The role of complement in inflammation and phagocytosis

Tolerance is dependent on complement C3 fragment iC3b binding to antigen-presenting cells

Systemic tolerance can be induced by the introduction of antigen into an immune-privileged site. Here we investigated the role of complement in the induction of tolerance after intraocular injection. We found that the development of antigen-specific tolerance is dependent on a complement activation product. The ligation of the complement C3 activation product iC3b to complement receptor type 3 (the iC3b receptor) on antigen-presenting cells resulted in the sequential production of transforming growth factor-beta2 and interleukin-10, which is essential for the induction of tolerance. These observations may extend to the development of both neonatal tolerance and other forms of acquired tolerance.

Importance of the terminal complement components for immune defence against Candida

Candida activates complement via all three pathways leading to opsonisation and anaphylaxis. The aim of the study was to investigate the influence of the terminal complement system on Candida infections. Thus, fungal cell growth, mitochondrial activity and phagocytosis by polymorphonuclear leukocytes (PMNLs) as well as specific virulence factors, such as release of secreted aspartic protease (Sap) and adherence to epithelial cells, were assessed under the influence of normal or C6/C7-depleted serum. Candida (C.) dubliniensis was used in all experiments as prototype because of its known increased expression of Saps and its strong geno- and phenotypical similarity to the most abundant Candida species C. albicans. Being exposed to sufficient quantities of complement, fungal growth decreased and phagocytosis increased but mitochondrial activities of the yeast increased as well. Concerning the virulence factors, both adhesion and especially Sap release were markedly reduced in the presence of high serum concentrations. Interestingly, at low serum concentrations some opposite effects (an augmented cell growth, a higher Sap release and a stronger adhesion) were observed. In particular, it was shown that the presence of terminal complement factors, and thus the generation of the membrane attack complex, clearly induced a higher fungal mitochondrial activation and has an effect on host defence against yeast cells by augmenting phagocytosis.

In vitro mechanisms of action of rituximab on primary non-Hodgkin lymphomas

To assess the sensitivity of primary non-Hodgkin lymphoma cells to rituximab-mediated cytotoxicity, we compared the potency of several rituximab-mediated killing mechanisms on fresh lymphoma cells. All lymphoma cells tested were equally sensitive to antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-mediated phagocytosis of tumor cells, and rituximab-induced apoptosis. However, they were differentially lysed by complement-dependent cytotoxicity (CDC). We found that taking into account both CD20 and complement regulatory protein expression on tumor cells could predict CDC sensitivity in vitro. Importantly, the sensitivity of lymphoma cells to CDC was consistent with the reported different clinical response rates of lymphomas: rituximab induced high CDC killing of follicular lymphoma cells, whereas mantle cell lymphoma and diffuse large cell lymphoma cells were moderately sensible to CDC, and small lymphocytic lymphoma cells were almost all resistant. We propose that CDC is a determinant mechanism of rituximab-induced killing in vivo. Poor sensitivity to CDC in vitro might predict a poor clinical response, whereas high sensitivity to CDC would only indicate a likelihood of response to rituximab treatment.

1. Overview of the immune response

Host defense against pathogenic microbes requires dramatically different responses, depending on the character of the pathogen and on the tissue under attack. Central to the immune system's ability to mobilize a response to an invading pathogen is its ability to distinguish self from nonself. The host has evolved both innate and adaptive mechanisms to respond to and eliminate pathogenic microbes. Both of these mechanisms include self-nonself discrimination. This overview describes key mechanisms used by the immune system to respond to invading microbes and identifies settings in which disturbed immune function exacerbates tissue injury.

C5 is required for CD49d expression on neutrophils and VCAM expression on vascular endothelial cells following mesenteric ischemia/reperfusion

Complement activation is critical in the development of local mucosal damage and inflammation as well as of remote organ injury after mesenteric ischemia/reperfusion. To further define the role of C5 activation in local and remote tissue injury, C5 deficient (C5(-/-)) and wild-type control (C5(+/+)) mice treated with an anti-C5 mAb were subjected to sham or ischemia followed by up to 4 h of reperfusion. The development of local (intestinal) and remote (lung) injury was associated with the expression of CD49d on the surface of circulating blood neutrophils and with VCAM on the endothelial cells of intestinal and lung vessels. Because CD49d heterodimerizes with integrin beta1 on the surface of neutrophils and can bind VCAM on the endothelium, we propose that complement activation causes organ damage by upregulating molecules that lead to inappropriate homing of neutrophils.

Milk complement and the opsonophagocytosis and killing of Staphylococcus aureus mastitis isolates by bovine neutrophils

Phagocytosis of bacteria by bovine polymorphonuclear neutrophils (PMN) has long been regarded as essential for host defense against mastitis infection. Complement-mediated opsonisation by complement component 3 (C3) binding is an important component of the innate immune system. We investigated the role of milk complement as an opsonin and its involvement in the phagocytosis and killing of Staphylococcus aureus isolates from cases of bovine mastitis by bovine blood PMN. We show that deposition of milk C3 component occurred on six different isolates of S. aureus and that the alternative pathway was the sole complement pathway operating in milk of uninflamed mammary gland. This deposition was shown to occur at the same location as the capsule, but not on capsular antigen. Milk complement enhanced the chemiluminescence response of PMN induced by S. aureus. Nevertheless, the association of S. aureus to cells and the overall killing of bacteria by bovine PMN were not affected by the presence of milk complement. Therefore, as all milk samples contained antibodies to capsular polysaccharide type 5 and to other surface antigens, it is likely that milk antibodies were responsible for these two phagocytic events. Results of this study suggest that the deposition of milk complement components on the surface of S. aureus does not contribute to the defence of the mammary gland against S. aureus.

A pox on thee! Manipulation of the host immune system by myxoma virus and implications for viral–host co-adaptation

The poxviruses have evolved a diverse array of proteins which serve to subvert innate and adaptive host responses that abort or at least limit viral infections. Myxoma virus and its rabbit host are considered to represent an ideal poxvirus-host system in which to study the effects of these immunomodulatory proteins. Studies of laboratory rabbits (Oryctolagus cuniculus) infected with gene knockout variants of myxoma virus have provided compelling evidence that several myxoma virus gene products contribute to the pathogenic condition known as myxomatosis. However, myxomatosis, which is characterized by skin lesions, systemic immunosuppression, and a high mortality rate, does not occur in the virus' natural South American host, Sylvilogus brasiliensis. Moreover, in Australia where myxoma virus was willfully introduced to control populations of O. cuniculus, myxomatosis-resistant rabbits emerged within a year of myxoma virus introduction into the field. In this review I discuss the characterized immunomodulatory proteins of myxoma virus, their biochemical properties, their pathogenic effects in laboratory rabbits, the role of the host immune system in the susceptibility or resistance to myxomatosis, and the evidence that immunomodulatory genes may have been attenuated during the co-adaptation of myxoma virus and O. cuniculus in Australia.

