hemostasis, and on the other side, there are coagulation proteins that modulate complement. In addition, complement and coagulation and their regulatory proteins strongly interact each other to modulate endothelial, platelet and leukocyte function and phenotype, creating a potentially devastating amplifying system that must be closely regulated to avoid unwanted damage and\or disseminated thrombosis. In view of its ability to amplify all complement activity through the C3b-dependent amplification loop, the alternative pathway of complement may play a crucial role in this context. In this review, we will focus on available and emerging evidence on the role of the alternative pathway of complement in regulating hemostasis and vice-versa, and on how dysregulation of either system can lead to severe thromboinflammatory events.

Nonstructural Protein 1 of Variant PEDV Plays a Key Role in Escaping Replication Restriction by Complement C3

Zoonotic coronaviruses represent an ongoing threat to public health. The classical porcine epidemic diarrhea virus (PEDV) first appeared in the early 1970s. Since 2010, outbreaks of highly virulent PEDV variants have caused great economic losses to the swine industry worldwide. However, the strategies by which PEDV variants escape host immune responses are not fully understood. Complement component 3 (C3) is considered a central component of the three complement activation pathways and plays a crucial role in preventing viral infection. In this study, we found that C3 significantly inhibited PEDV replication in vitro, and both variant and classical PEDV strains induced high levels of interleukin-1β (IL-1β) in Huh7 cells. However, the PEDV variant strain reduces C3 transcript and protein levels induced by IL-1β compared with the PEDV classical strain. Examination of key molecules of the C3 transcriptional signaling pathway revealed that variant PEDV reduced C3 by inhibiting CCAAT/enhancer-binding protein β (C/EBP-β) phosphorylation. Mechanistically, PEDV nonstructural protein 1 (NSP1) inhibited C/EBP-β phosphorylation via amino acid residue 50. Finally, we constructed recombinant PEDVs to verify the critical role of amino acid 50 of NSP1 in the regulation of C3 expression. In summary, we identified a novel antiviral role of C3 in inhibiting PEDV replication and the viral immune evasion strategies of PEDV variants. Our study reveals new information on PEDV-host interactions and furthers our understanding of the pathogenic mechanism of this virus. IMPORTANCE The complement system acts as a vital link between the innate and the adaptive immunity and has the ability to recognize and neutralize various pathogens. Activation of the complement system acts as a double-edged sword, as appropriate levels of activation protect against pathogenic infections, but excessive responses can provoke a dramatic inflammatory response and cause tissue damage, leading to pathological processes, which often appear in COVID-19 patients. However, how PEDV, as the most severe coronavirus causing diarrhea in piglets, regulates the complement system has not been previously reported. In this study, for the first time, we identified a novel mechanism of a PEDV variant in the suppression of C3 expression, showing that different coronaviruses and even different subtype strains differ in regulation of C3 expression. In addition, this study provides a deeper understanding of the mechanism of the PEDV variant in immune escape and enhanced virulence.

Complement in Tumourigenesis and the Response to Cancer Therapy

In recent years, our knowledge of the complement system beyond innate immunity has progressed significantly. A modern understanding is that the complement system has a multifaceted role in malignancy, impacting carcinogenesis, the acquisition of a metastatic phenotype and response to therapies. The ability of local immune cells to produce and respond to complement components has provided valuable insights into their regulation, and the subsequent remodeling of the tumour microenvironment. These novel discoveries have advanced our understanding of the immunosuppressive mechanisms supporting tumour growth and uncovered potential therapeutic targets. This review discusses the current understanding of complement in cancer, outlining both direct and immune cell-mediated roles. The role of complement in response to therapies such as chemotherapy, radiation and immunotherapy is also presented. While complement activities are largely context and cancer type-dependent, it is evident that promising therapeutic avenues have been identified, in particular in combination therapies.

Functional Evaluation of AMD-Associated Risk Variants of Complement Factor B

Purpose

The 32W and 32Q variants of complement factor B (CFB) are associated with reduced risk of developing neovascular age-related macular degeneration (AMD) compared with the common 32R allele. The objective of this study was to determine if the most protective R32Q variant affects the neovascular process in a manner consistent with the reported reduced disease association.

Methods

The 32R, 32W, and 32Q human CFB variants were expressed in human embryonic kidney 293T cells and purified from culture supernatant. The ex vivo mouse fetal metatarsal explant model was used to investigate the effect of these three human CFB variants on angiogenesis. Metatarsal bones were isolated from mouse embryos and cultured in the presence of the three CFB variants, and angiogenesis was measured following immunostaining of fixed samples. ELISAs were used to quantify C3 and VEGF protein levels in metatarsal culture and quantitative PCR to measure Cfb, C3, and Vegf expression.

Results

We show here that the three CFB variants have different biological activities in the mouse metatarsal assay, with CFBR32 exhibiting significantly greater angiogenic activity than CFBQ32 or CFBW32, which were broadly similar. We also observed differences in macrophage phenotype with these two variants that may contribute to their activities in this experimental model.

