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M Loos

Publications and source records attributed to M Loos.

At least 55 records · Page 3Linked to original sources
PubMed1992

Purification and characterization of a Salmonella typhimurium agglutinin from gut mucus secretions.

One of the earliest events in Salmonella typhimurium pathogenesis seems to be the interaction of the bacterium with the mucus of the gut. After exposing S. typhimurium to guinea-pig colon, we were able to demonstrate by electron microscopy that S. typhimurium bacteria were trapped on, or in, the mucus layer. Specific components isolated from crude mucus secretions were found to aggregate the bacteria. The degree of bacterial aggregation was dependent on the protein concentration of the crude mucus and on time. Aggregation of S. typhimurium could be abolished by sugars: L-fucose exhibited the strongest inhibition, followed by D-glucose, D-galactose and D-mannose. Lectins were also capable of inhibiting aggregation, the lectin of Ulex europaeus (UEA I), specific for L-fucose, was found to be a stronger inhibitor of bacterial aggregation than Con A. The agglutinin for S. typhimurium isolated from guinea-pig colonic crude mucus preparation was characterized as a 15 kDa glycoprotein. An affinity-purified anti-15 kD antibody inhibited, dose-dependently, the aggregation of S. typhimurium by crude mucus material.

Agglutinins↗
PubMed1992

Modulation of type II collagen-induced arthritis in DBA/1 mice by intravenous application of a peptide from the C1q-A chain.

In this report we are able to show that intravenous (i.v.) application (day 0) of a nonapeptide (residues 26-34) from the human C1q A-chain (designated peptide A-C1q) prior to intradermal (i.d.) administration of chicken type II collagen (CII) in arthritis-susceptible DBA/1 mice (H2q), leads to abrogation of polymorphonuclear neutrophil (PMN) invasion into the joints. This nonapeptide exhibits epitope characteristics and high homology to residues 137-147 of CB11 (a cyanogen bromide fragment of chicken CII, known to contain both arthritis inducing and suppressing determinants). Arthritis index was lowest in animals pretreated i.v. with CII (as internal control), though animals pretreated i.v. with peptide K (residues 137-147 with an additional glycine residue from CB11) or peptide A-C1q exhibited comparative arthritic indices. Only in the arthritis-positive control group (day 0: PBS i.v.) did i.d. application of CII lead to invasion of PMN into the synovial layer and the joint space. Analysis of antibody (Ab) responses at day 48 after i.v. immunization (day 0) and CII challenge (day 7) revealed IgE-Abs to native CII and also to native C1q. IgG titers to CII were highest in animals pretreated with peptide A-C1q. Abs from this group, exhibiting activity to peptide A-C1q (immunizing antigen), were of mainly IgG1 and IgG3 isotypes. Evaluation of the immune response following i.v. application of peptide A-C1q or CII, prior to i.d. CII administration, in DBA/1 mice, revealed IgM responses to peptide A-C1q and peptide K, but not to CII. Intravenous application of peptide A-C1q led to generation of IgG3-Abs reacting only with peptide A-C1q and peptide K, but not with native CII. Additionally, i.v. application of peptide A-C1q elicited IgG responses to a pentapeptide, resembling amino acid residues 26-30 (K-G-E-Q-G) of the C1q A-chain. This five residue antigenic determinant is present in peptide K, in chicken and human CII as well as in human C1q. No specific IgE response to any of the antigens tested could be detected. Since a peptide from the C1q A-chain is both capable of eliciting immune responses and modulating CII-induced arthritis in mice, we postulate that the collagen-like complement component C1q is involved in the development of CII-induced inflammatory arthritic lesions, and may represent, in vivo, the early antigen responsible for inducing anticollagen antibodies prior to CII in hyaline cartilage becoming available as antigen.

Adjuvants, Immunologic↗
PubMed1992

A 66-kilodalton heat shock protein of Salmonella typhimurium is responsible for binding of the bacterium to intestinal mucus.

