Recognition of two distinct groups of human IgM and IgA based on different binding to staphylococci

Interactions between ricinus agglutinin and human IgA

By affinity chromatography on Sepharose columns containing insolubilized ricinus agglutinin, all immunoglobulins of the IgA2 subclass and the polymers of IgA1 were retained and could be eluted with lactose. Monomeric IgA1 showed a more heterogeneous reaction with ricinus agglutinin. The major part was unretarded, whereas some of it was weakly bound to the column and could be eluted with lactose.

Binding of IgA to protein-A-containing staphylococci: relationship to subclasses

Among 54 human monoclonal IgA proteins, 5 inhibited the binding of labeled human monoclonal IgM (IgM Se and IgM Ba) to protein-A-containing staphylococci, whereas 48 did not have this ability. One protein (IgA Ha) showed discordant findings in the IgM Se and IgM Ba inhibitions assays. Among the 54 IgA proteins, 49 were of the IgA1 and 5 of the IgA2 subclass. All of the 5 IgA2 proteins inhibited the binding of IgM Se and IgM Ba to staphylococci, whereas the 48 proteins that reacted negatively in the two inhibition assays belonged to the IgA1 subclass. These findings show that the ability to react with staphylococci is a property of the IgA2 subclass. IgM proteins may also be divided into two groups based on different reactivities with protein A. It is proposed to call the two IgM subclasses IgM1 and IgM2, where the latter is defined by ability to react with protein A.

By-passing selection: direct screening for antibody-antigen interactions using protein arrays

We have developed a system to identify highly specific antibody-antigen interactions by protein array screening. This removes the need for selection using animal immunisation or in vitro techniques such as phage or ribosome display. We screened an array of 27 648 human foetal brain proteins with 12 well-expressed antibody fragments that had not previously been exposed to any antigen. Four highly specific antibody-antigen pairs were identified, including three antibodies that bind proteins of unknown function. The target proteins were expressed at a very low copy number on the array, emphasising the unbiased nature of the screen. The specificity and sensitivity of binding demonstrates that this 'naive' screening approach could be applied to the high throughput isolation of specific antibodies against many different targets in the human proteome.

Staphylococcus aureus protein A recognizes platelet gC1qR/p33: a novel mechanism for staphylococcal interactions with platelets

The adhesion of Staphylococcus aureus to platelets is a major determinant of virulence in the pathogenesis of endocarditis. Molecular mechanisms mediating S. aureus interactions with platelets, however, are incompletely understood. The present study describes the interaction between S. aureus protein A and gC1qR/p33, a multifunctional, ubiquitously distributed cellular protein, initially described as a binding site for the globular heads of C1q. Suspensions of fixed S. aureus or purified protein A, chemically cross-linked to agarose support beads, were found to capture native gC1qR from whole platelets. Moreover, biotinylated protein A bound specifically to fixed, adherent, human platelets. This interaction was inhibited by unlabeled protein A, soluble recombinant gC1qR (rgC1qR), or anti-gC1qR antibody F(ab')(2) fragments. The interaction between protein A and platelet gC1qR was underscored by studies illustrating preferential recognition of the protein A-bearing S. aureus Cowan I strain by gC1qR compared to recognition of the protein A-deficient Wood 46 strain, as well as inhibition of S. aureus Cowan I strain adhesion to immobilized platelets by soluble protein A. Further characterization of the protein A-gC1qR interaction by solid-phase enzyme-linked immunosorbent assay techniques measuring biotinylated gC1qR binding to immobilized protein A revealed specific binding that was inhibited by soluble protein A with a 50% inhibitory concentration of (3.3 +/- 0.7) x 10(-7) M (mean +/- standard deviation; n = 3). Rabbit immunoglobulin G (IgG) also prevented gC1qR-protein A interactions, and inactivation of protein A tyrosil residues by hyperiodination, previously reported to prevent the binding of IgG Fc, but not Fab, domains to protein A, abrogated gC1qR binding. These results suggest similar protein A structural requirements for gC1qR and IgG Fc binding. Further studies of structure and function using a truncated gC1qR mutant lacking amino acids 74 to 95 demonstrated that the protein A binding domain lies outside of the gC1qR amino-terminal alpha helix, which contains binding sites for the globular heads of C1q. In conclusion, the data implicate the platelet gC1qR as a novel cellular binding site for staphylococcal protein A and suggest an additional mechanism for bacterial cell adhesion to sites of vascular injury and thrombosis.

A study of the interactions between an IgG-binding domain based on the B domain of staphylococcal protein A and rabbit IgG

The nonantigenic interaction between a recombinant immunoglobulin G (IgG)-binding protein based on the B domain of Protein A from Staphylococcus aureus (termed SpA1) and the Fc fragment of rabbit IgG has been investigated. The contribution to binding of four putative hydrogen bond contacts between SpA1 and IgG-Fc were examined by the individual substitution of the residues in SpA1 involved in these interactions by others unable to form hydrogen bonds. It was found that the most important of the hydrogen bonds involved Tyr 18 which, when replaced by Phe, resulted in a twofold decrease in IgG-binding affinity. The residues of SpA1 proposed to make close, mainly hydrophobic, contacts with Fc were replaced by residues with potential electrostatic charge to establish the importance of the hydrophobic interaction in the complex. The IgG-binding affinities of the mutant proteins were compared to the wild-type protein by a competitive enzyme-linked immunosorbent assay. The replacement of individual hydrophobic residues by His generated a number of novel IgG-binding proteins with reduced binding affinity at pH 5.0 but which maintained strong binding affinities at pH 8.0. The elution profile of human IgG1-Fc (Fc fragment of human IgG1) from a column made from an immobilized two-domain mutant protein shows that the complex dissociates at a higher pH relative to that of the non-mutated protein thus offering favorable elution characteristics.

