Structure and function of the complement receptors, CR1 (CD35) and CR2 (CD21).
Explore the source record for details and available documents.
Amino Acid Sequence↗
SEARCH · Search PubMed
Results for “Receptors, Complement”
Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Nonopsonic binding of Mycobacterium tuberculosis to complement receptor type 3 is mediated by capsular polysaccharides and is strain dependent.
The choice of host cell receptor and the mechanism of binding (opsonic versus nonopsonic) may influence the intracellular fate of Mycobacterium tuberculosis. We have identified two substrains of M. tuberculosis H37Rv, designated H37Rv-CC and -HH, that differed in their modes of binding to complement receptor type 3 (CR3) expressed in transfected Chinese hamster ovary (CHO-Mac-1) cells: H37Rv-CC bound nonopsonically, whereas H37Rv-HH bound only after opsonization in fresh serum. H37Rv-CC also bound nonopsonically to untransfected CHO cells, whereas H37Rv-HH binding was enhanced by serum and was mediated by the 1D1 antigen, a bacterial adhesin previously identified as a polar phosphatidylinositol mannoside. H37Rv-CC and -HH had identical IS6110 DNA fingerprint patterns. Of five M. tuberculosis clinical isolates examined, four displayed the same binding phenotype as H37Rv-CC, as did the Erdman strain, whereas one isolate, as well as Mycobacterium smegmatis, behaved like H37Rv-HH. Nonopsonic binding of H37Rv-CC to CHO cell-expressed CR3 was apparently to the beta-glucan lectin site, as it was cation independent and inhibited by laminarin (seaweed beta-glucan) and N-acetylglucosamine; laminarin also inhibited the binding of H37Rv-CC to monocyte-derived macrophages. Further, binding of H37Rv-CC to CHO-Mac-1 cells was inhibited by prior agitation of bacteria with glass beads (which strips outer capsular polysaccharides) and by preincubation with amyloglucosidase, as well as by the presence of capsular D-glucan and D-mannan from M. tuberculosis Erdman, but not by Erdman D-arabino-D-mannan, yeast mannan, or capsular components from H37Rv-HH. Analysis of capsular carbohydrates revealed that H37Rv-CC expressed 5-fold more glucose and 2.5-fold more arabinose and mannose than H37Rv-HH. Flow cytometric detection of surface epitopes indicated that H37Rv-CC displayed twofold less surface-exposed phosphatidylinositol mannoside and bound complement C3 less efficiently than H37Rv-HH; these differences were eliminated after treatment of H37Rv-CC with glass beads. Thus, outer capsular polysaccharides mediate the binding of H37Rv-CC to CR3, likely to the beta-glucan site. Moreover, there are strain-dependent differences in the thickness or composition of capsular polysaccharides that determine the mode of binding of M. tuberculosis to mammalian cells.
Animals↗
Coupling of C3b to erythrocytes by disulfide bond formation: preparation of EC3b for hemolytic and complement receptor assays.
We describe a new method of preparing C3-coated erythrocytes by coupling C3 to thiol-activated erythrocytes. The procedure involves three steps. Firstly, sheep erythrocytes were treated with N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) to introduce 3-(2-pyridyldithio) propionyl residues into membrane proteins. Secondly, C3 was cleaved with trypsin or CoVF, Bb enzyme to obtain C3b exposing the SH group (C3b-SH). Finally, the C3b-SH was coupled to the thiol-activated erythrocytes (TA-E) through thiol/disulfide exchange to form the TA-EC3b conjugate. E coated with C3d was prepared by treating TA-EC3b with KSCN inactivated serum and plasmin. Studying the rosette formation between TA-EC3b or TA-EC3d and cells expressing C3b (CR1) and C3d (CR2) receptors and the inhibition thereof with anti-CR1 and anti-CR2 antibodies as well as with C3-sheep E membrane protein complexes, we found that TA-EC3b and TA-EC3d bound exclusively to CR1 and CR2, respectively. In addition, TA-EC3b like EAC1423b bound factors B and H as tested by hemolytic and direct binding assays. The advantage of TA-EC3 for complement receptor and hemolytic assays are the simplicity of the preparation method and the general applicability of the TA-EC3.
