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PubMed1984

Restoration of complement function in vivo by plasma infusion in factor I (C3b inactivator) deficiency.

The serum complement activities of a 1-year-old infant with recurrent life-threatening bacterial infections and persistent C3-Coombs-positive red blood cells were investigated. The patient's serum had a depressed serum level of CH50, C3, factor B, and factor H as well as undetectable antigenic or functional factor I. The complement profile of the parents was normal, with the exception of factor I, which was approximately 50% of normal in each parent. The Coombs positivity of the patient's red blood cells could be reversed in vitro by incubation with normal serum containing factor I. Infusion of normal plasma into the patient resulted in increased levels of CH50, with concomitant increases in serum C3, factor B, and factor H levels. The patient's red blood cells became transiently Coombs negative. At no time after plasma infusion was factor I detectable in the patient's serum. All complement functions and the C3 Coombs reactivity of the patient's red blood cells returned to preinfusion levels within 14 days. These findings are consistent with an inherited deficiency of factor I and emphasize the critical role this protein plays in the regulation of the alternative complement pathway. Plasma therapy may be an adjunct to the management of acute infection in patients with factor I deficiency.

Afibrinogenemia↗

PubMed1974

Studies on the in vivo effects of antibody. Interaction of IgM antibody and complement in the immune clearance and destruction of erythrocytes in man.

Purified human IgM isoagglutinins were utilized to sensitize (51)Cr-labeled erythrocytes so as to produce a known number of complement-fixing sites. These cells were then reinfused into the erythrocyte donor. A minimum of 20 C1-fixing sites/erythrocyte were required for decreased survival. As the amount of antibody coating the erythrocytes was increased, a larger percentage was sequestered. With 80 C1-fixing sites, more than 75% of the injected erythrocytes were removed from the circulation within 10 min. In each case, the clearance pattern consisted of rapid hepatic sequestration followed by a gradual return of a portion of the erythrocytes into the circulation where they survived normally. Clearance was shown to be dependent upon activation of the classical complement pathway, since sensitized cells survived normally in hereditary angioedema patients with low levels of C4 and no detectable C2. Exposure of sensitized cells to fresh serum for 15 min led to the deposition of 550-800 C3 molecules/C1-fixing site. Such cells were immune adherence positive, were agglutinated by anti-C3b, formed rosettes with human alveolar macrophages, and were sequestered in vivo, presumably because of the interaction of cell-bound C3b with the C3b receptor on hepatic macrophages. After exposure to heated serum as a source of the C3b inactivator, the cells were immune adherence negative, were agglutinated only by anti-C3d, did not form rosettes with macrophages, and survived normally in vivo despite, being Coombs positive. Cleavage of cell-bound C3b to C3d may explain the release phase of the IgM clearance pattern. Whereas erythrocytes coated with IgM antibody and complement were previously thought to be sequestered in the liver because of extensive membrane damage, these experiments suggest that clearance is determined by the interaction of erythrocyte-bound complement fragments with specific receptors on hepatic macrophages.

Adolescent↗

PubMed2005

CD46-utilizing adenoviruses inhibit C/EBPbeta-dependent expression of proinflammatory cytokines.

The majority of adenovirus serotypes utilize the coxsackievirus-adenovirus receptor (CAR) for virus-host cell attachment, but subgroup B and subgroup D (adenovirus type 37 [Ad37]) viruses recognize CD46. CD46 is a ubiquitously expressed receptor that serves as a cofactor for the inactivation of the complement components C3b and C4b, and it also serves as a receptor for diverse microbial pathogens. A reported consequence of CD46 engagement is a reduced capability of human immune cells to express interleukin-12 (IL-12), a cytokine involved in both the innate and adaptive immune responses. Studies were thus undertaken to determine whether CD46-utilizing Ads alter the expression of proinflammatory cytokines. Subgroup B (Ad16 and -35) and Ad37, but not Ad2 or -5, significantly reduced IL-12 production by human peripheral blood mononuclear cells stimulated with gamma interferon (IFN-gamma) and lipopolysaccharide. IL-12 mRNA (p35 and p40 subunits) levels as well as other cytokine mRNA levels (IL-1alpha and -beta, IL-1Ra, and IL-6) were decreased upon interaction with CD46-utilizing Ads. Analysis of transcription factor activity required for cytokine expression indicated that CD46-utilizing Ads preferentially inhibited IFN-gamma-induced C/EBPbeta protein expression, consequently reducing its ability to form DNA complexes. Interference with IFN-gamma signaling events by CD46-utilizing Ads, but not CAR-utilizing Ads, reveals a potentially critical difference in the host immune response against distinct Ad vectors, a situation that has implications for gene delivery and vaccine development.