Binding of murine myeloma proteins of different Ig classes and subclasses to Fc-reactive surface structures in gram-positive cocci

Twelve different murine myeloma proteins were tested for binding to seventy Gram-positive strains belonging to group A, C and G streptococci and to Staphylococcus aureus. Group A streptococci, known to bind human IgG, were incapable of binding any of eight murine IgG immunoglobulins tested except for one strain that bound an IgG2b myeloma protein. In contrast, group C and G streptococci interacted with murine immunoglobulins of subclasses IgG2a, IgG2b and IgG3, and G strains also to a lesser extent with IgG1. Bovine and equine-group C streptococci did not differ from human group C streptococci in their IgG reactivity. Staphylococcal strains showed a high reactivity with murine myeloma components of IgG subclasses 2a, 2b and 3 and a low but definite binding of an IgG1 myeloma protein. IgA myeloma protein S-122 interacted with nine of fifteen group A streptococci. This binding could not be inhibited by human IgG and the reactivity is thus different from Fc-mediated binding of immunoglobulins. One of three IgA myeloma proteins tested, TEPC 15, bound to staphylococci. The Fc specificity of this interaction was confirmed by chromatography on protein A-Sepharose and by inhibition studies using polyclonal human IgG. The protein A reactivity of this monoclonal protein was detected in IgA aggregates and absent in the monomeric form of IgA.

A new bioluminescent assay for studies of protein G and protein A binding to IgG and IgM

It has been reported that protein G (PrG) specifically binds to IgG, but not to IgM. In the present paper, I report that using a bioluminescent immunoassay, that utilizes the recombinant calcium-dependent protein, Aequorin, as a photoprobe, IgM as well as IgG binds to PrG. The method presented here may also be used in general to study the glycosylation of proteins.

Humoral immune response in a marsupial Monodelphis domestica: anti-isotypic and anti-idiotypic responses detected by species-specific monoclonal anti-immunoglobulin reagents

We examined the humoral immune response of the laboratory opossum (Monodelphis domestica) as a model marsupial species. To evaluate antibody responses, IgM and IgG preparations were purified from the sera of naïve Monodelphis. These two immunoglobulin (Ig) preparations were used to generate specific murine monoclonal antibodies for use in ELISA-based serology. Individual Monodelphis were then immunized with a multideterminant protein antigen, a murine monoclonal antibody (Mab) IgG preparation designated Pab 405. In contrast with the primary IgM response of eutherian mammals, the primary response of Monodelphis to mouse IgG involved both IgG and IgM. The specificity of this anti-mouse IgG response appeared isotypic in nature, specifically, the immune sera recognized Ig determinants common to both Pab 405 and a control IgG Mab. Further, to evaluate the antibody responses to mouse IgG, immune sera were adsorbed against a control IgG Mab to remove the anti-isotypic reactivity. The adsorbed Monodelphis sera recognized idiotope specificities expressed on Pab 405. Based on an inhibition ELISA, the anti-idiotype (anti-Id) response recognized an idiotope on Pab 405 associated with its antigen combining site. These results demonstrate that Monodelphis respond to a multideterminant protein antigen such as murine IgG, similarly but not identically to eutherian mammals, and can serve as a useful marsupial model for additional comparative immunological studies.

Purification of murine immunoglobulin M from spent tissue culture supernatant by one-step gel filtration chromatography procedure

Optimal purification of immunoglobulin M (IgM) grown as spent tissue culture supernatant can be achieved by a straightforward size-exclusion chromatography procedure. Preparative isolation of IgM was achieved by precipitation with saturated ammonium sulphate to achieve a 45% solution. IgM was then purified by gel filtration chromatography with a solution of 100 mM Tris + 150 mM NaCl at pH 8. Denaturing electrophoresis and Western immunoblotting revealed two prominent bands at 80 and 25 kDa, indicative of the heavy and light chains of IgM respectively. The specific immunoreactivity of this IgM was assessed by a modified enzyme antigen capture assay. In contrast to affinity and ion-exchange chromatographies, gel filtration allows retention of IgM immunoreactivity.

Complementarity-determining region 2 is implicated in the binding of staphylococcal protein A to human immunoglobulin VHIII variable regions

Staphylococcal protein A (SPA) has two distinct binding sites on human immunoglobulins. In addition to binding to the Fc region of most IgG molecules, an "alternative" binding site has been localized to the Fab region of human immunoglobulins encoded by heavy chain variable gene segments belonging to the VHIII family. Comparison of amino acid sequences of closely related SPA-binding and -non-binding proteins suggested that VHIII-specific residues in the second complementarity-determining region (CDR2) were likely responsible for SPA binding activity. Site-directed mutagenesis of a single amino acid residue in CDR2 converted an IgM rheumatoid factor which did not bind SPA to an SPA binder. These findings, therefore, locate a critical site involved in SPA binding to the CDR2 of human immunoglobulins encoded by VHIII family gene segments.

