Biomedical subjects

M Loos

Publications and source records attributed to M Loos.

At least 37 records · Page 2Linked to original sources

PubMed1989

Acquired C1 inhibitor (C1-INH) deficiency type II. Replacement therapy with C1-INH and analysis of patients' C1-INH and anti-C1-INH autoantibodies.

The response of two patients with autoantibody-mediated C1-inhibitor (C1-INH) deficiency to replacement therapy with C1-INH was studied over a period of 3 d. In patient 1 an acute attack of angioedema was successfully managed by infusion of 1,000 U of C1-INH concentrate. C1-INH function returned to normal levels within 30 min, while CH50 and C4 peaked after 6-7 h and C1 hemolytic activity reached 50-60% of normal after 3 d. Immediately after the injection an increase in C1-INH-anti-C1-INH complexes was observed. Based on NH2-terminal sequence analysis of the patients' Mr 96,000 C1-INH, it is concluded that this fragment is generated after cleavage of C1-INH in its active site by one of its target proteases without generating a covalent C1-INH-enzyme complex. In a second patient with a four to five times higher anti-C1-INH antibody titer, the infusion of 500 ml of plasma or of 2,000 U of C1-INH concentrate influenced neither the severity of the patient's angioedema nor the tested parameters, except for an increase in the amount of C1-INH-anti-C1-INH complexes. Analysis of patients' anti-C1-INH antibodies revealed that the antibodies recognize different epitopes within the C1-INH. This suggests that patients with acquired angioedema type II are a heterogenous group with respect to the C1-INH autoantibodies.

Amino Acid Sequence↗

PubMed1989

Interaction of fluid phase C1/C1q and macrophage membrane-associated C1q with gram-negative bacteria.

Many gram-negative bacteria are killed after treatment with normal non-immune sera and directly bind and activate C1 in the absence of antibodies. For the immediate killing of such serum-sensitive bacteria, like R-forms of Salmonella strains, all serum complement components are essential. When purified serum C1 to C9 are used, further activation of the cascade requires an additional serum factor. This glycoprotein differs from antibody and mediates the attachment of C4b to the bacterial cell surface. The antibody-independent interaction with C1 occurs via C1q, which binds to LPS. In addition outer membrane proteins bind C1q and C1. The association of these porins with LPS may potentiate the antibody-independent C1q and C1 binding to serum-sensitive bacteria. Porins can contribute to complement activation mainly through the classical pathway. LPS and porins from bacterial cell walls are also involved in the binding of gram-negative bacteria to macrophages. This antibody-independent attachment and ingestion of gram-negative bacteria is mediated by endogenous macrophage-membrane associated C1q.

Animals↗

PubMed1989

The acquired C1-INH deficiencies with autoantibodies (AAE type II).

A new type of acquired C1-inhibitor (C1-INH) deficiency has been recognized (AAE type II) which is characterized by the presence of autoantibodies to C1-INH and by a circulating 96 KD C1-INH molecule. The clinical manifestations and biochemical abnormalities of this novel autoimmune disease resemble those found in the other forms of acquired C1-INH deficiency (AAE type I), including recurrent angioedema and low serum levels of C2, C4, C1, C1q and C1-INH activity. However, in contrast to AAE type I, AAE type II is not associated to other diseases. Evidence has been provided that the anti-C1-INH antibodies play a major role in the development and maintenance of AAE type II. These autoantibodies seem to impede C1-INH activity, thus allowing unopposed activation of the complement and/or contact system and to induce the generation of the 96 KD C1-INH species in the patients' plasma.

Angioedema↗

PubMed1989

The biosynthesis of C1q, the collagen-like and Fc-recognizing molecule of the complement system.

C1q, the collagen-like and Fc-recognizing component of the complement system, is mainly synthesized in macrophages and epithelial cells. Inhibitors of collagen biosynthesis, known to inhibit the post-translational hydroxylation of proline and lysine residues, were as effective in macrophages as inhibitors of C1q synthesis and secretion as has been described for collagen. This indicates that post-translational processing of C1q is dependent upon its collagen portions and triple helical formation within the cells. The macrophage-derived C1q is immuno- and physicochemically identical with serum C1q indicating that macrophages have to be considered as a major source for serum C1q. This was recently confirmed by Northern blot analysis using a cDNA probe for the B-chain of murine C1q. In contrast, an extremely weak signal was found in kidney, lung, gut, muscle and liver RNA. Besides the 11 S C1q molecule macrophages also synthesize a low molecular weight (LMW) form of C1q. The biological function of this 4 S LMW-C1q is still unclear. Macrophage-derived and secreted C1q is reinserted into the macrophage membrane. It is unlikely that the membranous form of C1q is bound via C1q-receptors into the membrane of macrophages since the B-chain of membrane-associated C1q is structurally different to that of fluid-phase C1q. The demonstration of a distinct membrane form of C1q supports earlier functional studies which implicated C1q as a membrane-associated molecule with receptor functions for those molecules which also interact with fluid-phase C1q, such as polyanions, the Fc portions of immune complexes, and bacteria (LPS and outer membrane proteins, OMP).

