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PubMed2005

Low erythrocyte complement receptor type 1 (CR1, CD35) expression in preeclamptic gestations.

PROBLEM: Erythrocyte complement receptor type 1 (E-CR1) is the main immune complex clearance mechanism in humans. Decreased E-CR1 expression is noted in certain inflammatory disorders. Recent evidence implicates inflammation in the pathogenesis of preeclampsia. We investigated whether E-CR1 is decreased in preeclampsia. METHOD OF STUDY: E-CR1 protein expression was quantified by radioimmunoassay. Plasma concentration of soluble CR1 was quantified using a specific enzyme linked immunosorbent assay. Quantitative genotypes were evaluated by HindIII restriction fragment length polymorphism analysis. RESULTS: E-CR1 expression was reduced in patients with preeclampsia. Lack of neoantigen expression (indicative of enzymatic cleavage of CR1) or elevated plasma-soluble CR1 was evidence against an acquired loss of E-CR1. Genotype analysis revealed a higher frequency of a CR1 allele associated with low E-CR1 expression in preeclampsia when compared with normal pregnant controls. CONCLUSIONS: E-CR1 expression is decreased in preeclamptic patients and levels correlate with severity of disease. This condition may have a genetic basis in some patients.

Erythrocytes↗
PubMed2000

Expression of human complement receptor 2 (CR2, CD21) in Cr2-/- mice restores humoral immune function.

Complement receptor type 2 (CR2, CD21) is expressed by both human and murine B cells and has been demonstrated to play a pivotal role in the humoral immune response. We have reconstituted Cr2-/- mice with an 80-kb human genomic fragment (designated P1-5) containing the full-length human CR2 (hCR2) gene. Transfection of P1-5 into the mouse A20 B cell line confirmed that it would direct expression of the hCR2 protein in mouse B cells. Immunoprecipitation analysis in these cells revealed that hCR2 coassociates with mouse CD19. After creation of transgenic mice using P1-5, we found significant expression of hCR2 on peripheral blood and splenic B cells by flow cytometric analysis. RT-PCR analysis of tissues and purified cell populations from transgene-positive mice revealed that hCR2 expression was restricted to B cells and the spleen in a pattern that matches mouse CR2. To rigorously assess the functional capabilities of hCR2, the transgene was bred onto Cr2-/- mice, which have a notable defect in response to SRBC Ag. We found that Cr2-/- mice expressing hCR2 had a substantial restoration of the humoral immune response to SRBC as compared with nontransgenic Cr2-/- littermate controls. Overall, this study suggests that hCR2 is able to substitute for mouse CR2 in the murine immune system. Therefore, hCR2-transgenic mice offer a valuable model system to further examine immunologic roles as well as structure-function relationships important for hCR2 function in primary cells in vivo.

Animals↗
PubMed1985

Disease-associated loss of erythrocyte complement receptors (CR1, C3b receptors) in patients with systemic lupus erythematosus and other diseases involving autoantibodies and/or complement activation.

Although surface membrane density of complement receptor type one (CR1) on erythrocytes (E) is probably an inherited trait among normal individuals, recent evidence from our laboratories suggests that the reduced number of CR1 per E observed in patients with systemic lupus erythematosus (SLE) results from acquired as well as genetic factors. In the present investigation, the number of CR1 per E was quantitated with 125I-monoclonal anti-CR1 and was found to vary inversely with disease activity in patients with SLE who were followed serially for as long as 14 mo. Although evidence for E surface-bound immune complexes or fixed C3b/iC3b was not obtained, periods of disease activity and low amounts of CR1 per E correlated with the presence of 100 to 800 molecules per E of fixed C3dg fragments (less than 100 C3dg per E in normal subjects). Reduced CR1 and excess fixed C3dg on E also were observed in patients with other disorders associated with complement activation, including chronic cold agglutinin disease, autoimmune hemolytic anemia, paroxysmal nocturnal hemoglobinuria (PNH), Sjögren's syndrome, and mycoplasma pneumonia. A significant negative correlation (r = -0.498) between CR1/E and fixed C3dg/E was demonstrable in 255 individual assays evaluated by regression analysis. CR1 decreased and fixed C3dg increased during active disease; the converse was obtained during remission. In patients with active SLE, both serum complement activity and E CR1 decreased, whereas fixed C3dg fragments increased. By piecewise linear regression analysis, the appearance of 100 to 400 C3dg molecules on patients' E corresponded to a 27 to 60%, reduction in the number of CR1 per E (p less than 0.0002), confirming that fixation of C3 to E was correlated with a loss of CR1. In patients with PNH, low values for CR1 were observed on moderately complement-sensitive PNH type II E in association with increased fixed C3 fragments; however, the markedly complement-sensitive PNH type III E had essentially normal amounts of CR1 and bore little fixed C3. The addition of soluble DNA/anti-DNA immune complexes to normal blood generated levels of fixed C3dg fragments on E comparable to those observed on E from patients with SLE. Kinetic experiments indicated that C3b was fixed to E during the process of immune complex binding and release from E CR1, and that this fixed C3b was subsequently degraded rapidly to fixed iC3b and more slowly to fixed C3dg without the loss of CR1 that occurs in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)