The interaction between different domains of staphylococcal protein A and human polyclonal IgG, IgA, IgM and F(ab')2: separation of affinity from specificity

Binding properties of staphylococcal protein A (SpA) to different human immunoglobulins have been investigated. In this analysis, intact SpA as well as SpA-derived fragments containing one to five IgG-binding domains of different compositions, were used. The affinity binding constants of the different proteins to human polyclonal IgG, IgA, IgM and F(ab')2-fragments as well as their binding capacity to the immunoglobulin molecules were determined. The results show that although all the proteins bound to IgG, regardless of size or composition, the binding strength differed significantly. Proteins containing five domains have a stronger affinity for IgG than those containing one or two. There were no marked differences in binding strength between different domains. However, the binding ability to IgA and IgM showed a marked difference between the various SpA-derived proteins of different compositions. This discrepancy was correlated to differences in their relative binding properties to isolated F(ab')2-fragments of IgG. Hence, we conclude that the binding affinity is mainly affected by the number of domains, whereas the binding specificity is to a large extent determined by which domains are selected.

Immunoglobulin binding specificities of the homology regions (domains) of protein A

Protein A binds immunoglobulins and it has two target structures, one in Fc gamma (CH) and the other in selected VH regions. The protein has five homology regions (domains), A, B, C, D, and E. Fc-binding and VH-binding have been reported to be non-competitive, suggesting that different domains are responsible for the binding of the two ligands. On the other hand, all five domains have been reported to bind Fc. I studied binding of different immunoglobulins by protein A or its domain B (rBB). The results show that separate domains bind VH and Fc. If all five domains are capable of binding Fc, the ones that bind VH have low affinity for Fc. Furthermore, the number of Fc-binding domains varies depending on the type of the IgG being bound. Human IgG1 or IgG2 or rabbit IgG (Fc) seem to be bound by several domains (possibly four), and domain B is one of them. Mouse IgG1 or IgG2b are bound by fewer domains not including B. Murine IgG2a is also bound by fewer domains but B is one of them.

The alternative binding site for protein A in the Fab fragment of immunoglobulins

Twenty-six new human or murine monoclonal immunoglobulins (IgM, IgA, murine IgG1 or human IgG3) with a known V-region sequence were tested for alternative (non-Fc) binding to Staphylococcal protein A. Seven of them did not bind at all. Four immunoglobulins (all mouse IgG1) were bound but easily eluted (at pH 6). They were probably bound via the Fc part. All eleven were classified as negative for alternative binding. Fifteen immunoglobulins were found to bind more firmly; they came off the protein A column at pH 4-3 (alternative binders). Amino acid sequences of immunoglobulins that have been typed in the present work or earlier (25 binders and 26 non-binders) were compared. The light chain, the C region of the heavy chain and the D and JH segments look irrelevant for alternative binding. The N-terminal portion (amino acids 1-94) of the H chain probably forms the ligand of protein A. A peptide making the ligand cannot be reliably localized within this stretch but binder proteins had a high homology in residues 6-29. All mouse immunoglobulins expressing VH genes of families J606 or S107 were alternative binders; those expressing other families were non-binders.

Differential binding properties of protein A and protein G for dog immunoglobulins

We studied the binding of dog immunoglobulins G, A, M and E to protein A and protein G. Passive cutaneous anaphylaxis (PCA) testing was used for the measurement of dog IgE and enzyme-linked immunosorbent assays (ELISA) were used for the measurements of dog IgG, IgA and IgM. Protein A from lyophilized cells of Staphylococcus aureus bound 97% of IgE, 98% of IgG, 81% of IgA, and 97% of IgM. Protein A-Sepharose CL-4B bound 87% of IgE, 100% of IgG and IgA, and 98% of IgM. In a stepwise elution with varying pH, a small amount of IgE was eluted at pH 5 and pH 6 and all the remaining Igs were eluted at pH 3 from the protein A column. In contrast to protein A, dog IgE was not bound to Protein G-Sepharose, while 100% of IgG, 95% of IgA, and 44% of IgM were bound to Protein G-Sepharose.

High-performance liquid chromatography of amino acids, peptides and proteins. XCIII. Comparison of methods for the purification of mouse monoclonal immunoglobulin M autoantibodies