Adenoviridae↗

PubMed1969

Isolation of a fragment (C3a) of the third component of human complement containing anaphylatoxin and chemotactic activity and description of an anaphylatoxin inactivator of human serum.

A small fragment of C3, called C3a, which has smooth muscle contracting activity, was isolated by three different methods. At pH 8.6, C3a behaved as cation, and using the Archibald method, its mol wt was determined to be 7000. A specific antiserum to C3a showed the fragment to be antigenically distinct from the rest of the C3 molecule, i.e., the C3b portion. The same antiserum and an anti-whole C3 were able to inhibit the biologic activity of C3a. In addition to anaphylatoxin activity, leukocyte chemotactic activity was shown to reside in C3a. Treatment with trypsin caused the cationic fragment to become anionic and abolished the anaphylatoxin but not the chemotactic activity. C3a fragments with identical biologic activity and comparable cationic properties, as determined by acid disc electrophoresis, were obtained by treatment of C3 with C3 convertase, C3 inactivator complex, trypsin, and plasmin. Thrombin produced a similar C3 fragment which was inactive. It was concluded that C3a corresponds to an unusually basic portion of C3 which may be liberated by attack of a variety of enzymes on a highly susceptible region of the native C3 molecule. C3b was cleaved by trypsin and less efficiently by thrombin or plasmin into two antigenically distinct pieces: the larger C3c fragment corresponding to beta(1A) and the smaller C3d fragment to alpha(2D) of aged serum. The c- and the d-fragments were separated and characterized. Isolated C3a rapidly lost its anaphylatoxin activity when treated with small amounts of a partially purified, thermolabile 10S alpha-pseudoglobulin of human serum. The conditions of inactivation suggested an enzymatic reaction. The anaphylatoxin inactivator also destroyed the activity of C5-derived anaphylatoxin and of lysyl bradykinin.

Anaphylaxis↗

PubMed1978

Membrane sialic acid on target particles modulates their phagocytosis by a trypsin-sensitive mechanism on human monocytes.

Monolayers of human peripheral blood monocytes in the absence of exogenous proteins ingest a variety of natural particulate activators of the human alternative complement pathway. Sheep erythrocytes, which do not ordinarily activate the human alternative complement pathway or initiate a direct monocyte phagocytic response, can be modified to exhibit both functions by the deletion or alteration of membrane sialic acid residues. Enzymatic removal of the sialic acid residues with sialidase or their conversion to heptulosonic acid derivatives by limited oxidation with NaIO4 and reduction with BH4- have equivalent dose-response effects on the capacity of the altered sheep erythrocytes to initiate the phagocytic response by human monocytes or to activate the alternative pathway in human serum. The deposition of C3b on native sheep erythrocytes had little effect on their ingestion by human monocytes, whereas the fixation of C3b on desialated sheep erythrocytes had a synergistic effect on the percentage of monocytes ingesting such a particle. The monocyte receptor essential for ingestion of desialated sheep erythrocytes or desialated sheep erythrocytes bearing C3b was inactivated by concentrations of trypsin that also prevented the monocytes from ingesting natural activators of the human alternative complement pathway, but did not alter the receptors for C3b or the Fc portion of IgG. The capacity of the nonimmune host to respond to desialated particles by initiating the monocyte ingestive process and by activating the alternative complement pathway to provide the synergy afforded by C3b deposition on that particle represents a primitive biochemical basis for differentiation of nonself from self.

Cell Membrane↗

PubMed1976

Studies of the presence of membrane receptors for complement, IgG and the sheep erythrocyte rosetting capacity on the same human lymphocytes.

Normal peripheral blood lymphocytes were tested by a mixed rosette method, employing different sized erythrocytes as indicators to identify lymphocytes simultaneously possessing membrane markers found commonly on B and T cells. Only small populations of these lymphocytes were detected regularly in normal lymphocyte preparations. One type of lymphocyte (ranged from 0.5%-8%) was shown to possess the following markers: receptors for human and rabbit IgG, receptors for the third complement component C3b and C3b inactivator-cleaved C3b (C3d), and the capacity to rosette spontaneously with uncoated sheep erythrocytes (SRBC). Another lymphocyte cell type was shown to possess both SRBC and IgG receptors but lack membrane immunoglobulins and complement receptors. This population was detected in lymphocyte preparations depleted of complement receptor cells, and an increased number of these cells was found in rosette preparations incubated with human serum. The possible presence of some lymphocytes possessing both complement and SRBC receptors and lacking other markers was considered. The possibility that these small populations of human lymphocytes are sub-populations of T cells with certain cytotoxic function is postulated.

