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PubMed1986

Structure and functions of gp 140, the C3d/EBV receptor (CR2) of human B lymphocytes.

Analysis of the interaction of human C3 fragments with human B lymphoma cell line, led us to isolate gp 140, the C3 receptor of Raji cells. Rabbit anti-gp 140 was prepared against this highly purified receptor. Using these polyclonal antibodies, it was found that: gp 140 is the C3d receptor (CR2) which reacts with the C3d site expressed on C3d, C3dg, C3bi and at a less extent on C3b. Gp 140 is a specific marker of human B lymphocytes; gp 140 is also the Epstein-Barr virus receptor (EBVR); CR2 is a membrane site involved in B-cell regulation; and the C3d/C3dg receptor (CR2) of human B lymphocytes is distinct to the C3dg receptor (CR4) of human neutrophils.

B-Lymphocytes↗
PubMedDate not supplied

A simple method for preparation of C3c fragment from trypsinized serum-reacted zymosan.

A simple method for preparing relatively pure C3c fragment from serum-reacted zymosan is described. Although hyperimmunization studies indicate contamination of the "C3c" product by C3d and immunoglobulin antigenic materials, these are present in such small amounts that they do not impair the effectiveness of the product as a reagent for absorbing anti-C3c reactivity from polyspecific antisera. Furthermore, two of the three hyperimmune sera contained such weak anti-C3d that they could serve as monospecific anti-C3c antiglobulin reagents if used at moderate dilution. Neutralization of accompanying anti-IgG and weak anti-IgM is easily accomplished with readily available purified immunoglobulins. Preliminary studies indicate that the C3c product should be adaptable to quantitative radioimmunoassay of anti-C3c antibody concentrations and equilibrium constants.

Absorption↗
PubMed1998

Participation of factor B in residual immune complex red cell binding activity observed in serum from a C2-deficient systemic lupus erythematosus patient may delay the appearance of clinical symptoms.

OBJECTIVE: To investigate whether participation of factor B (FB) in immune complex transport might explain long periods of clinical remissions in a homozygous C2-deficient patient with systemic lupus erythematosus (SLE) treated regularly with plasma infusions. METHODS: Immune complex red cell binding (ICRB) was assayed as enzyme activity, C3d by enzyme-linked immunosorbent assay, and FB by immunoelectrophoresis. RESULTS: C2-deficient sera showed low-grade ICRB, which correlated with levels of FB. This activity could be blocked with antibodies to C1q, C4, or FB, but not by antibodies to C2. C3d levels in the patient's plasma changed during infusion, followed by a gradient increase during remission. Comparison of ICRB, C3d, and FB suggested an inverse relationship between FB levels and clinical symptoms. CONCLUSION: In C2 deficiency, FB may interact with C4 to provide a low-grade ICRB. This activity could be clinically significant in patients with C2 deficiency and explain why they are less prone to SLE than patients with C1q or C4 deficiency.

Antibodies↗
PubMed1982

Malignant centroblastic-histiocytic lymphoma of the skin.

A mixed B-cell type centroblastic lymphoma with extraordinarily many histiocytes in a 68-year-old man is reported. Multiple skin tumours were the only clinical manifestation during the first 5 months. The disease then progressed to the lymph nodes, spleen, and parenchymal organs, but the bone marrow remained unaffected until death, 11 months after the onset of signs. C3d receptors were the only surface markers of the centroblasts. The histiocytes were normal with respect to morphology, muramidase staining, and Fc and C3b receptors. This highly unusual spread from skin to lymphoid and parenchymal organs is discussed in the light of lymphoid cell kinetics.

Aged↗
PubMed1983

Fc-receptor function in minimal change nephrotic syndrome of childhood.

This study was undertaken to establish whether the Fc-receptor function of circulating monocytes (CM) and/or of splenic macrophages (SM) is modified during the course of minimal change nephrotic syndrome (MCNS) of childhood. The Fc-receptor function of SM was ascertained by measuring the spleen to liver uptake ratio 40 min after IV injection of heat-damaged autologous erythrocytes labeled with 99Tc, whereas the Fc-receptor function of CM was determined by a "rosetting" test. The Fc-receptor function was followed in six girls presenting with a MCNS and receiving no therapy at the time of testing. The Fc-receptor function of SM was decreased in five patients during an acute phase of MCNS. In four of these five patients, the Fc-receptor function of CM was also altered. No significant correlations were observed between the Fc-receptor blockade and the C3, C3d, C4, C3PA or immune complex-plasma levels. The Fc-receptor blockade was persistent in three girls during remission. A prior incubation of CM with trypsin did not completely reverse the Fc-receptor blockade. Further studies are now being pursued in order to determine whether this persisting abnormality is inherited and mainly observed in relapsing nephrotic syndrome.

