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PubMed1983

Complement studies of sera and other biologic fluids.

The complement system consists of at least 15 proteins whose sequential activation, split products, and interaction with other plasma proteins and cells are important in inflammation. Measurement of complement is useful in many rheumatic and immunologic diseases. Most attention has focused on low levels usually due to immune complex disorders. A logical starting point is measurement of the total hemolytic complement, CH50; if this is low, one can see which component is involved. If only one component concentration is decreased, an inherited defect may be present; multiple low levels usually reflect an acquired process. Serial levels of CH50, C4, and C3 are particularly useful in monitoring patients with systemic lupus erythematosus and vasculitis. Complement may also be involved in effusions.

Angioedema↗
PubMed2000

The human and mouse MHC class III region: a parade of 21 genes at the centromeric segment.

The human major histocompatibility complex (MHC) class III region contains 57-60 structural genes spanning 654-759 kb of genomic DNA. Analysis of the sequence identities of the human and mouse genomic regions between NOTCH4 and complement C2 yields important information on the locations of the coding and regulatory sequences. It also provides insights into the relationship between protein function and level of sequence conservation, and on the clustering of genes with related functions.

Animals↗
PubMed1997

Relationship between protein complotypes and DNA variant haplotypes: complotype-RFLP constellations (CRC).

From the study of 52 families and 15 homozygous typing cells, 234 MHC complement haplotypes were characterized for features in the DNA of the complotype region: C2/Sst I (2.75, 2.70, 2.65, and 2.40 kb), BF/Taq I (6.6 and 4.5 kb), C4 5'/Bgl II (15 and 4.5 kb), C4 5'/Taq I (7.0, 6.4, 6.0 and 5.4 kb) and C4 3'/Xba I/BamH I (11 and 4 + 7 kb) restriction fragment length polymorphisms (RFLP's), by the presence or absence of C4A, C4B, CYP21A and CYP21B genes and by duplications. Nineteen (of over 1000 theoretically possible) complotype-RFLP constellations (CRC's) were found. The 9 CRC's with two C4 and CYP21 genes were designated A through I. CRC's Bdup and Ddup were like B and D but had duplicated C4B-CYP21B genes. The remaining CRC's had deletions of C4 and/or CYP21 genes and were designated Bdel, Cdel and the like. Individual complement alleles and complotypes were nor randomly distributed among the CRC's. Some complotypes, such as SC01, SC02 and FIC30, were restricted to only 1 CRC; others, such as SC31, FC31, and SC30, were found in several CRC's. Some of the CRC's contained a single complotype, others contained several. Remarkably, there are about 30 CRC-specified complotypes with frequencies of .01 or higher and 14 of .02 or higher. A number of evolutionary origins of complement alleles and complotypes are suggested by the relationships among CRC's. Approximate normal frequencies of the undeleted CRC's were A = .27, B = .19, Bdup = .02, C = .17, D = .07, Ddup = .02, E = .06, F = .05, and G = .02. Thus, CRC's without deletions accounted for 88% of normal complotypes. Since the frequency of Bdel, with a deletion of C4A, was .12, 10 CRC's accounted for all observed normal caucasian MHC haplotypes.

Chromosome Mapping↗
PubMed1998

Microbial immunology: a new mechanism for immune subversion.

The number of mechanisms that have evolved in microbes to subvert the immune response seems limitless. Tubercle bacilli have found a novel way to coat themselves with the C3 complement protein and invade macrophages by interactions with complement receptors.

Bacterial Proteins↗
PubMed1998

Mycobacterium tuberculosis and the complement system.

Accumulated evidence to date confirms the importance of the C3-CR pathway in the phagocytosis of pathogenic mycobacteria. Detailed receptor-ligand studies for phagocytosis are creating the framework to test the hypothesis that the entry pathway for these bacteria influences the immediate host cell response and their intracellular fate. These types of study are particularly important for improving our understanding of the outcome of primary infection in humans, where the number of bacilli is presumed to be very low.

Complement Activation↗
PubMed1978

The biochemistry of complement.

Current biochemical studies of the complement system are illustrated by description of the activation of complement by the classical pathway after interaction with antibody aggregates. This is described in terms of the structures of the components involved, their assembly and the mechanism of activation.

Amino Acid Sequence↗
PubMed1990

HLA extended haplotypes in steroid-sensitive nephrotic syndrome of childhood.

Idiopathic nephrotic syndrome has been postulated to have an immunopathogenic basis. To determine whether steroid-sensitive nephrotic syndrome is associated with greater than expected frequencies of specific extended haplotypes of the major histocompatibility complex, we studied genetic markers (Class I, II, III HLA alleles and glyoxalase I) in 173 subjects in 42 families of patients with nephrotic syndrome of childhood. The single allele, DQW2, was found in 72% of steroid sensitive patients compared with only 35% of the controls (P = 0.003). In half of 32 steroid sensitive, but not 10 steroid resistant, patients, one or both of two specific extended haplotypes (alleles that segregate together) were identified. The first, [HLA-A1, B8, DR3, DRW52, SCO1], occurred in 11 of 64 haplotypes, or 17%, compared to 5% of controls (P = 0.017). The other, [HLA-B44, DR7, DRW53, FC31], occurred in 10 of 64 haplotypes, 16% compared to 3.8% of controls (P = 0.014). Five patients had both haplotypes. Patients with these specific extended haplotypes had a greater frequency of relapses than did those with other haplotypes. These data provide additional support for the hypothesis that steroid-sensitive nephrotic syndrome has an immunogenetic basis.