Animals↗

PubMed1988

A rapid and simple ELISA for the determination of duplicate monoclonal antibodies during epitope analysis of antigens and its application to the study of C1(-)-INH.

A rapid and simple ELISA has been developed for identifying the specificities of two monoclonal antibodies recognizing either similar or distinct epitope(s) of an antigen. The method utilizes microtiter plates coated with one of the monoclonal antibodies either by direct adsorption of the purified antibody to the plastic or by immobilization of the antibody from ascites or hybridoma supernatants via immobilized polyclonal anti-mouse immunoglobulin antibodies. After preincubation of the antigen with the second monoclonal antibody, the mixture is added to the surface-immobilized first antibody. The amount of antigen bound to the first antibody is subsequently measured by rabbit polyclonal antibodies to the antigen and peroxidase-conjugated anti-rabbit immunoglobulin antibodies. Binding of antigen to the first antibody is only observed when the second monoclonal antibody binds to a distinct epitope. The major advantages of this procedure are its simplicity, rapidity and independence of radioisotopes. Using this method a library of monoclonal antibodies against human C1(-)-INH has been tested and several duplicate monoclonal antibodies have been identified. Furthermore, the above analytical procedure was capable of detecting conformational changes of the C1(-)-INH molecule induced either by binding of a monoclonal antibody to C1(-)-INH or by enzymatic cleavage of C1(-)-INH.

Antibodies, Monoclonal↗

PubMed1988

Enzymatic alteration of C1q, the collagen-like subcomponent of the first component of complement, leads to cross-reactivity with type II collagen.

Native serum C1q, the collagenous-like subcomponent of the first component of complement, is not recognized by polyclonal anti-collagen type II antibodies. However, when purified C1q was subjected to limited proteolysis by collagenase it showed antigenic cross-reactivity with collagen type II. The same cross-reactivity was observed with hemolytically active C1q in synovial fluids of patients with rheumatoid arthritis (RA), whereas C1q from synovial fluids of patients with osteoarthritis (OA), villo-nodular synovitis and ankylosing spondylitis was not recognized by this antibody. However, incubation of synovial fluid C1q of OA patients with synovial fluid leucocytes from RA patients led to an alteration of OA-C1q which was now recognized by the anti-collagen type II antibody.

Animals↗

PubMed1988

Evidence for the presence of autoantibodies to the collagen-like portion of C1q in systemic lupus erythematosus.

We investigated the connection between the C1q solid-phase binding assay (C1q SPBA) and double-stranded DNA antibodies, and analyzed the immune complex material in systemic lupus erythematosus (SLE) sera. Comparison with a new monoclonal assay for C1q-bearing immune complexes (the 242G3 assay) revealed that the immune complexes in SLE bind specifically to solid-phase C1q, and not to fluid-phase C1q. The C1q solid-phase binding activity sedimented as 7S IgG, was insensitive to DNase treatment, and could be selectively absorbed by C1q-coupled beads and by bovine serum albumin-anti-bovine serum albumin C1q beads, but not by DNA. Thus, antibodies to double-stranded DNA do not interfere in the C1q SPBA. Isolated IgG from SLE serum precipitated the collagen-like portions, and not the globular, Fc-recognizing portions, of C1q. F(ab')2 fragments of IgG from SLE patient serum were able to bind C1q. These data show that in SLE sera, especially in those with low levels of CH50 and C1q, autoantibodies that react with the collagen-like part of C1q are detectable. Since in the C1q SPBA, the C1q molecule is randomly fixed to the solid phase, we can detect not only immune complexes, but also antibodies that react with the collagen part of C1q; this may explain the high percentage of positive results for SLE sera in the C1q SPBA, in contrast to results of other immune complex assays.

Antigen-Antibody Complex↗

PubMed1988

Guinea pig macrophages synthesize a low molecular weight form of C1q with affinity for the C1r2C1s2-complex but which does not bind to Fc in immunoglobulin aggregates.