Adolescent↗
PubMedDate not supplied

Antigen receptor triggered upregulation of CD86 and CD80 in human B cells: augmenting role of the CD21/CD19 co-stimulatory complex and IL-4.

The impact of BCR:CD21 co-engagement on B cell expression of molecules critical for T cell activation was investigated with receptor-specific mAbs conjugated to high MW dextran as stimulatory ligands. In the absence of IL-4, BCR:CD21 co-ligation augmented BCR-triggered CD86 only under conditions of very low BCR ligand dose or affinity, and CD80 was minimally induced by BCR and/or CD21 crosslinking. In the presence of IL-4, BCR:CD21 co-ligation augmented CD86 and CD80 expression under conditions of greater BCR engagement. However, with very high level BCR engagement, no bonus effect of BCR:CD21 crosslinking was observed. Co-ligation-promoted CD86 and CD80 expression was associated with heightened B cell activation of resting allogeneic T cells. The data suggest that co-clustering of BCR and the CD21/CD19 co-stimulatory complex following B cell engagement with C3d-bound microbial or self-antigens will enhance B cell recruitment of T cell help only when IL-4 is present and/or BCR engagement is very limiting.

Adolescent↗
PubMed1982

A comparative evaluation of receptor reactivities for C3b, iC3b, and C3d on Raji lymphoblastoid cells.

Raji cells were described to carry receptors for iC3b, C3d, C3b-beta 1 H and beta 1 H. Controversial opinions, however, exist whether or not these cells carry also receptors for C3b. Using highly purified C3, definitely devoid of beta 1 H and C5, for preparation of C3b intermediates, it could be shown that Raji cells bound to C3b cells. Furthermore, Raji cells reacted with monoclonal antibodies that interfered with binding of C3b to human erythrocytes, lymphocytes and renal cells. The receptor for C3b on Raji cell, however, exhibited some special properties and, therefore, required some distinct experimental conditions for its detection: (1) The origin of the erythrocytes used for preparation of the C3b intermediates seemed to be important; this was not the case when iC3b and C3d receptor reactivity was assessed. (2) Rosettes already formed between Raji cells and EAC1423b showed the tendency to disintegrate within the first 30 min after the rosette formation assay. Again, this effect could not be observed with iC3b- and C3d-dependent rosette formation. (3) Incubation of the Raji cells at 37 degrees C as well as 4 degrees C before rosette formation resulted in a rhythmic loss and reappearance of C3b receptor reactivity. At room temperature (19-22 degrees C) this effect was much less expressed. There was no influence of preincubation at 4 and 37 degrees C, respectively, on the iC3b and C3d receptor reactivity of Raji cells. (4) Diisopropylfluorophosphate (DFP) present during rosette formation enhanced, within a certain range of concentration, the percentage of C3b-dependent rosette formation. iC3b and C3d receptor reactivity was not influenced. A similar reaction pattern was observed with pokeweed mitogen (PWM)-stimulated tonsil lymphocytes. In the concentrations tested, DFP showed no effect on the rosette formation between C3b, iC3b, and C3d cells, respectively, and unstimulated tonsil lymphocytes. The data presented suggest that C3b receptors on Raji cells undergo some special metabolism, possibly controlled by fluid phase or cell-bound proteases. This might be a common property of C3b receptors on blast-like and transformed cells, differing from that of unstimulated small lymphocytes.

Binding Sites, Antibody↗
PubMed1995

Reduced CD21 (CR2) and CD54 (ICAM-1) expression in MT2 cells with HIV-1 or HIV-2 strains.

Alterations in the expression of cell-surface receptors have been reported in HIV-infected cells for CD4, CD25 (IL-2 receptor), CD2, CD3 and CD8 and CD26. In the present study we provide evidence that CD21 is down-regulated in the human T-lymphoblastoid cell line MT2 after infection with HIV-1 and -2 isolates. The same effect was observed with ICAM-1 (CD54). CD21 expression was monitored by means of fluorescence intensity, its functional ability to bind to C3d and by quantitative measurement of CD21-antigen in supernatants and cell lysates using an immunoassay. In addition, the decrease of CD21 and ICAM-1-specific mRNA suggests a mechanism at a transcriptional level. Our data suggest that HIV might have a direct influence on the receptor expression.