Blotting, Southern↗
PubMed1997

Extrahepatic C6 is as effective as hepatic C6 in the generation of renal C5b-9 complexes.

In order to study the contribution of extrahepatic C6 to anti-Thy1.1 nephritis, C6 deficient PVG/c- livers were grafted in C6 sufficient PVG/c+ rats (Tx-L). Infusion of anti-Thy1.1 antibodies in Tx-L and PVG/c+ rats resulted in generation of C5b-9 complexes and subsequent glomerular injury, while infusion of anti-Thy1.1 antibodies in PVG/c- rats revealed no detectable C6 deposition. Because C6 mRNA was expressed in both liver and kidney tissue of PVG/c+ rats, we assessed whether production of C6 in the kidney alone was sufficient for glomerular injury. One kidney of a PVG/c- rat was replaced with a PVG/c+ kidney (Tx + K) followed by administration of anti-Thy1.1 antibodies. C6 deposits were detectable neither in PVG/c+ kidneys nor in PVG/c- kidneys of Tx + K rats, indicating that C6 production in PVG/c+ kidneys alone is not sufficient to contribute to renal injury. That C6 production had occurred was suggested by the presence of equal amounts C6 mRNA in control PVG/c+ kidneys and in grafted PVG/c+ kidneys of Tx + K rats. C6 mRNA expression in kidney tissue of PVG/c+ rats is presumably derived from peritubular sites. In conclusion, we have demonstrated that extrahepatic, but not renal synthesis of, C6 is sufficient to contribute to glomerular injury during anti-Thy1.1 nephritis.

Animals↗
PubMed1989

Secretion, cleavage and binding of complement component C3 by the human monocytic cell line U937.

Secretion of complement component C3 by U937 cells was studied. Preliminary evidence for a cell-associated proteolytic activity specific for C3 is given, as well as for a covalent-like binding of C3 fragments to the cell membranes. Secretion of C3, in the presence of 10 ng of phorbol 12-myristate 13-acetate/ml, is 120-140 ng/10(6) cells per 24 h on the third day after addition of the activator. As shown by SDS/polyacrylamide-gel electrophoresis, the intracellular pro-C3 (200 kDa) and the extracellular secreted C3 (alpha-chain 110 kDa and beta-chain 75 kDa) are identical with the forms of C3 previously characterized from human serum. Incubation of U937 cells in the presence of exogenous radiolabelled C3 shows that membrane-bound proteinase(s), not related to the classical-pathway or the alternative-pathway C3 convertases, is (are) able to cleave C3; this cleavage leads to the binding of the resulting C3 fragments to the cell membrane through reaction of membrane acceptors with the carbonyl group of C3 revealed after disruption of the intramolecular thioester bond. The proteolysis appears to be fairly specific to C3, as C4, which also possesses an intramolecular thioester bond, is not cleaved and does not bind to the cells. p-Nitrophenyl p'-guanidinobenzoate (1 mM) and di-isopropyl phosphorofluoridate (2 mM) are potent inhibitors of the proteolysis, whereas soya-bean trypsin inhibitor (1 mM), leupeptin (0.1 mg/ml) and 1,10-phenanthroline (1 mM) were ineffective. Immunological characterization of the cell-bound C3 fragments with monoclonal antibodies shows an evolution of the proteolysis of the fragments from iC3b to C3dg epitopes. Extraction of membrane-bound fragments by detergent, followed by SDS/polyacrylamide-gel electrophoresis, shows two fragments, of 43 kDa and 46 kDa, with C3dg-like characteristics.

Cell Line↗
PubMed1991

The principal site of glycation of human complement factor B.

Accumulating amino acid sequence data have made it increasingly evident that many essential complement proteins have potentially modifiable lysine residues in putative critical functional regions. Evidence is now presented that glucose is covalently attached to lysine-266 of purified human complement Factor B as a result of glycation. Purified B was treated with NaB3H4, which reduces such bound glucose to a mixture of radiolabelled hexitols. Amino acid analysis revealed the expected radiolabelled hexitol-lysine epimers. In addition, fluorography of dried gels resolving the major high-molecular-mass h.p.l.c.-fractionated CNBr-cleavage peptides of NaB3H4-reduced B indicated that this radioactivity was specifically associated with the 15 kDa fragment derived from the N-terminal region of fragment Bb. Amino acid sequence analysis suggested that the C-terminal lysine (residue 266 of B) of the N-terminal Lys-Lys doublet of this peptide is preferentially modified. If such glycation can subsequently be shown to occur in vivo, then perhaps this modification might also be found to affect the functional activity of B and offer a potential explanation for some of the immunopathological complications of diseases exposing key plasma proteins, such as this active-site-containing proteinase of the multimeric alternative-complement-pathway C3/C5 convertases, to long-term high concentrations of glucose, such as the decreased resistance to infection and impaired chemotaxis and phagocytosis characteristic of diabetes.

Amino Acid Sequence↗