Assay for the two different types of lymphocyte complement receptors

The crystal structure of human CD21: Implications for Epstein-Barr virus and C3d binding

Human complement receptor type 2 (CD21) is the cellular receptor for Epstein-Barr virus (EBV), a human tumor virus. The N-terminal two short consensus repeats (SCR1-SCR2) of the receptor interact with the EBV glycoprotein gp350/220 and also with the natural CD21 ligand C3d. Here we present the crystal structure of the CD21 SCR1-SCR2 fragment in the absence of ligand and demonstrate that it is able to bind EBV. Based on a functional analysis of wild-type and mutant CD21 and molecular modeling, we identify a likely region for EBV attachment and demonstrate that this region is not involved in the interaction with C3d. A comparison with the previously determined structure of CD21 SCR1-SCR2 in complex with C3d shows that, in both cases, CD21 assumes compact V-shaped conformations. However, our analysis reveals a surprising degree of flexibility at the SCR1-SCR2 interface, suggesting interactions between the two domains are not specific. We present evidence that the V-shaped conformation is induced by deglycosylation of the protein, and that physiologic glycosylation of CD21 would result in a more extended conformation, perhaps with additional epitopes for C3d binding.

Identification of murine complement receptor type 2

A rabbit antiserum reactive with the human complement component C3d/Epstein-Barr virus receptor (complement receptor type 2, CR2) immunoprecipitates a Mr 155,000 murine B-cell surface antigen. The apparent molecular weight and cellular distribution of this murine antigen are similar to those of human CR2. Cells expressing the murine protein bind sheep erythrocytes coated with antibody and murine C1-C3d but do not bind Epstein-Barr virus at all. The monospecific antiserum to human CR2 together with goat F(ab')2 anti-rabbit IgG blocks attachment of the C3d-coated erythrocytes to receptor-bearing murine B lymphocytes. To further characterize murine CR2, a lambda gt11 library from the murine late pre-B-cell line 70Z/3 was screened with human CR2 cDNA. A partial cDNA clone of 3.5 kilobases with 79% amino acid sequence identity to human CR2 in the unique intracytoplasmic region and 63% identity to the sixth human CR2 repeat was obtained. Blot hybridization with the murine cDNA clone identified an RNA species of approximately 4.7 kilobases, similar in size to human CR2 mRNA, from a murine B-cell line but not from a murine T-cell line.

Morphologic, cytochemical and neurochemical characterization of the human medulloblastoma cell line TE671

Medulloblastoma cell line TE671 was characterized by morphologic, cytochemical, neurochemical, and growth criteria. In contrast to the uniform, in vivo histopathologic appearance of the tumor, TE671 in vitro exhibits six morphologic subtypes (Types I-VI) in varying percentages over 14 days in culture. TE671 grows as a monolayer by the merging of separate foci. Cells were positive for Periodic acid Schiff (PAS) and reticulum, and negative for the glial marker, glial fibrillary acid protein (GFAP). Receptors for human C3b (EAC) were present on 19% of the cells. Neural associated isoenzymes, neuron specific enolase (NSE) and creatine kinase (CK-BB) were demonstrated in TE671. Progeny of a single clonogenic cell manifested the morphologic heterogeneity of cell types (I-VI). The absence of markers specific for glial cells suggests that TE671 is an early (less differentiated) precursor. TE671, the only continuous human medulloblastoma cell line, provides an experimental model with which to compare and identify the subpopulation of neoplastic cells in medulloblastoma ex vivo.

Localization of the binding site on IgG for solubilized placental Fc gamma receptor

Placental Fc gamma R (FcR) inhibited the rosette formation between monocytes and rabbit IgG-sensitized erythrocytes (EA), whereas the rosette formation with granulocytes was not impaired. Staphylococcal protein A (SpA) inhibited the rosette formation with both cell types. Results obtained in absorption and agglutination experiments showed that SpA blocked the binding of FcR to IgG, and Cl did not. Furthermore, FcR did not interfere with the binding of SpA to IgG, whereas C1 affected this binding. FcR apparently bind to the C gamma 3 region. Since FcR inhibited the binding of EA to monocytes, the monocyte FcR binding site is probably also located within the C gamma 3 region.

