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PubMed1979

Staphylococcus aureus opsonization mediated via the classical and alternative complement pathways. A kinetic study using MgEGTA chelated serum and human sera deficient in IgG and complement factors C1s and C2.

Staphylococcus aureus opsonization was studied kinetically by: (1) determination of the uptake of [3H]-thymidine labelled bacteria by human PMN's; (2) fluorescent anti-C3 and anti-IgG staining of opsonized bacteria; and (3) measuring bacterial complement consumption. Maximum opsonization in normal serum occurred within 5 min of incubation. About 80% of staphylococci were then taken up by PMN's, and IgG and C3b could be detected on the bacterial surface. In the absence of a functional classical complement pathway, as in sera deficient in C1s and C2 and in MgEGTA chelated serum, maximal opsonization was only achieved after 30--60 min incubation. Opsonization in IgG deficient serum occurred at a rate similar to that found in C2 deficient or MgEGTA chelated serum. Opsonization was greatly enhanced when sera were reconstituted. It was concluded that in IgG deficient serum Staphylococcus aureus opsonization is mediated via the alternative complement pathway. Dilution of normal serum primarily affected the classical complement pathway, resulting in a decreased rate of opsonization. In normal serum IgG did not appear to be a rate-limiting factor. S. Aureus opsonization was best studied by the phagocytosis assay and the fluorescent-antibody technique. Measuring haemolytic complement consumption was found to be an insensitive indicator of bacterial complement activation and opsonization.

Complement Activation↗
PubMed1987

Variations in the enzymatic properties of human complement subcomponent C1s by treatment with human plasma kallikrein.

We have investigated the effect of plasma kallikrein digestion upon hydrolytic activities of human C1s. Incubation of C1s (85 kDa) with plasma kallikrein led to progressive cleavages on the heavy chain to yield C1s-K1 (70 kDa) then C1s-K2 (53 kDa). Although these cleavages caused little change in the C2 hydrolytic and esterase activities of C1s, a marked loss in the C4 hydrolytic activity was observed. C1s-K1 and C1s-K2 were purified by DE-52 chromatography and it was found that the proteolysis of C1s into C1s-K1 was accompanied with a decrease in the C4 hydrolytic activity. Although the turnover numbers for the hydrolysis of C4 by C1s-K1 and C1s-K2 were almost the same as that of intact C1s, the Kms for C4 of C1s-K1 and C1s-K2 were found to be increased to 10 times that of intact C1s. This result suggests that the apparent decrease in the C4 hydrolytic activity upon plasma kallikrein digestion of C1s is not due to disruption in the active site but is due to decrease in the affinity between C4 and the C1s derivatives. In support of this assumption, C1s-K1 was found to be devoid of the ability to bind C4b-Sepharose. C1s is capable of forming a dimer through the C1s-binding domain in the N-terminal side of the heavy chain. Although C1s-K1 is still capable of forming a dimer, C1s-K2 fails to form a dimer, suggesting that the N-terminal C1s-binding site is released during cleavage of C1s-K1 into C1s-K2.(ABSTRACT TRUNCATED AT 250 WORDS)

Chromatography, Affinity↗
PubMed1983

Heparin-stimulated modification of C1-inhibitor by subcomponent C1s of human complement.

C1-inhibitor and C1s form a very stable complex which migrates with an apparent molecular mass of 180 kDa in dodecyl sulfate gel electrophoresis. A small fraction of the inhibitor (100 kDa) was found to be converted to a large (95 kDa) and a small (2 to 5 kDa) fragment during this reaction. It is concluded that C1-inhibitor is modified by C1s in a similar way as are the related plasma inhibitors alpha 1-proteinase inhibitor, antithrombin III and antiplasmin by their specific proteinases. The fraction of modified C1-inhibitor increased when heparin was present during complex formation. This reaction was complete after 15 s and is comparable with the fast heparin induced formation of modified antithrombin III. Treatment with hydroxylamine led to a complete dissociation of the inhibitor-enzyme complex by dodecyl sulfate. The large inhibitor fragment (and not unmodified inhibitor as reported by other authors) was released.

Complement Activating Enzymes↗
PubMed1981

Conformational changes of the subunits C1q, C1r and C1s of human complement component C1 demonstrated by 125I labeling.