Adolescent↗

PubMed1989

Interactions between earthworm hemolysins and sheep red blood cell membranes.

The hemolytic activity exhibited by the coelomic fluid of the Annelid Eisenia fetida andrei is mediated by two lipoproteins of mass 40 and 45 kDa, each of them capable of hemolysis. Such an activity is not inhibited by zymosan, inulin or lipopolysaccharide (LPS), nor by hydrazine or methylamine, suggesting that earthworm hemolysins are not related to C3 or C3b complement components. Among the membrane lipids tested (phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, sphingomyelin and cholesterol) only sphingomyelin inhibited hemolysis. The analysis of E.f. andrei proteins bound to sphingomyelin microvesicles, as well as to sheep red blood cell (SRBC) membranes, revealed a polymerization of E.f. andrei 40 kDa and/or 45 kDa hemolysins. Consequently, sphingomyelin appears a likely candidate for hemolytic complex receptor. Electron microscopy observations suggested that the polymerization causes an open channel through the lipid bilayer. As demonstrated using metal ions, heparin, chondroitin sulfate, poly(L-lysine) and protamine chloride, the mode of action of earthworm hemolytic complex is not analogous to that of C9 or perforine.

Animals↗

PubMed1976

The cofactors required by C3 nephritic factor to generate a C3 convertase in vitro.

The mechanisms by which a C3 convertase is generated by C3 nephritic factor (NeF) were investigated using purified NeF, C3, C3b, factor B and factor D of the alternative pathway of complement activation. NeF could generate a C3 convertase with C3 and B in the absence of D, and without cleavage of B. At lower concentrations of NeF the addition of D was required to generate a C3 convertase, and B cleavage now occurred. The generation of both the D-independent and D-dependent C3 convertases with NeF was inhibited by preincubation of the C3 source with C3b inactivator (KAF); isolated C3b was more efficient than the C3 preparations used in generating the D-independent C3 convertase with NeF. These experiments indicate that C3b is required for the formation of both convertases, and that the reaction occurring with apparently native C3 is due to trace amounts of C3b. It is concluded that the C3 convertase generated by NeF in the absence of D is C3bB (NeF), and that generated in the presence of D is the feedback convertase C3bBb. The relevance of these experiments to reactions which may occur in vivo is discussed.

Biological Products↗

PubMed1988

Differing complement-mediated opsonic activity of rabbit interstitial fluids from autologous serum.

Lack of appropriate methods for withdrawing extravascular or interstitial fluid from an animal host has limited in vitro study on the role of complement in the local defence of the extravascular space. In the present study, we obtained fluids from membrane diffusion chambers (porosity 0.22 micron) implanted into the kidneys, peritoneal cavity and soft tissues in rabbits. The complement-mediated opsonic activity (CMOA) of these fluids for Staphylococcus aureus ATCC 502A and Escherichia coli 01 was then compared to that of autologous sera. Soft tissue and renal interstitial fluids were as opsonic for E. coli as autologous sera but were however, poor opsonins for S. aureus. The peritoneal fluid was marginally effective in opsonization of both bacterial strains. While chelation of the fluids with MgEGTA (to block the classical pathway) did not diminish CMOA for E. coli, it reduced the CMOA for S. aureus by half. Conversely, heat-inactivation of the fluids and serum eliminated the opsonic activity for E. coli but only decreased the opsonic activity for S. aureus by half. Following a 24 h in vivo growth of E. coli in the implanted chambers, the CMOA was drastically reduced. Concomitant to the reduction in functional complement in the fluids, E. coli recovered from the chambers were found coated, though not maximally, with C3b as evidenced by studies with fluorescent antibody. The differences in opsonic content of extravascular fluids observed here might explain why certain sites of the body may be more vulnerable to attack by some bacterial species which are not effectively opsonized and therefore phagocytized.

Animals↗

PubMed1999

Nephritogenic lambda light chain dimer: a unique human miniautoantibody against complement factor H.