Conclusions

We have demonstrated that the biological activities of CFBR32, CFBW32, and CFBQ32 are consistent with their AMD risk association, and we provide functional evidence of roles for these variants in angiogenesis that may be relevant to the pathogenesis of the neovascular form of AMD.

Emphysema-associated Autoreactive Antibodies Exacerbate Post-Lung Transplant Ischemia-Reperfusion Injury

Chronic obstructive pulmonary disease-associated chronic inflammation has been shown to lead to an autoimmune phenotype characterized in part by the presence of lung autoreactive antibodies. We hypothesized that ischemia-reperfusion injury (IRI) liberates epitopes that would facilitate preexisting autoantibody binding, thereby exacerbating lung injury after transplant. We induced emphysema in C57BL/6 mice through 6 months of cigarette smoke (CS) exposure. Mice with CS exposure had significantly elevated serum autoantibodies compared with non-smoke-exposed age-matched (NS) mice. To determine the impact of a full preexisting autoantibody repertoire on IRI, we transplanted BALB/c donor lungs into NS or CS recipients and analyzed grafts 48 hours after transplant. CS recipients had significantly increased lung injury and immune cell infiltration after transplant. Immunofluorescence staining revealed increased IgM, IgG, and C3d deposition in CS recipients. To exclude confounding alloreactivity and confirm the role of preexisting autoantibodies in IRI, syngeneic Rag1^-/- (recombination-activating protein 1-knockout) transplants were performed in which recipients were reconstituted with pooled serum from CS or NS mice. Serum from CS-exposed mice significantly increased IRI compared with control mice, with trends in antibody and C3d deposition similar to those seen in allografts. These data demonstrate that pretransplant CS exposure is associated with increased IgM/IgG autoantibodies, which, upon transplant, bind to the donor lung, activate complement, and exacerbate post-transplant IRI.

Complement Component C3 Binds to the A3 Domain of von Willebrand Factor

von Willebrand factor (VWF) is a multimeric protein composed of monomeric subunits (∼280 kD) linked by disulfide bonds. During hemostasis and thrombosis, ultralarge (UL) VWF (ULVWF) multimers initiate platelet adhesion. In vitro, human C3 binds to ULVWF multimeric strings secreted by and anchored to human endothelial cell to promote the assembly and activation of C3 convertase (C3bBb) and C5 convertase (C3bBbC3b) of the alternative complement pathway (AP). The purified and soluble C3 avidly binds to recombinant human VWF A1A2A3, as well as the recombinant isolated human VWF A3 domain. Notably, the binding of soluble human ULVWF multimers to purified human C3 was blocked by addition of a monovalent Fab fragment antibody to the VWF A3 domain. We conclude that the A3 domain in VWF/ULVWF contains a docking site for C3. In contrast, purified human C4, an essential component of the classical and lectin complement pathways, binds to soluble, isolated A1, but not to ULVWF strings secreted by and anchored to endothelial cells. Our findings should facilitate the design of new therapeutic agents to suppress the initiation of the AP on ULVWF multimeric strings during thrombotic and inflammatory disorders.

AICAR suppresses TNF-α-induced complement factor B in RPE cells

Age related macular degeneration is the leading cause of blindness in the developed world. Although its precise cause remains elusive, dysfunction of the retinal pigment epithelium (RPE) and dysregulation of complement have been implicated in its pathogenesis. The goal of this study was to evaluate the role of an AMP-dependent kinase (AMPK) activator, 5-aminoimidazole-4-carboxamide riboside (AICAR), on tumor necrosis factor alpha (TNF-α) induction of complement factor B (CFB) in RPE cells. We found that AICAR inhibited TNF-α-induced CFB expression in ARPE-19 and human primary RPE cells in a dose-dependent fashion. Treatment of cells with dipyridamole, which blocks AICAR cellular uptake abolished these effects. In contrast, the adenosine kinase inhibitor, 5-iodotubericidin, which inhibits the conversion of AICAR to the direct activator of AMPK, ZMP, did not reverse the effects on TNF-α-induced CFB expression, suggesting AMPK-independent effects. Indeed, knockout of AMPK in RPE cells using Clustered Regularly Interspaced Palindromic Repeats (CRISPR)/Cas9 did not abolish the inhibitory effects of AICAR on RPE CFB expression. Collectively, our results suggest that AICAR can suppress TNF-α-induced CFB expression in RPE cells in an AMPK-independent mechanism, and could be used as a therapeutic target in certain complement over-activation scenarios.

