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PubMed1983

Circulating immune complexes and peripheral B lymphocytes in non insulin dependent diabetic patients.

Serum circulating immune complexes (CIC) were measured in 27 patients with non insulin dependent diabetes (NIDD). This was done by measuring the degree of binding to human red blood cells by the C3b complement fraction. At the same time, the percentage of B lymphocytes in peripheral blood was evaluated by means of the direct immunofluorescence technique for surface IgG and EAC rosettes for cells with receptors to C3b complement fraction. Twenty normal control subjects were simultaneously studied by the same methodology. An increase in serum CIC was observed in NIDD patients, as compared to healthy subjects. Values were 35.8 +/- 3.2 and 25.6 +/- 2.1 micrograms/ml, respectively. The percentage of cells with surface IgG was 10.2 +/- 0.8 in diabetic patients; this value was significantly higher than that found in the control group (6.0 +/- 0.8). No significant quantitative difference in the percentage of EAC binding cells was found between NIDD patients and the control group. When NIDD patients were divided into two groups, those with and those without microvascular complications, neither differences in CIC levels nor in the percentage of B lymphocytes were found. Nor any correlation could be found between the highest individual CIC levels and the highest percentage of lymphocytes with surface IgG. These data show an increase of CIC levels and of cells with surface IgG in NIDD patients who had not received insulin at least not in a constant or prolonged therapy. This could allow us to suspect the existence of antigen-antibody complexes different to insulin-antiinsulin CIC found in insulin dependent diabetes.

Adult↗
PubMed1984

Increased expression of the C3b receptor by neutrophils and complement activation during haemodialysis.

Activation of complement and the relative number of C3b receptors expressed by neutrophils was assessed in patients undergoing haemodialysis with new and reused cellulosic membranes, and with polymethylmethacrylate (PMMA) membranes. Activation of complement was assessed by radioimmunoassay of plasma C3adesArg, and neutrophil C3b receptors were measured by fluorescent flow cytometry of cells indirectly stained with F(ab')2 anti-C3b receptor. During first use of cellulosic dialysis membranes by four patients, the mean expression of C3b receptors by neutrophils in blood taken from the afferent line of the extra-corporeal system after 10, 20, 60 and 120 min of dialysis increased to 127, 189, 255 and 296%, respectively. The mean plasma C3adesArg concentrations in the corresponding samples of blood were 225, 320, 236 and 160% of the pre-dialysis levels. During third and fifth use of the same membranes by these patients, the mean C3b receptor expression by neutrophils did not exceed 150% of the predialysis determination, and correspondingly minimal increases in plasma C3adesArg were observed. Analysis of blood taken simultaneously from the afferent and efferent lines of the first use cellulosic dialysis system indicated that the increase in C3b receptor expression by neutrophils and generation of C3adesArg occurred when blood came in contact with the dialysis membrane. Haemodialysis of four additional patients with the non-complement activating PMMA membrane caused only modest or no increases in neutrophil C3b receptors. Thus, complement activation in vivo is associated with up-regulation of neutrophilic C3b receptors, indicating that this cellular response previously described only in model, in vitro systems, is a physiological mechanism by which this cell can augment its capacity for responding to C3b opsonized material.

Biocompatible Materials↗
PubMed1984

Interaction of C3 with antigen-antibody complexes in the process of solubilization of immune precipitates.

The binding properties of activated C3 to immune complexes were studied by using solubilization phenomenon as a model system. IgG or F(ab')2 immune precipitates were solubilized by the six isolated alternative pathway proteins, and the solubilized complexes were analyzed by SDS-PAGE. As a result of solubilization, we observed some high m.w. bands. Under reducing conditions, the bands with m.w. of 150,000 and 115,000 appeared in the case of IgG and F(ab')2 complexes, respectively. Two-dimensional SDS-PAGE revealed that hydroxylamine treatment resulted in the dissociation of the 150,000-m.w. polypeptide into the C3 alpha-65 and the heavy chain of IgG. Similarly, the 115,000-m.w. polypeptide was dissociated into the C3 alpha-65 and the Fd chain. Therefore, it is likely that iC3b binds covalently to the Fd region of the heavy chain of IgG via an ester bond. Under nonreducing conditions, iC3b-IgG and iC3b-F(ab')2 complexes had apparent m.w. of 340,000 and 270,000, respectively, corresponding to one iC3b molecule bound to one antibody molecule. In addition, a considerable amount of iC3b also binds to antigen molecules via an ester bond. The findings that C3 binds to the F(ab')2 molecules and bovine serum albumin, which contain only a small amount of carbohydrate, suggest that C3 may not bind to the carbohydrate moiety of antibody molecules. Indeed, various carbohydrate molecules did not inhibit the solubilization even at high concentrations. In contrast, acetyl tyrosine having an aromatic ring and a hydroxyl group produced the best inhibition of the solubilization. Furthermore, we demonstrated that generation of C3b in the presence of 3H-tyrosine resulted in covalent binding of the tyrosine specifically to the C3 alpha' chain, indicating that the inhibition of solubilization may be due to the competition between tyrosine and immune complexes for the covalent binding of C3. Thus, it could be concluded that C3 binds covalently to the amino acid residues of antigen and antibody molecules during solubilization.