A unique monoclonal Ig lambda light chain dimer (protein LOI) was isolated from the serum and urine of a patient with hypocomplementemic membranoproliferative glomerulonephritis. In vitro the lambda light chain dimer efficiently activated the alternative pathway of complement (AP). When added to normal human serum, LOI temporarily enhanced AP hemolytic activity, but during a prolonged incubation the hemolytic activity was depleted. Protein LOI was found to bind to factor H, the main regulator molecule of AP. By binding to the short consensus repeat domain 3 of factor H, the dimer LOI blocked one of three interaction sites between H and C3b and thus inhibited the activity of H and induced an uncontrolled activation of the AP. Structural analysis showed that LOI belonged to the Vlambda3a subgroup of lambda light chains. The variable (V) region of LOI was most closely related to the predicted product of the Vlambda3 germline gene Iglv3s2, although it contained several unique residues that in a tertiary homology model structure form an unusual ring of charged residues around a hydrophobic groove in the putative Ag binding site. This site fitted considerably well with a putative binding site in the molecular model of domain 3 of factor H containing a reciprocal ring of charged amino acids around a hydrophobic area. Apparently, functional blocking of factor H by the Ab fragment-like lambda light chain dimer had initiated the development of a severe form of membranoproliferative glomerulonephritis. Thus, the lambda light chain dimer LOI represents the first described pathogenic miniautoantibody in human disease.

Amino Acid Sequence↗

PubMed1977

Receptor-binding sites on C3 and C3b.

Human erythrocytes carry C3b receptors: Daudi lymphoid cells carry exclusively C3d receptors. With these two types of cells, it could be shown that isolated, uncleaved human C3 and soluble C3b possess two stable binding sites: SBS1-specific C3b receptors, and SBS2-specific for C3d receptors. Upon binding of freshly cleaved C3b (nascent C3b) via its labile binding site (generated on C3b through cleavage of C3) to the C3 acceptors on cell surfaces, the SBS2 becomes concealed. Kinetic experiments show that immediately after the action of fetal calf serum or partially purified C3b-inactivator on EAC1423b the SBS2 is accessible again. The reappearance of SBS2 does coincide with cleavage of surface-bound C3b into C3c and C3d but not with the release of C3c from the cell; C3c remains attached and is released only with delay. Concomitant with the cleavage event the number of SBS1 is reduced, stressing the importance of an unaltered steric configuration of the C3b structure for the expression of SBS1. An alternative explanation might be that the SBS1 is located at the site connecting C3c and C3d, so that it becomes altered upon dissection of the two fragments.

Binding Sites, Antibody↗

PubMed1991

Selective inactivation of human neutrophil elastase by synthetic tannin.

Tannins of natural or synthetic origin are well-known adjuvants in topical anti-inflammatory therapy of skin diseases. In this study, the influence of synthetic tannin on neutrophil accumulation, enzyme release, and on the proinflammatory activity of neutrophil-derived enzymes was investigated. The results show that synthetic tannin (Tamol) specifically inhibits the neutrophil serine protease human leukocyte elastase (HLE) in an irreversible manner with a half-maximal inhibitory concentration (IC50) of 0.3 microgram/ml. Exogenous protein partially abolished the tannin-dependent HLE inhibition (IC50 of Tamol at 1% protein-concentration:1.0 microgram/ml). Synthetic tannin did not influence the activities of other neutrophil enzymes like Cathepsin G, beta-glucuronidase, and myeloperoxidase. The specificity of Tamol for HLE was further substantiated by the lack of inhibition of other serine proteases. Additionally, Tamol had no effect on f-met-leu-phe-induced neutrophil chemotaxis and did not alter enzyme degranulation of neutrophils in response to f-met-leu-phe and opsonized zymosan. We conclude from our results that the anti-inflammatory properties of synthetic tannin may at least in part be due to inactivation of the proinflammatory protease HLE.

Cell Degranulation↗

PubMed1998

Expression and functional analysis of glycosyl-phosphatidyl inositol-linked CD46 in transgenic mice.