Flavoxobin, a serine protease from Trimeresurus flavoviridis (habu snake) venom, independently cleaves Arg726-Ser727 of human C3 and acts as a novel, heterologous C3 convertase

We have recently shown that crude Trimeresurus flavoviridis (habu snake) venom has a strong capability for activating the human alternative complement system. To identify the active component, the crude venom was fractionated and purified by serial chromatography using Sephadex G-100, CM-cellulose C-52, diethylaminoethyl-Toyopearl 650M, and Butyl-Toyopearl, and the active fractions were evaluated by the C3a-releasing and soluble membrane attack complex-forming activities. Two peak fractions with the highest activities were detected after gel filtration and ion exchange chromatography, and the first fraction was purified to homogeneity. The homogeneous protein was examined for its N-terminal amino acid sequence by Edman degradation. The determined sequence of 25 amino acids completely coincided with that of a previously reported serine protease with coagulant activity, flavoxobin, purified from the same snake venom. To elucidate the molecular mechanism of the complement activation, the reactive products of the mixture of the purified human C3 and flavoxobin were examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The digesting pattern revealed that flavoxobin cleaves the alpha chain of the C3 molecule into two fragments. The N-terminal amino acid sequences for the remnant fragments of C3 disclosed that flavoxobin severs the human C3 at the Arg726-Ser727 site to form C3b and C3a the way C3bBb, the human alternative C3 convertase, does. In conclusion, flavoxobin acts as a novel, heterologous C3 convertase that independently cleaves human C3 and kick-starts the complement cascade.

Vaccinia virus complement control protein enhances functional recovery after traumatic brain injury

Inflammation is a major contributor to the neuropathological consequences of traumatic brain injury (TBI). Previous studies have shown that proinflammatory complement activation fragments are present in the injured brain within the first 24 h after trauma. To investigate whether complement activation within the injured brain leads to the neuropathology and subsequent functional impairment associated with TBI, we examined what effect administration of a complement inhibitor, the vaccinia virus complement control protein (VCP), would have on spatial learning and memory in brain injured rats, as measured using the Morris Water Maze (MWM) procedure. Animals were subjected to a lateral fluid percussion brain injury of moderate severity and, 15 min later, received a 10-microL injection of either full-length VCP, a truncated version of VCP (VCPt), which lacks the complement inhibitory activity but retains the heparin binding activity of VCP, or saline directly into the cortex. Results of such intervention indicated that, at 2 weeks postinjury, both VCP and VCPt treatment attenuated impairments in spatial memory, but not neuropathological damage, as compared to the saline treated controls. These results were surprising and suggest that the neuroprotective effects following administration of VCP after acute brain injury are mediated by mechanisms other than complement inhibition. Potential mechanisms are discussed.

Neuroinvasion by pathogens: a key role of the complement system

Complement (C) is one of the most critical defence mechanisms of the innate immunity against cerebral infection by viruses, bacteria and fungi, with different molecular pathways contributing to the clearance of the invading pathogens. There is now compelling evidence that C proteins can be synthesized by brain cells in response to the infectious challenge and leading to cytotoxic and cytolytic activities against the harmful intruders. However, since there is also emerging evidence that uncontrolled C biosynthesis/activation can lead to brain inflammation with loss of neurons and oligodendrocytes, it is important to highlight that C may have adverse effects in infectious diseases of the CNS and induce profound tissue damage. The role of C in brain infection may even be more versatile. Many invading pathogens are not helpless against C attack and can use the membrane-bound C molecules to invade the host, either by binding directly or after decoration with C fragments. During budding viruses can acquire complement inhibitors from the host cell membrane and thus behave like 'Trojan horses' that are sheltered from the local innate immune response. Moreover, pathogens have evolved means of molecular mimicry with the expression of C inhibitor-like molecules to escape recognition and clearance by the C system. We herein provide a comprehensive and insightful review of the expression and the role of the C system in the brain. The three main focuses are: (i) C activation and lysis of pathogens in the brain; (ii) C-dependent neuroinvasion mechanisms (iii) uncontrolled C activation in inflamed CNS contributing to tissue damage.

Complement activation in the human brain after traumatic head injury

The complement cascade has been suggested to be involved in the development of secondary brain injuries following brain contusions, based on animal experiments. The aim of the present study was to examine the possible involvement of the complement cascade following traumatic head injury in the human brain. Sixteen patients were included in this study, 12-77 years of age, treated at the neurointensive care unit for traumatic brain contusions. All of these patients were operated with frontal or temporal lobe resection due to intractable intracranial hypertension. The resected tissue was analyzed with regard to components related to complement activation. The time interval between accident and operation was 2-82 h. Brain tissue from three patients operated with hippocampectomy due to epilepsy, including temporal lobe resection, were used as controls. We found increased immunoreactivity for complement components C1q, C3b, and C3d and the membrane attack complex (MAC), C5b-9, in the immediate vicinity of neurons in the penumbra area of the contusion. These findings constitute histological evidence for activation of the complement cascade in the penumbra of cortical contusions in the human brain. Using in situ hybridization, we also found C3-mRNA in the penumbra, suggesting a local synthesis of complement. Furthermore, upregulation of the endogenous complement regulator clusterin was found in some neurons in the same area. We suggest that unknown compounds in the debris from injured neurons or myelin breakdown products trigger complement activation, including formation of C5b-9. Activated complement components may stimulate accumulation of inflammatory cells and formation of brain edema, as well as having membrane destructive effects by the end product MAC, thereby being mediators in the development of secondary brain damage.

Anaphylatoxin C5a actions in rat liver: synergistic enhancement by C5a of lipopolysaccharide-dependent alpha(2)-macroglobulin gene expression in hepatocytes via IL-6 release from Kupffer cells

The effects of the anaphylatoxins C5a and C3a on the liver are only poorly characterized in contrast to their well known systemic actions. Recently, it has been demonstrated that the anaphylatoxin C5a enhanced glucose output from hepatocytes (HC) indirectly via prostanoid release from Kupffer cells (KC). In the present study, it is shown that recombinant rat C5a (rrC5a), together with LPS, activated the gene of the acute phase protein alpha(2)-macroglobulin (alpha(2)MG) in HC also indirectly via IL-6 release from KC. RrC5a alone increased neither IL-6 mRNA in nor IL-6 release from KC, whereas LPS alone did so. However, rrC5a synergistically enhanced the LPS-dependent increase in IL-6 mRNA and IL-6 release. Only rIL-6, but not TNF-alpha or IL-1beta, enhanced alpha(2)MG mRNA in HC. In line with the actions of rrC5a and LPS on KC, conditioned medium of KC stimulated only with rrC5a did not increase alpha(2)MG mRNA in HC. However, medium of KC stimulated with rrC5a plus LPS induced alpha(2)MG mRNA expression in HC more strongly than medium from cells stimulated only with LPS; thus, C5a acted synergistically with LPS. The stimulatory effects of KC-conditioned medium could partially be inhibited by a neutralizing anti-IL-6 Ab, indicating that KC-derived IL-6 was a major mediator in C5a- plus LPS-elicited alpha(2)MG gene expression. These results suggest that C5a, besides enhancing glucose output via prostanoids, is involved in the initiation of the acute phase response in HC via proinflammatory cytokines from KC. This provides evidence for another important function of C5a in the regulation of hepatocellular defense reactions.