Coupling of C3b to erythrocytes by disulfide bond formation: preparation of EC3b for hemolytic and complement receptor assays

We describe a new method of preparing C3-coated erythrocytes by coupling C3 to thiol-activated erythrocytes. The procedure involves three steps. Firstly, sheep erythrocytes were treated with N-succinimidyl 3-(2-pyridyldithio) propionate (SPDP) to introduce 3-(2-pyridyldithio) propionyl residues into membrane proteins. Secondly, C3 was cleaved with trypsin or CoVF, Bb enzyme to obtain C3b exposing the SH group (C3b-SH). Finally, the C3b-SH was coupled to the thiol-activated erythrocytes (TA-E) through thiol/disulfide exchange to form the TA-EC3b conjugate. E coated with C3d was prepared by treating TA-EC3b with KSCN inactivated serum and plasmin. Studying the rosette formation between TA-EC3b or TA-EC3d and cells expressing C3b (CR1) and C3d (CR2) receptors and the inhibition thereof with anti-CR1 and anti-CR2 antibodies as well as with C3-sheep E membrane protein complexes, we found that TA-EC3b and TA-EC3d bound exclusively to CR1 and CR2, respectively. In addition, TA-EC3b like EAC1423b bound factors B and H as tested by hemolytic and direct binding assays. The advantage of TA-EC3 for complement receptor and hemolytic assays are the simplicity of the preparation method and the general applicability of the TA-EC3.

Immunologic status in infants and children following surgery

The investigation of cellular and humoral immunologic parameters (T and B lymphocytes and immunoglobulins) with respect to postoperative infection in children revealed changes in the T lymphocytes in particular. Preoperative complications (ileus, shock, infection), anesthesia and surgery lead to transient immunosuppression. The duration of this T cell suppression is age-dependent; suppression is longest in newborns (up to three weeks on the average) and shortest in older children (one week on the average). IgA and IgG concentrations show only slight abnormal changes; IgM concentrations, however, increase significantly during the postoperative period in all age groups. Prophylactic and therapeutic measures for the prevention of postoperative infections can be considered on the basis of immunologic changes related to surgery.

Effect of infectious bovine rhinotracheitis virus infection on bovine alveolar macrophage function

Bovine alveolar macrophages isolated in culture were assessed for immunological activity in assays for Fc and complement receptors, for phagocytosis, and for effector cell function in antibody-dependent cell cytotoxicity. In the case of uninfected alveolar macrophages, Fc receptors were detected on approximately 94% of macrophages and complement receptors were detected on 39%. Phagocytosis of immunoglobulin G-coated sheep erythrocytes occurred in 58% of macrophages, and phagocytosis of opsonized Candida parapsilosis, mediated by the complement receptor, was observed in 68% of cells. Alveolar macrophages were efficient effector cells in antibody-dependent cell cytotoxicity. Infection of macrophages with infectious bovine rhinotracheitis (IBR) virus resulted in reductions in Fc-mediated receptor activity and phagocytosis after approximately 12 and 6 h, respectively. Complement receptor activity was initially elevated and then markedly reduced. Macrophages retrieved from IBR-immune and -susceptible donors were affected to a similar extent. The ability of macrophages to participate in antibody-dependent cell cytotoxicity was reduced dramatically from 2 h after IBR virus infection, suggesting that IBR virus-infected alveolar macrophages undergo alterations in immunological activity long before morphological changes in the cells become apparent.

Surface IgM kappa of prolymphocytic leukaemia cells with antibody activity to surface antigens of sheep and guinea-pig red blood cells

The immunological findings of a B-cell prolymphocytic leukaemia forming spontaneous rosettes with sheep (SRBC) and guinea-pig red blood cells (GPRBC) are reported. The B-cell lineage was revealed by Ia-like antigen, surface IgM kappa and lack of cytotoxicity of anti-human T-cell serum. Despite B-cell characteristics, prolymphocytes formed spontaneous rosettes with SRBC. Inhibition procedures demonstrated rosette formation to be the result of antibody activity of surface IGM to SRBC and GPRBC. Pretreatment of prolymphocytes with pronase or antibodies to mu or kappa-chains inhibited rosette formation. Furthermore, pre-treatment of SRBC with the patient's serum or IgM decreased rosette formation demonstrating circulating antibodies to antigen(s) of SRBC. Antigen(s) on SRBC and GPRBC are not related to Forssman or Paul Bunnel antigen.

