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PubMed1985

Neutrophils express a receptor for iC3b, C3dg, and C3d that is distinct from CR1, CR2, and CR3.

In the present study we examined human neutrophils for the expression of a receptor capable of binding C3dg and defined the relationship of this receptor to those that have been previously described, namely CR1, CR2, and CR3. C3dg was isolated from serum depleted of plasminogen, supplemented with 20 mM Mg++, and incubated at 37 degrees C for 6 to 8 days. The purified protein was homogeneous when analyzed by polyacrylamide gel electrophoresis and exhibited an apparent m.w. of 41,000. C3dg was polymerized by treatment with dimethyl suberimidate, and the dimer was isolated by gel filtration. Binding of both monomeric and dimeric 125I-labeled C3dg to neutrophils was saturable, and the latter ligand bound to an average of 12,400 sites/cell among nine normal individuals. At 4 degrees C, bound monomeric C3dg dissociated from neutrophils with an average t1/2 of 30 min, whereas dimeric C3dg dissociated with a t1/2 in excess of 120 min. Specific binding of multimeric C3dg was cation independent and was competitively inhibited by molar concentrations of iC3b and C3d that were equivalent to the inhibitory concentrations of unlabeled C3dg; C3b was less able to compete with C3dg for binding to these sites. The capacity of this neutrophil receptor to bind iC3b, C3dg, and C3d suggested its possible identity as CR2 or CR3. However, no specific binding to neutrophils of 125I-labeled HB-5 monoclonal anti-CR2 was detected. Furthermore, uptake of 125I-labeled C3dg was not inhibited by saturating concentrations of rabbit anti-CR1, anti-Mac-1, or OKM10. Thus, a receptor resides on neutrophils that binds the C3d region of iC3b and C3dg and is distinct from CR1, CR2, and CR3.

Animals↗
PubMed1986

Influence of C3 level on the determination of C3d in plasma and synovial fluid by radial immunodiffusion.

The influence of C3 levels on the determination of C3d in plasma and synovial fluid by radial immunodiffusion was investigated. In the method used, C3 is precipitated by 11% polyethylene glycol (PEG), and C3d is measured in the supernatant. In 51 healthy donors, a weak though significant correlation between C3 and C3d levels was found. The mean concentration of C3d was 1.6% of that in aged serum from healthy donors. So, small amounts of C3 (i.e., 1-2% of the normal plasma level) in the 11% PEG supernatants may contribute significantly to the C3d levels measured. A radioimmunoassay that detects C3, C3b, iC3b and C3c was used to measure C3 levels in the PEG supernatants. In PEG supernatants of 4 plasma samples, 0.3-0.6% of the C3 level in normal plasma was found, whereas in those of 2 synovial fluids much higher levels were found (4-10% of the normal plasma level). When purified 125I-labeled antibodies against C3c were added to the gel of the radial immunodiffusion, C3c antigen was detected in the precipitation rings obtained with all PEG supernatants of plasma samples from patients. Therefore, the quantitative contribution of C3 to the precipitation rings in the C3d radial immunodiffusion was analyzed after the addition of an excess of anti-C3c antibodies to the gel. No effect on the size of the C3d-precipitation rings obtained with plasma samples from patients was observed. However, the C3d precipitation rings obtained with synovial fluids were significantly smaller when the gel used in the radial immunodiffusion contained an excess of anti-C3c antibodies together with the anti-C3d serum. We conclude that it is necessary to add an excess of anti-C3c antibodies to the gel used for the radial immunodiffusion, for the determination of C3d levels in synovial fluid. An antiserum against human C3b, which contains both anti-C3c and anti-C3d antibodies, can be used for this purpose.

Blood Donors↗
PubMed1993

Evidence for three binding sites for C3 (hemolytically inactive), C3b and C3d on a CR2-positive Burkitt lymphoma-derived cell line (Raji).