The role of complement receptor 3 (CR3) in Neisseria gonorrhoeae infection of human cervical epithelia

Neisseria gonorrhoeae is an important sexually transmitted pathogen and a major cofactor in HIV-1 infection. This organism uses different mechanisms to infect male and female genital tract epithelia. Receptor-mediated endocytosis of N. gonorrhoeae is the principle mechanism of entry into male urethral epithelial cells. Infection in men leads to a pronounced inflammatory response. In contrast, N. gonorrhoeae infection in women induces ruffling of the cervical epithelia, allowing a macropinocytic mechanism of entry. Infection in women is frequently asymptomatic, suggesting suppression of the inflammatory response. N. gonorrhoeae-induced membrane ruffling and inflammation suppression are consistent with the ability of this bacterium to enter cervical epithelial cells, in vitro and in vivo, by interaction with complement receptor 3 (CR3), a receptor that does not trigger an inflammatory response. This receptor is present on cervical epithelial cells but not on male urogenital tract epithelia. N. gonorrhoeae engagement of CR3 initiates a unique mechanism of bacterial-induced membrane ruffling and internalization. These studies explain why the pathology of N. gonorrhoeae infection differs between males and females. Additionally, the observation that this receptor is present on cervical epithelia may provide insight into the pathogenesis of other sexually transmitted pathogens.

Detection of anaphylatoxin receptors on CD83+ dendritic cells derived from human skin

Dendritic cells (DC) are recruited to sites of inflammation for the initiation of immune responses. As the anaphylatoxins C5a and C3a are important mediators of inflammation, we investigated the expression of their receptors (C3aR and C5aR) on human DC. DC were isolated from human skin or generated from purified blood monocytes and were identified by their expression of CD1a or CD83. Freshly isolated or cultured dermal CD1a+ and CD83+ DC bound anti-C5aR and anti-C3aR monoclonal antibodies (mAbs), as detected by flow cytometry. C5a induced calcium fluxes in dermal CD1a+ and CD83+ DC, which could be inhibited by C17/5, an anti-C5a mAb. C3a did not induce calcium fluxes in these cells. Anaphylatoxin receptor expression was down-regulated on dermal DC by adding tumour necrosis factor-alpha (TNF-alpha) to the culture medium. On CD1a+ CD83- cells generated from isolated blood monocytes by culture with 6.25 ng/ml of granulocyte-macrophage colony-stimulating factor (GM-CSF) and 125 U/ml of interleukin-4 (IL-4), expression of both C5aR and C3aR was observed. In these cells, both C5a and C3a induced calcium fluxes. After addition of TNF-alpha to the culture medium, the majority of the CD1a+ cells expressed CD83+. These cells - expressing a phenotype of 'mature DC' - down-regulated the expression of the anaphylatoxin receptors and lost their reactivity to the respective ligands. Our results demonstrate the expression of the anaphylatoxin receptors C5aR and C3aR on human skin-derived DC and blood-derived cells expressing the DC-associated membrane molecule, CD1a. Furthermore, the expression of anaphylatoxin receptors on CD83+ dermal DC is indicative of an intermediate stage of maturation of these cells, which was not observed on in vitro-differentiated CD83+ cells.

Complement activation directly induced by Helicobacter pylori

BACKGROUND AND AIMS

Helicobacter pylori is a frequent gram-negative colonizer of the human stomach. Its interaction with complement may be involved in the pathogenesis of chronic gastritis, and was mechanistically studied in vitro.

METHODS

Four H. pylori strains, 2 cytotoxin-associated genes (cag)A+ and 2 cagA-, were isolated from infected patients. Bacteria or purified H. pylori lipopolysaccharides (LPSs) were incubated with nonimmune serum at 37 degrees C; the activation products C3b/iC3b/C3c (C3bc) and terminal complement complex (TCC) were then quantified by immunoassays. The serum sensitivity of 1 strain (L01, cagA+) was tested by counting the numbers of colony-forming units.

RESULTS

All strains and LPSs generated large amounts of C3bc and TCC. Blocking of the classic complement pathway by the calcium chelator ethylene glycol tetraacetic acid (EGTA) markedly reduced the complement products, suggesting that H. pylori and its LPSs directly engage the classic activation pathway. H. pylori was shown to be serum sensitive, but 30% or more nonimmune serum was necessary to induce marked killing. After 5 minutes, swelled bacteria coated with C3bc and TCC were shown.

CONCLUSIONS

H. pylori is complement sensitive and activates the classic pathway even in the absence of specific antibodies. Released cell wall constituents such as LPSs can activate complement and may explain why this bacterium induces gastric pathology without invading the mucosa.

Role and significance of the complement system in mucosal immunity: particular reference to the human breast milk complement

The complement system plays an important role in a host's defence mechanisms, such as in immune bacteriolysis, neutralization of viruses, immune adherence, immunoconglutination and in enhancement of phagocytosis. The possible role of this important biological system in biological fluids on the mucosal surfaces, including breast milk, has however been largely neglected. Its contribution to the 'common' mucosal immunity is still enigmatic and largely speculative. Assessment of the complement system in human breast milk, which has so far largely been limited to different assays of the individual component proteins, is reviewed. A brief review of the classical and the alternative pathways of complement activation is presented. The potential physiological roles of various complement components and their activation fragments in human milk in particular, and other mucosal surfaces in general, are also presented. It was concluded that the complement system might play a complementary role to other immunological and non-immunological protective mechanisms on the mucosal surfaces.

Blood histamine levels (BHL) in infants and children with respiratory and non-respiratory diseases

BACKGROUND

Blood histamine levels are decreased after severe allergic reactions and in various chronic diseases.

AIMS

To study blood histamine levels in infants and children with acute infectious and non-infectious, non-allergic, disease.

METHODS

Blood histamine levels were investigated by a fluorometric method in infants and children admitted to hospital with bronchiolitis, non-wheezing bronchitis, acute infections of the urinary tract, skin and ear-nose-throat, gastroenteritis, or hyperthermia of unknown aetiology. Results of blood histamine levels and white blood cell counts were compared with those obtained for children recovering from benign non-infectious, non-allergic illnesses.

RESULTS

As compared with control children, white blood cell numbers were significantly increased in children with acute infections of the urinary tract, skin and ear-nose-throat, and were significantly decreased in children with gastroenteritis. Blood histamine levels were significantly lower in children with gastroenteritis and hyperthermia than in children with other diseases and control children. It was not possible to correlate blood histamine levels and the number of blood basophils.

CONCLUSIONS

BHL are significantly decreased in infants and children with acute gastroenteritis and hyperthermia of unknown aetiology. The mechanisms responsible for the decrease in blood histamine levels in children with gastroenteritis and hyperthermia are discussed.

C3A binds to the seven transmembrane anaphylatoxin receptor expressed by epithelial cells and triggers the production of IL-8

The complement (C) plays an important role in many acute inflammatory processes. C3a is an inflammatory polypeptide named anaphylatoxin, generated during C activation and which acts through a specific receptor C3aR. In this study, we demonstrated that the epithelial cell line ECV 304 constitutively expressed C3aR (by flow cytometry and immunofluorescence) and that binding of purified C3a to epithelial cells resulted in a time- and dose-dependent upregulation of interleukin-8 (IL-8). Pre-treatment of ECV 304 with pertussis toxin inhibited IL-8 response induced by C3a, indicating that the action of C3a was mediated by a G protein coupled pathway.