Animals↗
[Effect of complement modulation with the soluble complement receptor sCR1 on survival and function of kidney xenotransplant. An experimental study with a new guinea pig to rate transplant model].
In this study a modified experimental kidney xenograft model was developed, which reproduced, in a reliable way, the course of hyperacute rejection. In this model guinea-pig kidneys were transplanted to rats using end-to-side anastomoses with recipient aorta and vena cava, respectively, and ureter drainage for diuresis monitoring. The aim of this study was to investigate the protective effects of complement modulation by soluble complement receptor 1 (sCR1) on the xenografts. Twenty-four xenotransplantations were performed and recipients randomized for treatment either by 3 ml saline or 50 mg/kg sCR1 as a 3-ml bolus. It was found that sCR1 was highly efficient in delaying hyperacute rejection from 10.5 +/- 2.1 min in the control group to at least 2 h in the therapy group and in prolongation of graft function. The complement activity was significantly reduced in the sCR1-treated rats, even at the time of rejection, as a result of complement modulation in this group of xenograft recipients. Xenografts from saline-treated animals showed necroses, interstitial haemorrhages and platelet aggregates occluding the vessels as soon as 10 min after the reperfusion started. No such changes could be seen even after 120 min in the xenografted kidneys of sCR1-treated rats. Also C3 deposits in the glomeruli and interstitium were markedly reduced.
Animals↗
Small molecule antagonists of complement receptor type 3 block adhesion and adhesion-dependent oxidative burst in human polymorphonuclear leukocytes.
The leukocyte integrin complement receptor type 3 (CR3, Mac-1, CD11b/CD18) is the predominant beta(2) integrin receptor of polymorphonuclear leukocytes (PMNs). This cell surface receptor plays a central role in innate immunity against pathogens as well as being a major cellular effector of inflammation and tissue injury. Two small molecules, compounds 1 and 2, have been identified, that interact with CR3 and prevent CR3 from binding to its natural ligand, C3bi. Compounds 1 and 2 have IC(50) values of 0.14 and 0.33 microM, respectively, for the inhibition of binding of monomeric C3bi-alkaline phosphatase to immobilized CR3. Both compounds also inhibit binding of CR3 to biotinylated sheep red blood cells opsonized with C3bi, with IC(50) values in the micromolar range. Inhibition of ligand binding by the compounds is not easily reversed and requires light, suggesting the formation of a covalent adduct through photoactivation. Compounds 1 and 2 also inhibit adhesion of human PMNs to fibrinogen in response to tumor necrosis factor (TNF) or PMA, with IC(50) values of 2.5 to >10 microM. They block the adhesion-dependent production of H(2)O(2) stimulated by TNF or phorbol 12-myristate 13-acetate (PMA) with IC(50) values of 0.2 to 0.8 microM and 1 to 3 microM, respectively. Limited structure-activity relationship studies based on compound 2 indicate the importance of the two benzothiazole rings, an ethyl side chain, and the length of the carbon chain linking the rings. Further modification of these groups may help in making compounds appropriate for in vivo studies.
Benzothiazoles↗
Complement receptor enhancement and chemotaxis of human neutrophils and eosinophils by leukotrienes and other lipoxygenase products.