The present investigation shows that C3 (hemolytic inactive) as well as C3b and C3d bind Raji, a CR2-positive Burkitt lymphoma-derived cell line. Pretreatment of the cells with OKB-7 inhibited the binding of C3, whereas pretreatment with HB-5 inhibited the binding of C3b. Furthermore, the cells coated either with OKB-7 or HB-5 bound high amounts of C3d. TPA-treated cells showed binding for C3b and weak binding for C3 and C3d. Taken together, the data suggest that Raji cells may express three binding sites for C3, C3b and C3d which can be differently modulated by anti-CR2 MoAbs and TPA.

Antibodies, Monoclonal↗
PubMed1991

Expression of complement receptor CR2 (CD21) on human subcorneal keratinocytes in normal and diseased skin.

Human keratinocytes are able to synthesize and express cell surface moieties characteristic of effector and/or accessory cells of the immune system (CD16, CD36, HLA-DR, intercellular adhesion molecule-1). In the present study, skin biopsies from healthy volunteers, from patients with psoriasis vulgaris (PV), mycosis fungoides (MF), purpura pigmentosa chronica (PPC), acute urticaria (AU) and from positive tuberculin skin tests were investigated with regard to the reactivity with the monoclonal antibodies to complement receptors CR1 CR2 and CR3 by means of a multistep immunoperoxidase method. In the clinically involved skin of all patients with PV, MF or PPC, and in biopsies obtained from positive tuberculin tests, specific epidermal intercellular staining with OKB7 and Leu anti-CR2 was seen on subcorneal keratinocytes. This finding suggests a differentiation-linked expression of CR2 on human keratinocytes in cytokine-mediated skin diseases whereas CR1 and CR3 are apparently not expressed.

Antigens, CD↗
PubMed1981

Quantitation of red blood cell-bound C3d in normal subjects and random hospitalized patients.

A sensitive radiolabelled anti-antiglobulin method was devised and applied to quantitating red blood cell-bound C3d (RBC-C3d) in samples from 174 normal blood donors. C3d was demonstrable on all RBC examined; 98% of values fell over a broad range, with the highest values being approximately 3.5 X the lowest values (equivalent to 50-160 molecules of C3d per cell). RBC-C3d did not correlate with sex or age (over 18-65 years); indirect evidence suggests that values for the paediatric age group will fall in the same normal range. Studies on samples obtained weekly for 10-12 weeks from six adult males and six adult females indicated stable levels of RBC-C3 for individual subjects; i.e. high normals, mid normals and low normals remained in their characteristic range levels over the period of observation. For comparison, RBC-C3d was measured in samples from 313 randomly selected hospitalized adult patients. 33% of the values were above the normal range; 8% were elevated to a level likely to have been detectable by a direct anti-C3d antiglobulin test. The great majority of elevated values occurred in patients not ordinarily considered to have autoimmune conditions. The results provide background for studies of the aetiology and significance of RBC-C3d in health and disease.

Adult↗
PubMed1986

Changes of serum complement concentrations in tumour patients prior and after radiotherapy.

Peripheral blood concentrations of leucocytes, platelets and complement factors Clq, C3c, C3d, C4 and C5 were examined in 30 patients suffering from malignant tumours prior and after radiotherapy. In general, a decrease of blood cell concentrations as well as serum complement levels was noted using regression analysis. Two groups were formed: patients with (group I) and without (group II) foregoing tumour surgery. A positive correlation was found for all complement factors prior therapy in group I, whereas only some complement components did correlate in group II. The results in group I are in agreement with complements classical pathway activation. We conclude that the alternative pathways influence is responsible for the different results in group II.

Combined Modality Therapy↗
PubMedDate not supplied

Early steps in fusion between Epstein-Barr virus and a human hepatoma cell line (Li7A).

Epstein-Barr virus, the causative agent of mononucleosis and several human cancers, infects cells via complement receptor type 2 (CR2). Expression of this receptor is restricted to B lymphocytes, some epithelial cells and immature thymocytes; expression of CR2-like proteins has been also found on T cells. In the present report, we identified the presence, on the membrane of Li7A cells, of a novel EBV receptor distinct from CR2 capable of triggering fusion with EBV virions with more rapid kinetics than that found with lymphoblastoid cells (Raji).