Isolation of lymphocyte membrane complement receptor type two (the C3d receptor) and preparation of receptor-specific antibody

A glycoprotein binding complement component C3d was isolated from media used for culture of Raji human lymphoblastoid cells. Analysis by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and gas/liquid chromatography indicated that the C3d-binding glycoprotein consisted of a single polypeptide chain with extensive intrachain disulfide bonds, a molecular weight of 72,000, and several different bound carbohydrates. Several lines of evidence indicated that this medium-derived C3d-binding protein originated from membrane complement receptor type two (CR2, the C3d receptor), presumably shed during membrane turnover. The C3d-binding protein bound to sheep erythrocytes coated with C3d (EC3d) but not to sheep erythrocytes coated with C3b (EC3b). Antisera, prepared by immunization with the purified C3d-binding glycoprotein, inhibited lymphocyte rosette formation with EC3d but not with EC3b. Analysis by sodium dodecyl sulfate gel electrophoresis of the radiolabeled and solubilized lymphocyte antigens reactive with the anti-C3d-binding protein sera revealed a single-chain cell-surface protein of molecular weight 72,000 that was apparently identical to the isolated C3d-binding protein. Parallel assay of lymphocytes for Cr2 by direct immunofluorescence with F(ab')2 anti-C3d-binding protein (anti-CR2) and rosette formation with EC3d indicated that both assays had the same specificity and nearly the same sensitivity. With both systems CR2 expression was limited to B cells, and was undetectable on T cells, monocytes, or neutrophils.

Release of endogenous C3b inactivator from lymphocytes in response to triggering membrane receptors for beta 1H globulin

Human bone marrow-derived lymphocytes and cells from B lymphoblastoid lines were shown to have specific membrane receptors for beta 1H globin. Lymphocytes responded to the presence of beta 1H by releasing endogenously-synthesized C3b-inactivator. Very little spontaneous release of C3b-inactivator occurred in the absence of beta 1H. beta 1H-treated lymphocytes that either lacked complement receptor type one (CR1, the C4b-C3b receptor) or had their CR1 blocked with Fab'-anti-CR1 formed rosettes with C3b-coated sheep erythrocytes (EC3b) by adherence to complement receptor type two (CR2, the C3d-C3bi receptor). The mechanism of the beta 1H-induced EC3b rosette formation was shown to involve the release of lymphocyte C3b-inactivator that cleaved bound C3b into C3bi forming EC3bi. This lymphocytes-generated EC3bi then bound to CR2, forming rosettes. beta 1H-induced EC3b rosettes were completely inhibited by the presence of either anti-C3b-inactivator, F(ab')2-anti-CR2, Fab-anti-C3c, or Fab-anti-C3d, but were unaffected by the presence of fluid-phase concentrations of beta 1H up to 5.5 mg/ml or Fab'-anti-CR1. Analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis and fluorography demonstrated that cell-free supernates of beta 1H-treated lymphocytes cleaved 3H-labeled C3b on EC3b into C3bi. Inhibition studies with chelating agents and sodium azide suggested that the release of C3b inactivator might involve a calcium and energy-dependent transport of this enzyme across the membranes of beta 1H-triggered cells. Because plasma beta 1H and C3b-inactivator are known to have important functions in the distinction of alternative pathway-activating substances from normal tissue, it is possible that this beta 1H receptor-C3b-inactivatory releasing system in lymphocytes may have an analogous function.