Complement activation by recombinant adenoviruses

Recombinant adenoviruses are currently the most important vector system in gene therapy. Adenoviruses frequently cause upper respiratory tract infections in humans and anti-adenoviral antibodies are found in 35-70% of the population. Therefore in the majority of potential patients receiving adenoviral gene therapy, the contact of virus particles and blood will lead to the formation of antigen-antibody complexes. These complexes have the ability to induce inflammatory reactions via an activation of the complement system. We have determined the level of C3a (the most reactive complement component) generated in isolated citrate plasma of healthy individuals after challenge with recombinant and wild-type adenoviruses in amounts corresponding to virus blood levels to be expected in patients during adenoviral gene therapy. All plasma samples containing anti-adenoviral antibodies showed a substantial, dose-dependent generation of C3a. A virus plasma level of about 7.5 x 10(9) particles/ml (which was calculated to be the highest blood level reached during clinical trials in the past) induced an average release of about 3000 ng/ml C3a (baseline levels <140 ng/ml). Analyzing the nature of anti-adenoviral antibodies showed, that not only antibodies with neutralizing properties (anti-Ad5), but also non-neutralizing anti-adenoviral antibodies are capable of complement activation. This study suggests that complement activation can be ignored in local low-dose applications of recombinant adenoviruses, but warrants attention after systemic application of large viral quantities. In clinical protocols aiming at systemic virus application, measures for monitoring and controlling the complement system should be included on a regular basis.

Immune function

The innate and the adaptive immune systems have evolved to provide a rapid and specific means for protecting hosts against the many microbes experienced over a lifetime. These two immune responses interact cooperatively to enhance the host defense. Defects in either of these two pathways can have devastating consequences, as evidenced [figure: see text] by primary immune deficiencies, many of which are discussed in this issue of the Pediatric Clinics of North America. The immune system has a central role in the pathogenesis of many disorders that involve an inflammatory response, including allergic and autoimmune diseases. New and more effective therapies for these many disorders will develop as the understanding of the immune system and its many secreted mediators continues to increase.

Reduction of the uptake by a macrophagic cell line of nanoparticles bearing heparin or dextran covalently bound to poly(methyl methacrylate)

Amphiphilic and fluorescent covalently labelled core-shell nanoparticles based on poly(methyl methacrylate) (PMMA), were prepared by random copolymerisation of N-Vinyl carbazole (NVC) with MMA, initiated on polysaccharidic radicals, yielding diblock copolymers of either dextran-P(MMA-NVC) (Nanodex* particles), or heparin-P(MMA-NVC) (Nanohep* particles). Nanoparticles made from random copolymers of P(MMA-NVC) (PMMA*) were used as controls. The interactions between particles and a J774A1 murine macrophage-like cell line were quantified by direct measurement of the cell-associated fluorescence. The association with the cells occurred within 30 min. Nanodex* and Nanohep* showed considerably less association than the control PMMA* particles. Some of the particle uptake could be attributed to phagocytosis, but more than 50% of the cell-associated fluorescence persisted at low temperature or in the presence of cytochalasin B. The results suggest that both the adsorption and the internalisation processes can be inhibited by the presence of the polysaccharide chains. In conclusion, these results confirm that nanoparticles prepared with heparin or dextran chains on their surface, probably in a brush-like configuration, show "stealth" properties in vitro as had previously been observed in vivo. If this biomimetic approach can also be applied to biodegradable polymers, these systems would provide at least an alternative to PEG-modified particles as long-circulating drug carriers systems or imaging agents.

Complement activation on immunoglobulin G-coated hydrophobic surfaces enhances the release of oxygen radicals from neutrophils through an actin-dependent mechanism

Neutrophil granulocytes are among the first cells to encounter a plasma protein-coated implant and may through frustrated phagocytosis release toxic oxidative species. We used two model surfaces, hydrophobic and hydrophilic glass, to investigate the effects of plasma immunoglobulin G (IgG)-complement interactions for neutrophil adhesion and respiratory burst. The respiratory burst was measured with luminol-amplified chemiluminescence and cell adhesion was determined by labeling neutrophils with 2', 7'-bis-(carboxy-ethyl)-5(6)-carboxyfluorescein. We demonstrate that the IgG-triggered neutrophil adhesion and oxygen radical production is augmented in the presence of normal human serum, in particular on hydrophobic surfaces, indicating that complement factors enhance the neutrophil activation. We propose that the complement factors C3, C5a, and C1q are especially important for this amplification, but factor B is probably not. Disturbance of the actin filament dynamics with cytochalasin B or jasplakinolide blocked the neutrophil radical generation on all surfaces. However, these drugs did not affect the number of adherent neutrophils. We suggest that there is a synergistic interaction between adsorbed IgG, and the complement system, which amplifies the neutrophil acute inflammatory responses through a dynamic actin cytoskeleton on synthetic surfaces.

Complement components of the innate immune system in health and disease in the CNS

The innate immune system and notably the complement (C) system play important roles in host defense to recognise and kill deleterious invaders or toxic entities, but activation at inappropriate sites or to an excessive degree can cause severe tissue damage. C has been implicated as a factor in the exacerbation and propagation of tissue injury in numerous diseases including neurodegenerative disorders. In this article, we review the evidence indicating that brain cells can synthesise a full lytic C system and also express specific C inhibitors (to protect from C activation and C lysis) and C receptors (involved in cell activation, chemotaxis and phagocytosis). We also summarise the mechanisms involved in the antibody-independent activation of the classical pathway of C in Alzheimer's disease, Huntington's disease and Pick's disease. Although the primary role of C activation on a target cell is to induce cell lysis (particularly of neurons), we present evidence indicating that C (C3a, C5a, sublytic level of C5b-9) may also be involved in pro- as well as anti-inflammatory activities. Moreover, we discuss evidence suggesting that local C activation may contribute to tissue remodelling activities during repair in the CNS.

Early local generation of C5a initiates the elicitation of contact sensitivity by leading to early T cell recruitment

We have shown previously that an early complement C5-dependent cascade is required to recruit T cells to elicit 24-h contact sensitivity (CS) responses. In this paper, we have characterized molecular events of this early required cascade by biochemically analyzing extracts of mouse ears undergoing elicitation of CS. Chemotactic activity was found after local Ag challenge, in CS ear extracts early (by 1 h), in CS ear extracts late (through 24 h), in previously immunized mice, but not in ears of vehicle-immunized or non-immune-challenged mice. The early chemotactic activity at 2 h was likely caused by C5a, because it was neutralized in vitro by anti-C5a Ab, was inactive on C5aR-deficient (C5aR-/-) macrophages, and was absent in C5-deficient mice. The activity was present in T cell-deficient mice, but elaboration was Ag-specific. This T cell-independent, Ag-specific elaboration of C5a early in CS ear responses likely led to T cell recruitment, because subsequent local IFN-gamma mRNA and protein expression, as markers of T cell arrival and activation, began by 4 h after Ag challenge. In contrast to early C5a chemotactic activity, late chemotactic activity 24 h after Ag challenge was unaffected by anti-C5, was active on C5aR-/- macrophages, was T cell-dependent, and by ELISA appeared largely due to chemokines (macrophage-inflammatory protein-1alpha and -1beta, IFN-gamma-inducible protein-10, and monocyte chemoattractant protein-1). Importantly, early generation of C5a was required for T cell recruitment because C5aR-/- mice had absent 24-h CS. Taken together, these findings indicate an important linkage of C5a as a component of early activated innate immunity that is required for later elicitation of acquired T cell immunity, probably by facilitating the initial recruitment of T cells into the Ag-challenged local site in CS responses.