Genome-wide expression differences in anti-Vegf and dexamethasone treatment of inflammatory angiogenesis in the rat cornea

Angiogenesis as a pathological process in the eye can lead to blindness. In the cornea, suppression of angiogenesis by anti-VEGF treatment is only partially effective while steroids, although effective in treating inflammation and angiogenesis, have broad activity leading to undesirable side effects. In this study, genome-wide expression was investigated in a suture-induced corneal neovascularization model in rats, to investigate factors differentially targeted by dexamethasone and anti-Vegf. Topical treatment with either rat-specific anti-Vegf, dexamethasone, or normal goat IgG (sham) was given to sutured corneas for 48 hours, after which in vivo imaging, tissue processing for RNA microarray, and immunofluorescence were performed. Dexamethasone suppressed limbal vasodilation (P < 0.01) and genes in PI3K-Akt, focal adhesion, and chemokine signaling pathways more effectively than anti-Vegf. The most differentially expressed genes were confirmed by immunofluorescence, qRTPCR and Western blot. Strong suppression of Reg3g and the inflammatory chemokines Ccl2 and Cxcl5 and activation of classical complement pathway factors C1r, C1s, C2, and C3 occurred with dexamethasone treatment, effects absent with anti-Vegf treatment. The genome-wide results obtained in this study provide numerous potential targets for specific blockade of inflammation and angiogenesis in the cornea not addressed by anti-Vegf treatment, as possible alternatives to broad-acting immunosuppressive therapy.

Endothelial cells: source, barrier, and target of defensive mediators

Endothelium is strategically located at the interface between blood and interstitial tissues, placing thus endothelial cell as a key player in vascular homeostasis. Endothelial cells are in a dynamic equilibrium with their environment and constitute concomitantly a source, a barrier, and a target of defensive mediators. This review will discuss the recent advances in our understanding of the complex crosstalk between the endothelium, the complement system and the hemostasis in health and in disease. The first part will provide a general introduction on endothelial cells heterogeneity and on the physiologic role of the complement and hemostatic systems. The second part will analyze the interplay between complement, hemostasis and endothelial cells in physiological conditions and their alterations in diseases. Particular focus will be made on the prototypes of thrombotic microangiopathic disorders, resulting from complement or hemostasis dysregulation-mediated endothelial damage: atypical hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. Novel aspects of the pathophysiology of the thrombotic microangiopathies will be discussed.

Mechanism of TH2/TH17-predominant and neutrophilic TH2/TH17-low subtypes of asthma

BACKGROUND

The mechanism of T_H2/T_H17-predominant and T_H2/T_H17-low asthma is unknown.

OBJECTIVE

We sought to study the immune mechanism of T_H2/T_H17-predominant and T_H2/T_H17-low asthma.

METHODS

In a previously reported cohort of 60 asthmatic patients, 16 patients were immunophenotyped with T_H2/T_H17-predominant asthma and 22 patients with T_H2/T_H17-low asthma. We examined bronchoalveolar lavage (BAL) fluid leukocytes, cytokines, mediators, and epithelial cell function for these asthma subgroups.

RESULTS

Patients with T_H2/T_H17-predominant asthma had increased IL-1β, IL-6, IL-23, C3a, and serum amyloid A levels in BAL fluid, and these correlated with IL-1β and C3a levels. T_H2/T_H17 cells expressed higher levels of the IL-1 receptor and phospho-p38 mitogen-activated protein kinase. Anakinra, an IL-1 receptor antagonist protein, inhibited BAL T_H2/T_H17 cell counts. T_H2/T_H17-low asthma had 2 distinct subgroups: neutrophilic asthma (45%) and pauci-inflammatory asthma (55%). This contrasted with patients with T_H2/T_H17-predominant and T_H2-predominant asthma, which included neutrophilic asthma in 6% and 0% of patients, respectively. BAL fluid neutrophils strongly correlated with BAL fluid myeloperoxidase, IL-8, IL-1α, IL-6, granulocyte colony-stimulating factor, and GM-CSF levels. Sixty percent of the patients with neutrophilic asthma had a pathogenic microorganism in BAL culture, which suggested a subclinical infection.

CONCLUSION

We uncovered a critical role for the IL-1β pathway in patients with T_H2/T_H17-predminant asthma. A subgroup of patients with T_H2/T_H17-low asthma had neutrophilic asthma and increased BAL fluid IL-1α, IL-6, IL-8, granulocyte colony-stimulating factor, and GM-CSF levels. IL-1α was directly involved in IL-8 production and likely contributed to neutrophilic asthma. Sixty percent of neutrophilic patients had a subclinical infection.

Acute murine antigen-induced arthritis is not affected by disruption of osteoblastic glucocorticoid signalling

Background

The role of endogenous glucocorticoids (GC) in the initiation and maintenance of rheumatoid arthritis (RA) remains unclear. We demonstrated previously that disruption of GC signalling in osteoblasts results in a profound attenuation of K/BxN serum-induced arthritis, a mouse model of RA. To determine whether or not the modulation of the inflammatory response by osteoblasts involves T cells, we studied the effects of disrupted osteoblastic GC-signalling in the T cell-dependent model of antigen-induced arthritis (AIA).

Methods

Acute arthritis was induced in pre-immunised 11-week-old male 11β-hydroxysteroid dehydrogenase type 2 transgenic (tg) mice and their wild-type (WT) littermates by intra-articular injection of methylated bovine serum albumine (mBSA) into one knee joint. Knee diameter was measured every 1–2 days until euthanasia on day 14 post injection. In a separate experiment, arthritis was maintained for 28 days by weekly reinjections of mBSA. Tissues were analysed by histology, histomorphometry and microfocal-computed tomography. Serum cytokines levels were determined by multiplex suspension array.