The lipoxygenase products of arachidonic acid, 5-HPETE, 5-HETE, LTB4, LTC4 and LTD4, were examined for their capacity to enhance the expression of complement (C3b) receptors and to evoke chemotaxis of human neutrophils and eosinophils. With the exception of LTD4 all gave enhancement of C3b receptors. LTB4 and LTC4 enhanced over the concentration range 10(-7) to 10(-11) moles/l, and 5-HETE and 5-HPETE from 5 X 10(-6) to 5 X 10(-10) moles/l. The rank order of activity, as assessed by the magnitude of enhancement, was LTB4 (concentration for maximal effect = 10(-7) moles/l) greater than 5-HETE (5 X 10(-7)) greater than 5-HPETE (5 X 10(-6)) greater than LTC4 (10(-9)). High dose inhibition was observed with LTC4 and 5-HETE. Chemotaxis experiments performed in parallel over the same concentration ranges indicated that neither neutrophils nor eosinophils migrated towards LTC4 or LTD4. However, LTB4 evoked chemotaxis with a linear dose response from 10(-9) to 10(-7) moles/l and 5-HPETE and 5-HETE from 5 X 10(-8) to 5 X 10(-6) moles/l. At 10(-7) moles/l LTB4 was approximately 6 and 8 X more potent in chemotaxis than 5-HPETE and 5-HETE respectively. In general, complement receptor enhancement and chemotaxis of eosinophils were similar to that observed with neutrophils and did not vary with the patient source.
Arachidonate Lipoxygenases↗
Mapping of the region of complement receptor (CR) 1 required for Plasmodium falciparum rosetting and demonstration of the importance of CR1 in rosetting in field isolates.
The malaria parasite Plasmodium falciparum induces a number of novel adhesion properties in the erythrocytes that it infects. One of these properties, the ability of infected erythrocytes to bind uninfected erythrocytes to form rosettes, is associated with severe malaria and may play a direct role in the pathogenesis of disease. Previous work has shown that erythrocytes deficient in complement receptor (CR) 1 (CR1, CD35; C3b/C4b receptor) have greatly reduced rosetting capacity, indicating an essential role for CR1 in rosette formation. Using deletion mutants and mAbs, we have localized the region of CR1 required for the formation of P. falciparum rosettes to the area of long homologous repeat regions B and C that also acts as the binding site for the activated complement component C3b. This result raises the possibility that C3b could be an intermediary in rosetting, bridging between the infected erythrocyte and CR1. We were able to exclude this hypothesis, however, as parasites grown in C3-deficient human serum formed rosettes normally. We have also shown in this report that rosettes can be reversed by mAb J3B11 that recognizes the C3b binding site of CR1. This rosette-reversing activity was demonstrated in a range of laboratory-adapted parasite strains and field isolates from Kenya and Malawi. Thus, we have mapped the region of CR1 required for rosetting and demonstrated that the CR1-dependent rosetting mechanism occurs commonly in P. falciparum isolates, and could therefore be a potential target for future therapeutic interventions to treat severe malaria.
Animals↗
Opsonized streptococcal cell walls cross-link human leukocytes and erythrocytes by complement receptors.
Serum-opsonized group A streptococcal cell walls, consisting of peptidoglycan-polysaccharide polymers (PG-APS), induced monolayers of human neutrophils, monocytes, and eosinophils to aggregate. When erythrocytes were present in the incubation medium, they also were associated with the leukocyte aggregates. By immunofluorescence staining, PG-APS was localized at the site of cell-to-cell contact. By scanning electron microscopy the cells appeared to adhere to one another by surface contact; filopodia often acted as connectors, particularly in leukocyte-erythrocyte interaction. Cellular binding of PG-APS and aggregation were dependent upon C3 fixation. No aggregation was observed when heat-inactivated serum was used as an opsonin. In contrast to peptidoglycan, an activator of the alternative complement pathway, the group-specific polysaccharide moiety of PG-APS induced no cellular aggregation. Rosette formation was observed in suspensions when neutrophils were incubated with erythrocytes coated with C3b-opsonized PG-APS. Cell monolayers bound serum-opsonized PG-APS, but aggregation was observed only when serum was present in the incubation medium. Similar results were obtained with C5-deficient serum. No aggregation was observed with heat-inactivated serum or bovine serum albumin. A heat-labile serum component(s) appears to be required to elicit leukocyte aggregation. It is suggested that C3 fixed to PG-APS acts as a bridge to link cells together in clusters as a result of common recognition of C3 by leukocyte and erythrocyte complement receptors.