Analysis of plasma protein adsorption onto polystyrene particles by two-dimensional electrophoresis: comparison of sample application and isoelectric focusing techniques

Two-dimensional electrophoresis (2-DE) was previously established for analysis of plasma protein adsorption patterns on particulate carriers for intravenous drug targeting. This study addresses a possible effect of polymeric particles on protein separation in the first dimension, e.g., hindrance of protein entry into the gel or interaction of particles with the gel matrix. Polystyrene beads of mean diameter 100, 200 and 1000 nm were used as model carriers. Two different separation techniques were performed in the first dimension of 2-DE to study possible interactions of the beads with the different gel matrices, i.e., carrier ampholytes (CA) and immobilized pH gradients (IPGs). Comparison of gels obtained from samples including the particles from samples separated from the polystyrene beads showed no noteworthy differences. Therefore, a negative effect of the particles can be excluded, and particle separation from the sample is not necessary. Another goal of this study was the transfer of analytical protocols for isoelectric focusing from CA to IPGs with regard to enhanced reproducibility, faster sample processing, and easier handling. Transfer from CA to IPGs was carried out successfully and showed improved resolution of basic proteins. In contrast to that, lower amounts of a few high molecular mass proteins were detected, especially when sample application cups were employed. A qualitative change in the obtained protein pattern was not observed. Increased entry of high molecular weight proteins was achieved by in-sample rehydration instead of using sample cups.

The role of the immune system in conjunctival wound healing after glaucoma surgery

The immune system has a fundamental role in the development and regulation of ocular healing, which plays an important role in the pathogenesis of most blinding diseases. This review discusses the mechanisms of normal wound healing, describing the animal and fetal wound healing models used to provide further insight into normal wound repair. In particular, conjunctival wound repair after glaucoma filtration surgery will be used to illustrate the contributions that the different components of the immune system make to the healing process. The potential role of macrophages, the possible regulatory effect of lymphocytes, and the important role of growth factors and cytokines in the wound healing reaction are discussed. The significance of the immune system in the pathogenesis of aggressive conjunctival scarring is addressed, particularly assessing the predisposing factors, including drugs, age, and ethnicity. The rationale behind the pharmacological agents currently used to modulate the wound healing response and the effects these drugs have on the function of the immune system are described. Finally, potential new therapeutic approaches to regulating the wound healing response are reported.

Expression of a complete and functional complement system by human neuronal cells in vitro

We demonstrate in vitro expression of complement components, i.e. C3, factor H (FH), factor B (FB), C4, C1-inhibitor (C1-inh), C1q, C5, C6, C7 and C9, by four human neuroblastoma cell lines IMR32, SKNSH, SH-SY5Y and KELLY. Activating proteins C4, C9 and C1q, and regulatory proteins FH and C1-inh were produced constitutively by the four cell lines. C3, C6 and FB were mainly produced by SKNSH and SH-SY5Y. Western blot experiments showed that secreted proteins were structurally similar to their serum counterparts. An additional polypeptide of 43 kDa with FH immunoreactivity was detected, which could correspond to the N-terminal truncated form found in plasma. Regulation of complement expression by inflammatory cytokines, lipopolysaccharide and dexamethasone was tested in vitro. These factors had no significant effects on activating synthesis of components C3, FB and C4, but expression of regulating components C1-inh and FH was strongly increased particularly by IFN-gamma and tumor necrosis factor-alpha. The rate of synthesis of complement components was dependent on the differentiation of neuroblastoma cells. This effect of differentiation was also observed on normal rat neurons. Rat cerebellar granule cells constitutively expressed mRNA for C4 and C1q, but expression of C3 mRNA was induced by differentiation. This study shows that neurons could be another local source of complement in the brain, besides astrocytes and microglia. Human neuroblastoma cell lines can constitute an interesting model to analyze complement biosynthesis by human neurons. Local complement expression by neurons in vivo may be implicated in some physio-pathological processes.

Local neutrophil influx following lateral fluid-percussion brain injury in rats is associated with accumulation of complement activation fragments of the third component (C3) of the complement system

Traumatic brain injury can lead to locally destructive secondary events mediated by several inflammatory components. Following lateral fluid-percussion (FP) brain injury in rats, we examined cortical and hippocampal sections for neutrophil infiltration and accumulation of complement component C3. Neutrophil influx into the brain after injury was detected by an improved myeloperoxidase (MPO) microassay and manual cell counting, while C3 accumulation was detected using immunocytochemistry. MPO levels were elevated in the injured cortical tissue, whereas C3 immunoreactivity was increased in both injured cortical and ipsilateral hippocampal sections. These results show that the FP model of head injury leads to an intense local inflammatory reaction and subsequent tissue destruction.

Induction of functional anaphylatoxin C5a receptors on hepatocytes by in vivo treatment of rats with IL-6

In normal rat liver, anaphylatoxin C5a receptors (C5aR) are only expressed by nonparenchymal cells, mainly Kupffer cells and hepatic stellate cells, but not by parenchymal cells, i.e., hepatocytes (HC). Nevertheless, C5a stimulates glucose output by HC. This HC-specific defense reaction is induced indirectly via prostanoids secreted by the C5aR-expressing Kupffer cells and hepatic stellate cells. It is shown here that under inflammatory conditions simulated by in vivo treatment of rats with IL-6 C5aR mRNA and protein were induced in HC in a time-dependent manner. Maximal mRNA and protein expression were observed at 4-8 h and 8-10 h, respectively, after IL-6 injection. The newly expressed receptors were functional, because recombinant rat C5a significantly activated glycogen phosphorylase in HC isolated from IL-6-treated but not in HC from control rats. In perfused livers of IL-6-treated animals in contrast to control animals, recombinant rat C5a-induced glucose output was not impaired by inhibition of prostanoid synthesis and function with the cyclooxygenase inhibitor indomethacin and the thromboxane receptor antagonist daltroban. These results indicate that HC-specific defense reactions might be differently regulated under normal and inflammatory conditions as shown here for the indirect prostanoid-dependent or direct C5a-induced activation of hepatocellular glycogen phyosphorylase and glucose output in control or IL-6-treated rats, respectively.

Generation of complement fragment C5a in milk is variable among cows

The appearance of chemotactic fragments of complement at sites of infection is an important component of innate immunity. The contribution of C5a, the most biologically active complement fragment, to the recruitment of phagocytes in milk is not well defined, in particular the amount of C5a that is released in normal milk before inflammation. The generation of C5a in normal milk upon activation of complement by invading bacteria depends on the amount of available C5 and on the activity of the C3/C5-convertase of the alternative pathway. Concentrations of C5 were measured in one fore and one rear uninfected quarter of 19 Holstein cows. Values were consistent within cows, but widely dispersed among cows (0.19 to 1.94% blood concentration). C5 concentrations in milk were loosely related to concentrations in blood. By comparison, the range of milk concentrations of C3 (1.4 to 4.4%, mean 2.46 +/- 0.63% of blood concentration) was narrower. Two groups of six cows with high milk concentrations of C5 (cows H5: mean = 1.31%) and six cows with low milk concentrations of C5 (cow L5: mean = 0.21%) were constituted for further analysis of complement activation. There was a positive correlation between concentrations in milk of BSA and C5, but not between concentrations of BSA and C3. The activities of the C3- and C5-convertases were assessed through the deposition on complement-activating bacteria (Streptococcus agalactiae) of C3 and C5 fragments, respectively. The deposition of C3 was 1.7-fold higher, and the deposition of C5 was 2.75-fold higher in milk from H5 cows than in milk of L5 cows. Higher concentrations of C5 and better functioning of C5-convertase were mirrored by a much higher concentration of C5a in milk from H5 cows (12.30 ng/ml) than in milk of L5 cows (0.76 ng/ml) after activation of complement with zymosan. These results indicate that cows differed widely in their capacity to generate C5a in milk before inflammation, and that milk C5 concentrations were a primary limiting factor for C5a generation. Cows with the lowest milk concentrations of C5 are likely unable to use the complement system for the initial recruitment of leukocytes.