Pathopysiological aspects of immune complex diseases. Part II. Phagocytosis, exocytosis, and pathogenic depositions

Elimination of IC by the phagocytic system occurs mainly by macrophages and contrarotates to the pathogenic effect. Decisive to prevent systemic IC disease is the capacity of the phagocytic system. In the case of its saturation, the danger of the occurrence of IC disease is greatly enhanced. Conclusive evidence seems to exist that IC of extremely small or extremely high lattice structure (precipitates) are less pathogenic than soluble IC of medium network. Small IC in extreme antigen and antibody excess or precipitates exhibit a reduced complement activating potency. Small IC in extreme antigen or antibody excess hardly interact in vitro with membrane receptors and do not induce IC disease when injected or formed in vivo. Highly lattices IC, especially precipitates, are eliminated extremely quickly from the circulation, mainly by macrophages and there deposition in the kidney is significantly reduced. Thus, lack of quality of the antibody to precipitate the antigen and a reduced capacity and effectivity of the phagocytic system to eliminate the IC may be extremely important in the generation of IC diseases. Facing the overwhelming and partly even inconsistant data of this topic, one may doubt whether IC diseases may be regarded to be a defined and coherent disease. Too many variables and questions exist concerning the nature of the antigen, especially in tumor and autoimmune diseases, concerning the quality of the antibody and the characteristics of the pathogenic IC and concerning localization and the elimination process. Nevertheless, common pathophysiological pathways of IC diseases may be recognized.

Analysis of the different types of leukocyte membrane complement receptors and their interaction with the complement system

The specificity, distribution, and structure of 8 different types of leukocytes membrane complement (C) receptors (CR1, CR2, CR3, and receptors for C1q, beta 1H, C3e, C3a, and C5a) are discussed. Recent data are reviewed on the synthesis of C components by macrophages and B lymphocytes, and how these components may function in the activation of these two cell type by the C system. Commonly used C receptor assay procedures are evaluated in terms of both specificity and sensitivity. Specific assay procedures are recommended for measuring CR1 (C4b-C3b receptor), CR2 (C3d receptor), CR3 (C3bi receptor), and the beta 1H receptor. Assays include both rosette and fluorescence procedures for detection of C receptors on either mouse or human leukocytes. Primary systems have been selected for optimal sensitivity and specificity, and where possible, acceptable alternative systems that are less sensitive or specific are suggested for laboratories lacking facilities for C purification.

The detection of membrane-associated complement components (C 3 and C 4) on circulating human normal and leukemic leukocytes and on cultured cells with monkey erythrocytes

Monkey erythrocyte (Mk) rosette formation is described as an exquisitely sensitive method for the detection of complement (C) components on the membrane of human leukocytes. Blocking of the immune adherence receptor on Mk blocked subsequent rosette formation as did pretreatment of leukocytes with antiserum to the C components C 3 and C 4. In vitro C deposition by immune complex formation with normal human lymphocytes enhanced Mk rosette formation, and this could be inhibited with antiserum to C 3. The use of Mk rosette formation revealed that cells from a wide variety of human lymphoid and myeloid leukemias carry membrane-bound C. It was also shown that several lymphoblastoid cell lines, including a T cell line, probably synthesize both C 3 and C 4. Mk rosette formation is not dependent on metabolic activity of the rosetting leukocyte, and it is suggested that this technique will be of value in detecting C deposition in a variety of situations.

Human megakaryocytes. I. Characterization of the membrane and cytoplasmic components of isolated marrow megakaryocytes

Human marrow megakaryocytes have been isolated with high purity and yield by processing marrow cells sequentially through density centrifugation and velocity sedimentation. Analysis of the isolated cells for various platelet-associated components by immunofluorescence demonstrated that fibrinogen, plasma factor VIII antigen (factor VIII:AGN) platelet myosin, platelet glycoproteins I and III are present on the membrane and in the cytoplasm of over 90% of marrow megakaryocytes. Parallel studies of human and mouse megakaryocytes and platelets for IgG receptor (FcR), complement receptor type one (CR1) (C3b receptor), complement receptor type two (CR2) (C3d receptor), and Ia antigen by fluorescence and (or) rosette formation methods were performed. FcR were present on most human megakaryocytes and platelets. The Ia antigen was detected on a proportion (10-15%) of human megakaryocytes but it was undetectable on human platelets. CR1 was found on 20-40% of mouse megakaryocytes and also on a proportion of mouse platelets. These differentiation markers may be of use in monitoring megakaryocyte maturation.

