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M Mannik

Publications and source records attributed to M Mannik.

At least 37 records · Page 2Linked to original sources
PubMed1991

Human IgA and IgG F(ab')2 that bind to staphylococcal protein A belong to the VHIII subgroup.

Staphylococcal protein A (SPA) is a bacterial membrane protein that possesses, in addition to its Fc gamma-binding activity, a distinct specificity for the Fab region of some IgM, IgA, IgG, and IgE. The Fab site that binds to SPA has been localized to the V region of the Ig H chain. In a previous study of human monoclonal and polyclonal IgM, we demonstrated that binding to SPA was highly restricted to molecules of the VHIII subgroup, and that nearly all VHIII IgM were able to bind SPA. The present study examines the VH composition of SPA-binding and SPA-nonbinding fractions of purified human polyclonal IgA, and IgG F(ab')2 fragments. We found that 22% of the IgA and 15% of the IgG F(ab')2 bound to SPA-agarose. Analysis with VH subgroup-specific antisera indicated that the SPA-binding fraction of IgA was dominated by the VHIII subgroup, and the SPA-binding fraction of IgG F(ab')2 contained only VHIII molecules. Furthermore, substantial portions of the total VHIII protein in IgA and in IgG F(ab')2 bound to SPA. We conclude that Fab binding to SPA is both restricted to and highly prevalent among human VHIII molecules, regardless of Ig class. These results suggest that protein A is an Ig superantigen.

Antibody Specificity↗
PubMed1991

Autoantibodies to the collagen-like region of C1Q deposit in glomeruli via C1Q in immune deposits.

The autoantibodies to the collagen-like region of C1q (CLR), purified from two patients with systemic lupus erythematosus, deposited in mouse glomeruli when human C1q was present in antigen-antibody complexes in glomeruli. The immune deposits with C1q in mouse glomeruli were achieved by the administration of cationized immune complexes containing human C1q. The presented data suggest that the autoantibodies to CLR could enhance the pathogenic role of immune complexes deposited in glomeruli by binding to C1q in immune deposits. These findings may explain the association of autoantibodies to CLR with proliferative lupus nephritis.

Animals↗
PubMed1991

Glomerular subendothelial and subepithelial immune complexes, containing the same antigen, are removed at different rates.

To examine the persistence of immune deposits in the subendothelial and subepithelial areas of the glomerular basement membrane in rats, immune deposits were formed by injection of radiolabelled, cationized human serum albumin (HSA) as antigen, followed by rabbit antibodies to HSA. The disappearance of the radiolabelled antigen from immune deposits in glomeruli was described by a curve consisting of two exponential components. By electron microscopy, subendothelial and subepithelial immune deposits were initially present in glomeruli. At later time-points, only subepithelial immune deposits were present. The fast component of disappearance, attributed to subendothelial deposits, had a half-life of 3.89 +/- 0.32 h. The slow component of disappearance from glomeruli, attributed to subepithelial deposits, had a half-life of 85.5 +/- 3.1 h. Since some of the injected, radiolabelled antigen was sequestered in other compartments of the body, the possibility was raised that antigen from these sites might be released and contribute to the persistence of deposits in glomeruli. This possibility, however, was excluded when transplantation of kidneys with immune deposits to untreated recipients revealed no difference in the amount of antigen persisting in nontransplanted and transplanted kidneys.

Animals↗
PubMed1990

A small proportion of cationic antibodies in immune complexes is sufficient to mediate their deposition in glomeruli.

Positively charged antibodies mediate enhanced deposition of circulating immune complexes at the glomerular basement membrane. The presented experiments demonstrate that when soluble immune complexes were prepared with a mixture of antibodies containing 10 to 25% cationic antibodies, then noncationic antibodies in the complexes were deposited in mouse glomeruli. One or two cationic antibodies in each immune complex sufficed for deposition of the complexes. Proof for this was obtained by two kinds of experiments. First, the injected immune complexes were prepared in Ag excess from mixtures of radiolabeled noncationic rabbit antibodies to human serum albumin (HSA) and unlabeled cationized rabbit antibodies to HSA, thus permitting the specific quantitation of the deposition of noncationic antibodies in glomeruli because of the presence of cationized antibodies within the same complexes. As a control experiment, immune complexes prepared only with noncationic antibodies resulted in very little deposition in kidneys over the same time period. Second, detection of the localization of the noncationic antibody in deposits in glomeruli by immunofluorescence microscopy was accomplished using immune complexes prepared with mixtures of noncationic goat antibodies to HSA and cationized rabbit antibodies to HSA. Thus, the synthesis of a small population of cationic antibodies during the immune response may lead to the formation of circulating immune complexes with enhanced propensity for deposition in glomeruli in patients with SLE or other immune complex diseases.

Animals↗
PubMed1990

The location of binding sites on C1q for DNA.