Biosynthetically labelled C1q secreted by guinea pig peritoneal macrophages was analysed by sedimentation through sucrose gradients followed by SDS-PAGE. In addition to the haemolytically active C1q of mol. wt 460,000 Da a low mol. wt (LMW) form of C1q was identified which had no detectable affinity for Fc of aggregated immunoglobulin, but which retained the ability to associate with the C1r2s2-complex. This LMW-C1q was covalently associated with two additional polypeptides of mol. wt 46 and 50 kDa.

Animals↗

PubMed1988

The second component of human complement: detection of two hemolytic forms in plasma by pH variation.

The second component of human complement (C2) in pseudoglobulin prepared from normal plasma eluted as a single peak at high conductivity (30 mS) and pH 4.5 from the cationic exchangers S-Sepharose or Mono S in the Fast Protein Liquid Chromatography (FPLC) System. The C2 was stable at pH 4.5 and 0 degrees C if enzyme inhibitors were used and the pH was raised to 6.0 after elution from the columns. After rechromatography on Mono S in the FPLC System at the median isoelectric point of 5.5 or pH 6.0, the C2 eluted as two distinct hemolytic forms: the first peaked at 16 mS, the second at 30 mS. The two forms of C2 did not correlate with the allotypic variant of C2 in individual, normal human plasmas. After elution at pH 4.5 from S-Sepharose and rechromatography at pH 5.5 or 6.0 on Mono S, the hemolytic activities of the two forms in individual plasmas eluted in 3 patterns: 1) high activity at 16 mS, low activity at 30 mS; 2) low activity at 16 mS, high activity at 30 mS; 3) high activity at 16 mS, high activity at 30 mS. The specific activities of both forms were approximately the same; both eluted the same after gel filtration at pH 5.5, and both had the same pattern on SDS-PAGE and immunoblots. The pattern of elution was characteristic for each individual plasma, and the first hemolytic form appeared to elute independent of the second form. At pH 4.5, C2 was completely separated from Factor B, a functionally and structurally similar protein of the alternative complement pathway, whereas at pH 5.5 or 6.0, the two proteins eluted together. From these results, the two forms of hemolytic C2 can be purified for structural and functional analyses.

Chromatography, Ion Exchange↗

PubMed1988

The second component of human complement: use of glycosidases and glucosylation to distinguish the two forms.

The two forms of human plasma C2 that were described in the preceding report (1) were investigated for their functional and biochemical differences. Incubation with the neuraminidase (NAN'dase) of Clostridium perfringens at 37 degrees C resulted in a four- to fivefold increase in the hemolytic activity of both forms. The increase in activity was different than the increase caused by treatment with iodine. The mechanism of increased activity of NAN'dase-treated C2 was the generation of increased molecules of activated C3 (C3b), resulting in more molecules of C5 binding to (C4b, 2a, 3b)n. Removal of N-acetyl-neuraminate from C2 did not alter its binding to a cationic exchanger. Nonenzymatic glucosylation was used to distinguish the two forms of C2. Incubation of highly pure C2 with 14C-D-glucose resulted in the gradual accumulation of radioactivity in acid-precipitable material. The two forms of C2 were glucosylated in vitro for seven days with 14C-D-glucose in phosphate-buffered saline at 25 degrees C. Form 2 bound twice as much 14C-D-glucose as form 1. Glucosylated form 2, but not form 1, lost some of its affinity to bind to a cationic exchanger. Since the interaction between glucose and protein occurs at free amino groups, we conclude that form 2 of C2 has approximately twice as many free amino groups as form 1. This explains the reason for the existence of two forms of C2 in plasma independent of the allelic variant.

Complement C2↗

PubMed1988

Patients with CLL and hypocomplementaemia have an impaired serum bactericidal activity against the Salmonella minnesota Re mutant.

The bactericidal effect of 25 serum samples from 23 patients with chronic lymphocytic leukaemia (CLL) against the Salmonella minnesota S form and Re mutant has been studied. No killing of the S form was observed in any of the sera tested, whereas a normal bactericidal effect was found against the Re mutant (group 1) in 17/25 sera of CLL patients. By contrast, in 8 serum samples from 6 CLL patients no killing or a markedly delayed killing of the Re strain was observed (group 2). Significant differences in the complement levels were found between the sera of group 1 and group 2. In group 1 mostly normal or elevated complement levels were observed, while in group 2 levels of C4 and C2 were found to be strongly decreased. A significant correlation was found between the bactericidal effect on the one hand and the C4 and C2 levels on the other.