Carcinoma, Hepatocellular↗
PubMed1988

Immunohistochemical study of Warthin's tumour with special regard to the germinal centre.

In order to analyze the role of the lymphoid stroma of Warthin's tumour, the author made an immunohistochemical study especially focussing on the germinal centre (GC). In the GCs, IgM and IgE were much more clearly observed in a lace-like network than other heavy chains, and also could be detected electron microscopically on the surface of GC cells and follicular dendritic cells (FDCs). Plasma cells scattered beneath the epithelial component were mainly positive for IgG and IgA. IgG-positive plasma cells were more predominant than IgA plasma cells. Among the cases examined, there was a significant difference in the number of IgE-positive GC and plasma cells. In the GCs five complement components (C1g, C4, C3c, C3d, C5) and complement receptors (C3bR and C3dR) were positive, displaying a lace-like pattern, which were proved, electron microscopically, to coincide with the surface of FDCs and GC cells. IgE-positive GCs showed the same result. DRC1, which specifically reacts to FDC-membrane, was located only in GCs, and electron microscope also revealed positive findings on the surface of FDCs. The above mentioned findings in the GC of Warthin's tumour were similar to those of lymph nodes except for the frequent distribution of IgE. Salivary amylase was seen in the GC on rare occasions, but was not positive on the surface of GC cells and FDCs. It is suggested that FDCs play an important role in immunological behaviour with complement and complement receptors in the GC of Warthin's tumour.

Adenolymphoma↗
PubMed1987

Activation of human platelets through gp140, the C3d/EBV receptor (CR2).

gp140, the C3d/EBV receptor (CR2), previously isolated and characterized from human B lymphocytes, was identified on human platelets: by measuring the specific binding of either polyclonal anti-gp140 IgG and monoclonal anti-C3d/EBVR antibodies, as OKB-7 and HB-5, or human C3d; by isolating gp140 from solubilized platelet components with polyclonal anti-gp140 IgG or monoclonal OKB-7, using immunoprecipitation and electro-immunoblotting assays; by inducing specific activation of human platelets. Cross-linking of this receptor by polyclonal anti-gp140 IgG induced aggregation of human platelets and stimulated ATP release. Absence of lactate dehydrogenase release and inhibition by EDTA and prostacyclin of anti-gp140-induced aggregation, support strongly active aggregation and absence of lysis. Platelet aggregation by anti-gp140 required metabolic activities and was modulated by fibrinogen, paf-acether or thrombin. OKB-7 triggered human platelet aggregation when cross-linked by anti-mouse second-step antibodies. In the same way, platelet activation by C3d fragment was detected, in presence of fibrinogen, only when C3d was cross-linked on the cell surface by anti-C3d F(ab')2 fragments.

Adenosine Triphosphate↗
PubMed1982

C3c and C3d fragments of human C3 bind myeloma IgG1 and IgG3 proteins.

Eight human myeloma proteins, two of each IgG subclass, were studied for binding to solid-phase C3c and C3d by the ELISA technique. Myeloma IgG1 kappa, IgG1 lambda, IgG3 kappa and IgG3 lambda proteins bound to C3c and C3d, while two IgG2 kappa, and two IgG4 kappa proteins failed to show significant binding affinity. The results suggest that like C1q, the stable binding sites of C3, located on the C3c and C3d parts of the molecule, have affinity for IgG subclasses 1 and 3.

Animals↗
PubMed1989

The influence of C3-coated homologous erythrocytes on pokeweed-mitogen-induced polyclonal differentiation of human B cells.