Previous studies have suggested that C1q reacts with DNA via both the globular region of C1q (GR) and the collagen-like region of C1q (CLR). In this study, the binding of dsDNA and ssDNA to GR and CLR was quantitated by a solid-phase assay. Both dsDNA and ssDNA bound to the GR and CLR of C1q in an ionic strength-dependent manner. Under physiologic salt concentrations, however, dsDNA and ssDNA bound preferentially to CLR and not to GR. The binding of dsDNA to C1q was not affected by heat inactivation of C1q or its exposure to pH 4.45, which abolished the binding of heat-aggregated human IgG (AHG) with C1q. The preincubation of the solid-phase C1q with AHG did not decrease the binding of dsDNA or ssDNA to the solid-phase C1q. These results indicate that the major sites for binding DNA to C1q are located in the CLR of C1q and are not overlapping with those for AHG or immune complexes.

Binding Sites↗
PubMed1990

Immune deposits in articular cartilage of patients with rheumatoid arthritis have a granular pattern not seen in osteoarthritis.

Frozen sections of articular cartilage, obtained from patients with rheumatoid arthritis (RA) or osteoarthritis (OA) undergoing joint replacement, were stained with fluoresceinated specific antisera to IgG, IgM, IgA, C1q, C4, and C3. Specimens positive for IgG were examined for IgG subclasses using mouse monoclonal antibodies. IgG was present in 22 of 34 cartilage specimens obtained from patients with RA, and in 14 of these 22 patients, a granular pattern was present. IgM, IgA, C1q, and C3 when present showed a similar granular pattern. In articular cartilage of patients with RA, all IgG subclasses tended to be present. The remaining eight specimens positive for IgG from patients with RA had staining patterns also seen in patients with OA. IgG staining was present in 31 of 117 cartilage specimens obtained from patients with OA and none had the granular pattern seen in RA. Intermittent linear staining at the surface was the most common pattern seen in cartilage from patients with OA. The different patterns of immune deposits in articular cartilage in RA and OA suggest that antibodies with different specificities are present or that different mechanisms of immune deposit formation exist in these disorders.

Antibodies, Monoclonal↗
PubMed1989

Human IgM molecules that bind staphylococcal protein A contain VHIII H chains.

Staphylococcal protein A (SPA) is a bacterial membrane protein which has distinct binding sites for Fc gamma and for the Fab region of some IgM, IgG, IgA, and IgE molecules. This study establishes a structure-function correlation responsible for the binding of Ig Fab regions to SPA. Binding of 24 isolated human monoclonal IgM proteins to SPA was measured in a solid phase RIA. VH and V kappa subgroups of each IgM were determined by SDS-PAGE, transfer blotting, and detection with antisera prepared against specific first framework region peptides. Binding to SPA was seen with 10 of 11 VHIII IgM, but none of the 7 VHI or 6 VHII. Similarly, polyclonal IgM fractionated on a SPA-Sepharose CL4B column showed nearly complete partition of VHIII molecules into the SPA-binding fraction, and VHI and VHII subgroup proteins into the fall-through. We conclude that SPA binding is a functional marker for VHIII H chains in human IgM molecules.

Binding Sites↗
PubMed1989

Binding of double-stranded DNA to glomeruli of rats in vivo.

In vivo binding of double-stranded DNA (dsDNA) to renal glomeruli of rats was examined. 125I-dsDNA (600 basepairs) was perfused with 131I-IgG as a blood marker into the right renal artery of normal rats, and blood flow was restored. After 10 minutes, isolated glomeruli showed a specific uptake of DNA, which increased in a saturable fashion with increasing doses of administered DNA. To exclude the possibility that 125I in the glomeruli represented only DNA breakdown products, we extracted the DNA from the glomeruli for analysis by polyacrylamide gel electrophoresis. The extracted DNA was 120-200 bp in size, which is large enough to bind antibodies to DNA. In contrast, the radioactivity of DNA taken up by the liver or renal tissues other than glomeruli was predominantly trichloroacetic acid soluble, i.e., less than 15 bp. Immunofluorescence studies showed that antibodies to DNA, administered after DNA, were present in glomeruli. Our data indicate that dsDNA binds to glomeruli in vivo in a saturable manner, and remains large enough to be antigenic. Therefore, the binding of DNA to glomeruli, followed by interaction with antibodies to dsDNA may be a mechanism for DNA-anti-DNA complex formation in glomeruli in patients with systemic lupus erythematosus.

Animals↗
PubMed1989

Antibodies to the collagen-like region of C1q in sera of patients with autoimmune rheumatic diseases.