Anemia, Hemolytic↗
PubMed1981

Distribution of complement receptor subtypes in non-Hodgkin's lymphomas of B-cell origin.

Surface receptors specific for either the C4b (CR1) or C3d (CR2) component of complement were examined on the neoplastic cells from 30 cases of non-Hodgkin's lymphoma of B-cell origin and on cells derived from 9 normal lymphoid tissues. Lymphocyte suspensions from non-neoplastic peripheral blood, tonsils, and lymph node contained three categories of complement receptor lymphocytes (CRL): cells with receptors for both C4b and C3d (CR1+, CR2+); cells with receptors for C4b but not C3d (CR1+, CR2-), and cells with receptors for C3d but not C4b (CR1-, CR2+). The mean of the proportion of total CRL expressing receptors only of C3d (CR1-, CR2+) was 0.35 for non-neoplastic tissues and 0.28 for malignant lymphomas of follicular center cell (FCC) origin. However, the proportion of cells with this phenotype was significantly higher in well differentiated lymphocytic lymphomas (WDL) and chronic lymphocytic leukemia (CLL) (0.65) and in intermediately differentiated lymphocytic lymphomas (IDL) (0.59). Histologic compartmentalization of the CRL subtypes was observed in frozen sections of normal lymphoid tissue. CR1+ cells were present in lymphoid follicles interfollicular areas, and in splenic red pulp. CR2+ cells were confined to lymphoid follicles. These findings strongly suggest that complement receptor phenotypes may be useful markers of B-cell differentiation.

B-Lymphocytes↗
PubMed1991

Immune complex binding efficiency of erythrocyte complement receptor 1 (CR1).

C3b-coated immune complexes adhere to the complement receptor 1 (CR1, CD35) on human erythrocytes. This multi-valent binding might be favoured by the known clustering of CR1 and by the multiple C3b-binding sites on each CR1. The size of the CR1 clusters correlates directly with the number of CR1/erythrocytes, and the different structural CR1 alleles bear between two and five C3b-binding sites. Using radiolabelled hepatitis B surface antigen-antibody complexes, we investigated whether CR1 numbers and structural alleles modulate the ability of erythrocytes to bind immune complexes, and assessed if any reorganization of immune complexes takes place at the erythrocyte surface after the initial binding reaction. The binding efficiency (immune complexes/CR1) correlated with CR1 number as determined by the maximal binding at 4 degrees C, the kinetics of binding at 37 degrees C, and the binding in the presence of excess immune complexes and of immune complexes of small size. Binding efficiencies were similar for erythrocytes with low CR1 from normal subjects and patients with AIDS or SLE. A monoclonal antibody blocking the C3b-binding sites (3D9) of CR1 interfered with binding efficiency at a lower concentration on cells bearing low CR1 numbers, suggesting that CR1 clustering is essential. The larger alleles of CR1 (DD and BB) were more efficient than AA alleles. The distribution of immune complexes, visualized by immunofluorescence, was heterogeneous on erythrocytes: about two out of three cells bore between one and 12 immune complexes. No visible immune complex reorganization took place after initial binding, as prefixed erythrocytes displayed the same immune complex distribution and number/erythrocytes as unfixed erythrocytes. The contribution of CR1 alleles in immune complex binding efficiency was confirmed by morphological analysis. These results demonstrate that immune adherence efficiency is the resultant of the CR1 clustering, as well as the particular alleles carried by erythrocytes. Moreover, there is little or no immune complexes surface reorganization after the initial binding reaction.