The present study was undertaken in order to test the hypothesis that homologous erythrocytes (E) coated in vivo with C3d could modulate the immunoglobulin (Ig) synthesis of human peripheral blood mononuclear cells (PBMC), stimulated with pokeweed mitogen (PWM) in vitro. E from healthy individuals were found to enhance markedly the Ig synthesis of PMBC cultures stimulated with suboptimal doses (0.01 microgram/ml) of PWM. E coated in vivo with increasing amounts of C3d (1.4-6.3 times the amounts on normal E), obtained from patients with systemic lupus erythematosus, failed to induce any significant increase in Ig synthesis of PBMC cultures stimulated with suboptimal PWM doses, compared with cultures co-stimulated in parallel with normal E. In contrast, an increase in IgM and IgG synthesis was observed in about 50% of PBMC cultures from different donors when stimulated with PWM in the presence of E coated with C3b in vivo (from a patient with congenital factor I deficiency), compared with the Ig synthesis in cultures co-stimulated in parallel with normal E. In contrast to the inability of C3d-coated E to modulate B-cell proliferation, the monoclonal anti-CR2 antibody OKB7 was found to be mitogenic for unstimulated peripheral B cells.

Antigens, Differentiation, B-Lymphocyte↗
PubMed1983

Clinical application of a new nephelometric technique to measure complement activation.

A new nephelometric technique to measure C3d as an indicator of complement activation, is described. C3d is isolated at high concentration of polyethyleneglycol (PEG), incubated with commercially available anti-C3d antiserum at a final concentration of 2.5% PEG and then measured in a Behring Laser Nephelometer. In contrast to previously available techniques our assay detects the low concentrations of C3d present in all normal subjects, which result from the continuous C3 catabolism occurring in vivo. We have also measured C3d blood concentrations in a large number of patients with diseases associated with complement activation. Raised C3d concentrations were found in 68% of rheumatoid arthritis, 57% of primary biliary cirrhosis, 38% of chronic active hepatitis, 100% of Gram-negative bacteraemia and 100% of malaria. The nephelometric technique has proved to be sensitive, economical and fast, and could be adapted for routine determination of C3d blood concentrations to monitor disease activity and response to treatment.

Arthritis, Rheumatoid↗
PubMed1998

The role of complement and complement receptors in induction and regulation of immunity.

Covalent attachment of activated complement C3 (C3d) to antigen links innate and adaptive immunity by targeting antigen to follicular dendritic cells (FDC) and B cells via specific receptors CD21 and CD35. Recent characterization of knockout mice deficient in complement components C3, C4, or the receptors CD21 and CD35 as well as biochemical studies of the CD21/CD19/Tapa-1 coreceptor on B cells have helped to elucidate the mechanism of complement regulation of both B-1 and B-2 lymphocytes. Interestingly, natural antibody of the adaptive immune system provides a major recognition role in activation of the complement system, which in turn enhances activation of antigen-specific B cells. Enhancement of the primary and secondary immune response to T-dependent antigens is mediated by coligation of the coreceptor and the B cell antigen receptor, which dramatically increases follicular retention and B cell survival within the germinal center. Most recent evidence suggests that complement also regulates elimination of self-reactive B cells, as breeding of mice that are deficient in C4 or CD21/CD35 with the lupus-prone strain of lpr mice demonstrates an exacerbation of disease due to an increase in autoantibodies.

Animals↗
PubMed1998

Enhanced molecular mimicry of CEA using photoaffinity crosslinked C3d peptide.

Antigen mimicry of using anti-idiotypic antibodies for use as cancer vaccines has been disappointing due to the weak immunogenicity of immunoglobulin variable domains. To enhance the immunogenicity of an anti-idiotype vaccine we incorporated a molecular adjuvant peptide into the antibody. The peptide is derived from the C3d region known to bind CR2 receptors on B-cells. A photoreactive peptide is synthesized that affinity-labels a single site in the antibody variable domain. The molecular adjuvant peptide is crosslinked to the anti-idiotype mimetic by chemical means without modifying other sites on the antibody. The C3d-conjugated anti-idiotype antibody induces a strong idiotype and antigen-specific response in mice.

Adenosine↗