A comparison of methods for the purification of naturally occurring mouse monoclonal autoantibodies, of the immunoglobulin M (IgM) isotype, has been performed to determine the optimal strategies for the isolation of IgM from ascites fluid and in vitro tissue culture hybridoma supernatants. In order to quantify each purification procedure, the concentration of IgM in eluted fractions was determined by using a double-sandwich mu-chain-specific anti-IgM enzyme-linked immunosorbent assay, and the purity of the IgM was determined by a bicinchoninic acid-based protein assay and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The most efficient single-step purification was based on size-exclusion chromatography on high-resolution Superose 6 HR 10/30 fast protein liquid chromatography (FPLC) columns. This procedure resulted in recoveries of monoclonal IgMs of ca. 71-86% with purities between 68 and 86%. Single-step chromatography of monoclonal IgM, on Superose 6 FPLC columns resulted in a 21-fold purification of IgM, prepared by the in vitro culture of hybridoma cells in dialysis membrane. Size-exclusion chromatography, performed with Sephacryl S-300 columns, resulted in reduced resolution of monoclonal IgM, with yields of ca. 57-80% and purity of ca. 42-58% compared with the high-resolution Superose 6 FPLC columns. "Non-ideal" size-exclusion chromatography on Superose 6 FPLC columns resulted in selective retention of monoclonal IgMs and elution of IgM with high-ionic-strength buffers in the trailing peak. Recovery of IgM with this strategy was high (ca. 82-92%) but the purity was not comparable to the single-step fractionation of IgM on Superose 6 FPLC columns. Single-step anion- and cation-exchange and mixed-mode hydroxyapatite chromatography resulted in only partial purification of monoclonal IgM with the applied procedures. With these latter separation techniques, monoclonal IgM was eluted with a variety of other ascites fluid or supernatant proteins, including those with apparent molecular weights identical to those of mouse IgG and albumin. Sequential purification of monoclonal IgMs by Mono Q anion exchange, followed by Superose 6 FPLC columns, resulted in a 2- to 3-fold purification of IgM but did not separate IgM from high-molecular-weight contaminants with apparent molecular weights similar to those of alpha 2-macroglobulin and IgG. Enrichment of monoclonal IgM from ascites fluid by ammonium sulphate precipitation revealed increasing IgM recovery with increasing ammonium sulphate final concentrations up to 60%.(ABSTRACT TRUNCATED AT 400 WORDS)

Low and high molecular weight cytomegalovirus-specific immunoglobulin M antibody in renal transplant patients with cytomegalovirus infections

Sera from 27 renal transplant patients with primary and recurrent CMV infections and which were known to contain CMV-specific IgM antibodies were investigated by indirect immunofluorescence for the presence of virus-specific high molecular weight IgM (19S IgM) and low molecular weight IgM (7S IgM). After sucrose gradient fractionation of the sera, 19S IgM was found in all 27 patients, whereas 7S IgM was present in 11 out of 19 (56%) patients with primary CMV infection and in 1 out of 8 (12%) patients with recurrent CMV infection. The presence of 7S IgM was unrelated to the titre of the virus-specific IgM in whole serum. The presence of IgM rheumatoid factor was monitored by a sensitive fluorescence assay using measles virus antigen/antibody complexes. The absorption of the serum fractions with heat-aggregated gamma globulin failed to remove the specific IgM staining indicating that it was not due to IgM rheumatoid factor. On the other hand adsorption with protein A/sepharose removed the specific IgM staining from the 7S IgM fractions but not from the 19S IgM fractions. This suggests that specific 19S and 7S IgM antibodies may belong to different subclasses of IgM.

The regulation of membrane-bound and secreted immunoglobulins in the human lymphoid cell line LICR-LON and human hybridomas

The synthesis of membrane-bound and secreted immunoglobulin was investigated in the human line LICR-LON-HMy2, a cell line often used for the derivation of human hybridomas. PAGE-SDS analysis of immunoprecipitates obtained from 35S-methionine labelled cell lysates shows that LICR-LON synthesize a hitherto undetected membrane form of IgG (with a heavy chain of mol. wt 62,000) in addition to the secretor form of IgG already described (55,000 heavy chain). Tunicamycin treatment, pulse-chase experiments and Western blot analysis showed that both chains are synthesized as independent proteins. Hybridomas obtained after fusion of LICR-LON and human peripheral blood lymphocytes retained the ability of the parental cell line to synthesize gamma m and gamma s. Some of these hybrids synthesize and secrete IgM which presumably originates from the parental B-lymphocytes. Precipitation and PAGE-SDS analysis of membrane proteins after iodination of intact cells revealed only one heavy chain band, corresponding in size to that of the gamma m. No indication of the synthesis of the membrane form of IgM was found in the hybrids. These data show that the parental (lymphoid) phenotype (m and s-IgG) is codominant with the more differentiated phenotype (s-IgM) of the fusion partner cell (plasma cell). These observations are compatible with a class-specific m-s regulation operating on a different chromatin structure at the expressed Ig loci of each parental chromosome.

Removal of nonspecific hemagglutination inhibitors, immunoglobulin G, and immunoglobulin A with streptococcal cells and its application to the rubella hemagglutination inhibition test

A streptococcus, AW 43 strain, was found to bind nonspecific serum inhibitors of rubella virus hemagglutination (HA). This was demonstrated by titration of nonspecific HA inhibitors and by immunoelectrophoresis. Absorption of sera with the mixture of AW 43 cells, which bind IgA in addition to nonspecific HA inhibitors, and AR 1 cells, another strain of streptococci which bind IgG, removed nonspecific HA inhibitors, IgG, and IgA simultaneously, leaving behind IgM and a trace of IgA. Pretreatment of sera with those streptococcal cells prior to the rubella hemagglutination inhibition (HI) test enabled to circumvent kaolin treatment of sera, which partially removes IgM antibodies, and to determine exclusively the early-appearing antibodies. The rise and fall of the HI antibodies thus determined correlated well with that of the IgM antibodies determined by enzyme-linked immunosorbent assay (ELISA). Thus, this modified rubella HI test may be useful for serodiagnosis of recent rubella virus infection.