Antibodies to the collagen-like region of C1q have recently been observed in sera of patients with systemic lupus erythematosus (SLE). In this study, we documented that these antibodies were present in 47.3% of SLE patient sera, whereas they were uncommon in sera from patients with rheumatoid arthritis (2.8%) and Sjögren's syndrome (12.8%), as well as in normal sera (6.4%). Markedly elevated antibody levels (greater than 4 SD above the normal mean) were observed almost exclusively in sera of patients with SLE. Levels of antibodies to the collagen-like region correlated highly with levels of solid-phase C1q-binding IgG when analyzed by the C1q solid-phase assay for immune complexes (r = 0.87). We previously found that, after sucrose density gradient ultracentrifugation, a predominance of the solid-phase C1q-binding IgG in SLE sera sediments as monomeric IgG. These findings, together with the present data, indicate that reactivity of SLE patients' sera in the C1q solid-phase assay reflects primarily the presence of antibodies to the collagen-like region, and not the presence of immune complexes.

Arthritis, Rheumatoid↗
PubMed1989

IgG subclasses of antibodies to the collagen-like region of C1q in patients with systemic lupus erythematosus.

Low molecular weight C1q-binding IgG in the sera of patients with systemic lupus erythematosus consists of autoantibodies to the collagen-like region of C1q. In this study, the IgG subclass distribution of these autoantibodies was examined by radial immunodiffusion with polyclonal antibodies specific for each subclass. The purified antibodies to the collagen-like region of C1q possessed the IgG subclass distribution present in normal serum.

Antibodies↗
PubMed1989

Deposition of immune complexes containing cationized antibodies in myocardial small blood vessels of mice.

Small myocardial blood vessels constitute a site for preferential deposition of preformed cationic immune complexes. This preferential deposition was demonstrated with a limited dose (100 micrograms) of cationized rabbit antibodies to human serum albumin, injected into C57B1/6J mice either alone or in the form of preformed immune complexes. Heart, kidney, liver, intestine, and skeletal muscle were examined for immune deposits by immunofluorescence microscopy. Highly cationized antibodies injected alone showed deposition in glomeruli and in the liver along the sinusoids but not in other tissues. Immune complexes containing native rabbit antibodies deposited only in liver in a Kupffer cell pattern. Moderate and highly cationized antibodies in immune complexes deposited in myocardial small blood vessels, liver, and glomeruli, but not in intestine or skeletal muscle. These complexes deposited via electrostatic interactions since unrelated polycationic molecules, protamine sulfate or cationized rabbit serum albumin, injected 1 min prior to cationic antibodies in immune complexes blocked deposition in myocardial small vessels, glomeruli, and liver. Administration of protamine or cationized rabbit serum albumin 1 min after deposition of cationized immune complexes resulted in displacement of the immune deposits in heart, kidney, and liver, but not when the injection was given 1 hr later. The presented data indicate that with passage of time the immune deposits rearrange and forces other than charge-charge interactions retain them in myocardial vessels.

Animals↗
PubMed1989

Development of immune complexes in the skin.

Complement activation by immune complexes induces inflammation, but during this process the nature of the complexes is altered. Once immune complexes have attained sufficient lattice to activate complement, further increase of the lattice and immune precipitation are limited by the incorporation of complement components. The presence of complement components in immune complexes facilitates their disposal from circulation by complement receptors on red cells in humans. Without complement activation the disposal of immune complexes of sufficient lattice is mediated by Fc receptors. The development of immune deposits in tissues can arise by several mechanisms. Circulating immune complexes may be deposited in a number of vascular beds. Immune deposits in tissues may also arise by local formation. This process may involve structural antigens in tissues, cell surface antigens that are shed after interaction with specific antibodies or antigens that have become planted in tissues and then combine with antibodies. Charge-charge interactions enhance deposition of immune complexes in several organs, involving fixed negative charges in tissues and positive charges on antigens or antibodies in immune complexes. Successful detection of immune deposits in dermal vessels requires the examination of fresh lesions. Local vascular changes contribute significantly to deposition of immune complexes in dermal vessels. Charge-charge interactions enhance this deposition and contribute to the development of deposits at the dermal-epidermal junction in experimental animals.

Animals↗
PubMed1988

Antigenic specificities of human monoclonal and polyclonal IgM rheumatoid factors. The C gamma 2-C gamma 3 interface region contains the major determinants.