Animals↗
Organization of the genes encoding complement receptors type 1 and 2, decay-accelerating factor, and C4-binding protein in the RCA locus on human chromosome 1.
The organization and physical linkage of four members of a major complement locus, the RCA locus, have been determined using the technique of pulsed field gradient gel electrophoresis in conjunction with Southern blotting. The genes encoding CR1, CR2, DAF, and C4bp were aligned in that order within a region of 750 kb. In addition, the 5' to 3' orientation of the CR1 gene (5' proximal to CR2) was determined using 5'- and 3'-specific DNA probes. The proximity of these genes may be related to structural and functional homologies of the protein products. Overall, a restriction map including 1,500 kb of DNA was prepared, and this map will be important for positioning of additional coding sequences within this region on the long arm of chromosome 1.
CD55 Antigens↗
Functional properties of membrane-associated complement receptor CR1.
It was previously shown that membrane receptors for C3b (CR1) purified from human erythrocytes were powerful inhibitors of the complement cascade and that they encompass the regulatory functions of the serum proteins beta 1H (H) and C4-binding protein (C4bp). In the present report we study the functional properties of membrane-associated CR1. When tonsil lymphocytes, which contain between 30 and 60% of CR1-bearing B cells, are incubated with the red cell complement intermediate EAC14oxy2lim or EAC14oxy23lim, they inhibit both C42 and C423 in a dose-dependent manner. These effects are mediated by membrane-associated molecules. Indeed, mild trypsinization of the lymphocytes abolishes their activity, and formaldehyde-fixed cells are as effective as viable cells. The inhibitory effects are in part mediated by CR1. The lymphocyte activities are reversed about 60% if monoclonal antibodies to CR1 or fluid phase C3b are present in the incubation medium. Moreover, upon addition of C3b-inactivator (l), lymphocytes release C3c fragments from EAC14oxy23b. The release of C3c was also abolished by antibodies to CR1. These results support the idea that CR1, as well as other molecules from the lymphocyte membrane, can function as inhibitor(s) of complement activation in their vicinity.
Animals↗
Mononuclear phagocyte system complement receptor dysfunction in rheumatoid arthritis.
To explore the relationship between complement-dependent and Fc receptor-mediated clearance mechanisms, clearance studies were performed in nine patients with definite rheumatoid arthritis and 49 normal controls. Kinetic analysis allowed evaluation of the four rate constants governing both complement- and Fc-mediated clearance processes. This analysis revealed that patients with rheumatoid arthritis had significantly reduced values for the constants regulating complement-dependent clearance (p less than 0.001). Complement-mediated clearance dysfunction was associated with normal serum complement levels and normal Fc receptor function. These data indicate that complement-mediated clearance defects are neither the simple result of a hypocomplementemic complement opsonization deficiency nor merely the reflection of profound Fc dysfunction. Defects in the two clearance processes can occur independently. These data demonstrate a specific complement receptor defect in the fixed tissue macrophages of patients with rheumatoid arthritis.
Adult↗
Expression of major histocompatibility complex antigens and CR3 complement receptors in activated microglia following an injection of ricin into the sciatic nerve in rats.