Biochemical properties of fibrinogen binding protein (clumping factor) of the staphylococcal cell surface

The staphylococcal fibrinogen binding protein of a strain of coagulase-negative Staphylococcus aureus was purified 229 fold in terms of the haemagglutination unit compared to the starting material by affinity chromatography on fibrinogen-Sepharose. By polyacrylamide gel electrophoresis in both reduced and unreduced gels, the protein showed one major band and minor bands with relative molecular masses of 62,000, 61,000, and 59,000, respectively. The isoelectric point was between 10.2 and 10.8 determined by isoelectric focusing in polyacrylamide gel. By the agar diffusion test one band was obtained against anti-whole cell rabbit serum. Amino acid analysis of fibrinogen binding protein showed glycine, glutamic acid, lysine, alanine, aspartic acid, and arginine as the major components. Protein A or teichoic acid extracted from the homologous strain did not show fibrinogen binding activity assayed by haemagglutination and anti-fibrinogen binding activity of anti-whole cell Fab. The amount of the fibrinogen binding protein to absorb the activity of anti-whole cell Fab was decreased to 1/60 of that of the starting material. Sheep red blood cells coated with the fibrinogen binding protein agglutinated in 0.001% (w/v) fibrinogen solution.

Antibodies to spermatozoa and seminal plasma antigens detected by various enzyme-linked immunosorbent (ELISA) assays

Various ELISA methods have been applied by different research centers to test the efficiency of this approach for the diagnosis of sperm-immune infertility cases. The antigens used were either whole spermatozoa or solubilized spermatozoal membrane preparations and were immobilized on microtiter plates, except in one case where plastic beads were employed. Polyvalent second antibodies or protein-A labelled with enzymes served as tracers. A high frequency of positive sera was found in all groups including fertile controls with tests using whole spermatozoa as antigen. The methods using solubilized antigen preparations showed fewer positives on the whole and correlated better with the various clinical categories of the WHO sera. Whilst there was some agreement in the results between the various laboratories on a few sera, most of the positive sera found by one laboratory were reported as negative by others. More investigative work is needed to improve reproducibility between different laboratories and to reduce non-specific reactions with normal controls. A more precise definition of the proper cut-off levels for positives and negatives is also needed. Despite these short-comings, the development of an ELISA for the diagnosis of sperm-immune infertility cases seems to be justified in the long term.

Isolation of Staphylococcus aureus clumping factor

Immunochemically identical components were isolated from water-soluble phases of five Staphylococcus aureus strains by affinity chromatography on fibrinogen-linked Sepharose 4B. The elution was performed with 1 M MgCl2. The component could be isolated from sonicated preparations of whole cells, cell walls, and extracellular products of S. aureus but not from sonicated preparations of staphylococcal L-forms or from Staphylococcus epidermidis. Investigations of the eluted component by immunoelectrophoresis and Western blot analysis by use of different polyspecific antibodies to S. aureus raised in rabbits revealed only one immunoprecipitate or one band. By means of gel filtration on Sepharose CL 6B and sodium dodecyl sulfate-polyacrylamide gel electrophoresis a molecular mass of 420,000 and 360,000 was found, respectively. Chemical analysis showed a carbohydrate content of about 20% by weight. By crossed immunoelectrophoresis the isolated component was demonstrated to bind to human fibrinogen. The finding that this purified component inhibited the fibrinogen-induced clumping of staphylococci strongly suggests that the component is the S. aureus clumping factor.

Characterization of the specificity of monoclonal antibodies against Mycobacterium tuberculosis by crossed immunoelectrophoresis

The specificity of monoclonal antibodies against Mycobacterium tuberculosis was determined by crossed immunoelectrophoresis. Radiolabelled, non-precipitating monoclonal antibody was incorporated in the top gel together with unlabelled polyvalent, precipitating anti-bacillus Calmette-Guérin (BCG) antibody. Inclusion of labelled antibody in individual precipitate lines was demonstrated by autoradiography. Each monoclonal antibody was localized in a single precipitate line: antibody TB73 reacted with BCG antigen 56; TB71 and TB72 reacted with BCG antigen 78; and TB78 reacted with BCG antigen 82. The technique permits precise determination of the specificity of monoclonal antibodies at the level of reactivity with native immunogenic components of complex microorganisms without prior antigen purification.

Complement activation by clumping factor and protein A from Staphylococcus aureus strain E 2371

Purified surface components from Staphylococcus aureus strain E 2371, which bind to human plasma proteins, were tested for their ability in vitro to activate complement present in normal human serum. Staphylococcal clumping factor as well as protein A both isolated from strain E 2371 were capable of activate complement, while the fibronectin-binding protein showed no activity. At identical molar concentrations clumping factor was more potent than protein A to induce complement consumption. Both clumping factor and protein A were able to activate the alternative complement pathway as demonstrated in serum chelated with ethylene-glycerol-tetra-acetic acid (10 mM) in the presence of MgCl2 (10 mM).