Antibodies, Monoclonal↗
PubMed1975

Different roles of IgG and complement receptors in phagocytosis by polymorphonuclear leukocytes.

The functions of IgG and complement receptors in phagocytosis of immune complexes by mouse polymorphonuclear leukocytes were examined by in vitro experiments. The immune complexes were sheep red cells (E) sensitized with IgG antibody (EA) or with antibody and complement (EAC). Inhibition experiments with Fab fragments of rabbit IgG antibody anti-mouse IgG have shown that the complement receptor is primarily involved in the attachment phase, whereas participation of the IgG receptor is necessary for inducing the mechanism of phagocytosis. The possible relevance of these findings for the in vivo mechanism of defense infection, and for the control of antibody synthesis is discussed.

Animals↗
PubMedDate not supplied

[Erythrocyte complement receptor (C3b) expression in multiple sclerosis].

The study was carried out in 121 patients with multiple sclerosis and a control group of 519 healthy individuals. In 13 cases of multiple sclerosis and 12 controls family studies were carried out. Complement receptors (C3bR) on the erythrocytes were demonstrated by the haemagglutination test using human IgG heat-aggregated and guinea pig serum which served as a source of complement. On the basis of haemagglutination intensity and results of radioimmunoassay three phenotypes of complement receptor were isolated: high HH(C3bRh/C3bRh) producing strong agglutination, medium HL (C3bRh/Cbl) producing weak agglutination, and low phenotype LL (C3bR1/Cbl) in which no visible agglutination of erythrocytes was noted. Considerable differences were observed in the distribution of these phenotypes between controls and multiple sclerosis patients in whom the low phenotype (C3bR1/C3bR1) was more frequent. Family studies of controls suggested presence of two codominant alleles C3bRh and C3bR1 with Mendelian inheritance while similar studies of multiple sclerosis patients it was found that e.g. a child with multiple sclerosis whose parents had high C3bR phenotypes, that it were homozygotes for the C3bRh gene, had low phenotype. On the other hand, the high phenotype was found in a child of a female multiple sclerosis patient with the low phenotype (C3bR1/C3bR1). These observations suggest that reduced expression of the complement receptor on the erythrocytes depends in multiple sclerosis on the disease process in the first place, and not on genetic factors.

Adult↗
PubMed1980

Complement receptors on normal human lymphocytes containing parallel tubular arrays.

Membrane complement receptors have been identified on a subpopulation of normal lymphocytes containing cytoplasmic inclusions called parallel tubular arrays (PTA) using two different rosetting techniques. The first technique utilizes as indicator cells erythrocytes that were coated with complement by the classic pathway of complement activation (EAC rosettes). The second technique utilizes as indicator cells Salmonella typhi, which were coated with complement by the alternate pathway of complement activation (FBC rosettes). In the latter technique, lipopolysaccharide material in the bacterial cell wall directly activates complement without the use of a sensitizing antibody. This eliminates binding of marker particles by lymphocytes having Fc receptors. The presence of PTA lymphocytes at the center of EAC rosettes and FBC rosettes was demonstrated by electron microscopy, indicating that the PTA lymphocyte has a complement receptor. Examination of FBC rosettes revealed that the adherent complement-coated bacteria were usually partially surrounded by pseudopodal extensions of the PTA lymphocyte. In addition, some PTA lymphocytes phagocytized the complement-coated bacteria but not the complement-inactivated bacteria. These phagocytic cells were placed in the lymphocytic series instead of the monocytic series by virtue of complete lack of endogenous peroxidase activity.

Bone Marrow↗
PubMed1988

Recombinant human tumor necrosis factor increases granulocyte cell-surface complement receptor number.