Results

In both short and long term experiments, arthritis developed in tg and WT mice with no significant difference between both groups. Histological indices of inflammation, cartilage damage and bone erosion were similar in tg and WT mice. Bone volume and turnover at the contralateral tibia and systemic cytokine levels were not different.

Conclusions

Acute murine AIA is not affected by a disruption in osteoblastic GC signalling. These data indicate that osteoblasts do not modulate the T cell-mediated inflammatory response via a GC-dependent pathway.

Human skin mast cells express complement factors C3 and C5

We examine whether complement factor C3 or C5 is synthesized by human skin-derived mast cells and whether their synthesis is regulated by cytokines. C3 and C5 mRNAs were assessed by RT-PCR, and proteins by flow cytometry, confocal microscopy, Western blotting, and ELISA. C3 and C5 mRNAs were each expressed, and baseline protein levels/10(6) cultured mast cells were 0.9 and 0.8 ng, respectively, and located in the cytoplasm outside of secretory granules. C3 accumulated in mast cell culture medium over time and by 3 d reached a concentration of 9.4 ± 8.0 ng/ml, whereas C5 levels were not detectable (<0.15 ng/ml). Three-day incubations of mast cells with IL-1α, IL-1β, IL-17, IFN-γ, IL-6, or anti-FcεRI did not affect C3 protein levels in culture medium, whereas incubations with PMA, TNF-α, IL-13, or IL-4 enhanced levels of C3 1.7- to 3.3-fold. In contrast with C3, levels of C5 remained undetectable. Importantly, treatment with TNF-α together with either IL-4 or IL-13 synergistically enhanced C3 (but not C5) production in culture medium by 9.8- or 7.1-fold, respectively. This synergy was blocked by attenuating the TNF-α pathway with neutralizing anti-TNF-α Ab, soluble TNFR, or an inhibitor of NF-κB, or by attenuating the IL-4/13 pathway with Jak family or Erk antagonists. Inhibitors of PI3K, Jnk, and p38 MAPK did not affect this synergy. Thus, human mast cells can produce and secrete C3, whereas β-tryptase can act on C3 to generate C3a and C3b, raising the likelihood that mast cells engage complement to modulate immunity and inflammation in vivo.

Sleep and circadian rhythm regulate circulating complement factors and immunoregulatory properties of C5a

The sleep-wake cycle is characterized by complex interactions among the central nervous, the endocrine and the immune systems. Continuous 24-h wakefulness prevents sleep-associated hormone regulation resulting in impaired pro-inflammatory cytokine production. Importantly, cytokines and hormones also modulate the complement system, which in turn regulates several adaptive immune responses. However, it is unknown whether sleep affects the activation and the immunoregulatory properties of the complement system. Here, we determined whether the 24-h sleep-wake cycle has an impact on: (i) the levels of circulating complement factors; and (ii) TLR4-mediated IL-12 production from human IFN-γ primed monocytes in the presence or absence of C5a receptor signaling. For this purpose, we analyzed the blood and blood-derived monocytes of 13 healthy donors during a regular sleep-wake cycle in comparison to 24 h of continuous wakefulness. We found decreased plasma levels of C3 and C4 during nighttime hours that were not affected by sleep. In contrast, sleep was associated with increased complement activation as reflected by elevated C3a plasma levels during nighttime sleep. Sleep deprivation prevented such activation. At the cellular level, C5a negatively regulated TLR4-mediated IL-12p40 and p70 production from human monocytes. Importantly, this regulatory effect of C5a on IL-12p70 production was effective only during daytime hours. Thus, similar to hormones, some complement factors and immunoregulatory properties of C5a are influenced by sleep and the circadian rhythm. Our findings that continuous wakefulness has a negative impact on complement activation may provide a rationale for the immunosupportive functions of sleep.

Biomarkers of endothelial cell activation serve as potential surrogate markers for drug-induced vascular injury

Drug-induced vascular injury (DIVI) is a nonclinical finding that often confounds the toxicological evaluation of investigational drugs, but there is an absence of qualified biomarkers that can be used to detect and monitor its appearance in animals and patients during drug development and clinical use. It is well known that endothelial cell (EC) activation plays a key role in the expression and evolution of DIVI, and the various immunological and inflammatory factors involved in its expression may serve as potential biomarker candidates. Activated ECs change their morphology and gene expression, generating endothelial adhesion molecules, pro-coagulant molecules, cytokines, chemokines, vasodilators, nitric oxide, and acute-phase reactants. This review provides a brief historical background of EC activation and the search for biomarkers of early EC activation for monitoring DIVI. At present, no biomarkers of EC activation have been qualified to predict DIVI in the nonclinical or clinical context, and a robust pathologic foundation for their use is still lacking. We propose three categories of EC activation biomarkers: recommended surrogate markers, potentially useful markers, and emerging candidate markers. This review alerts pharmaceutical companies, research institutions, and regulatory agencies to the continuing need for reliable biomarkers of EC activation in drug development.