Effect of human IgG and fibrinogen on Staphylococcus aureus intraperitoneal infection in mice

Human serum and plasma have been demonstrated to enhance mortality in Staphylococcus aureus intraperitoneal infection in mice. Two different mechanisms seem to be involved. The effect of serum could be removed by adsorption to S. aureus protein A coupled to Sepharose 4 B and could be reconstituted by the addition of human IgG to IgG-depleted serum. Plasma diluted 1/10 in combination with purified fibrinogen also enhanced mouse mortality. Both effects could be demonstrated, when a coagulase-free variant of S. aureus was used. The results of viable counts of S. aureus in blood and peritoneum of the mice indicate that the enhancing effect of IgG alone and the enhancing effect of fibrinogen in combination with diluted plasma have different mechanisms.

Interaction of porcine immunoglobulin M with protein A of Staphylococcus aureus

Intrigued by reports that the mitogenic effect of protein A on B lymphocytes was due to a direct interaction of cell surface immunoglobulin with protein A, the binding of 19 S, 8 S, and Fab mu fragments of 125I-labeled IgM isolated from porcine serum was investigated. Approx. 60% of purified 19 S porcine IgM interacted specifically with Protein A-Sepharose. Mild reduction and alkylation of 19 S IgM to yield monomeric IgM did not appear to alter its ability to bind to protein A. Elution of either molecular species of IgM from protein A and subsequent repassage over Protein A-Sepharose resulted in nearly quantitative rebinding of the IgM to protein A. Fab mu fragments prepared by digestion of 19 S IgM with pepsin exhibited binding characteristics similar to that observed for intact and monomeric IgM. These results suggest that: (1) there are at least two populations of porcine serum IgM, one that binds to protein A and one that does not; (2) these populations are not interconverting; (3) the ability of IgM to bind to protein A is not dependent on the 19 S pentameric structure extant in sera, but rather is an intrinsic property of some and not all four chain IgM protomers; and (4) a binding site for protein A on porcine IgM is localized in the Fab mu (including the C mu 2 domain) regions of the molecule.

Heterogeneity of human polyclonal IgE reacting with staphylococcal protein A

A small part of polyclonal IgE (6%) was bound to protein A-Sepharose from the serum of M.P., containing a high concentration of IgE. No monoclonal IgE isolated from the serum of V.L. was bound to this sorbent. This binding of polyclonal IgE appears to be heterogeneous since a multiphasic pattern was observed with discontinuous pH gradient elution from protein A-Sepharose. Also, like IgE from the whole serum, monomeric IgE isolated from the serum of M.P. on Sepharose 6B showed this binding heterogeneity. It is suggested that IgE molecules with different affinities for protein A could belong to different isotypic or allotypic variants.

Use of human IgM derived fragments to study structures responsible for protein A-reactivity

The protein A-binding site of human IgM was studied by affinity chromatography on SpA-Sepharose using fragments derived from a human monoclonal SpA-reactive IgM, Iz. Neither Fabmu nor (Fc) 5mu fragments were retained on the column but IgM reactivity was unaffected by thermic treatment during proteolysis. Products intermediate between IgM and (Fc) 5mu fragments produced during shorter proteolysis showed a reactivity related to their content in Fabmu regions. On the other hand mild reduction of IgM Iz to monomeric subunits results in a dramatic loss of SpA-affinity. However these subunits, like F(ab') 2mu but unlike Fab'mu fragments, showed a significant interaction with the column. Thus, the principal requirement for SpA reactivity with IgM Iz seems to be related to the presence of Fabmu regions in a polymeric state resembling native IgM.

Cross-reacting opsonic antibodies to clinically important pneumococcal serotypes after pneumococcal vaccination

Opsonic activity of serum to pneumococcal serotypes 6 B, 9 V and 19 A was measured in 16 patients before and after immunization with a pneumococcal vaccine. The capsular polysaccharides of these serotypes are not included among, but are antigenically related to the vaccine polysaccharides. Patients responding to immunization with a twofold increase in serum antibodies to vaccine polysaccharides 6 A, 19 F and 23 F were studied. Increased opsonic activity towards serotypes 6 B, 9 V and 19 A was found in 12, four and ten patients respectively. In ten of the patients antibodies to serotypes 6 B, 9 V and 19 A were measured by a staphylococcal protein-A binding assay. A twofold increase in antibodies was found in postvaccination samples from ten, three and seven patients respectively. These results indicate that humans responding to pneumococcal vaccination, may also develop opsonic antibodies to other clinically important pneumococcal serotypes. The degree of cross-immunization appears to vary between individuals and between different pneumococcal serotypes.

Binding of immunoglobulins to protein A and immunoglobulin levels in mammalian sera

The use of protein A from S. aureus (SpA) as an anti-IgG reagent in immunological techniques has extended in recent years, together with knowledge about its interaction with immunoglobulins of different species. Current data with respect to the binding of protein A to immunoglobulins and to the levels of immunoglobulins in the sera of some mammalian species are reviewed.