Inhibitory effect of bilirubin on complement-mediated hemolysis

We investigated the in vitro action of the bile pigments, unconjugated bilirubin (UB) and bilirubin monoglucuronide (BMG) on complement (C) cascade reaction. Both UB and BMG inhibited hemolysis in the classical pathway (CP) in a dose-dependent manner at low micromolar concentrations, UB showing a stronger effect than BMG. The analysis of the action of UB on the hemolytic activity of the C1, C4, C2 and C-EDTA components of the C cascade revealed that the C1 step was the most inhibited. An enzyme immunoassay was developed to evaluate the effect of UB on the binding of C1q, one of the subcomponents of C1, to human IgM and IgG. The study demonstrated that the unconjugated pigment interferes both the C1q-IgM and -IgG interactions, thus tentatively explaining the inhibitory action of UB on hemolytic activity of C1. We conclude that the anti-complement effect of UB is mainly exerted on the C1 component, the recognition unit of CP. The potential clinical implication of the reported effects in hyperbilirubinemia is discussed.

Complement activation by model drug carriers for intravenous application: determination by two-dimensional electrophoresis

The interactions of intravenously injected drug carriers with blood proteins are considered as an important factor for the fate of the particles after their administration. Protein adsorption on latex particles applied as model for intravenous drug carriers was analysed using two-dimensional electrophoresis (2-DE). The particles were incubated in citrated plasma, serum and heat-inactivated serum, respectively. Incubation in the various media resulted in clear differences in the protein adsorption patterns. Two characteristic protein spots were determined to be enriched on the 2-DE gels only after incubation of the particles in serum. Employing N-terminal microsequencing these protein spots were identified to be fragments of the complement protein C3. Enrichment of these particular spots was most likely a result of complement activation by the particles. Mechanism of C3 binding to the particle surface and subsequent inactivation by cleavage are discussed in order to explain the results. It could be demonstrated that 2-DE analysis provides the possibility to distinguish between adsorption and covalent attachment of C3 to particulate surfaces. The findings indicate that complement activation was caused by covalent binding of the C3 component C3b to the particles' surface. The influence of the incubation medium on the in vitro protein adsorption of particulate drug carriers has to be considered when a correlation between the protein adsorption pattern and the in vivo behaviour of the particles is approached.

Properdin deficiency in a large Swiss family: identification of a stop codon in the properdin gene, and association of meningococcal disease with lack of the IgG2 allotype marker G2m(n)

Properdin deficiency was demonstrated in three generations of a large Swiss family. The concentration of circulating properdin in affected males was < 0.1 mg/l, indicating properdin deficiency type I. Two of the nine properdin-deficient males in the family had survived meningitis caused by Neisseria meningitidis serogroup B without sequel. Two point mutations were identified when the properdin gene in one of the properdin-deficient individuals was investigated by direct solid-phase sequencing of overlapping polymerase chain reaction (PCR) products. The critical mutation was found at base 2061 in exon 4, where the change of cytosine to thymine had generated the stop codon TGA. The other mutation was positioned at base 827 in intron 3. The stop codon in exon 4 was also demonstrated by standard dideoxy sequencing in three additional family members. The question was asked if genetic factors such as partial C4 deficiency and IgG allotypes could have influenced susceptibility to meningococcal disease in the family. No relationship was found between C4 phenotypes and infection. Interestingly, the two properdin-deficient males with meningitis differed from the other properdin-deficient persons in that they lacked the G2m(n) allotype, a marker known to be associated with poor antibody responses to T-independent antigens. This implies that the consequences of properdin deficiency might partly be determined by independent factors influencing the immune response.

The role of complement activation in tumour necrosis factor-induced lethal hepatitis

Injection of tumour necrosis factor (TNF) in animals causes severe liver cell toxicity, especially when D-(+)-galactosamine (GalN) is co-administered. After challenge with TNF/GalN, serum complement activity (CH50 and APCH50) decreased dramatically, suggesting strong activation of both the classical and the alternative pathways. TNF or GalN alone had no such effect. A cleavage product of complement protein C3 [C3(b)] was deposited on the surface of hepatocytes of TNF/GalN-treated mice. Intravenous administration of cobra venom factor (CVF), which depletes complement, inhibited the development of hepatitis. However, CVF pretreatment also protected C3-deficient mice. Pretreatment of mice with a C1q-depleting antibody did not prevent TNF/GalN lethality, although the anti-C1q antibody had depleted plasma C1q. Factor B-deficient and C3-deficient mice, generated by gene targeting, proved to be as sensitive to TNF/GalN as control mice. Furthermore, induction of lethal shock by platelet-activating factor, an important mediator in TNF-induced hepatic failure, was not reduced in C3-deficient mice. These data indicate that complement, although activated, plays no major role in the generation of acute lethal hepatic failure in this model and that CVF-induced protection is independent of complement depletion.

Increase by anaphylatoxin C5a of glucose output in perfused rat liver via prostanoids derived from nonparenchymal cells: direct action of prostaglandins and indirect action of thromboxane A(2) on hepatocytes

In the perfused rat liver the anaphylatoxin C5a enhanced glucose output, reduced flow, and elevated prostanoid overflow. Because hepatocytes (HCs) do not express C5a receptors, the metabolic C5a actions must be indirect, mediated by e.g. prostanoids from Kupffer cells (KCs) and hepatic stellate cells (HSCs), which possess C5a receptors. Surprisingly, the metabolic C5a effects were not only impaired by the prostanoid synthesis inhibitor, indomethacin, but also by the thromboxane A(2) (TXA(2)) receptor antagonist, daltroban, even though HCs do not express TXA(2) receptors. TXA(2) did not induce prostaglandin (PG) or an unknown factor release from KCs or sinusoidal endothelial cells (SECs), which express TXA(2) receptors, because (1) daltroban did neither influence the C5a-induced release of prostanoids from cultured KCs nor the C5a-dependent activation of glycogen phosphorylase in KC/HC cocultures and because (2) the TXA(2) analog, U46619, failed to stimulate prostanoid release from cultured KCs or SECs or to activate glycogen phosphorylase in KC/HC or SEC/HC cocultures. In the perfused liver, Ca(2+)-deprivation inhibited not only flow reduction but also glucose output elicited by C5a to similar extents as daltroban. Similarly, in the absence of extracellular Ca(2+), flow reduction and glucose output induced by U46619 were almost completely prevented, whereas glucose output induced by the directly acting PGF(2alpha) was only slightly lowered. Thus, in the perfused rat liver PGs released after C5a-stimulation from KCs and HSCs directly activated glycogen phosphorylase in HCs, and TXA(2) enhanced glucose output indirectly mainly by causing hypoxia as a result of flow reduction.