Primed CD8(+) T-cell responses to allogeneic endothelial cells are controlled by local complement activation

CD8 T cells primed by transplantation recognize allogeneic class I MHC molecules expressed on graft vascular endothelium and contribute to allograft injury. We previously showed that immune cell-derived complement activation fragments are integral to T cell activation/expansion. Herein we tested the impact of local complement production/activation on T cell/endothelial cell (EC) interactions. We found that proinflammatory cytokines upregulated alternative pathway complement production by ECs, yielding C5a. We further found that ECs deficient in the cell surface C3/C5 convertase regulator decay accelerating factor (DAF, CD55) induced greater CD8 T-cell proliferation and more IFNgamma(+) and perforin(+) effector cells than wild-type (WT) ECs. Allogeneic C3(-/-) EC induced little or no CD8 responses. Abrogation of responses following C5a receptor (C5aR) blockade, or augmentation following addition of recombinant C5a demonstrated that the effects were mediated through T-cell-expressed-C5aR interactions. Analyses of in vivo CD8 cell responses to transplanted heart grafts deficient in EC DAF showed similar augmentation. The findings reveal that EC-derived complement triggers secondary CD8 T-cell differentiation and expansion and argue that targeting complement and/or C5aR could limit T-cell-mediated graft injury.

Gene profiling studies in the neonatal ovine lung show enhancing effects of VEGF on the immune response

Preterm and young neonates have an increased predisposition to respiratory distress syndrome (RDS) associated with an immature development of lung surfactant. Glucocorticoids (GCs) are the major immunomodulatory agents used to increase lung development and reduce the mortality and morbidity of preterm infants with RDS. However, their safety remains uncertain, and the precise mechanisms by which they improve lung function are unclear. In previous studies, we found that vascular endothelial growth factor (VEGF) enhances the innate immune response by respiratory epithelial cells, causes a monocytic infiltration into the lung, and reduces the severity of infection by respiratory syncytial virus (RSV), a respiratory pathogen known to affect preterm infants at a high prevalence. The purpose of this study is to measure the effects of VEGF administration on local immune responses in neonatal lambs, as the ovine lung is well suited for comparison to the human lung, due to similarities in alveolar development, immune responses, and RSV susceptibility. We hypothesized that VEGF induces the expression of genes necessary for host immune responses. We analyzed global gene expression profiles in the lungs of neonate lambs treated with VEGF by real-time qPCR. We report that VEGF induced the expression of chemokines (IL-8, RANTES, MCP-1), cytokines (IFN-gamma, IL-6, TNF-alpha, GMCSF), Toll-like receptor (TLR)-4, complement family members (C3, CFB, CFH) and collectins (SP-A, SP-D). These results suggest that VEGF can regulate local immune gene expression in vivo and should be further explored as a potential exogenous therapy for various lung diseases.

Up-regulation of complement factor B in retinal pigment epithelial cells is accompanied by complement activation in the aged retina

Complement activation is involved in the pathogenesis of age-related macular degeneration. How complement is activated in the retina is not known. Previously we have shown that complement factor H (CFH) is constitutively expressed by retinal pigment epithelial (RPE) cells and the production of CFH is negatively regulated by inflammatory cytokines and oxidative insults. Here we investigated the production and regulation of complement factor B (CFB) in RPE cells. Immunohistochemistry showed that CFB is expressed at low levels on the apical portion of the RPE cells in normal physiological conditions. With age, CFB expression increases and extends to the basal part of RPE cells. Confocal microscopy and real-time PCR of RPE cultures indicated that the production of CFB by RPE cells is positively regulated by TNF-alpha, IFN-gamma and long-term (30 days) photoreceptor outer segments treatments. Increased CFB expression in RPE cells in vivo is accompanied by the accumulation of complement C3 and C3a deposition at the Bruch's membrane and the basal layer of RPE cells. Our results suggest that RPE cells play important roles in regulating complement activation in the retina. Increased complement activation in the aged retina may be important for retinal homeostasis in the context of accumulating photoreceptor waste products.

Glucocorticoids enhance or spare innate immunity: effects in airway epithelium are mediated by CCAAT/enhancer binding proteins

Although it is widely accepted that glucocorticoids (GC) are a mainstay of the treatment of diseases characterized by airway inflammation, little is known about the effects of GC on local innate immunity. In this article, we report that respiratory epithelial cells manifested a local "acute phase response" after stimulation with TLR activation and TNF-alpha and that GC spared or enhanced the epithelial expression of molecules that are involved in host defense, including complement, collectins, and other antimicrobial proteins. As expected, GC inhibited the expression of molecules responsible for inflammation such as cytokines (IFNbeta and GM-CSF) and chemokines (RANTES and IL-8). Studies using Western blotting, EMSA, and functional analysis indicated that the selective effects of GC are mediated through activation of the transcription factor C/EBP. Knockdown of C/EBPbeta by small interfering RNA blocked the enhancement by GC of host defense molecule expression but had no effect on inflammatory gene expression. These results suggest that GC spare or enhance local innate host defense responses in addition to exerting anti-inflammatory actions. It is possible that the known ability of GC to reduce the exacerbation of diseases in which infectious organisms serve as triggering factors (e.g., asthma, allergic bronchopulmonary aspergillosis, and chronic obstructive pulmonary disease) may result in part from enhanced innate immune responses in airway mucosa.