The ventral horn motor neurons in the lower lumbar cord underwent rapid degeneration following an injection of Ricinus communis agglutinin-60 (RCA) into the sciatic nerve. The cell death which was most drastic between the fifth and seventh post-injection day elicited a significant increase in the number of microglia. The activated microglia were scattered throughout the neuropil but the dramatic feature was their close association with the somata of the degenerating neurons. Often several microglial cells were seen surrounding the soma of a degenerating neuron. Immunocytochemical study showed that both the interstitial as well as the perineuronal activated microglia were labelled with the monoclonal antibodies OX-18 and OX-42 for the detection of MHCI encoded antigen and type three complement receptors, respectively. Intense immunoreactivity was observed especially in the perineuronal microglia with OX-18. Electron microscopic study confirmed the identification of the activated microglia. Although the activated microglia closely apposed the neuronal soma, there was no sign of a direct endocytosis. The cytoplasm of the activated microglia, however, contained massive lipofuscin bodies in longer survival animals. Electron microscopic immunocytochemical study showed that the immunoreactivity of the activated microglia was localized along their plasma membrane facing the neuronal soma. Since the microglia cells on the contralateral side of the ventral horn were not marked by the antibodies used, it was postulated that the vigorous expression of MHCI antigen and CR3 receptors on the activated microglia was induced by the neuronal degeneration resulting from the application of the toxin ricin.
Animals↗
Complement and complement receptors.
Explore the source record for details and available documents.
Animals↗
Attempts to evaluate the role of the third complement component (C3) and complement receptor lymphocytes (CRL"+") in the induction of the humoral immune response.
It has been shown that spleen and bone marrow complement receptor lymphocytes (CRL"+") are responsible for T-dependent anti-SRBC response. This has been shown by comparison of the T-dependent anti-SRBC and T-independent anti-SIII response in irradiated mice repopulated with normal or CRL depleted spleen cell populations. Unseparated spleen cells obtained from animals immunized 48 h before with SRBC, and CRL depleted cell population from animals receiving T-independent antigens (levan, SIII) were shown to be predominantly stimulated when uptake of isotope labelled leucine or tymidine was studied. It was also shown that triggering of enhanced antibody production by T cell derived signal generated during GvH reaction is C3 dependent.
Animals↗
Release of arachidonic acid by stimulation of opsonic receptors in human monocytes: the FcgammaR and the complement receptor 3 pathways.
The role of the opsonic receptors FcgammaR and CR3 on the release of arachidonic acid (AA) by human monocytes was studied using IgG-ovalbumin (OVA) equivalence immune complexes (IC), anti-OVA IgG bound to OVA-coupled latex beads, and C3bi-bound IC. Release of AA was produced by IC and latex-OVA beads bound to IgG, whereas binding of C3bi to IC inhibited the ability of IC to release AA. In contrast, coating of zymosan particles with C3bi enhanced AA release as compared with that produced by non-coated particles. Masking of C3bi on C3bi-bound IC by incubation with anti-C3 IgG resulted in the recovery of their ability to release AA, thereby suggesting that binding of C3b by IC reduces their flogogenic effects, whereas opsonization of microbial walls by complement may enhance their proinflammatory potential. The binding/uptake of opsonized zymosan particles was inhibited by anti-CR3 Ab and C3bi-bound IC, but not by beta-glucan, mannan, and anti-Toll-like receptor 2 Ab. These findings show that cooperative engagement of CR3 on both the lectin-like site involved in beta-glucan binding and the I-domain involved in C3bi binding, as it can be observed in the innate immune response, produces AA release, whereas the unique interaction of C3bi-bound IC with the I-domain of CR3, as it may occur in the adaptive immune response, diverts the IC lattice from a productive interaction with FcgammaR linked to AA release.
Arachidonic Acid↗
Internalization of circulating apoptotic cells by splenic marginal zone dendritic cells: dependence on complement receptors and effect on cytokine production.
