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PubMed1991

Two major serum components antigenically related to complement factor H are different glycosylation forms of a single protein with no factor H-like complement regulatory functions.

Factor H is a 150-kDa serum glycoprotein with key regulatory functions in the alternative pathway of complement activation. Two glycoproteins with a molecular mass of approximately 42 and 37 kDa that react with an antiserum against factor H were purified from human plasma. The two glycoproteins have identical N-terminal amino acid sequences but differ in glycosylation. Sequence comparisons indicated that they both correspond to a 1.4-kb mRNA recently cloned from human liver cDNA. The serum concentration of the two glycoproteins together was estimated to be approximately 40 mg/liter. They were found not to exert factor H-like regulatory functions in the alternative pathway. Thus, the 42-kDa glycoprotein described here appears to be distinct from the previously characterized factor H-related protein of similar size, suggesting that human serum contains two factor-H related molecules which both have a molecular mass of 41 to 43 kDa but which differ largely in structure.

Amino Acid Sequence↗
PubMed1989

Biosynthesis of complement factor H by human umbilical vein endothelial cells. Regulation by T cell growth factor and IFN-gamma.

The present studies were initiated to characterize a 150-kDa molecule with inhibitory activity for C3bBb formation, which is present in human umbilical vein endothelial cells (HUVEC). Therefore, human endothelial culture supernatants (HECS) were analyzed for the presence of human complement factor H by ELISA. It was found that H was present in HECS. An immunoblot analysis of affinity purified H from HECS showed that the size of HUVEC H was identical to that of plasma H. The mean production of H by HUVEC of first passage cultures was 40 ng/10(6) cells/day. The synthesis of HUVEC H was fully inhibitable by the addition of cycloheximide to the cultures, suggesting that H is de novo synthesized. Additional evidence for de novo synthesis was obtained by using biosynthetic labeling with [35S] methionine, immunoprecipitation, and SDS-PAGE. It was demonstrated that, indeed, HUVEC produce and secrete factor H. Two forms of the protein were identified, the 150-kDa form and also a 45-kDa form, both forms have been identified in plasma. The functional activity of HUVEC H is identical to that of plasma H. IFN-gamma induced enhanced synthesis of H by HUVEC, whereas it had no effect on C3 synthesis. Supernatant from stimulated PBMC, T cell growth factor, enhanced synthesis of both H and C3. The present studies indicate that H is produced by HU-VEC and that H may function as an inhibitor of complement activation at the endothelial cell level and, thereby, together with molecules like decay accelerating factor and membrane cofactor protein, may influence resistance of endothelial cells to complement mediated damage.

Binding, Competitive↗
PubMed1985

Suboptimal C3b/C3bi deposition and defective yeast opsonization. I. Evidence for the absence of essential co-factor activity.

Defective yeast opsonization in sera with no demonstrable abnormality of known complement components is associated with the absence of inactivity of a co-factor which enhances the deposition of C3 fragments (C3b/C3bi) derived from both classical and alternative pathways of complement activation. The factor binds strongly to zymosan at 4 degrees C and loses its biological activity completely when heated for 30 min at 56 degrees C but not when similarly heated at 50 degrees C. Sera with defective deposition of C3 fragments may be readily corrected with small quantities of sera having normal function. Sera with the defect do not correct other similar sera.

Adult↗
PubMed1994

Crystallization of human methylamine-treated complement C3 and C3b.

Human methylamine-treated complement C3 (C3-MA) and C3b (C3b-MA) have been crystallized using ammonium sulfate as precipitant. The crystals of the two compounds are morphologically indistinguishable though they belong to different space groups. We show that only minor alterations in packing are responsible for the change in space group. Crystals of C3-MA are tetragonal [P4(1(3))22, a = b = 135, c = 610 A] with two molecules per asymmetric unit. Crystals of C3b-MA are also tetragonal [P4(1(3))2(1)2, a = b = 191, c = 610 A] with four molecules per asymmetric unit. The maximum diffraction observed is 7.7 A at cryogenic temperature using synchrotron radiation.

Journal Article↗
PubMed1987

Virulence-plasmid is associated with the inhibition of opsonization in Yersinia enterocolitica and Yersinia pseudotuberculosis.

Plasmid-cured variants of virulent strains of Yersinia enterocolitica and Y. pseudotuberculosis were obtained by selection after growth in calcium-deficient medium. To obtain antigen preparations consisting of whole bacteria the original plasmid-containing strains and the plasmid-cured variants were grown in conditions favouring expression of the temperature-inducible outer membrane proteins of Yersinia (YOP) (37 degrees C, calcium-deficient culture medium). The presence or absence of the YOP on the bacteria was verified by immunoblotting. Opsonophagocytosis of YOP-negative Yersinia preparations (YOP-) was compared to that of YOP-containing ones (YOP+) in human polymorphonuclear leukocyte (PMN) chemiluminescence (CL) assay. The attachment of complement C3b on the surface of the bacteria after opsonization with normal human serum was determined by using a fluorescent anti-C3c-antibody and flow cytometry. YOP+ bacteria resisted opsonization in the absence of specific antibodies, as indicated by diminished C3b-fixation on bacteria and weaker CL response. This implies that virulence-plasmid-coded structures provide Y. enterocolitica and Y. pseudotuberculosis with an ability to avoid complement-mediated opsonization and phagocytosis.