Pro-inflammatory cytokines from Kupffer cells downregulate hepatocyte expression of adrenomedullin binding protein-1

Polymicrobial sepsis is characterized by an early, hyperdynamic phase followed by a late hypodynamic phase. Adrenomedullin (AM), a vasodilatory peptide, inhibits this transition from the early phase to the late phase. Adrenomedullin binding protein-1 (AMBP-1) enhances AM-mediated activities. The decrease of AMBP-1 levels in late sepsis reduces the vascular response to AM and produces the hypodynamic phase. Studies have indicated that the administration of LPS downregulates AMBP-1 production in the liver. Since hepatocytes are the primary source of AMBP-1 biosynthesis in the liver, we employed a co-culture strategy using hepatocyte and Kupffer cells to determine whether LPS directly or by increasing pro-inflammatory cytokines from Kupffer cells downregulates AMBP-1 production. Hepatocytes and Kupffer cells isolated from rats were co-cultured and treated with LPS for 24 h. LPS significantly attenuated AMBP-1 protein expression in a dose-dependent manner. Since AMBP-1 is basically a secretory protein, cell supernatants from co-culture cells treated with LPS were examined for AMBP-1 protein levels. LPS treatment caused a dose related decrease in AMBP-1 protein secretion. Similarly, LPS treatment produced a significant decrease in AMBP-1 protein expression in hepatocytes and Kupffer cells cultured using transwell inserts. LPS had no direct effect on AMBP-1 levels in cultured hepatocytes or Kupffer cells alone. To confirm that the observed effects in co-culture were due to the cytokines released from Kupffer cells, hepatocytes were treated with IL-1beta or TNF-alpha for 24 h and AMBP-1 expression was examined. The results indicated that both cytokines significantly inhibited AMBP-1 protein levels. Thus, pro-inflammatory cytokines released from Kupffer cells are responsible for downregulation of AMBP-1.

Cross-talk between the complement system and endothelial cells in physiologic conditions and in vascular diseases

The endothelial layer represents a continuous physical barrier that controls coagulation and allows selective passage of soluble molecules and circulating cells across the vessel wall into the tissue. The functional activity of the endothelial cells may be influenced by their interaction with components of the complement system. In this review we shall discuss the complex interplay that can be established between the endothelium and complement proteins or activation products. Endothelial cells may also secrete several complement components which contribute to the circulating pool. This process can be regulated by cytokines and other pro-inflammatory stimuli. In addition, complement activation products stimulate endothelial cells to acquire a pro-inflammatory and pro-coagulant status. Expression of regulatory molecules on the cell surface provides protection against an undesired attack by complement activation products. Unrestricted complement activation under pathological conditions may lead to structural and functional changes of the endothelium resulting in vascular disease.

Differential regulation of endothelial cell activation by complement and interleukin 1alpha

Activation of complement on endothelium triggers physiological changes that promote coagulation, thrombosis, and inflammation. Unlike agonists such as cytokines and endotoxin that induce these changes through transcription of many genes, complement, particularly the membrane attack complex, primarily induces release of IL-1alpha by the endothelial cells; the cytokine may then be removed by normal blood flow or may promote activation of the full range of endothelial cell responses in an autocrine or paracrine manner. We studied the intracellular signaling pathways used by complement to activate interleukin (IL)-1alpha transcription in cultured endothelial cells. The membrane attack complex and other pore-forming proteins stimulated calcineurin and activated selective transcription of the IL-1alpha gene. In contrast, the action of cytokines such as IL-1alpha was not selective and not dependent on calcineurin activity. Transcription of IL-1alpha, whether stimulated by complement and calcineurin or by "conventional agonists," such as IL-1alpha independent of calcineurin, proceeded via binding of nuclear factor kappaB transcriptional activators to the IL-1alpha gene promoter. These findings define a molecular mechanism through which complement regulates IL-1alpha production by endothelial cells and explain how blood flow may determine the extent of complement-stimulated inflammation.

Novel roles for acylation stimulating protein/C3adesArg: a review of recent in vitro and in vivo evidence

Recent experimental evidence is shedding more light on the physiological actions of acylation-stimulating protein (ASP)/C3adesArg. The role of ASP in regulating lipid metabolism has primarily focused on its participation in the stimulation of triglyceride synthesis (TGS) and glucose transport. Although there is no doubt that ASP, an adipocyte-produced hormone, plays a key physiological role, accumulating evidence suggests that the effects of ASP go beyond its acute effects on lipid metabolism. In this review, we present novel findings of ASP/C3adesArg effects on preadipocyte differentiation. In 3T3-L1 and 3T3-F442A cells, ASP can substitute for insulin and enhance differentiation as measured by intracellular lipid droplet accumulation, clonal expansion, and increased expression of differentiation markers. Specifically, ASP increased basal TGS by 250% after 9 days differentiation, with similar effects induced by insulin. With ASP treatment, expression of C/EBPdelta was up-regulated early in differentiation (day 2) and decreased thereafter. Expression of PPARgamma and late markers of differentiation, such as adipsin and diacylglycerol acyltransferase-1, were also increased. Effects on clonal expansion were indicated by a twofold increase in [(3)H] thymidine incorporation in 3T3-L1 cells compared to treatment with IBMX + DX alone. Further, the effects of ASP extended beyond adipose tissue to endocrine effects on hormone secretion of insulin (pancreatic cells); cytokines TNFalpha, IL-1beta, and IL-6 (myeloid cells); prolactin, growth hormone, and adrenocorticotropin (pituitary cells). Finally, the potential implication of C5L2, the newly discovered ASP receptor, and its expression profile in various tissues are discussed relative to ASP function.