Salmonella typhimurium infections have increased during the last few years. However, the interplay of virulence factors in S. typhimurium pathogenesis is still poorly understood, particularly with regard to the mechanisms and components of the bacterium which are involved in its interaction with the intestinal mucus. We have observed that S. typhimurium is aggregated by incubation with colonic mucus (guinea pig model). To quantify this phenomenon, an aggregation assay was established. By using this assay, it was found that the aggregation profile of S. typhimurium strains freshly isolated from patients (age 9 and older) with salmonellosis correlated with the severity of the disease. An isolate with high aggregation behavior was chosen for characterization of the bacterial component involved in binding to colonic mucus material. The component of S. typhimurium responsible for aggregation was purified and characterized as a 66-kDa protein which was able to completely inhibit mucus-mediated bacterial aggregation. This protein was recognized by monoclonal antibodies against the 65-kDa heat shock protein (HSP) of Mycobacterium leprae. The 66-kDa protein of S. typhimurium was inducible by incubating the bacteria at 50 degrees C and was secreted into the supernatant, from which it could be isolated in both dimeric and polymeric forms. The monoclonal anti-HSP 65, as well as a polyclonal antibody against the 66-kDa protein of S. typhimurium, caused dose-dependent inhibition of the aggregation of S. typhimurium by crude mucus preparations. This is the first report showing that a bacterial HSP is involved in mucus-mediated interaction of pathogens with the host.

Adolescent↗
PubMed1991

Gene expression of the A- and B-chain of mouse C1q in different tissues and the characterization of the recombinant A-chain.

Immunoscreening of a mouse macrophage cDNA library with an anti-mouse C1q-antibody resulted in the isolation of cDNA clones. The deduced amino acid sequence was homologous to the A-chain of human C1q. Homology on the DNA level was found to be 76% and on the protein level 72% thus it appeared the clones coded for the mouse C1q A-chain. An immunoblot of murine serum C1q separated by SDS-PAGE was detected with an A-chain specific antibody that had been affinity purified on recombinant mouse C1q A-chain expressed in Escherichia coli. The antibody preparation reacted exclusively with the mouse C-chain (as defined by SDS-PAGE). Northern blot analysis with strand-specific cDNA probes coding for the A- and B-chain of murine C1q showed that mouse peritoneal macrophages produced the highest concentration of C1q gene transcripts. RNA from mouse spleen, thymus, heart, and brain gave substantial hybridization signals, whereas RNA preparations from liver, kidney, lung, and small intestine appeared to contain only trace amounts of C1q mRNA. In a Northern blot analysis of different guinea pig cells and tissues, only RNA preparations from peritoneal macrophages hybridized with the mouse C1q probes. These results indicate that macrophages are a major site of C1q biosynthesis.

Amino Acid Sequence↗
PubMed1991

C1q-bearing immune complexes detected by a monoclonal antibody to human C1q in rheumatoid arthritis sera and synovial fluids.

Using a monoclonal antibody directed against the C-chain of human C1q, we detected C1q-bearing immune complexes (IC) in sera and synovial fluids of rheumatoid arthritis (RA) patients. In a sandwich-ELISA, C1q-bearing IC were captured by the solid-phase monoclonal antibody and then detected with peroxidase-labeled F(ab')2-antibodies to either human IgG or IgM. The results of this assay were compared to an ELISA-modification of the C1q-solid-phase binding assay (C1q-SPBA). C1q-bearing IC were detected in 81.1% of RA-sera and the 65.2% of RA-synovial fluids. IgG as well as IgM was present in 72.6% of the sera and 70% of the synovial fluids which were positive in both assays. Most RA sera that were only positive for C1q-bearing IC, contained IgG alone (81.5%). The corresponding synovial fluids showed IgG alone (53%) or both IgG and IgM (41.1%). IgM alone (25%) could be detected in sera, e.g. in juvenile forms of RA. The levels of IC were higher in synovial fluid than in paired serum. In comparison to normal human serum (NHS) and patients with osteoarthritis, complement activity (CH50 titers) and C1q-values in patients with RA were frequently elevated. Since the formation of C1q-bearing IC is an indicator for the classical complement pathway activation, an assay with monoclonal anti-C1q antibody may be a useful tool in the diagnosis of rheumatoid diseases.

Antibodies, Monoclonal↗
PubMed1990

Studies on the interaction of C1q, a subcomponent of the first component of complement, with porins from Salmonella minnesota incorporated into artificial membranes.

Purified outer membrane proteins (OMP) of Salmonella minnesota, Re-form, were incorporated into liposomes. These induced in macrophages a chemiluminescence signal identical to that of the intact Re-form. This signal was abolished by preincubation of porin-containing liposomes with purified C1q. Incorporation of isolated OMP into black lipid membranes (BLM) resulted in channel-formation which could not be inhibited by isolated C1q. Additionally, incubation of OMP-containing liposomes with BLM resulted in pore-formation within the BLM. This was amplified when lipid A was present within the liposomes. Preincubation of OMP-containing liposomes with purified C1q abolished pore-formation within the BLM.

Animals↗
PubMed1990

[Autoantibodies against the complement component C1q in systemic lupus erythematosus].