Bacterial Outer Membrane Proteins↗
PubMed1997

Mechanism of complement inactivation by glycoprotein C of herpes simplex virus.

Glycoprotein C (gC) of both herpes simplex virus type 1 (HSV-1) and HSV-2 interacts with complement C3b and protects the virus from complement-mediated neutralization. To study the mechanism by which gC modulates complement activation, we expressed both gC-1 and gC-2 in a baculovirus expression system. Baculovirus recombinants containing gC genes spanning the entire gC-1 sequence (gC-1-TMR) or only the extracellular domain(s) of gC-1, gC-2, or a deletion mutant of gC-1 lacking residues 33 through 123 were expressed in sf9 insect cells. Binding of the expressed proteins to human C3 and C3 fragments was assessed by direct and competition ELISA. All four expressed proteins bound to C3, C3b, and C3c but not to C3d, suggesting 1) that the binding sites for these proteins are located in the C3c region of C3; and 2) that gC, in contrast to other C3-binding proteins, interacts with native C3. We have also examined the interaction of native C3 with gC-1 expressed on the HSV-1-infected cells. Analogous to recombinant proteins, gC-1 expressed on the infected cells also bound to native C3. The ability of baculovirus-expressed gCs to inhibit the interaction of C3b with its ligands was also analyzed. We found that gC-1, but not gC-2, inhibited the binding of C5 and properdin to C3b and also inhibited the alternative pathway-mediated lysis of rabbit erythrocytes. Inhibition of alternative pathway-mediated lysis and properdin binding to C3b, but not of C5 binding to C3b, required the transmembrane segment of the gC-1. The specificity of gC interactions was examined by studying the interaction of gC with C3 from various species. In contrast to properdin, both gCs bound to cobra C3; this finding suggests that gC-1 and properdin bind to different sites on C3b. Further analyses suggested that gC-1 sterically hindered access of C5 and properdin to C3b.

Binding, Competitive↗
PubMed1981

Inhibition of monocyte complement receptor enhancement by low molecular weight material from human lung cancers.

We have studied the effect of dialysates from lung cancer homogenates to alter both the expression of complement (C3b) receptors per se and also to inhibit leucoattractant-induced enhancement of complement rosettes on monocytes from healthy individuals. Enhancement and enhancement-inhibition by tumour extracts were compared with material derived from normal lung excised from distance from the tumour. There was no significant difference between tumour homogenate (TH) and normal lung homogenate (NLH) in terms of enhancement of complement rosettes per se. In contrast, TH produced a dose- and time-dependent inhibition of leucoattractant-induced enhancement of C3b rosettes which was significantly different from that obtained with NLH. This enhancement-inhibition was observed with four undifferentiated, four squamous and three adenocarcinomas of lung. The degree of enhancement-inhibition was not related to the type of tumour or varying accompanying histological features such as necrosis and the degree of infiltration with inflammatory cells. Following gel filtration on Sephadex G-50 each type of cancer gave a major peak of inhibitory activity which eluted with molecules having an apparent molecular size of approximately 3,000 daltons. A second larger peak (8,000-10,000 daltons) was also detected with extracts from the undifferentiated and adenocarcinomas. These results support previous findings, mainly from experimental animals, indicating that 'anti-macrophage/monocyte principles' are elaborated from certain tumour types.

Carcinoma↗
PubMed1984

Receptor associated defects of cultured monocytes in bronchial carcinoma.

Using peripheral blood monocytes from individuals with bronchial carcinoma (BC) we have measured changes, over an 8 day culture period, in monocyte/macrophage complement (C3b) and IgG (Fc) rosettes, chemotactic factor (CF)-induced enhancement of C3b and IgG (Fc) rosettes, and the phagocytic index (PI) for yeast particles. The same measurements were made on monocyte/macrophages from individuals with non-malignant respiratory diseases (NMRD) and healthy controls (HC). Following 8 days of culture there was a significant increase in C3b rosettes, IgG (Fc) rosettes and the PI in NMRD and HC. In contrast there was no significant increase in C3b rosettes in BC. The PI increased in BC, but on day 8 was still significantly less than control monocytes/macrophages. IgG (Fc) rosettes increased in BC following culture to a similar degree as that observed with NMRD and HC. In addition, there were no differences between BC and HC in CF-induced enhancement of IgG (Fc) rosettes at either day 0 or day 8 of culture whereas complement receptor enhancement in BC was impaired both at the beginning and end of the 8 day culture period. These results indicate that in advanced BC there is an abnormality in the expression of monocyte/macrophage complement receptors (which is not readily demonstrable for IgG [Fc]receptors) and that the defect persists following an 8 day culture period.