Vascular adhesion and transendothelial migration of eosinophil leukocytes

Tissues respond to injury with inflammation in an effort to protect and repair the damaged site. During inflammation, leukocytes typically accumulate in response to certain chemicals produced within the tissue itself. The passage of leukocytes through the vascular lumen into tissues occurs in several phases, including rolling, activation, firm adhesion, transendothelial migration, and subendothelial migration. Although infiltration of eosinophil leukocytes is one of the most important aspects of allergic inflammatory reactions, eosinophils also participate in nonallergic inflammation. Eosinophil accumulation is regulated not only by endothelial adhesion molecules, but also by interactions between eosinophil adhesion molecules and extracellular matrix elements. This review summarizes the regulation of eosinophil leukocyte adhesion and migration. A better understanding of eosinophil recruitment responses may lead to the development of novel therapeutics for chronic allergic diseases.

Regulation by complement C3a and C5a anaphylatoxins of cytokine production in human umbilical vein endothelial cells

C3a and C5a anaphylatoxins are cytokine-like polypeptides generated during complement (C) system activation and released at the inflammatory site. They exert several biological activities through binding to the G-protein-coupled receptors C3aR and C5aR, respectively. Cloning and Northern blot experiments have indicated that both receptors are expressed by myeloid as well as nonmyeloid cells (e.g., endothelial and epithelial cells). To better understand the roles of C anaphylatoxins during inflammation, we investigated their effects on the expression of cytokine and chemokine genes by cultured human umbilical cord endothelial cells (HUVEC). HUVEC constitutively expressed both anaphylatoxin receptors, and addition of physiological concentrations of C3a or C5a (nM range) caused a strong up-regulation of IL-8, IL-1beta, and RANTES mRNA in a time- and dose-dependent manner. Conversely, a decrease in IL-6 mRNA was observed, but only with C5a stimulation. These variations in mRNA levels were inhibited by pretreatment with anti-C5aR and anti-C3aR antibodies as well as pertussis toxin, indicating that G-proteins are involved in anaphylatoxin-activated signal transduction pathways. Finally, we showed that C3a and C5a both strongly activate downstream MAP kinase signaling pathways (p44 and p42 Erk kinases).

A hypothesis accounting for the inconsistent benefit of glucocorticoid therapy in closed head trauma

Because of disagreement between clinical studies, the American College of Neurological Surgeons (ACNS) most recent recommendation (1996) is that glucocorticoids should not be used in the treatment of closed head trauma (CHT). The current paper reviews clinical studies of glucocorticoids and CHT in order to examine what factors might have accounted for the inconsistent results leading to the ACNS's recommendation. A careful analysIs of these studies reveals that, contrary to the ACNS's sweeping conclusion, the available data support the use of glucocorticoids for patients with CHT, but only in specific cases. Glucocorticoids may be beneficial in the treatment of CHT uncomplicated by intracranial hemorrhage; in situations where intracranial hemorrhage accompanies CHT, glucocorticoid treatment appears detrimental. The second part of this paper examines possible mechanisms accounting for the differential effectiveness of glucocorticoids in CHT patients with and without intracranial hemorrhage. These mechanisms include vasospasm, free radical damage, blood-borne factors, and glutamate neurotoxicity.

C3a and C5a enhance granulocyte adhesion to endothelial and epithelial cell monolayers: epithelial and endothelial priming is required for C3a-induced eosinophil adhesion