Carboxymethyl benzylamide sulfonate dextrans (CMDBS), a family of biospecific polymers endowed with numerous biological properties: a review

The functionalized dextrans termed carboxymethyl benzylamide sulfonate dextran (CMDBS) represent a family encompassing a wide range of polymers. These soluble macromolecular compounds, which are substituted with specific chemical functional groups, are designed to interact with living systems. By analogy with glycosaminoglycan heparin, a natural highly charged anionic polysaccharide that exerts a variety of biological effects, we postulated that CMDBS compounds also possess binding sites capable of specific interactions with biological constituents, depending on the overall composition of the polymer. The synthesis and heparin-like properties of these CMDBS have been extensively investigated. Thus, it appears that dextran derivatives can mimic the action of heparin in regard to its interactions with antithrombin and serine proteases involved in blood coagulation. Other derivatives interact with various components of the immune system or with adhesive proteins such as fibronectin in modulating the proliferation of Staphylococcus aureus. Because they are able to stimulate wound healing in various in vivo models, these polysaccharides may also constitute a family of tissue repair agents because of their protecting and potentiating effects with heparin binding growth factors. Moreover, dextran derivatives in contact with cells such as endothelial cells, smooth muscle cells, or tumoral cells can affect both cell proliferation and metabolism. It appears that these bioactive polymers are also efficient tools to investigate the precise mechanism of action of individual biological activities by contrasting their mode of action to that of heparin. In addition to their numerous biological properties and biospecificity, functionalized dextrans are relatively simple to manufacture and exempt of donor contaminant, which make them attractive in a variety of clinical applications.

Serum complement levels in children in communities with different levels of air pollution in Japan

To investigate the effects of air pollution on human health, we determined serum concentrations of complement components C3c and C4 in 1037 children who lived in 4 communities with different levels of air pollution in Japan. Serum levels of C3c and C4 were higher in children who lived in Osaka, which had a high level of air pollution, than in children who lived in areas of low air pollution. In boys, both C3c and C4 levels were increased significantly as concentrations of air pollution increased in the communities. In girls, however, the relationship was not significant. Serum levels of C3c and C4 did not differ with respect to asthma or wheezing. These findings suggest that serum C3c and C4 levels in children reflect the effects of exposure to air pollutants in urban districts. Boys appeared to be more susceptible to the effects of air pollution than girls.

Expression of cytokines by human astrocytomas following stimulation by C3a and C5a anaphylatoxins: specific increase in interleukin-6 mRNA expression

C3a and C5a anaphylatoxins are two proinflammatory peptides generated during complement activation that act through distinct Gi protein-coupled receptors named C3aR and C5aR, respectively. We have demonstrated previously that human astrocytes expressed C3aR and C5aR constitutively and were able to produce a functional complement. In this study, we examined the effect of an anaphylatoxin stimulation on cytokine expression by human astrocyte cell lines. Interleukin (IL)-1beta, IL-6, tumor necrosis factor-alpha, and transforming growth factor-beta mRNA expression was studied by quantitative RT-PCR. Whereas IL-1beta, tumor necrosis factor-alpha, and transforming growth factor-beta mRNA levels remained unchanged, stimulation of astrocytoma cells (T98G, CB193, U118MG) by C3a, C5a, and peptidic C3aR and C5aR agonists induced an increase in the IL-6 mRNA level. The amount of IL-6 was markedly increased at 3 and 6 h and returned to the basal level at 9 h of stimulation. This response was specific, because pretreatment of cells with pertussis toxin or with polyclonal anti-C3aR or anti-C5aR antibodies completely blocked the IL-6 mRNA increase. The IL-6 response was also investigated at the protein level, but IL-6 protein was detected neither in cell lysates nor in supernatants of stimulated cells. The anaphylatoxin-mediated transcriptional activation of IL-6 gene suggests that C3a and C5a could play a role in priming glial cells during the inflammatory process in the brain.

Synergistic enhancement of chemokine generation and lung injury by C5a or the membrane attack complex of complement

Complement plays an important role in many acute inflammatory responses. In the current studies it was demonstrated that, in the presence of either C5a or sublytic forms of the complement-derived membrane attack complex (MAC), rat alveolar macrophages costimulated with IgG immune complexes demonstrated synergistic production of C-X-C (macrophage inflammatory protein-2 and cytokine-induced neutrophil chemoattractant) and C-C (macrophage inflammatory protein-1alpha and monocyte chemoattractant-1) chemokines. In the absence of the costimulus, C5a or MAC did not induce chemokine generation. In in vivo studies, C5a and MAC alone caused limited or no intrapulmonary generation of chemokines, but in the presence of a costimulus (IgG immune complexes) C5a and MAC caused synergistic intrapulmonary generation of C-X-C and C-C chemokines but not of tumor necrosis factor alpha. Under these conditions increased neutrophil accumulation occurred, as did lung injury. These observations suggest that C5a and MAC function synergistically with a costimulus to enhance chemokine generation and the intensity of the lung inflammatory response.

Anticomplement activity of triterpenes from Crataeva nurvala stem bark in adjuvant arthritis in rats

Adjuvant arthritis is widely used as an experimental model for rheumatoid arthritis and inflammation. It is useful in the evaluation of anti-inflammatory drugs. Lupeol is a naturally occuring triterpene isolated from Crataeva nurvala stem bark, and its ester lupeol linoleate was synthesized. The effects of lupeol and lupeol linoleate on the development of complement in adjuvant arthritis in rats were studied and compared with those of indomethacin. The effect of lupeol linoleate in reducing the foot-pad thickness and complement activity in arthritic rats was even greater than that of unesterified lupeol and indomethacin. Because complement is highly involved in inflammation, the results suggest that the anti-inflammatory activity of triterpenes may be due to their anticomplementary activity.

Contribution of Renal Secreted Complement C3 to the Circulating Pool in Humans

Complement C3 produced within the kidney may be an important mediator of local inflammatory and immunological injury. The overall level of renal C3 production and consequently its contribution to the total circulating C3 level are, however, unknown. This was investigated by using the conversion of C3 from recipient to donor allotype following renal transplantation. The C3 F and S allotypes of 80 consecutive renal donor-recipient pairs (148 individuals) were determined by amplification refractory mutation system analysis. The extent of allotype conversion in C3 F/S mismatched recipients was quantified at different stages after transplantation, using an enzyme-linked immunosorbent assay specific for the HAV 4-1 polymorphism of C3 that is strongly associated with C3F. Twenty-one of the eighty recipients were potentially informative, i.e., were C3 SS recipients of C3 FF or FS donor kidneys. In the early postoperative period, donor-derived C3 (HAV 4-1-positive) was undetectable, increasing to 9.6% of the total circulating C3 at times of acute allograft rejection. When graft dysfunction occurred from causes other than rejection, donor C3 remained undetectable. After stable graft function was attained (3–13 mo after transplantation), donor C3 made up 4.5% of the total circulating C3 pool. Our findings demonstrate that human transplant kidney in the resting state is a significant source of extrahepatic C3. Its heightened local synthesis during rejection episodes suggests a possible pathogenic role for C3 in this immunological process.

The selective cytotoxicity of cobra venom factor immunoconjugate on cultured human nasopharyngeal carcinoma cell line

The selective cytotoxicity of a CVF immunoconjugate on human nasopharyngeal carcinoma cell line was reported. Cobra venom factor (CVF), a C3b-like glycoprotein, was linked to BAC5, a murine monoclonal antibody directed against a human nasopharyngeal carcinoma-associated membrane antigen, by a disulfide bond. The high affinity to cultured human nasopharyngeal cells (CNE2) and the complement activating potency retained in CVF immunoconjugate. Although the equimolar concentration of BAC5 or CVF alone was harmless to CNE2 cells, the CVF immunoconjugate in the presence of fresh human serum exhibited selective cytotoxicity on CNE2 cells in a concentration- (IC50 3.07 x 10(-7) mol/L) and time-dependent manner. No cytotoxicity occurred on either CNE1 (another human nasopharyngeal carcinoma cell line) or MGC-803 (human gastric carcinoma cell line) cells. Furthermore, direct lytic factor (DLF, cardiotoxin) separated from cobra venom, augmented CVF immunoconjugate-induced cytotoxicity significantly. These results indicate that the CVF immunoconjugate has complement-mediated selective cytotoxicity on CNE2 cells, which can be potentiated by DLF.