Adult↗
PubMed1985

Fibronectin binds to complement-coated agarose beads and increases their association to mouse macrophages.

We have studied the binding of fibronectin to complement (C3b, C3bi, C3d)-coated agarose beads and its effect on cell association of such beads to mouse macrophages. Fibronectin bound to agarose beads preincubated in human serum, whereas no binding occurred after preincubation of the beads with complement-inactivated (50 degrees C for 20 min or ethylenediaminetetraacetic acid) sera. The binding of iodine-labelled fibronectin to beads preincubated in fibronectin-depleted serum (HS-FIB) was about twice that of beads preincubated in normal serum. Unlabelled fibronectin inhibited the following binding of labelled fibronectin to beads pretreated in HS-FIB. A similar amount of fibronectin bound to agarose beads coated with equimolar amounts of C3b, C3bi, or C3d, suggesting that the common domain C3d carries the main binding site(s) for fibronectin. Preincubation of serum-treated and trypsinized agarose beads with fibronectin led to an increased association (22%) of such beads to mouse macrophages. The results indicate that fibronectin promotes binding of complement-coated agarose beads to mouse macrophages, whereas the ingestion of the beads is mediated via complement C3 receptors.

Animals↗
PubMed1981

Immunological characterization of sural nerve biopsies from patients with Guillain-Barré syndrome.

Among eight sural nerve biopsies from patients with the Guillain-Barré syndrome (GBS), demyelination was observed in five and endoneural mononuclear cell infiltrates in three. Receptors for the activated third component of complement (C3b) were detected within the nerve fascicles. The receptor activity was reduced in five biopsies, and in vivo deposition of C3 within the endoneurium occurred in four. Immunoglobulins were found in four biopsies and appeared to be localized along the myelin sheaths. Both T and B lymphocytes could be detected in the mononuclear cell infiltrates, but the relative proportions of these cells could not be determined. Macrophages present in two biopsies were found to possess IgG Fc receptors. The results indicate that the complement receptors may play a role in the binding of complement-containing complexes in the nerve during the GBS disease process.

Adult↗
PubMed1984

A new enzyme-linked immunosorbent assay (ELISA) for measuring immunoconglutinins directed against the third component of human complement. Findings in systemic lupus erythematosus.

A new enzyme-linked immunosorbent assay, using purified activation product of the third component of human complement (C3b), detects immunoglobulins of the IgG isotype which demonstrate affinity for C3b (C3b-immunoconglutinins; C3b-IK). This assay offers significantly improved specificity compared to previous immunoconglutinin (IK) assays in that it not only defines the isotype and antigenic specificity of the IK but also eliminates false positive results associated with immune complexes or aggregated human gamma globulin, or with natural antibodies directed at heterologous reagents. Using this assay, we observed elevated C3b-IK levels in serum of 34 systemic lupus erythematosus (SLE) patients when compared to serum of 13 healthy controls. Comparing sera from patients with clinically active and clinically inactive lupus showed greater immunoconglutinin levels in the active group. Immunoconglutinin levels did not correlate with the erythrocyte sedimentation rate, total hemolytic complement, or with circulating immune complex levels by the Raji cell and C1q-binding assays.

Autoantibodies↗
PubMed1993

Reduced CR1 expression on aged human erythrocytes: immuno-electron microscopic and functional analysis.

Recognition and clearance of aged human erythrocytes (AE) is a complex process involving immune and non-immune reactions. Complement activation on the surface of AE and deposition of the C3b complement component appear to facilitate this process. Complement receptor type 1 (CR1, CD35) expressed on the surface of human erythrocytes binds to C3b molecules and promotes their inactivation by complement factor I. This may protect the erythrocytes from lysis by complement and by phagocytes. It has been previously reported that aging of human erythrocytes is accompanied by a decrease in the number of CR1 molecules expressed on their surface. Results presented here further support this finding with for the first time a presentation of immune-electron microscopic observation. Haemagglutination and binding assays showed that AE express significantly fewer CR1 (CD35) molecules than young erythrocytes (YE). This is associated in AE with reduced CR1-like factor I co-factor activity and increased deposition in vivo of C3, C4 and properdin as well as increased sensitivity to lysis in vitro by homologous and heterologous complement. Three different immuno-electron microscopical techniques have been used to clearly show the quantitative difference in CR1 (CD35) expression between AE and YE. Finally our results demonstrate that the previously reported clustered arrangement of CR1 (CD35) on human erythrocytes is similar on aged and young erythrocytes.

Antibodies, Monoclonal↗