Binding of human fibronectin to group A, C, and G streptococci

A total of 387 bacterial strains belonging to 35 species were tested in direct binding experiments for the uptake of purified radiolabeled human fibronectin. Positive binding was found in group A, C, and G streptococci and in Staphylococcus aureus. The group C streptococcal species Streptococcus equisimilis, Streptococcus zooepidemicus, Streptococcus equi, and Streptococcus dysgalactiae were uniformly reactive with fibronectin. Beta-hemolytic bovine group G streptococci showed the same degree of reactivity as human group G strains. In contrast, only 4 out of 15 alpha-hemolytic bovine group G strains were able to bind fibronectin. The uptake of fibronectin measured at room temperature with a human group G streptococcus was a slow, time-dependent process with maximum binding after approximately 1 h. Human polyclonal immunoglobulin G and serum albumin tested in inhibition experiments did not affect the fibronectin binding. Fibronectin seems, therefore, to interact with a surface component that is different from the specific binding sites previously described for human immunoglobulin G and serum albumin.

Immunochemical characterization of anti-albumin antibodies in liver diseases

Anti-albumin antibodies (AAA) were isolated from sera of hepatic patients and normal individuals by affinity chromatography on insolubilized glutaraldehyde-treated human albumin. Anti-albumin antibodies were found to belong to IgG and IgM classes in both normal and hepatic patients. The normal level of AAA increased in pathologic conditions, the increase recorded for IgM AAA being higher than that for IgG AAA. The dissociation rate of AAA from the radiolabeled antigen in normal and hepatic sera showed that the affinity of AAA was higher in normal sera than in sera of patients with chronic liver disease and acute viral hepatitis. Anti-albumin antibodies were fractionated into two populations (AAA1 and AAA2) by a two-step chromatographic procedure. AAA1 and AAA2 were found different as regards their affinity for the antigen; specifically, AAA1 affinity was higher than that of AAA2. The other difference between AAA1 and AAA2 might stand in their specificity for the haptenic and structural determinants present in the glutaraldehyde-treated albumin.

Mechanisms of proteinuria in human glomerulonephritis

We evaluated glomerular barrier function in 28 patients with glomerulonephritis. Neutral dextrans of graded size were used to characterize the size-selective properties of the barrier. Charge selectivity was characterized by electrofocusing excreted urinary proteins. A fractional IgG clearance (relative to freely permeable inulin), smaller or greater than 100 x 10(-5) was used to distinguish patients with minor (group I, n = 13) and major (group II, n = 15) urinary IgG leakage, respectively. Fractional clearances of smaller dextrans (radii 20-50 A) were similar, but those of larger dextrans (radii 52-60 A) were elevated in group II relative to group I patients. A model of solute transport through a bimodal pore size distribution revealed the values for pore radius in the lower mode to approximate 51-55 A in both group I and group II patients. Pore radius in the upper mode, by contrast, was much larger in group II than in group I patients, approximating 87-97 vs. 72-77 A, respectively. Electrofocusing of urinary protein from group I patients revealed mostly albumin (isoelectric point 5.2). In group II patients, however, immunoglobulin excretion was copious. Moreover, the distribution of anionic, neutral, and cationic species (isoelectric points 5.5-8.5) in urinary and plasma eluates of IgG2 and IgG4 was similar. We conclude that when glomerulonephritis is associated with selective albuminuria, as in group I,, there is an isolated reduction of electrostatic retardation of relatively small anionic proteins. Major urinary IgG leakage (group II), however, appears to result from the development in the glomerular membrane of a subpopulation of enlarged pores that are highly permeable towards proteins of large size and varying charge.

Separation of guinea pig IgG subclasses by affinity chromatography on protein A-sepharose

Guinea pig serum was chromatographed on a column of protein A-Sepharose equilibrated in citrate-phosphate buffer at pH 7.3. The bulk of serum proteins eluted in the starting buffer. Two peaks of protein A-bound serum proteins were eluted by a decreasing pH gradient, a smaller peak centered at pH 4.7 and a larger peak centered at pH 4.3. IgG contained in the peak eluted at pH 4.7 had fast gamma immunoelectrophoretic mobility and IgG in the peak eluted at pH 4.3 had slow gamma mobility. Antiserum to guinea pig IgG, when absorbed with the pH 4.7 peak, reacted only with the pH 4.3 peak. Antiserum to guinea pig IgG1, when absorbed with the pH 4.3 peak, reacted only with the pH 4.7 peak. The IgG in the pH 4.7 peak had the immunoelectrophoretic and antigenic characteristics of IgG1 and the IgG in the pH 4.3 peak had the characteristics of IgG2. The two subclasses were efficiently separated by pH-dependent affinity chromatography on protein A-Sepharose. The IgG1 in the pH 4.7 peak was contaminated with 10.8% IgG2, and the IgG2 in the pH 4.3 peak was contaminated with 2.7% IgG1.

Estimation of the secondary structure of protein A from S. aureus by CD-spectroscopy

The secondary structure of protein A(SpA) was estimated to 31% alpha-helix, 13% beta-structure and 56% random coil by CD-spectroscopy, which is close to the sum of the secondary structures of the SpA fragments. This supports that the SpA molecule is composed N-terminally of four Fc-binding units each consisting of two antiparallel alpha-helices interconnected by random coil segments and C-terminally of an region mainly in random coil.