Amines↗
PubMed1984

Stabilization of the amplification convertase of complement by monoclonal antibodies directed against human factor B.

Three IgM mouse monoclonal antibodies (MoAb), 5B5-A, 2D2-B, and 5B12-A, were prepared by fusion of spleen cells from mice immunized with human B with the SP 2/0 myeloma cell line. They were assessed for their effect on cell-bound and fluid-phase amplification convertases of complement (C) with purified proteins in vitro. 5B5-A and 2D2-B were similar in their effects on cell-bound preformed C3bBb in that they bound to cell-bound C3bBb, stabilized the C3bBb convertase, and rendered the C3bBb convertase relatively resistant to the plasma protein H. These two MoAb were also able to enhance C3 consumption in vitro in reaction mixtures containing C3b, C3, B, and D. At the same time, they presumably stabilized the C3 convertase and caused relative sparing of B hemolytic activity in the reaction mixtures. In contrast, 5B12-A, which also bound to Bb and C3bBb, did not induce any stabilization, but rather caused accelerated decay of cell-bound C3bBb. These results indicate that MoAb against B can have C3NeF-like activity. On the other hand, not all MoAb against B have stabilizing activity on the C3bBb convertase.

Animals↗
PubMed1984

Structure and function of the human C3b receptor.

The human C3b receptor (C3bR) is a glycoprotein that exists in two allotypic forms having Mr values of approximately 250,000 (F) and 260,000 (S). The number of receptors present on erythrocytes varies by eightfold among normal individuals and is genetically regulated by two codominant alleles that are distinct from the alleles determining the structural polymorphism. C5a and C5ades Arg induce rapid increases in the number of receptors expressed by neutrophils in vitro, and probably account for the increased receptor expression on neutrophils in patients undergoing hemodialysis. Cytoskeletal association of the C3bR on monocytes and neutrophils is suggested by experiments demonstrating receptor-mediated phagocytosis and adsorptive endocytosis through coated pits, and by the reciprocal coredistribution of cross-linked C3b and Fc receptors and the detergent insolubility of cross-linked C3bR. The factor H-like cofactor activity of the C3bR promotes the cleavage of bound C3b to iC3b, C3c, and C3d,g, which may enhance the clearance of circulating immune complexes and the generation of ligands for CR2 and CR3. The inherited partial deficiency of the erythrocyte C3bR in patients with systemic lupus erythematosus and the absence of glomerular C3bR in these patients with proliferative glomerulonephritis may contribute to systemic and organ-specific abnormalities in the clearance of immune complexes in this disease.

Complement C4↗
PubMed1984

Defective erythrocyte C3b receptor function associated with low serum complement (C3, C4) concentrations in insulin-dependent diabetes mellitus.

An immune adherence haemagglutination (IAHA) method was used to measure erythrocyte C3b receptor (EC3bR) activity in 110 patients with insulin-dependent diabetes mellitus (IDDM) and 223 controls. Results obtained from IDDM were correlated with serum complement concentrations (C3, C4) as well as with HLA types of the patients. We observed an increased frequency of defective EC3bR in IDDM (26.4%) compared to controls (10.8%, P less than 0.0005). Those patients who had defective EC3bR (IAHA negative) also had lower serum C3 and C4 concentrations than those with normal EC3bR function (IAHA positive). HLA-Dw3 positive patients had lower C4 concentrations than HLA-Dw3 negative patients and more often had defective EC3bR activity, although this difference was statistically not significant. Our results may indicate the close relationship between the risk factors which predispose to both IDDM and systemic lupus erythematosus.

Adolescent↗
PubMed1983

Application of immune-adherence haemagglutination assay to study genetic variability of C3b receptor on human erythrocytes.

Immune-adherence haemagglutination assay with human aggregated IgG (aggIgG) and guinea pig complement was standardized in order to study variability of C3b receptor on human erythrocytes. The results were expressed as the intensity of haemagglutination that corresponded to the density of C3b receptor sites as evidenced by radioimmunoassay results. The expression of C3b receptor was determined in 260 normal individuals. Among studied subjects at least two groups could be clearly distinguished-one with high and another with low expression of C3b receptor. The obtained results showed that despite intensive washing procedures or preincubation at 37 degrees C the low or high expression of C3b receptor did not change, which further supports the notion that the variable expression of C3b receptor on erythrocytes is inherited rather than acquired. It is concluded that standardized haemagglutination technique can be used for semiquantitative determination of erythrocyte C3b receptor and therefore allowing to study genetic variability of this receptor.