Under steady-state conditions, internalization of self-antigens embodied in apoptotic cells by dendritic cells (DCs) resident in peripheral tissue followed by DC migration and presentation of self-peptides to T cells in secondary lymphoid organs are key steps for induction and maintenance of peripheral T-cell tolerance. We show here that, besides this traffic of apoptotic cells mediated by peripheral tissue-resident DCs, splenic marginal zone DCs rapidly ingest circulating apoptotic leukocytes, process apoptotic cell-derived peptides into major histocompatibility complex class II (MHC-II) molecules, and acquire CD8alpha during their mobilization to T-cell areas of splenic follicles. Because apoptotic cells activate complement and some complement factors are opsonins for phagocytosis and play roles in the maintenance of peripheral tolerance, we investigated the role of complement receptors (CRs) in relation to phagocytosis of apoptotic cells by DCs. Apoptotic cell uptake by marginal zone DCs was mediated in part via CR3 (CD11b/CD18) and, to a lesser extent, CR4 (CD11c/CD18) and was reduced significantly in vivo in hypocomplementemic animals. Following phagocytosis of apoptotic cells, DCs exhibited decreased levels of mRNA and secretion of the proinflammatory cytokines interleukin 1alpha (IL-1alpha), IL-1beta, IL-6, IL-12p70, and tumor necrosis factor alpha (TNF-alpha), without effect on the anti-inflammatory mediator transforming growth factor beta1 (TGF-beta1). This selective inhibitory effect was at least partially mediated through C3bi-CD11b/CD18 interaction. Characterization of apoptotic cell/DC interaction and its outcome provides insight into the mechanisms by which apoptotic cells affect DC function without disrupting peripheral tolerance.
Animals↗
High voltage immunoelectron microscopy of complement receptor type 3-mediated capping and internalization of group A streptococcal cell walls by human neutrophils.
The mechanism of human neutrophil clearance of peptidoglycan group A-specific polysaccharide polymers derived from streptococcal cell walls (PG-APS) was investigated by high voltage immunoelectron microscopy (HVEM) in order to determine how neutrophils process this highly inflammatory bacterial debris. Neutrophil monolayers were incubated from 5-30 min with serum-opsonized PG-APS. Cells were lightly fixed with 0.5% glutaraldehyde, and the PG-APS was localized on the neutrophil surface by immunogold using antibodies to N-acetyl-glucosamine and 15 nm colloidal gold coupled to goat anti-rabbit IgG. Neutrophils were viewed unsectioned by stereo HVEM. Patches of PG-APS were distributed randomly on the plasmalemma of well-spread neutrophils within 5 min. In polarized cells, PG-APS was densely localized on the uropod and retraction fibers. Within 15 min, PG-APS was predominantly concentrated into a large aggregate, measuring approximately 1 micron in diameter, near the cell margin or nucleus. The aggregate of PG-APS was engulfed in the vicinity of the indentation of the nucleus (hof). Intact microfilaments were required for aggregation and internalization of PG-APS. Binding of PG-APS was dependent upon complement fixation. Furthermore, PG-APS elicited an increase in density of complement receptor type 3 (CR3, C3bi receptor) on the neutrophil surface as determined by morphometry of immunogold labeled anti-CR3. When cells were stained for both PG-APS and CR3, co-localization was observed, and stereomicroscopy revealed clusters of CR3 in areas associated with phagocytosis. These data suggest that neutrophils use an efficient mechanism for removal of bacterial debris. Unlike whole streptococci which are phagocytosed at multiple sites, these bacterial cell walls are first collected into a large aggregate, or cap, which is then internalized at one site.
Acetylglucosamine↗
Emergence of a subpopulation of lymphocytes bearing theta antigen and complement receptor during tumor growth.
Spleens from BALB/c mice transplanted with mammary tumors display a significant increase in the percentage of lymphocytes bearing complement receptors (CRL) while the percentage of cells bearing surface immunoglobulins (SIg) remains unchanged in comparison with that in spleens from normal animals. Upon separation on nylon columns, the increase in CRL in the spleens from tumor-bearing mice was limited to the non-adherent cell population. Simultaneous maker analysis disclosed that these CRL lacked detectable SIg. Indirect immunofluorescence indicated that these cells possessed theta antigen. Absence of SIg and the presence of theta antigen coupled with the restricted occurrence of these cells in the nylon-non-adherent population which responded to PHA and Con A but not to LPS indicate that these cells may constitute a subset of T cells. The paucity of this subpopulation of spleen lymphocytes in normal spleen suggests that their emergence is related to tumor growth.
Animals↗