The binding site specificity of 12 monoclonal and 11 polyclonal IgM rheumatoid factors (RF) isolated from human plasma or serum has been studied. All IgM RF bound best to sites on IgG and intact Fc. The monoclonal IgM RF did not bind at all to fragments lacking the C gamma 2 or C gamma 3 domains. In contrast, low level binding to the pFc' fragment, composed of the C gamma 3 domain, was seen with seven IgM RF, mainly from patients with rheumatoid arthritis (RA). IgG1 binding appeared to be a requisite specificity of all human IgM RF. IgM RF binding to IgG3 subclass was common among the monoclonal IgM RF. Most RA polyclonal IgM RF but only 2 of the monoclonal IgM RF possessed the IgG1, 2 and 4 binding pattern. Monoclonal IgM RF which bound best to histidine-modified IgG also bound well to IgG3. The 7-kDa fragment D of staphylococcal protein A inhibited the IgG binding of most monoclonal and to a lesser degree polyclonal IgM RF. Thus, the results indicate that the C gamma 2-C gamma 3 interface region of IgG contains the predominant determinants for monoclonal and polyclonal IgM RF. For some monoclonal IgM RF the binding site, even though at the interface of the C gamma 2 and C gamma 3 domains, is not the staphylococcal protein A site. Furthermore, polyclonal IgM RF possess specificities not encountered among the monoclonal IgM RF. These specificities may have special

Animals↗
PubMed1988

Absence of auto-antiidiotypic activity between the IgM and IgG fractions of human mixed cryoglobulins.

Experimental animal models and observations in humans suggest that levels of Id and auto-anti-Id fluctuate reciprocally after Ag stimulation. In human monoclonal B cell disorders, however, the co-existence of paraprotein Id and its auto-anti-Id has been described in essential mixed cryoglobulinemia and in association with acquired C1 inhibitor deficiency. Because the majority of cryoglobulin IgM possess rheumatoid factor activity and thus bind the Fc region of IgG, we examined potential idiotypic interactions between cryoglobulin IgM and F(ab')2 fragments of autologous cryoglobulin IgG fractions. A rabbit antibody to the pepsin agglutinator site of human F(ab')2 was used as detection reagent. By recognizing epitopes exposed on F(ab')2 after the removal of Fc determinants by pepsin digestion, this reagent eliminates the detection of contaminating intact IgG. In a sensitive assay, we were unable to detect idiotypic interactions between the separated IgM and pepsin-digested IgG fractions of 10 mixed cryoglobulins. On the basis of these results, we suggest that in mixed cryoglobulinemia, the coexistence of paraprotein Id and its auto-anti-Id is unlikely.

Antibodies, Anti-Idiotypic↗
PubMed1988

Low-molecular weight C1q-binding immunoglobulin G in patients with systemic lupus erythematosus consists of autoantibodies to the collagen-like region of C1q.

The majority of C1q-binding IgG in sera of some patients with systemic lupus erythematosus (SLE) cosediments with monomeric IgG. This study was undertaken to provide definitive proof that the low-molecular weight C1q-binding IgG consists of autoantibodies to C1q. Monomeric C1q-binding IgG was isolated from five SLE plasmas by C1q affinity chromatography and gel filtration. All C1q-binding IgG preparations and their F(ab')2 fragments bound to both C1q and the collagen-like region of C1q by an ELISA. To rule out the possibility that small DNA-antiDNA immune complexes caused this binding activity, Fab' fragments of the C1q-binding IgG preparations were digested with DNase I to degrade any DNA. The Fab' fragments continued to bind to C1q and its collagen-like region after this treatment. C1q-binding IgG was heterogenous on isoelectric focusing. Interaction of C1q-binding IgG with solid-phase C1q was retained in 1 M NaCl, whereas the binding of DNA or heat-aggregated IgG to solid-phase C1q was abrogated or markedly diminished. The association constant of C1q-binding IgG with solid-phase C1q was 2.7 X 10(7) M-1. We conclude that low-molecular weight C1q-binding IgG in the studied patients with SLE consists of autoantibodies to the collagen-like region of C1q.

Autoantibodies↗
PubMed1988

Fc epitopes for human rheumatoid factors and the relationships of rheumatoid factors to the Fc binding proteins of microorganisms.

Work from our laboratories has shown that the major antigenic determinants for rheumatoid factors (RFs) are in the C gamma 2-C gamma 3 interface region of IgG in the same area that binds staphylococcal protein A (SPA). Furthermore, the Fc binding proteins of groups A, C and G streptococci as well as the Fc binding proteins induced on cell surfaces by herpes simplex virus type I also bind to the same area of IgG. These binding site similarities between RFs and the microbial Fc binding proteins suggested conformational similarities between the RF antigen combining regions and the Fc binding regions of the microbial proteins. This hypothesis was supported by the observation that antibodies to SPA bind to the antigen combining regions of most RFs as well as to the Fc binding region of the T15 group A streptococcal Fc binding protein. These findings indicate that RFs bear the conformational internal image of these microbial proteins and suggest that RFs could arise as antibodies to the idiotypic determinants on antibodies to microbial Fc binding proteins. Alternatively, microbial Fc binding proteins could present IgG to the immune system in a way that renders specific areas of the C gamma 2-C gamma 3 interface region immunogenic. These relationships between RFs and microbial Fc binding proteins may prove to be important for our understanding of the generation of RFs in rheumatoid arthritis.

Binding Sites↗