Blood Bactericidal Activity↗

PubMed1987

Detection of C1q-bearing immune complexes by a monoclonal anti-C1q ELISA system.

A monoclonal antibody directed against the collagenous portion of human C1q was used to detect C1q-bearing immune complexes in patients with rheumatic disorders. Sera of patients with rheumatoid arthritis, systemic lupus erythematosus (SLE), osteoarthritis, as well as normal human sera (NHS) used as controls were tested in an ELISA system. C1q-bearing immune complexes were bound to a solid-phase monoclonal anti-C1q antibody, and detected with F(ab')2 antibodies to human IgG. Heat-aggregated human IgG was adjusted to the same concentration as the WHO standard for immune complexes and used for the standard curve in NHS. The mean value in NHS was 19.5 micrograms/ml equivalents of aggregated IgG. Using 2 SD over the mean as the upper limit for normal values, samples greater than 43 micrograms/ml were considered positive. Patients with osteoarthritis were negative; high levels of C1q-bearing immune complexes were detected in patients with rheumatoid arthritis (up to 800 micrograms/ml equivalents of aggregated IgG). With our assay C1q-bearing immune complexes were detected with high frequency (81%) in the sera of patients with rheumatoid arthritis, while a C1q solid-phase binding assay (C1q SPBA) revealed positive results only in 67% of rheumatoid arthritis sera. Compared to NHS, CH50 titers and C1q values of sera from patients with rheumatoid arthritis were frequently high. In contrast, the sera of SLE patients with low CH50 titers and low C1q levels had IgG immune complexes which could be detected only in the C1q-SPBA. C1q-bearing immune complexes were not detectable in the sera of patients with SLE. Since C1q triggers activation of the classical C pathway, this assay with monoclonal anti-C1q antibody appears to be useful for detecting immune complexes in rheumatoid arthritis patients with normal or elevated CH50 and C1q values, especially in the early stage of the disease.

Antibodies, Monoclonal↗

PubMed1987

Macrophage C1q: characterization of a membrane form of C1q and of multimers of C1q subunits.

It has been shown recently that C1q, a subcomponent of the first component of the classical complement pathway, is synthesized by macrophages and that endogenous C1q is detectable on the macrophage membrane. In this report, we demonstrate that membrane-associated C1q, which contains the A, B, and C chains of C1q, is structurally distinct from fluid-phase C1q in that the B chain of the membrane species is approximately 1000 m.w. less than its fluid-phase counterpart. By using biosynthetically ([3H]proline) labeled C1q from guinea pig peritoneal macrophages, we found that the membrane form of C1q is derived from already secreted C1q. The demonstration of a distinct membrane form of C1q supports earlier functional studies which implicated C1q as a membrane-associated molecule with receptor functions for those molecules which also interact with fluid-phase C1q, such as polyanions, immune complexes, and bacteria. Furthermore, we show that, in the vicinity of macrophages, C1q is very susceptible to oxidation manifested by the formation of disulfide bonds. By SDS-PAGE (nonreduced and reduced), we demonstrate the existence of disulfide-linked multimers (180,000 m.w., 360,000 m.w.) which are composed of the A, B, and C chains of C1q.

Animals↗

PubMed1987

Autoantibody-mediated acquired deficiency of C1 inhibitor.

During the past 25 years, three forms of deficiency of the inhibitor of the first component of complement (C1 inhibitor) with angioedema have been recognized; two forms are hereditary and one is acquired. As compared with hereditary angioedema, the syndrome of acquired C1-inhibitor deficiency is rare, and it is usually associated with lymphoproliferative diseases. We report another type of acquired C1-inhibitor deficiency with angioedema. Two patients with recurrent angioedema but no associated diseases were found to have IgG1 autoantibodies against C1 inhibitor. The anti-C1-inhibitor antibodies prevented binding of C1 inhibitor to activated C1s. Both patients had 60 to 70 percent of normal levels of C1 inhibitor, but it was functionally inactive, with a molecular weight of 96,000 (normal C1 inhibitor, 105,000). In vitro studies of the patients' serum revealed degradation of 125I-labeled 105,000-dalton C1 inhibitor into the inactive 96,000-dalton molecule, caused by activated C1s and not found in normal human serum. We conclude that these cases of acquired C1-inhibitor deficiency resulted from a blockade of C1-inhibitor function by the anti-C1-inhibitor antibodies and from subsequent inactivation of C1 inhibitor by the now uncontrolled enzyme, activated C1s. As in other forms of C1-inhibitor deficiency, the unopposed activation of the complement system led to angioedema.

