Essential role for the C5a receptor in regulating the effector phase of synovial infiltration and joint destruction in experimental arthritis.
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A characteristic feature of rheumatoid arthritis is the abundance of inflammatory cells in the diseased joint. Two major components of this infiltrate are neutrophils in the synovial fluid and macrophages in the synovial tissue. These cells produce cytokines including tumor necrosis factor alpha and other proinflammatory mediators that likely drive the disease through its effector phases. To investigate what mechanisms underlie the recruitment of these cells into the synovial fluid and tissue, we performed expression analyses of chemoattractant receptors in a related family that includes the anaphylatoxin receptors and the formyl-MetLeuPhe receptor. We then examined the effect of targeted disruption of two abundantly expressed chemoattractant receptors, the receptors for C3a and C5a, on arthritogenesis in a mouse model of disease. We report that genetic ablation of C5a receptor expression completely protects mice from arthritis. (+info)
Tumor and CD4 T-cell interactions: tumor escape as result of reciprocal inactivation.
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This paper addresses the capacity of naive, effector, and memory CD4 T cells to control growth of a major histocompatibility complex (MHC) class II-positive B-cell lymphoma in vivo. To assess the role of T cells on their own without contributions by B cells, antibodies, or natural killer (NK) cells, we generated pure effector or memory CD4 T cells in Rag-/-gc-/- mice deficient in endogenous lymphocytes and NK cells. Lymphoma cells expressing a model antigen were injected into mice with T cells of cognate specificity that were either naive or in effector or resting memory state. Naive T cells were unable to prevent tumor growth, probably due to delay of efficient cross-presentation by dendritic cells. However, both effector and memory T cells, dependent on the amount of antigen available, controlled the tumor for a considerable period of time without the need for dendritic cell stimulation. Nevertheless, the tumor eventually grew uncontrolled in all cases. This was not because of a defect in T-cell homing to the tumor site or loss of MHC class II or costimulatory molecules by the tumor, but reflected mutual paralysis of T-cell responsiveness and antigen processing by tumor cells. (+info)
Expression of complement 3 and complement 5 in newt limb and lens regeneration.
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Some urodele amphibians possess the capacity to regenerate their body parts, including the limbs and the lens of the eye. The molecular pathway(s) involved in urodele regeneration are largely unknown. We have previously suggested that complement may participate in limb regeneration in axolotls. To further define its role in the regenerative process, we have examined the pattern of distribution and spatiotemporal expression of two key components, C3 and C5, during limb and lens regeneration in the newt Notophthalmus viridescens. First, we have cloned newt cDNAs encoding C3 and C5 and have generated Abs specifically recognizing these molecules. Using these newt-specific probes, we have found by in situ hybridization and immunohistochemical analysis that these molecules are expressed during both limb and lens regeneration, but not in the normal limb and lens. The C3 and C5 proteins were expressed in a complementary fashion during limb regeneration, with C3 being expressed mainly in the blastema and C5 exclusively in the wound epithelium. Similarly, during the process of lens regeneration, C3 was detected in the iris and cornea, while C5 was present in the regenerating lens vesicle as well as the cornea. The distinct expression profile of complement proteins in regenerative tissues of the urodele lens and limb supports a nonimmunologic function of complement in tissue regeneration and constitutes the first systematic effort to dissect its involvement in regenerative processes of lower vertebrate species. (+info)
Comparison of subcutaneous and intraperitoneal staphylococcal infections in normal and complement-deficient mice.
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From a comparison of the effects produced by injecting different strains of Staphylococcus aureus either subcutaneously or intraperitoneally into normal, complement-deficient, or complement-depleted mice, it was possible to assess the pathogenic significance of various staphylococcal virulence factors and the defensive role of complement components in the two sites of infection. In skin lesions the inflammation-suppressing factor found in the cell walls of strain PS80 played a major role. In contrast, in intraperitoneal infection the antiphagocytic capsule of the Smith diffuse and M strains was more important. All strains used produced alpha-hemolysin, which is the ultimate lethal agent in intraperitoneal infection but is only one factor in the production of dermonecrosis. The severity of the skin lesions was inversely related to the amount of early fluid exudate rather than to the rate of bacterial growth, whereas in the peritoneum increased bacterial growth was associated with increased mortality. Both C3 and C5 were needed in the production of fluid exudate in response to staphylococcal skin infection. C3 appeared to be more important in the increased exudate formed in immune mice. In the peritoneum the opsonic and chemotactic actions for complement were important as shown by the results in cobra venom-treated normal mice and in C5-deficient B10D2 old-line mice. (+info)
Role for complement in mediating intestinal nitric oxide synthase-2 and superoxide dismutase expression.
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Inducible nitric oxide synthase (iNOS) and superoxide dismutase (SOD) play an important role in the pathology of ischemia-reperfusion. This study sought to determine if the proinflammatory effects of complement modulate iNOS and SOD in the rat after gastrointestinal ischemia and reperfusion (GI/R). An inhibitory or noninhibitory anti-complement component 5 (C5) monoclonal antibody (18A or 16C, respectively) was administered before GI/R. RT-PCR revealed a significant increase in intestinal iNOS mRNA compared with sham after GI/R that was attenuated significantly by 18A. Immunohistochemistry demonstrated increased iNOS protein expression within the intestinal crypts after GI/R. Cu/Zn SOD (mRNA and protein) was unaffected by GI/R, whereas Cu/Zn SOD activity was reduced significantly. Mn SOD protein expression was decreased significantly by GI/R. Anti-C5 preserved Cu/Zn SOD activity and Mn SOD protein expression. Staining for nitrotyrosine showed that anti-C5 treatment reduced protein nitration in the reperfused intestine. Immunohistochemistry demonstrated prominent phosphorylated (p) inhibitory factor-kappaB (IkappaB)-alpha staining of intestinal tissue after GI/R, whereas anti-C5 reduced p-IkappaB-alpha expression. These data indicate that complement may mediate tissue damage during GI/R by increasing intestinal iNOS and decreasing the activity and protein levels of Cu/Zn SOD and Mn SOD, respectively. (+info)
Pre-neutralization of C5a-mediated effects by the monoclonal antibody 137-26 reacting with the C5a moiety of native C5 without preventing C5 cleavage.