Effects of the anaphylatoxins C3a and C5a on eosinophil and neutrophil adhesion to HUVEC and to primary culture human bronchial epithelial cells (HBEC) were investigated. Activities on both leukocytes and on structural cells were examined. C3a upregulated beta2 integrin expression and caused shedding of L-selectin on eosinophils, but had no effect on neutrophil adhesion molecule expression. C5a upregulated beta2 integrins and caused shedding of L-selectin on both eosinophils and neutrophils. The potency of C5a was equivalent on both cell types; however, the magnitude of the changes in each of these adhesion molecules was significantly greater in neutrophils than eosinophils. Neither C3a nor C5a altered expression of ICAM-1, VCAM-1, E-selectin or P-selectin on either HUVEC or HBEC. C5a induced adhesion of both neutrophils and eosinophils to unstimulated HUVEC or HBEC, and adhesion was further enhanced when HUVEC and HBEC were "primed" with TNF-alpha and IFN-gamma, respectively. C3a failed to enhance adhesion of either eosinophils or neutrophils to unprimed HUVEC or HBEC, and enhanced only eosinophil adhesion to cytokine-primed HUVEC or HBEC. Similar to C3a, C3a(desArg) and a C3a-analog peptide E7 also enhanced eosinophil adhesion only to cytokine-primed HUVEC and HBEC. These results support the traditional view of anaphylatoxins as leukocyte-specific mediators. The specificity of C3a for eosinophils implicates this molecule as a potential participant in allergic inflammation. The pro-adhesive effects of C3a(desArg) suggest that this molecule, previously characterized as a spasmogenically inactive derivative of C3a, may also alter leukocyte dynamics and migration. Finally, activation of endothelium may represent an important control mechanism for C3a-mediated adhesion preventing unchecked eosinophil adhesion to uninflamed systemic vasculature.

Is complement a target for therapy in renal disease?

Complement deposition in the injured kidney is common, especially in glomerulonephritis. The precise role of the complement system in the mediation of tissue injury in the kidney has been defined in recent years, and this has assumed extra importance with the recent development of specific forms of therapy directed at the complement pathway. As well as the induction of cell lysis, complement has many subtle effects on cell biology, particularly on endothelial cells. Complement components are produced locally in the kidney. Detailed studies of certain rare forms of nephritis have provided evidence that complement activation can directly cause tissue injury. Appreciation of the importance of complement in hyperacute rejection of xenotransplants has given new impetus to the development of complement inhibitors. A narrative review is provided, with a brief overview of the complement pathway and its regulatory mechanisms, mechanisms of complement-induced tissue injury, local complement production, and the renal consequences of complement dysregulation. Currently available forms of therapy aimed at the complement system are reviewed, and possible future therapeutic strategies are suggested. The complement system plays a direct causal role in tissue injury in certain forms of renal disease. Specific forms of therapy are becoming available that can selectively interrupt complement activation or promote its regulation. Much of the drive for the development of these therapies comes from the field of xenotransplantation, but these forms of therapy should also be tested in various primary renal diseases.

Interleukin-1 alpha enhances the biosynthesis of complement C3 and factor B by human kidney proximal tubular epithelial cells in vitro

Local production in tubular cells of complement has been shown to occur in several kidney diseases by in situ hybridization, but the regulation at the local site during an inflammation is still unknown. In the present study, we demonstrate that human proximal tubular epithelial cells (PTEC) are able to produce complement components C3 and Factor B under non-stimulated conditions in vitro. The basal production of both was increased by 0.5 ng/ml interleukin-1 alpha (IL-1 alpha) for C3: from 95.5 +/- 4.0 ng/10(6) cells to 416.5 +/- 4.9 ng/10(6), and for Factor B: from 271 +/- 7.0 ng/10(6) cells to 457.5 +/- 7.0 ng/10(6) cells. In contrast cytokines such as TNF-alpha, IFN-gamma, IL-10 and IL-15 had no detectable effect. The upregulation by IL-1 alpha was dose- and time-dependent. The response to IL-1 alpha was shown to be mediated via the IL-1 receptor, as the addition of recombinant interleukin-1 receptor antagonist inhibited the IL-1 alpha induced complement production by more than 80%. IL-1 alpha enhanced mRNA expression of both C3 and Factor B as demonstrated by RT-PCR and dot-blot analysis. This indicated that IL-1 alpha upregulated the expression of the C3 and Factor B at the transcriptional level. We hypothesize that in vivo the production of C3 and Factor B at the local site during an inflammatory response in the kidney may be regulated by IL-1 alpha produced by inflammatory cells.

Interleukin-1 alpha, interleukin 6 and tumor necrosis factor alpha increase the synthesis and expression of the functional alternative and terminal complement pathways by human umbilical vein endothelial cells in vitro

The proinflammatory cytokines interleukin 1 alpha (IL-1 alpha), tumor necrosis factor alpha (TNF alpha) and interleukin 6 (IL-6) modulate the synthesis of complement factors B and C3 by endothelial cells (EC), and are considered to play an important role in the development of sepsis. By using agarose beads activating the alternative pathway of complement, we wanted to study the net effect of these cytokines on EC synthesis of the alternative and terminal pathways, measured by binding of anti-C3c and anti-TCC (terminal complement complex) antibodies to beads kept with the EC. Addition of IL-1 alpha and TNF alpha at concentrations of 50 and 100 U/ml resulted in a significant increase in binding of these antibodies to co-incubated beads, most pronounced for anti-C3c. IL-6 from 50-200 U/ml resulted in a stronger (two to fourfold) binding for both antibodies compared to experiments with IL-1 alpha and TNF. However, increased concentrations of IL-1 alpha (200 U/ml) and IL-6 (400 U/ml) resulted in a strong reduction in binding of anti-C3c and anti-TCC antibodies to the co-cultured beads. This study indicates that proinflammatory cytokines upregulate the synthesis by EC of the functional alternative and terminal pathways of complement.