Erythrocyte Membrane↗
PubMed1984

[The C3 activating capacity in human serum--measured as monocyte mediated chemiluminescence].

Phagocytosing monocytes form activated oxygen species which can be detected by the luminol-mediated chemiluminescence (CL). C3b-coated particles yield enhanced CL-signals due to their binding to the monocytes' C3b-receptor. Thus, the zymosan-induced monocyte-CL in a medium containing fresh or heat-inactivated serum provides a means of measuring in sera the capacity to activate C3.

Biological Assay↗
PubMed1984

Phagocytosis by human monocyte-derived macrophages. Independent function of receptors for C3b (CR1) and iC3b (CR3).

Human monocytes and monocyte-derived macrophages were examined for their ability to bind and ingest C3-coated sheep erythrocytes (E). Greater than 90% of monocytes and macrophages formed rosettes with EC3b and EC3bi prepared with 15,000-20,000 molecules of C3 per E. Binding of EC3b to the monocyte or macrophage surface was inhibited by rabbit anti-C3b receptor (CR1), but was not inhibited by two different monoclonal anti-C3bi receptor (CR3) antibodies. EC3bi rosette formation was inhibited by monoclonal anti-CR3, but not by anti-CR1. Monocytes and macrophages did not form rosettes with similarly prepared EC3d,g or EC3d. Macrophages cultured for 7 days, but not freshly isolated monocytes, phagocytosed both EC3b and EC3bi. This ability was a consequence of macrophage maturation, as no external stimuli were present during in vitro culture. Experiments directed to determine if EC3b was converted to EC3bi before ingestion suggested that macrophage CR1 and CR3 mediated phagocytosis independently. No evidence was obtained that during the phagocytosis assay, macrophage factor I converted EC3b to EC3bi. The number of E bound or ingested by monocytes and macrophages was dependent on the number of molecules of C3b or iC3b bound per E. Monocytes and macrophages did not require the presence of either Ca++ or Mg++ for rosette formation with EC3b, whereas both divalent cations were required for optimum rosette formation with EC3bi. The presence of divalent cations was required for macrophage phagocytosis of EC3b and EC3bi. For ingestion of EC3b, Mg++ alone was sufficient, and the addition of Ca++ did not increase the number of EC3b ingested. For ingestion of EC3bi, both Ca++ and Mg++ were required for optimal phagocytosis, and their effect was concentration dependent and additive.

Calcium↗
PubMed1982

Ligand binding specificity of a rabbit alveolar macrophage receptor for C3b.

We have recently reported the isolation from rabbit alveolar macrophages of a receptor which retained its ligand-binding activity for the third component of complement (C3) and for its major proteolytic derived activation fragment (C3b). The isolated receptor demonstrated a greater ability to bind C3b than an equimolar amount of C3. C3b differs from C3 in at least two ways: it is a proteolytic cleavage product of C3 and it lacks the internal thiolester bond of C3. We have analyzed the binding ability to isolated receptor to various C3 and C3b analogs and we demonstrate that the specificity of the C3b-C3b receptor interaction depends upon the lysis of the C3 thiolester bond and accompanying conformational change rather than upon proteolytic cleavage of the C3 molecule. Minimal, if any, binding of C3 with an intact thiolester bond to the isolated receptor was demonstrable.

Animals↗
PubMed1994

The leukocyte integrin p150,95 (CD11c/CD18) as a receptor for iC3b. Activation by a heterologous beta subunit and localization of a ligand recognition site to the I domain.

p150,95 is a member of the leukocyte integrin family of adhesion proteins. Compared with LFA-1 and Mac-1, p150,95 is less well functionally characterized. Although p150,95 has complement receptor activity for iC3b and has been designated complement receptor type 4, transfected cells expressing p150,95 do not bind iC3b-sensitized cells. We report that cells cotransfected with a human p150,95 alpha subunit and a chicken, but not human, beta subunit bind IgM-iC3b-coated erythrocytes, suggesting that interactions between the alpha and beta subunits can regulate p150,95 adhesiveness. Furthermore, purified human p150,95 binds to cell-bound iC3b-coated erythrocytes. Because binding to iC3b by cellular and purified p150,95 is specifically abolished by mAbs that localize to the I domain of p150,95, we suggest that the I domain of the p150,95 alpha subunit is an important ligand recognition site for iC3b.

Animals↗