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Complement C5a is aetiologically linked to inflammatory tissue damage in conditions like septicaemia, immune complex diseases and ischaemia-reperfusion injury. We here describe a monoclonal antibody (mAb), 137-26, that binds to the C5a moiety of human C5 and neutralizes the effects of C5a without interfering with C5 cleavage and the subsequent formation of lytic C5b-9 complex. Mouse anti-human C5 mAbs were generated and the reactivity with C5 and C5a was detected by ELISA and surface plasmon resonance. The inhibition of C5a binding to C5a receptor was studied using a radioligand binding assay. The effects of the antibody on C5a functions were examined using isolated neutrophils and a novel human whole blood model of inflammation. Haemolytic assays were used to study the effect on complement-mediated lysis. mAb 137-26 reacted with both solid- and solution-phase C5 and C5a in a dose-dependent manner with high affinity. The antibody competed C5a binding to C5a receptor and inhibited C5a-mediated chemotaxis of neutrophils. Furthermore, the antibody effectively abrogated complement-dependent E. coli-induced CD11b up-regulation and oxidative burst in neutrophils of human whole blood. mAb 137-26 was more potent than a C5a receptor antagonist and a previously described anti-C5a antibody. mAb 137-26 did not inhibit complement-mediated lysis, nor did it activate complement itself. Together, mAb 137-26 binds both the C5a moiety of native C5 and free C5a, thereby effectively neutralizing the biological effects of C5a. The antibody may have therapeutic potential in inflammatory diseases where C5a inhibition combined with an operative lytic pathway of C5b-9 is particularly desired. (+info)
Formation of high affinity C5 convertase of the classical pathway of complement.
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C3/C5 convertase is a serine protease that cleaves C3 and C5. In the present study we examined the C5 cleaving properties of classical pathway C3/C5 convertase either bound to the surface of sheep erythrocytes or in its free soluble form. Kinetic parameters revealed that the soluble form of the enzyme (C4b,C2a) cleaved C5 at a catalytic rate similar to that of the surface-bound form (EAC1,C4b,C2a). However, both forms of the enzyme exhibited a poor affinity for the substrate, C5, as indicated by a high Km (6-9 microM). Increasing the density of C4b on the cell surface from 8,000 to 172,000 C4b/cell did not influence the Km. Very high affinity C5 convertases were generated only when the low affinity C3/C5 convertases (EAC1,C4b,C2a) were allowed to deposit C3b by cleaving native C3. These C3b-containing C3/C5 convertases exhibited Km (0.0051 microM) well below the normal concentration of C5 in blood (0.37 microM). The data suggest that C3/C5 convertase assembled with either monomeric C4b or C4b-C4b complexes are inefficient in capturing C5 but cleave C3 opsonizing the cell surface with C3b for phagocytosis. Deposition of C3b converts the enzymes to high affinity C5 convertases, which cleave C5 in blood at catalytic rates approaching Vmax, thereby switching from C3 to C5 cleavage. Comparison of the kinetic parameters with those of the alternative pathway convertase indicates that the 6-9-fold greater catalytic rate of the classical pathway C5 convertase may compensate for the fewer numbers of C5 convertase sites generated upon activation of this pathway. (+info)
Pexelizumab, an anti-C5 complement antibody, as adjunctive therapy to primary percutaneous coronary intervention in acute myocardial infarction: the COMplement inhibition in Myocardial infarction treated with Angioplasty (COMMA) trial.
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BACKGROUND: Complement, activated during myocardial ischemia and reperfusion, causes myocardial damage through multiple processes. The COMplement inhibition in Myocardial infarction treated with Angioplasty (COMMA) trial was performed to determine the effect of pexelizumab, a C5 complement inhibitor, on infarct size in patients with ST-segment-elevation myocardial infarction (MI) undergoing primary percutaneous coronary intervention. METHODS AND RESULTS: In COMMA, 960 patients with MI (20% isolated inferior MI) were randomized to placebo, pexelizumab 2.0-mg/kg bolus, or pexelizumab 2.0-mg/kg bolus and 0.05-mg/kg per h infusion for 20 hours. Infarct size by creatine kinase-MB area under the curve, the primary outcome, did not differ significantly between groups (placebo median, 4393; bolus pexelizumab, 4526; bolus plus infusion pexelizumab, 4713 [ng/mL] x h; P=0.89 for bolus versus placebo; P=0.76 for bolus plus infusion versus placebo), nor did the composite of 90-day death, new or worsening heart failure, shock, or stroke (placebo, 11.1%; bolus, 10.7%; bolus plus infusion, 8.5%). The ninety-day mortality rate was significantly lower with pexelizumab bolus plus infusion (1.8% versus 5.9% with placebo; nominal P=0.014); the bolus-only group had an intermediate mortality rate (4.2%). CONCLUSIONS: In patients with ST-elevation MI undergoing percutaneous coronary intervention, pexelizumab had no measurable effect on infarct size. However, the significant reduction in mortality suggests that pexelizumab may benefit patients through alternative novel mechanisms and provides impetus for additional investigation. (+info)