C1s and C1r proenzymes and enzymes (C1s, C1r) and C1q were labeled with 125I. The distribution of the 125I label between H- and L-chain of C1s was only slightly dependent on the state of activation of C1s, and approx. 90% of the label was found in the H-chain. In the C1r proenzyme molecules 50% of the label was incorporated into the H-chain. The C1r H-chain label was reduced to 10% on activation of C1r to C1r, while the L-chain label increased to 90% of the total label. The presence of either C1s, C1q or C1qs during labeling reduced the C1r H-chain level, although C1r remained in the proenzyme form. The presence of C1s or C1rs enhanced the 125I uptake of C1q in Ca2+ or EDTA medium. This was unexpected because one would have anticipated a diminution of the C1q label due to the apposition of C1r and C1s, similarly as it occurs during C1rs complex and C1s dimer formation for the H-chain label of C1s. The results show that C1r and C1q alter their conformation during activation and C1 complex formation.

Calcium↗
PubMed1986

Functional model of subcomponent C1 of human complement.

The domain organization of the zymogen subunits of the first component of human complement C1s, C1r2 and the complex C1s-C1r2-C1s was studied by electron microscopy. In the absence of Ca2+, monomeric C1s was visualized as a dumb-bell-shaped molecule consisting of two globular domains (center-to-center distance 11 nm) connected by a rod. One of the globular domains is assigned to the light chain (B-chain) of the activated molecule, which is homologous to trypsin and other serine proteases. The second globular domain and the rod are assigned to the heavy chain (A-chain) of CIs. The subunit C1r is a stable dimer in the presence or absence of Ca2+. This dimer C1r2 was visualized as composed of two dumb-bells of dimensions similar to those observed for C1s. These are connected near the junctions between the rod and one of the globular domains. This leads to the structure of an asymmetrical X with two inner closely spaced globules (center-to-center distance 7 nm) and two outer globules at a larger distance (14 nm). By comparison with fragment C1rII2, in which part of the A-chain is removed, the inner globular domains were assigned to the catalytic B-chains. This characteristic structure of C1r2 is readily recognized in the central portion of the thread-like 54 nm long C1s-C1r2-C1s complex formed in the presence of Ca2+. By affinity-labeling of C1s with biotin and visualization of avidin-ferritin conjugates in the reconstituted complex, it was demonstrated that C1s forms the outer portion of the complex. A detailed model of C1s-C1r2-C1s is proposed, according to which two C1s monomers bind to the outer globes of C1r2 by contacts between their heavy chains and those of C1r. According to this model the catalytic domains of C1r are located in the center and those of C1s at the very tips of the C1s-C1r2-C1s complex. On the basis of the structure of C1s-C1r2-C1s, we derived a detailed model of the C1 complex (composed of C1q and the tetrameric complex) and we discuss this model with a view to finding a possible activation mechanism of C1.(ABSTRACT TRUNCATED AT 400 WORDS)

Complement Activating Enzymes↗
PubMed1989

Effect of human mast cell tryptase on human plasma proenzymes.

The effect of human skin mast cell tryptase on human plasma proenzymes (prothrombin, coagulation factor XII, complement C1s, protein C and plasminogen) was investigated. Tryptase had no effect on these proenzymes, when incubated with them at 37 degrees C for up to 90 min, as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by the ability to hydrolyze specific peptide p-nitroanilide substrates. After prolonged treatment with tryptase, proenzymes could be fully activated with their specific activators. The results indicate that tryptase neither activates these plasma proenzymes nor inactivates the corresponding active enzymes. As a positive control, the tryptase preparation was also incubated with human fibrinogen and rat thymus histones. Prolonged treatment with tryptase increased the thrombin-induced clotting time of fibrinogen. Tryptase also efficiently hydrolyzed histone H1 from rat thymus. Histones H3/H2B and H2A were hydrolyzed less efficiently than H1, and no hydrolysis of histone H4 by tryptase was detected under the experimental conditions.

Animals↗
PubMed1979

The purification and characterization of subcomponent C1s of the first component of bovine complement.

Bovine C1s, a subcomponent of the first component of complement, was purified in good yield by a combination of euglobulin precipitation and ion-exchange and molecular-sieve chromatography. Approx. 10 mg can be obtained from 3 litres of serum, representing a yield of 11%. The C1s is obtained in zymogen form, with a mol.wt. of 85000-88000, determined by gel filtration and SDS/polyacrylamide-gel electrophoresis. It is haemolytically active when tested with human C1q and C1r. Activation can be achieved by incubation with human C1r, resulting in cleavage of the C1s chain into two chains of 65000 and 27000 mol.wt. and the generation of an isoleucine N-terminal residue on the smaller chain. Active C1s binds an equimolar amount of di-isopropyl phosphorfluoridate to the smaller chain, which is the C-terminal part in the zymogen. The chains can be separated by ion-exchange in 8 M-urea. All of these characteristics show that bovine C1s is very similar to its human counterpart.

Amino Acids↗
PubMed1991

C1 inhibitor: different mechanisms of reaction with complement component C1 and C1s.