Autoantibodies against C1q, a subcomponent of the first complement component C1, could be detected in 49.4% of sera from patients with systemic lupus erythematosus (SLE). They are directed against the collagen-like portion of the C1q molecule and recognize only bound, but not fluid-phase C1q. The appearance of these autoantibodies in the course of SLE correlates with the detection of IgG in the C1q-Solid-Phase-Binding-assay, with high titres of dsDNA-antibodies and with depressed total complement activity (CH50) and C1q-values. Our investigations show that autoantibodies against the collagen-like portion of bound C1q but not immune complexes are the main constituent of C1q-binding IgG in SLE.

Autoantibodies↗
PubMed1990

Disulfide bridge formation between C1q and IgG in vitro.

The globular heads of C1q are known to possess free-SH groups. Here we show that these groups, which are concealed in the native molecule, are exposed by interaction of C1q with dialysis membrane. During iodination, I+ and I2 oxidize these sulfhydryls to produce disulfide-linked C1q aggregates. Approximately 15% of C1q bound to immunoglobulin aggregates is resistant to high conductivity elution and reducing agent is required to release it. These data show that dialysis, adsorption to Ig and iodination of C1q result in structural and functional changes in the molecule, and suggest a mechanism by which these changes occur. Disulfide bridging between C1q and IgG in vitro suggests that this may be a normal physiological function of C1q for which the free cysteines of human, mouse and guinea pig C1q have been conserved.

Animals↗
PubMed1990

Influence of recombinant alpha and gamma interferons on the in vitro proliferation of myeloid and leukemic progenitors.

We have compared the effect of alpha 2-C and gamma recombinant interferons (rIFNs) on normal myeloid progenitors (N-CFU-GM), chronic myeloid leukemia (CML) progenitors (CML-CFU-GM) and leukemic progenitors (L-CFU) of acute non-lymphoblastic leukemia (ANLL) patients. Within 14 days of continuous exposure in culture, a dose-dependent inhibition of CFU-GM was seen for most normal subjects. Resistance to rIFNs was frequent in leukemic patients and even more in acute leukemia than in CML. Stimulation of clonogenic cell growth was seen for a minority of leukemic patients. When only the sensitive cases were considered, no difference in sensitivity was noticed between normal, CML and ANLL patients. A good correlation was observed between the activity or the lack of activity of alpha and gamma rIFNs.

Bone Marrow↗
PubMed1989

Molecular cloning and characterization of the complementary DNA coding for the B-chain of murine Clq.

cDNA clones coding for the B-chain of murine Clq were isolated from a mouse macrophage library. The characterized clones include the total coding region plus a leader sequence. High homology was found with human Clq B-chain in the coding region (81%). Northern blot analysis of total RNA from different tissues of Balb/c mice showed one band of approximately 1.2 kb. The highest signal was found in RNA preparations of thioglycolate-activated peritoneal macrophages. The probe also hybridized with mRNA from spleen, thymus and heart. Extremely weak signals were found in liver, kidney, lung and intestine tissues.

Animals↗
PubMed1989

Common epitopes in Clq and collagen type II.

An epitope common for collagen type II and Clq was demonstrated by specific binding of a monoclonal anti-collagen type II antibody, MAb B1, to purified Clq. This was further substantiated by the affinity shown between F(ab')2 fragments of anti-Clq antibodies and rat chondrosarcoma collagen type II. The interaction between MAb B1 and Clq was demonstrated in hemolytic assays, in an enzyme-linked biotin-avidin assay and by the binding of Clq to MAb B1 immobilized on Sepharose 4B beads. MAb B1 recognized only purified Clq and not the macromolecular Cl complex, indicating that the epitope for MAb B1 was situated in the collagen-like region in Clq, where Clq and Cls are anchored. The binding of the purified collagen-like fragment of Clq to radiolabelled MAb B1 confirmed these findings. The affinity between MAb B1 and Clq was significantly increased if Clq was first reacted with heat aggregated IgG, indicating a demasking of the reactive epitope on binding to the aggregated IgG. The present findings raise the question of the pathogenetic significance of the presence of anti-collagen type II antibodies and free Clq, both of which are frequently seen in high amounts in rheumatoid arthritis.

Animals↗
PubMed1989

Monoclonal antibodies against components of the classical pathway of complement.

Activation of the classical pathway of complement involves several binding and enzymatic cleavage processes. Binding and enzymatic activation results in the appearance of new structures in the individual components. This report describes the different activation steps for C1q, C1r, C1s, C4 and C2 and summarizes monoclonal antibodies reported so far which recognize either conserved epitopes or activation-dependent epitopes with particular emphasis on neoepitopes occurring during the activation cascade.

Antibodies, Monoclonal↗
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↗