BACKGROUND: Complement activation plays a pivotal role in hyperacute xenograft rejection. In humans, activation of complement is regulated by a number of cell surface regulatory proteins. Membrane cofactor protein (CD46) is one such regulator that protects cells by acting as a cofactor for the factor I-mediated cleavage of C3b and C4b. Transgenic animals expressing human CD46 may provide organs that are resistant to complement attack. However, attempts to generate mice expressing human CD46 using cDNA-based constructs have been largely unsuccessful. METHODS: Transgenic mice expressing a glycosylphosphatidyl inositol (GPI)-linked form of CD46 were generated by microinjection of a hybrid CD46/CD55 cDNA under the control of the human intercellular adhesion molecule-2 promoter. Expression of CD46-GPI on the vascular endothelium was determined by immunohistochemistry. The ability of CD46-GPI to protect mouse tissues from human complement attack was determined using an ex vivo isolated perfused heart model. RESULTS: Three founder animals expressing CD46-GPI were identified. Histological analysis showed strong and uniform expression of CD46-GPI on the vascular endothelium of all organs examined. Ex vivo perfusion of transgenic mouse hearts with human plasma showed a reduction in C3c deposition and a slightly prolonged function compared with controls. CONCLUSIONS: High-level expression of CD46-GPI was achieved in transgenic mice by using a modified cDNA-based construct. The CD46-GPI was functional, providing some protection from complement-mediated damage in the ex vivo model, and may be useful in xenotransplantation if expressed in combination with CD55 and CD59.

Animals↗

PubMed1999

Distribution of membrane cofactor protein (MCP/CD46) on pig tissues. Relevance To xenotransplantation.

Membrane cofactor protein (MCP; CD46) is a 50-60 000 MW glycoprotein, expressed on a wide variety of cells and tissues in man, which plays an important role in regulating complement activation. Human MCP has also been shown to be the receptor for measles virus. We have recently identified the pig analogue of MCP and demonstrated that pig MCP has cofactor activity for factor I-mediated cleavage of C3b when these components are derived either from pig or human. As a consequence, pig MCP is an efficient regulator of the classic and alternative pathways of human and pig complement. In order to define the potential importance of MCP in protecting against complement activation in the pig, we have conducted a comprehensive survey of its distribution in pig cells and organs. As in humans, MCP in the pig is broadly and abundantly distributed. Pig MCP is highly expressed on all circulating cells, including erythrocytes, in contrast to its absence on human erythrocytes. Multiple isoforms of MCP are found on cells and in tissues, probably representing products of alternative splicing analogous to those found in man. MCP is abundantly expressed throughout all tissues examined with particularly strong staining on the vascular endothelium. Connective tissue elements within liver and testis are also strongly stained by anti-pig MCP antibodies. Pig MCP is expressed only weakly on skeletal muscle cells and expression is absent from smooth muscle cells in the lung and vessel walls, sites at which human MCP is expressed. Of particular note, MCP is not expressed in B-cell areas of the germinal centres of lymph nodes.

Animals↗

PubMed1975

Third component of complement (C3): structural properties in relation to functions.

The third component of complement (C3) fulfills a pivotal role in the functions of the complement system. We have investigated the topological relationships among its polypeptide chains, physiologic fragments, enzyme attack regions, and functional sites. C3 consists of two chains (alpha and beta) which are linked by disulfide bonds and noncovalent forces and which have molecular weights of, respectively, 120,000 and 75,000. C3 is activated by action of C3 convertase on the alpha-chain. With hydrolysis of one polypeptide bonds, C3a, the 9000 dalton activation peptide is dislocated from the NH2-terminal portion of the alpha-chain. A previously concealed binding region is thereby transiently revealed in the C3b-fragment (181,000 dalton) which displays affinity for apparently nonspecific acceptors present on biological membranes. Binding of nascent C3b membranes occurs through the C3d portion of the fragment because subsequent action of the C3b-inactivator or trypsin on bound C3b causes release of C3c, but not of C3d. Bound C3b and C3d possess stable sites that are capable of binding to specific receptors present on a limited variety of cells. We propose that all known physiologically occurring fragments of C3 arise by enzymatic cleavage of the alpha-chain: C3a, C3b, C3c, and C3d. Whereas C3a (alpha1) and C3e (alpha2) consist of a single chain and C3b consists of two chains (alpha' and beta), C3c is composed of the entire beta-chain and multiple fragments of the alpha-chain, each of which is linked by disulfide bonds to the beta-chain.

Binding Sites↗

PubMed2004

The classical and alternative pathways of complement activation play distinct roles in spontaneous C3 fragment deposition and membrane attack complex (MAC) formation on human B lymphocytes.