Cell Line, Transformed↗
PubMed1979

Chido, Rodgers and C4. In vivo and in vitro coating of red blood cells, grouping and antibody detection.

C4 sucrose/low ionic strength (LIS)-coated red blood cells (RBC) are excellent for the detection of the previously 'nebulous' antibodies, anti-Chido and anti-Rodgers, as well as for serum/plasma typing of these antigens by an inhibition technique. By enzyme treatment of such cells, it is confirmed that the Ch and Rg antigens reside on the C4d part of the C4 molecule. Freshly taken RBC from normal individuals were examined with a sensitive Auto-Analyzer technique with anti-Chido, anti-C4 and anti-C3 sera. All normal RBC were shown to have C4d and C3d components on their surface. The technique was also very sensitive for the detection of the Ch antigen, which was detected on the RBC of all Chido-positive individuals, and which did not show great variation in strength by this method. The mode of in vivo C4 fixation on normal RBC seems to be different from the fixation in LIS or by RBC antibody-mediated activation.

Antibodies↗
PubMed1990

A study of in vivo immune complex formation and clearance in man.

C and CR1 have been shown to participate in the clearance of injected, preformed, immune complexes in humans and in non-human primates. Their role in the physiologic disposal of immune complexes formed in vivo in humans was investigated in three patients receiving radioimmunotherapy for ovarian carcinoma. On day 0 each patient received, by intraperitoneal injection, 10 mg of 131I-mouse anti-tumor mAb (10 mCi/mg). On days 1 and 2, 18 mg of trace-labeled, 125I-human anti-mouse IgG was administered by i.v. infusion over 15 min, to accelerate the clearance of the 131I-anti-tumor antibody from the circulation and reduce the radiation dose to the marrow. Sequential blood samples were obtained after the injection of the second (anti-mouse) antibody, to monitor clearance. Immune complexes (shown by sucrose gradient centrifugation to be 19 to 40 S in size) formed within 5 min, and were cleared with a half-life of 11 +/- 1.7 min in the liver. Complexes were measured by 4% polyethylene glycol precipitation, and by solid phase C3d- and C1q-binding assays. Between 8 and 11% of the total available complexed material bound to CR1 on E. Peak binding of immune complexes to red cells occurred 10 min after the maximal complex load was detected by precipitation with polyethylene glycol. At that time, immune complexes bound to E constituted one-fifth of the total circulating pool of complexes. Coincident with immune complex formation and clearance, a 47% fall in serum C4, C3, and CH50 was measured, with the deposition of up to 1230 molecules of C4, and 2590 molecules of C3 on the surface of red cells. During 20 min after immune complex formation there was a mean loss of 32% of erythrocyte CR1. The changes in complement and CR1 on E and in serum observed in these patients resembled those seen in patients with SLE: i.e., a reduction in CR1 and an increase in C3 and C4 on E, and reduced serum C.

Adult↗
PubMed1984

p69,71 antigen complex detected by monoclonal antibody Leu 1 in the identification of particular stages of malignant B-cell differentiation.

Lymphomatous cell samples from 86 patients with B-cell neoplasia (34 chronic lymphocytic leukaemia, 8 hairy-cell leukaemia, 5 prolymphocytic leukaemia, 20 immunocytic lymphoma, 9 centrocytic lymphoma, 3 centroblastic/centrocytic lymphoma, 3 lymphoblastic lymphoma, 1 plasma cell leukaemia and 3 plasmacytoma) were studied using the monoclonal antibody Leu 1, detecting a p69,71 antigen complex present on nearly all thymocytes, most (greater than 85%) peripheral T-lymphocytes as well as some malignant B-cells. Furthermore, we compared the reactivity of Leu 1-positive B-cells with those exhibiting conventional surface markers such as mouse-erythrocyte-receptor, FcIgG-receptor, C3b- or C3d-receptor and surface immunoglobulins of the various heavy- and light-chain types. Our results demonstrate a correlation between the expression of p69,71 antigen complex and distinct phenotypes revealed by conventional markers and underline the value of Leu 1 monoclonal antibody in the differential diagnosis of human B-cell neoplasia.

Antibodies, Monoclonal↗
PubMed1994

Urine neopterin: a new parameter for serial monitoring of disease activity in patients with systemic lupus erythematosus.