Surface markers of complement receptor lymphocytes

Normal blood lymphocytes bearing complement receptors (CRL) were divided into two populations, one expressing both CR1 (C4b-C3b receptor) and CR2 (C3d receptor) and a second expressing only CR1. Nearly all of the population that expressed both CR1 and CR2 also bore membrane surface immunoglobulins (Ig) and Ia antigens. The majority of cells that had only CR1 lacked detectable surface Ig. These Ig- CR1+ CR2- cells could be distinguished from the majority of monocytes and immature granulocytes, in that the latter ingested latex particles and expressed CR2 as well as CR1. The Ig- CR1+ cells were further subdivided into an Ia-bearing subpopulation and another that lacked Ia. Among the Ig- Ia- CR1+ cells, one third formed spontaneous rosettes with sheep erythrocytes while all of the remaining CRL were erythrocyte-rosette negative. Essentially all CRL in normal blood had IgG Fc receptors, but a qualitative heterogeneity in the Fc receptors of Ia+ CRL vs. Ia- CRL was observed in their binding of different immune complex systems.

Surface markers and functional properties of non-Hodgkin's lymphoma cells in relation to histology

Cells from 32 adult patients with non-Hodgkin's lymphoma were studied with respect to surface markers and functional properties in short-term culture. Twenty-six lymphomas were of B-cell origin, including all nodular and diffuse lymphocytic lymphomas. Three tumors were of T-cell origin (one histiocytic lymphoma and two undifferentiated lymphomas). In the remaining three cases (histiocytic lymphomas) the immunological nature of the tumor cells could not be determined. All reactivity to mitogenic stimuli of cells from B-cell lymphomas was due to residual normal T cells. In follicular lymphocytic lymphomas more reactive T cells prevailed among the malignant B cells than in diffuse lymphocytic lymphomas. Heterogeneity among B-cell lymphomas was indicated by differences in intensity of fluorescence with anti-Ig reagents and in stimulatory capacity in mixed lymphocyte culture. T-cell lymphomas were characterized by high percentages of T cells together with impaired responses to stimuli. The results of immunological studies correlated well with the histological classifications of Rappaport, Lukes and Lennert.

Morphological and immunological similarity of the monocytes from pure and mixed monocytic leukaemias

Morphological and immunological marker data on a patient with 'pure' monocytic leukaemia are presented and compared with those of 6 cases of clearly mixed myelomonocytic leukaemia with a variable monocytic component. In all patients studied, the leukaemic monocytes expressed a receptor for the Fc of IgG, and IgG sensitization markedly enhanced phagocytosis of ox erythrocytes. A variable, but lower, percentage of the leukaemic monocytes had a receptor for mouse C3, but the cells uniformly lacked surface immunoglobulin and receptors for the Fc of IgM and for unsensitised mouse erythrocytes. Cytochemical and ultrastructural study also showed no clear difference between the monocytes of the 'pure' and mixed monocytic leukaemias. This report therefore lends no support to the concept of distinct types of monocytic leukaemia.

Receptors for Helix pomatia A haemagglutinin (HP) on a subpopulation of human B cells

Receptors for Helix pomatia A haemagglutinin (HP) have earlier been found on neuramidinase treated T-lymphocytes in human peripheral blood. In contrast, the majority of the B-lymphocytes, characterized by surface bound IgM and/or IgD(SIg)lack these receptors. Double marker experiments with fluorochrome labelled reagents have now shown that a minor fraction (3--24%) of the IgM/d bearing lymphocytes in normal human blood also have HP-receptors. These HP+ B-cells constitute approximately 1% of the HP+ lymphocytes in adult blood. Fractionation on HP-Sepharose columns showed that the HP+ B-cells are readily eluted with buffer containing 0.1 mg N-acetyl-D-galactosamine. In contrast, the majority of the HP+-SIg--cells require higher concentrations of the competing hapten for elution (1 mg D-Ga1NAc/ml buffer). This indicates that the HP-receptors on these B-cells differ qualitatively or quantitatively from those on the majority of the T-cells. Previous findings of HP-receptors on the SIg+ leukaemic cells in the blood of patients with chronic lymphocytic leukemia suggested that these structures are expressed on an immature variety of B-cells. This assumption is favoured by the present finding that approximately 80% of the lymphocytes with surface bound IgM/D in cord blood also have HP-receptors. Therefore, the HP-receptors seems to fall in the category of differentiation markers and constitutes a useful tool for characterization and separation of human lymphocytes within both the T- and the B-compartments.