A critical study of the use of staphylococci containing protein A for separation of IgG and IgM antibodies

This study was to determine the best conditions for using staphylococci bearing protein A to separate IgG from IgM. The validity of the technique was evaluated for detection of IgM with antimicrobial activity and for typing monoclonal IgM. The results indicate that separation of IgG and IgM is not entirely satisfactory in normal sera and worse in hyperglobulinemic sera. The detection and titration of IgM antimicrobial antibodies (rubella and hepatitis B core (HBc) specific IgM) was unreliable because IgG was only partially absorbed by staphylococcal cells, while a significant portion of IgM was bound. The use of higher concentrations of staphylococci did not improve the results because the more IgG was absorbed, the more IgM was also bound. It is shown that with anti-HBc specific IgM the risk of misinterpretation is very high with a sensitive radioimmunoassay technique allowing detection of trace amounts of nonabsorbed IgG. In contrast staphylococcal protein A proved useful in typing monoclonal IgM.

Polyacrylamide microbeads with entrapped protein A from S. aureus for cell separation

A technique was developed for the identification and separation of cells according to their surface antigenic markers, based on immobilization of protein A by entrapment in polyacrylamide microbeads. This method is further development of the previous techniques with SpA-containing S. aureus bacteria, but has the advantage of having less unspecific binding to the cells. We show that this technique might be a useful tool for the separation of cells, exemplified by separation of cells on Petri dishes coated with a monolayer of SpA-microbeads. The viability of separated cells was unaffected and adherent cells were easily removed by trypsin.

Binding of human immunoglobulin M to Staphylococcus aureus bearing protein A

Human immunoglobulin M binds to protein A-bearing Staphylococcus aureus. This binding is specific for protein A since it is inhibited by rabbit Fab against Staphylococcal protein A. Analysis of the IgM binding data gives an apparent KD of 0.94 nM and a maximum capacity of approximately 2 X 10(3) binding sites of IgM per bacteria.

Humoral immunity in leprosy: immunoglobulin G and M antibody responses to Mycobacterium leprae in relation to various disease patterns

A solid-phase radioimmunoassay, applying whole Mycobacterium leprae as antigen and radiolabeled protein A from Staphylococcus aureus as antibody-detecting reagent, was used for the determination of specific immunoglobulin G (IgG) and IgM antibody responses in leprosy patients. High IgG anti-M. leprae antibody levels were found in lepromatous leprosy patients, whereas the antibody response in tuberculoid leprosy patients varied from negative, i.e., comparable with responses measured in normal individuals, to strongly positive. In tuberculoid leprosy patients, a significant increase in IgG anti-M. leprae antibody levels was observed in the more widespread forms of the disease, but positive antibody responses were especially predominant among patients with active lesions. Lepromatous leprosy patients generally demonstrated high levels of both IgG and IgM anti-M. leprae antibodies, but no relation was found between the antibody responses and bacillary load or other clinical parameters. A marked decrease in specific IgG and IgM antibody levels was observed in lepromatous leprosy patients during their first year of treatment. Differences in mechanisms regulating the humoral immune response in tuberculoid and lepromatous leprosy patients were indicated, and the application of antibody assessments in leprosy control programs is discussed.

Isoelectric points and surface hydrophobicity of Gram-positive cocci as determined by cross-partition and hydrophobic affinity partition in aqueous two-phase systems

Thirty-nine streptococcal strains belonging to groups A, C, and G and 12 staphylococcal strains were investigated with respect to surface charge and hydrophobicity. Isoelectric points of the bacteria were determined by cross-partition experiments in dextran-polyethylene glycol two-phase systems containing charged polymers. The results obtained indicate that group A, C, and G streptococci have isoelectric points of pH 3.75 +/- 0.15 standard deviation. Staphylococci show an isoelectric point of around pH 2 and thereby differ markedly from the streptococci. Pretreatment of bacteria with human serum resulted in a significant change in the isoelectric points of streptococci. In a second series of experiments, an aqueous dextran-polyethylene glycol two-phase system containing polyethylene glycol palmitate or stearate was used to study the hydrophobic surface properties of the bacterial cells. The partition of the staphylococci was not influenced by the addition of up to 1% (wt/wt) polyethylene glycol palmitate or stearate, whereas the streptococci showed a large variation in affinity for polyethylene glycol-bound hydrophobic groups. The bacterial strains included in the study were also tested for uptake of human serum proteins. A positive correlation was found between the hydrophobic affinity of group A streptococci and the density of receptors for aggregated beta-2-microglobulin.

Human monoclonal autoimmune antibody produced in vitro: rheumatoid factor generated by Epstein-Barr virus-transformed cell line

The infection of selected lymphocytes from a rheumatoid arthritis patient with Epstein-Barr virus resulted in an immortalized cell line that secretes a monoclonal rheumatoid factor (RF). The cloned line has been growing for more than 24 months, and constantly produces a monoclonal IgM, lambda, 19S, RF (1-2 micrograms/ml/106 cells). The RF agglutinates human and rabbit IgG (but not IgM) and also protein A-coated erythrocytes, but fails to do so to mouse, goat and swine IgG-coated erythrocytes. When bound to immune complexes, this monoclonal RF dose not bind complement. In the cell supernatant RF is the only immunoglobulin and it comprises approximately 5% of the total proteins. The affinity of RF to aggregated human IgG, as detected in inhibition experiments, is higher than that of Fc receptors found on human non-T lymphocytes, K562 and Daudi cell lines.