OBJECTIVE: To investigate the role of serial measurement of urine neopterin concentration in monitoring the progression of systemic lupus erythematosus (SLE) disease activity scored using the British Isles Lupus Assessment Group (BILAG) index. METHODS: We followed prospectively 68 unselected SLE patients for a total of 464 patient months during which 233 separate assessments were carried out. At each assessment, urine neopterin, determined by high performance liquid chromatography, together with erythrocyte sedimentation rate (ESR) and plasma C3, C4, and C3d were measured and the SLE disease activity scored by a single observer. Serial data sets were analysed using time series modelling techniques. RESULTS: Single time point analysis showed a significant increase in urine neopterin concentrations in 14 patients who suffered flares of their disease during the study period (p = 0.02). Thirty patients with active disease went into disease remission with significant decreases in their urine neopterin values (p = 0.02). In the time series analysis, a statistically significant association was found between serial concentrations of urine neopterin and BILAG score (r = 0.6, p < 0.05); no other study parameter (ESR and serum C3, C4, and C3d) mirrored SLE disease activity as effectively. CONCLUSIONS: This study provides initial evidence that changes in urine concentrations of neopterin are significantly correlated with fluctuations in disease activity over time, scored using the BILAG index, amongst individual patients with SLE. Consequently, serial urine neopterin measurements appear to be clinically useful for monitoring disease activity and may contribute substantially to therapeutic decision making in these patients.

Adult↗
PubMed1995

C3-independent glomerulonephritis in guinea pigs: dependence upon primary humoral response.

We used C3-deficient (C3D) guinea pigs to evaluate the role of C3 in an active model of experimental nephritis. Normal strain 2 (C3N, n = 13) and C3D (n = 6) guinea pigs were immunized with cationized bovine gamma-globulin (CBGG). Fourteen days later (Day 0), daily intravenous injections of CBGG were given for 3 to 7 days and the animals were sacrificed on Day 10 or 21. Immunofluorescence (IF) microscopy of renal tissue revealed two patterns of glomerular IgG deposition: granular loop (11/13 C3N, 3/6 C3D), and predominantly mesangial (2/13 C3N, 3/6 C3D). Codeposited C3 was seen in all C3N and in no C3D animals. Electron microscopy showed subepithelial deposits in all. A significant correlation (P < 0.005) was seen between an animal's IF pattern and its level of serum antibodies to CBGG; those with lower antibody levels exhibited the mesangial pattern. C3D animals had lower mean antibody levels than C3N (P < 0.01), but both IF patterns were represented. Urine protein concentration, which was increased relative to controls, did not differ between C3N and C3D groups, but was significantly greater in those with loop IF. Serum albumin was significantly reduced in animals with loop IF. C3N animals showed a significant reduction in mean serum C3. In this model, immune deposit location and degree of proteinuria are independent of C3 deposition and dependent upon the level of antibody response to CBGG. Induction of antibody to CBGG is impaired in the absence of C3.

Animals↗
PubMed1983

The human C3b receptor.

The C3b receptor of human erythrocytes, neutrophils, monocytes, all mature B cells, a subpopulation of T cells, and glomerular podocytes is a single chain glycoprotein that exists in two allotypic forms having Mr's of approximately 250,000 (F) and 260,000 (S). The number of receptors present on erythrocytes varies by eight-fold among different individuals and is genetically regulated by two codominant alleles that are distinct from the alleles determining the structural polymorphism. The number of receptors expressed by neutrophils is subject to rapid increases from 5000 per cell to 40,000 per cell by exposure to nanomolar concentrations of C5adesArg, in vitro, and a similar mechanism is probably the basis for observing increased receptor expression on neutrophils in patients undergoing hemodialysis. Cytoskeletal association of the C3b receptor on monocytes and neutrophils is suggested by experiments demonstrating receptor-mediated phagocytosis, adsorptive endocytosis through coated pits, and restricted lateral diffusion, and by the reciprocal co-redistribution of cross-linked C3b and Fc receptors, and the detergent-insolubility of cross-linked C3b receptors. The factor H-like cofactor activity of the C3b receptor promotes the cleavage of bound C3b to iC3b, C3c and C3d, g, reactions that may enhance the clearance of circulating immune complexes and the generation of ligands for CR2 and CR3. The inherited partial deficiency of erythrocyte C3b receptors in patients with SLE, and the absence of glomerular C3b receptors in these patients with proliferative glomerulonephritis may contribute to systemic and organ-specific abnormalities in the clearance of immune complexes that contribute to the pathogenesis of this disease.

Endocytosis↗
PubMed1991

Fungal cell adhesion molecules in Candida albicans.