A brief review of the immune system

This article provides a brief review of the immune system and describes the features of innate and adaptive immunity and their similarities and differences. The mechanism of antigen presentation and major histocompatibility complex restriction is discussed as well as the structure and function of T cells and B cells. Three tables present a concise description of cytokines, interleukins, and chemokines.

Intravital microscopic investigation of xenogeneic microcirculation and impact of complement depletion by cobra venom factor

Discordant xenografts are hyperacutely rejected within minutes. Disturbances in the microcirculation are considered to be the central mechanisms of hyperacute xenogeneic rejection (HXR). In this study intravital fluorescence microscopy was applied to investigate the dynamics of microcirculatory alterations in a setting in which HXR was inhibited by complement (C) depletion. Blood flow was measured as rat livers were perfused with isogeneic rat or xenogeneic human blood to assess the pattern of either physiological isogeneic hemoperfusion or in the course of HXR. Next, the complement system of the perfusate was inactivated by cobra venom factor (CVF) in order to inhibit HXR. Liver sinusoids of the isogeneic group were homogeneously perfused (sinusoidal perfusion rate 93.6+/-0.3%), whereas in the xenogeneic group the sinusoidal perfusion rate dropped to 67.1+/-3%. The perfusion in the periportal zone of an acinus was significantly lower ( 59.0+/-3.3%) than in the pericentral zone (76.2+/-3.1%). Treatment with CVF improved the sinusoidal perfusion to a value of 85.6+/-2.3%, physiological perfusion, however could not be reached. In contrast to the isogeneic group, massive white blood cell (WBC) and platelet accumulation was found in the xenogeneic group, especially in the terminal portal vessels and in the periportal zone of liver acini. WBC and platelet counts show that the adherence of these cells appears rapidly in the first 5 min after reperfusion as firm adherence. CVF was not able to inhibit WBC and platelet accumulation, indicating that WBC endothelial interactions do not require an intact complement system. Bile flow, a parameter of liver function, decreased only slightly during isogeneic perfusion. The addition of CVF to the rat blood reduced the bile flow to one half of the untreated isogeneic flow, indicating a hepatotoxic side-effect of CVF. In xenogeneic perfusion the bile flow dropped to 62.6% and with the addition of CVF to 37.5% in the first 15 min after reperfusion. The bile flow of the CVF treated groups recovered during the perfusion but could not reach isogeneic values.

Stimulation by anaphylatoxin C5a of glycogen phosphorylase in rat hepatocytes via prostanoid release from hepatic stellate cells but not sinusoidal endothelial cells

In the perfused rat liver, the anaphylatoxin C5a has been shown to enhance glucose output. Since hepatocytes lack C5a receptor mRNA, the metabolic effect of C5a must be elicited indirectly via C5a receptor expressing non-parenchymal liver cells. Kupffer cells were found to be able to mediate the C5a action via release of prostanoids. However, elimination of the Kupffer cells by pretreatment of the animals with gadolinium chloride reduced the metabolic effect of C5a to only about 40%. Therefore, it was investigated whether not only Kupffer cells but in addition also hepatic stellate cells or sinusoidal endothelial cells released prostanoids in response to C5a. In isolated hepatic stellate cells but not in sinusoidal endothelial cells, recombinant rat C5a induced a time- and dose-dependent release of thromboxane B2 and prostaglandins D2, E2 and F2alpha. The rate of prostanoid release was maximal within the first two minutes and then declined again. C5a-induced prostanoid release from hepatic stellate cells was smaller than that from Kupffer cells and it differed in the prostanoid ratios (PGE2/PGD2/PGF2alpha/TXB2 = 1:1:0.1:0.6 and 1:4:1:3, respectively). RrC5a activated hepatocellular glycogen phosphorylase via prostanoid release in cocultures of hepatocytes with hepatic stellate cells but not with sinusoidal endothelial cells. Thus, the part of the rrC5a-induced glucose output in the perfused rat liver, which was not abrogated by elimination of the Kupffer cells with gadolinium chloride, most likely was mediated by prostanoids released from hepatic stellate cells.

Diminished adherence and/or ingestion of virulent Mycobacterium tuberculosis by monocyte-derived macrophages from patients with tuberculosis

The interaction between the macrophage and Mycobacterium tuberculosis is mediated by a variety of macrophage membrane-associated proteins. Complement receptors have been implicated in the adherence of M. tuberculosis to macrophages. In the present work, the adherence and/or ingestion of M. tuberculosis H37Rv to human monocyte-derived macrophages (MDM) from patients with tuberculosis (TB) and healthy controls was measured by microscopical examination, [3H]uracil incorporation, and CFU. The adherence and/or ingestion was enhanced by fresh serum and inhibited by heat inactivation, EDTA treatment, and anti-CR1 and anti-CR3 antibodies. Comparison of MDM from TB patients and healthy controls showed that the former exhibited a significantly decreased capacity to adhere and/or ingest M. tuberculosis, as determined by the number of CFU and 3H incorporation. The expression of CR1 (CD35) and CR3 (CD11b/CD18) on MDM from TB patients and healthy controls, as determined by flow cytometry, did not show significant differences. These results suggest that the lower ingestion of M. tuberculosis by MDM from TB patients is not due to defects in complement receptors, and therefore, there might be other molecules involved in the adherence and/or ingestion process that render MDM from TB patients ingest less mycobacteria than those from healthy controls.

Human thymocyte dipeptidyl peptidase IV (CD26) activity is altered with stage of ontogeny

The nonintegrin receptor CD26, also known as dipeptidyl peptidase IV (DPP IV) is a transmembrane 110- to 120-kDa serine aminopeptidase glycoprotein with multiple functions, including cellular trafficking through extracellular matrix, and costimulatory potential during T cell activation, and is an influence upon T cell differentiation during their maturation in the thymus. In order to further define the expression and functional activity of this membrane exopeptidase in human thymus, we utilized a nondisruptive, cytofluorogenic assay which allowed simultaneous measurement of intracellular DPP IV activity using a fluorochrome-conjugated peptide substrate with surface staining of plasma membrane-associated T lymphocyte lineage antigens CD4 and CD8, as well as CD26. Human thymi were examined using the three-color assay, and significant differences in time-dependent DPP IV activity were found among the thymocyte subsets defined by their CD4/CD8 phenotype. In this regard, CD4(-)/CD8(-) thymocytes displayed the lowest DPP IV activity and had higher activity than the smaller-sized CD26(+) cells. Thymocytes containing greater percentages of apoptotic cells expressed lower DPP IV activity than viable cells. Thus, DPP IV appears to be upregulated as thymocytes mature and is reduced among thymocyte populations enriched for cells undergoing programmed cell death, suggesting that CD26-associated enzymatic activity is ontogenically controlled during T cell maturation and may be involved in thymic deletion of emerging clones.