The contributions of the classical (CP) and alternative (AP) pathways of complement activation to the spontaneous deposition of C3 fragments and the formation of membrane attack complexes (MAC) on human B lymphocytes, were assessed by incubating peripheral blood mononuclear cells with autologous serum in the absence and presence of selective inhibitors of the AP and CP, respectively. While the total amount of C3 fragments deposited was relatively unaffected by blocking either pathway individually, deposition was virtually abrogated by their combined blockade. A marked difference was observed, however, in the nature of the fragments deposited as a result of CP and AP activation: C3b fragments deposited via the CP were extensively ( approximately 90%) converted to the terminal degradation product, C3dg, whereas about 50% of those deposited by the AP persisted as C3b/iC3b fragments. The extent of MAC formation was also found to be highly pathway dependent, with the AP being about 15-fold more efficient at initiating this process than the CP. A model accounting for the effectiveness of the AP in both preserving C3 fragment integrity and initiating MAC is presented.

Acetylglucosamine↗

PubMed2003

Vaccinia virus complement control protein increases early bacterial clearance during experimental peritonitis.

BACKGROUND: Complement is one of the first immunological pathways activated in peritonitis. It functions to initiate and augment the innate immune response. Complement activation has also been shown to contribute to multiple organ failure after sepsis. Vaccinia virus complement control protein (VCP) is an immunomodulatory protein encoded by vaccinia virus and binds complement components C3b and C4b of the complement cascade to inhibit both the classical and alternative pathways of complement activation. This study investigates the effect of complement inhibition by recombinant (r) VCP on bacterial clearance after cecal ligation and puncture (CLP). METHODS: Swiss Webster mice were intravenously given either 20 mg/kg rVCP in 0.2 mL of normal saline, or 0.2 mL of normal saline alone, at the time of CLP. After 4 and 18 h, samples of peritoneal washout, blood, liver, and lung were collected for bacteriology, myeloperoxidase (MPO) assay for neutrophil accumulation, differential cell counts, and interleukin (IL)12 ELISA. Statistical analysis was by Mann-Whitney U test for bacteriology, and analysis of variance (ANOVA) for MPO and IL-12 concentrations. RESULTS: Aerobic and anaerobic bacterial levels were significantly lower at 4 h after treatment with rVCP (p < 0.05) in peritoneal lavage, blood, and liver compared with controls. There were no differences in bacterial levels at 18 h. There were no differences in myeloperoxidase concentrations or in the differential cell counts between the groups at either 4 or 18 h after CLP. IL-12 concentrations in serum or peritoneal washout were also not different. CONCLUSIONS: rVCP enhances early bacterial clearance in mice after CLP, although not through neutrophil recruitment, as MPO concentrations and cell counts were not different. rVCP may, however, increase neutrophil function potentially by prevention of accumulation of complement factors that inhibit leukocytes. Further studies will be needed to elucidate this pathway.

Animals↗

PubMed1978

Effects of surface-active agents on neutrophil receptors.

An easily performed assay to identify the C3b and Fc receptors on human neutrophils was developed. Salmonella typhimurium were treated with fluorescein and then incubated in nonimmune fresh human serum, which led to C3b fixation via activation of the alternative pathway. Similarly, type II pneumococci were treated with fluorescein and opsonized with type-specific rabbit antiserum. Neutrophils bearing C3b and Fc receptors formed rosettes with the respective bacteria, which were easily readable because of their bright fluorescence. Incubation of neutrophils at 37 degrees C with C3-coated bacteria generated 54 +/ 4% C3b rosettes, whereas neutrophils incubated with immunoglobulin G-coated bacteria yielded 75 +/ 7% rosettes. Incubation at 4 degrees C inhibited the formation of C3b rosettes but not Fc rosettes. Heat inactivation of the fresh human serum at 56 degrees C for 30 min completely inhibited the formation of the C3b rosettes, and addition of heat-aggregated immunoglobulin G to the polymorphonuclear leukocyte blocked the ability of the polymorphonuclear leukocyte to bind immunoglobulin G-coated bacteria. Addition of 1.0 mM N-ethylmaleimide, 0.1 mg of trypsin per ml, 10 mM H2O2, O2- generated by xanthine-xanthine oxidase, and 8 times 10(-4) M hydrocortisone inhibited the C3b receptor, but did not inhibit the Fc receptor. In neutrophils, the selective effect of the various inhibitors suggests that the Fc and C3b receptors are distinct entities.

Binding Sites↗