Adherence of Candida albicans to host tissues is considered a crucial step in the pathogenesis of candidiasis. Using in vitro assays, it was demonstrated that the yeast-mycelium transition was an important phenomenon in the acquisition of adhesive properties. Proteins with MWs of 60, 68, 200 and greater than 200 kDa seemed to be involved in germ tube adherence to plastic surfaces. Likewise, recent investigations have revealed that C. albicans expresses on its surface receptors which interact with a wide variety of host proteins, particularly some extracellular matrix components like fibronectin, laminin and collagen. Plasmatic components, such as fibrinogen, iC3b and C3d, have also been proposed as mediators of adherence of C. albicans. Thus, by their reaction with laminin, fibrinogen and C3d, the mannoproteins of 68 and 60 kDa demonstrated multiple biological activities. Proteins of similar MWs were detected as C3d and iC3b receptors, the latter showing similarities with the neutrophil CR3. Based upon the antigenic, structural and functional homologies between the candidal receptors and mammalian integrins, it was postulated that these fungal cell adhesion molecules (F-CAM) are members of the integrin family. Interactions with host proteins and molecular mimicry of mammalian adhesion molecules may be a fertile area for further research.

Basement Membrane↗
PubMed1994

Interactions of opsonized immune complexes with whole blood cells: binding to erythrocytes restricts complex uptake by leucocyte populations.

The binding of opsonized, fluorescein-labelled bovine serum albumin (BSA)/rabbit anti-BSA complexes (IC) to washed human whole blood cells and isolated leucocytes in the presence of autologous serum was investigated by flow cytometry. In the presence of erythrocytes (E), the IC-binding to granulocytes (PMN), monocytes and lymphocytes was inhibited by up to 46%, 61% and 48%, respectively, depending on the incubation time and the IC-concentration tested. The E-mediated inhibition of the binding to PMN was found to correlate with the average numbers of CR1 per E during the initial 15 min of incubation. Thereafter, the difference between IC binding to PMN in absence and presence of E, decreased in accordance with decreasing binding to E. IC-uptake by PMN induced a drop in side-scatter characteristics, attributable to degranulation, which could be prevented by the presence of E. In contrast to the findings for PMN, the difference between IC-binding to monocytes in the absence and presence of E increased progressively over the 90 min observation period, suggesting that different mechanisms are involved in the late-phase IC uptake by monocytes and PMN. Lymphocytes were heterogeneous with respect to IC binding, the main contributors being B cells. E initially inhibited and then later enhanced the IC binding to lymphocytes, suggesting that E promote B cell uptake of C3d,g-covered IC via CR2. Our findings, that E can restrict the IC uptake by circulating leucocytes, and that an IC-induced degranulation of PMN may be prevented by E, indicate that E may act as a high capacity buffer limiting inappropriate activation of phagocytes by circulating IC.

Antigen-Antibody Complex↗
PubMed1977

C3b receptors in glomerular disease.

Using two indicator systems--sheep erythrocytes or fluoresceinated S. typhi coated with C3b the presence of a receptor for C3b (but not C3d) in the normal human glomerulus is confirmed. No receptor could be detected in other species tested (mouse, rat, guinea-pig, rabbit and rhesus monkey). Binding of indicator particles was reduced or lost in diseases associated with glomerular capillary deposition of C3, but not in those with mesangial deposition alone. However in some cases the receptor was lost in the absence of detectable C3 deposition. No receptors were detected in proliferating cells in glomerular crescents.

Animals↗
PubMed1995

Pep34, a synthetic peptide whose sequence corresponds to the intracytoplasmic domain of the Epstein-Barr virus receptor (CR2, CD21), regulates human B lymphocyte proliferation triggered through CR2.

CR2 is involved in regulation of human B lymphocyte proliferation by interacting, through distinct domains, with extracellular, cell surface or intracellular components. Contribution of CR2 intracytoplasmic domain in CR2 regulatory functions remains unclear. Thus, we used pep34, a 34 amino acid synthetic peptide whose sequence corresponds to CR2 intracytoplasmic domain. Pep34 was incorporated into B lymphocytes which were then activated by EBV or C3d through CR2. Our data demonstrate that pep34 inhibits 100% B lymphocyte proliferation triggered by EBV or C3d. Irrelevant peptide had no effect. When B lymphocyte proliferation was triggered by a multipotent B cell activator as SAC, pep34 did not exert any inhibitory effect. Our data demonstrate that pep34 inhibits B lymphocyte proliferation only when lymphocytes are triggered through CR2. Thus, this strongly supports that despite its short length. CR2 intracytoplasmic domain participates to regulatory functions of this receptor.

Amino Acid Sequence↗