Inactivation of human complement subcomponent C1-s by its regulator C1 inhibitor at physiological ionic strength proceeded at a 3-fold higher rate when C1-s was in the physiological C1- complex with subcomponents C1q and C1-r rather than as purified subunit. When the C1- complex was disassembled by chelation of calcium, the C1-s subcomponent was inactivated by C1 inhibitor at rates similar to those for the purified proteinase. Increasing ionic strength had little effect on the reaction of purified C1-s with C1 inhibitor but greatly diminished the rate of reaction of intact C1-. Addition of heparin accelerated the inactivation of purified C1-s by C1 inhibitor up to 25-fold but increased the inactivation of intact C1- only about 5-fold. These differences in the inactivation of C1-s by C1 inhibitor, depending on whether the proteinase is free or complexed with other subcomponents of C1-, suggest different mechanisms of reaction. Occurrence of subcomponent C1-s in a macromolecular complex with C1q and C1-r, thus, appears to be critical not only for directing its physiological activation but also its inactivation.

Complement C1↗
PubMed1982

Separation of Fc-binding serum proteins by preparative flat-bed isotachophoresis.

Preparative flat-bed isotachophoresis with discrete spacers was applied as a single-step procedure to separate 2 Fc-dependent activities of normal chicken serum, i.e., (1) the ability to raise the titre of haemagglutinating allo-antisera which is due to a high molecular weight beta-globulin (HEF), (2) the ability to activate guinea pig complement components in mixed complement reaction. The results demonstrate that the 2 activities can be clearly separated, and HEF must therefore be different from the first complement factor in the chicken. Under the chosen conditions the molecule active in the mixed complement reaction is not stacked in contrast to other serum protein including HEF. The same technique with human serum shows that human Clq behaves in the same was as the chicken complement factor. This means that by selective unstacking, flat-bed isotachophoresis can be used as an efficient single-step purification method for human and chicken Clq.

Animals↗
PubMed1988

Complement activation occurs through both classical and alternative pathways prior to onset and resolution of adult respiratory distress syndrome.

We have previously reported that plasma concentrations of the terminal complement (C) complex (TCC), C5b-9, increased significantly 2 days prior to onset of adult respiratory distress syndrome (ARDS) and also 1 day preceding its resolution. To determine the pathway of complement activation that preceded development and resolution of this acute inflammatory lung injury in septic patients, we quantified the C1rC1s-C1 inhibitor complex and the C3bP complex, which are generated following activation of classical and alternative complement pathways, respectively. Two days prior to diagnosis of ARDS, the plasma C1rC1s-C1 inhibitor complex and C3bP complex levels increased 22 and 14%, respectively. Furthermore, significant correlations were identified between concentrations of the TCC and C1rC1s-C1 inhibitor complex (r = 0.73, P = 0.003) and also with the levels of the TCC and C3bP complex (r = 0.81, P = 0.002) before onset of ARDS. Equally of interest, the C1rC1s-C1 inhibitor complex and C3bP complex concentrations increased 68 and 35%, respectively, 1 day before resolution of ARDS. Similarly, significant elevations of TCC concentrations preceding resolution of ARDS correlated with C1rC1s-C1 inhibitor complex (r = 0.66, P = 0.02) and also with C3bP complex (r = 0.72, P = 0.002) levels. Our results indicate that both the classical and alternative complement pathways are activated prior to onset of ARDS and also before its resolution in septic patients.

Complement Activating Enzymes↗
PubMed1979

Immunologic reactivity in the hypereosinophilic syndrome.

Because previous studies have suggested an important link between eosinophilia and immunologic reactivity, we investigated various components of the immune system in a large number of patients with the idiopathic hypereosinophilic syndrome (HES) to elucidate a possible role for immunologic phenomena in the etiology and pathogenesis of this disease. Immunoglobulin G, A, or M levels were only rarely abnormal. However, in 8 of 21 (38%) patients with HES, IgE levels were markedly elevated suggesting an association of an IgE-mediated mechanism with eosinophilia in this subgroup. Severe dermatographism was present in three fourths of patients, and 2 patients with intermittently elevated histamine levels manifested an unusual form of immediate-pressure urticaria. Serum complement determinations showed elevated C4 and C3 levels in 27% and 77% of patients, respectively. Antigen-antibody complexlike material measured by C1q binding was elevated in the serum of 7 of 22 (32%) patients; this finding may relate to the known ability of eosinophils to avidly phagocytose antigen-antibody complexes. When compared with normals, lymphocytes from patients with HES showed a variety of abnormalities of lymphocyte surface receptors and lymphocyte function. Thus, patients with HES demonstrate a variety of immunologic abnormalities which may be related primarily or secondarily to the pathogenesis of this syndrome.

Antigens, Surface↗