Adult↗

PubMed1987

[Formation of IgG antibodies to C1 inhibitor as the cause of life-threatening angioedema].

A clinical picture with recurrent (in some cases potentially fatal) edema of skin and internal organs based not on a hereditary C1 inhibitor deficiency, but an acquired loss of C1 inhibitor activity due to antibodies is described for the first time in two patients. The clinical symptoms commenced in middle age patients between 40 and 46 years old. Anti C1 antibodies of the IgG were found in both patients. Quantitatively, these C1 inhibitor protein was in the lower range of normal, whereas no inhibitor activity could be demonstrated functionally. The function of the complement components C1, C2 and C4 was greatly reduced. The therapeutic use of C1 inhibitor concentrate at a high doses (6 X 500 U) as well as administration of high-dose corticosteroids in several emergency situations was unsuccessful.

Adult↗

PubMed1987

Simplified methods for the purification, quantitation, and functional estimation of human complement C-1-inhibitor (C-1-INH) with a monoclonal anti-C-1-INH antibody.

New methods have been developed for the isolation, quantitative detection, and functional measurement of human complement C-1-inhibitor (C-1-INH). The two-step purification procedure for C-1-INH from human plasma or serum employs affinity chromatography with a monoclonal anti-C-1-INH antibody coupled to CNBr-activated Sepharose 4B followed by fractionation on a FPLC Mono Q HR 5/5 column. It yields functionally active, homogeneous C-1-INH with about 40% recovery. For quantitative estimation of C-1-INH an ELISA was performed. ELISA plates were coated with a polyclonal anti-C-1-INH antibody, serum or plasma was added and bound C-1-INH was detected with the monoclonal anti-C-1-INH antibody. The method has a sensitivity of 0.4 ng C-1-INH per assay corresponding to 20 ng/ml. For the detection of functionally active C-1-INH an ELISA was developed using C1-s-coated microtiter plates. After incubation with serum or plasma, C1-s-bound C-1-INH was monitored with the monoclonal anti-C-1-INH antibody. With this method it is possible to measure as little as 0.3 ng of functionally active C-1-INH in 20 microliter of a biological sample. All methods described in the present paper are easy to perform, rapid, sensitive, and highly reproducible.

Animals↗

PubMed1987

Antibody-independent killing of gram-negative bacteria via the classical pathway of complement.

The experiments in this paper provided evidence that, besides lipopolysaccharides (LPS), porins of gram-negative bacteria bind to C1q and C1. From these experiments, we concluded that the association of LPS and porins (outer membrane proteins, OMP) may potentiate the C1q and C1 binding in the absence of specific antibodies. This antibody independent binding of C1 to LPS and porins is a prerequisite for the activation of the classical pathway of complement leading to the killing of serum-sensitive bacteria.

Bacterial Outer Membrane Proteins↗

PubMed1987

Sensitivity of normal human bone marrow myeloid progenitor cells to anthracycline, cisplatin, anthracene and flavone acetic acid derivatives, and its relevance for the prediction of human plasma concentrations of anticancer drugs.

Many in vitro investigations with anticancer agents are performed at concentrations equal to the peak concentrations or fractions of the peak concentrations achieved in human plasma after administration of these agents. In an effort to develop an in vitro test capable of predicting these peak plasma concentrations prior to the completion of pharmacokinetic studies, the effect of several classes of anticancer agents against normal human bone marrow myeloid progenitor cells (CFU-GM) was studied. The investigated agents included anthracycline antibiotics, cisplatin and its analogs, anthracene derivatives and two flavone acetic acid derivatives. The CFU-GM were exposed to these agents for 30-60 min. An exponential relationship between drug concentration and CFU-GM growth was observed for all compounds with the exception of the flavone acetic acid derivatives which were inactive. For the latter two compounds, an inhibition of CFU-GM growth was observed after continuous exposure. When compared to the plasma concentrations after parenteral administration of these agents, there was a very good agreement between 1/10 of the peak plasma concentration and the concentration inducing a 90% inhibition of the CFU-GM growth for the anthracycline antibiotics and anthracene derivatives. In contrast, for cisplatin and its analogs, there was a better agreement between 1/10 of the peak plasma concentration and the concentration inducing a 10% inhibition of CFU-GM growth. The combination of concentrations inducing inhibitions of 10 and 90% of the CFU-GM growth provides a range of concentrations that predict reasonably well the peak plasma concentrations of several anticancer agents and that could be used as guides for other in vitro investigations.

Anthracenes↗