Exposure of human buffy-coat granulocytes to tumor necrosis factor (TNF) produced cellular activation as indicated by an increase in the neutrophil and monocyte cell-surface number of C3b receptors (measured by indirect immunofluorescence). The degree of receptor increase depended on the dose of TNF from 25 to 1250 pg/mL. Results of kinetic analysis confirmed this response: TNF, 250 pg/mL, caused an increase in the C3b receptor number within ten minutes. Purified neutrophils exhibited a similar increase in cell-surface C3b receptors dependent on the concentration of TNF. Tumor necrosis factor could be a mediator of granulocyte activation in patients.

Granulocytes↗
PubMed1993

Expression and functional characteristics of the complement receptor type 2 on adult and neonatal B lymphocytes.

In vivo antibody synthesis against thymus-independent type 2 (TI-2) antigens such as type-specific polysaccharides of pneumococci is low or absent during the first 2 years of life. Recently, we described a role for CR2 in the in vitro antibody response of B cells of adults to the TI-2 antigen type 4 pneumococcal polysaccharide. In the present study a decreased expression of CR2 is described on cord blood B cells using HB5 and OKB7 anti-CR2 MAb. Crosslinking of HB5 anti-CR2 antibodies on the B cell membrane leads to increases in intracellular calcium ([Ca2+]i) in both adult and neonatal B cells. In adult B cells, a synergism between CR2 and sIgM could be demonstrated on the level of calcium mobilization by occupying CR2 and crosslinking of sIgM with substimulatory concentrations of anti-IgM antibodies. This synergistic action between CR2 and sIgM could not be demonstrated in neonatal B cells. In addition, it is demonstrated that HB5 MAb cannot induce B cell differentiation in neonatal B cells, while adult B cells can be induced to differentiate into Ig-producing cells by this MAb.

Adult↗
PubMed1998

Analysis of complement receptor type 1 (CR1) expression on erythrocytes and of CR1 allelic markers in Caucasian and African American populations.

CR1 expression on erythrocytes (E) is regulated by an element that is tightly linked in Caucasians to the site of an RFLP of the CR1 gene. Genomic HindIII fragments of 7.4 and 6.9 kb identify alleles that are expressed in high (H allele) or low (L allele) amounts, respectively. When age-fractionated E of donors heterozygous for both the H and L alleles and for CR1 allotypes of differing molecular weights were analyzed in Western blots, the product of the L allele appeared to have an increased rate of loss during cell aging. A coding sequence polymorphism of CR1 predicted to cause a Pro-->Arg substitution in its proximal extramembranous region was tightly linked in Caucasians to the site of the HindIII RFLP. However, neither this polymorphism nor the HindIII RFLP correlated with CR1 expression among African Americans. Relative instability of CR1 encoded by the L allele thus may derive from another coding sequence polymorphism, or may require both the Pro-->Arg substitution and epistatic effects of another polymorphic gene.

Alleles↗
PubMed1986

Clinical and laboratory features of patients with an inherited deficiency of neutrophil membrane complement receptor type 3 (CR3) and the related membrane antigens LFA-1 and p150,95.

Over the last 3 years a group of more than 20 patients has been described worldwide who have a similar history of recurrent bacterial infections and an inherited deficiency of three related leukocyte membrane surface antigens known as CR3, LFA-1 (lymphocyte function-associated antigen type 1), and p150,95 (function unknown). These antigens share a common beta-chain structure linked noncovalently to one of three distinct alpha-chain types. It is believed that the patients with this disease have a reduced or absent ability to synthesize the common beta subunit of the antigen family, resulting in absent or reduced expression of all three antigen family members on different leukocyte types. Neutrophils have a reduced phagocytic and respiratory burst response to bacteria and yeast as well as a reduced ability to adhere to various substrates and migrate into sites of infection. In vitro functional studies of normal neutrophils, monocytes, and lymphocytes treated with monoclonal antibodies to the individual alpha and beta chains of these antigens suggest that most of the clinical features of the patients may be due to the neutrophil and monocyte deficiency of CR3. Although natural killer-cell activity is diminished or absent, no immune deficiency of the patients' lymphocytes attributable to the absence of LFA-1 has been detected. Diagnosis of this disease has been facilitated by the commercial availability of monoclonal antibodies specific for the alpha chains of CR3 and p150,95.

Adolescent↗