Isolation and some properties of an IgG Fc-binding protein from group A streptococci type 15

Antibody-mediated depletion of immunosuppressive factors from ovarian carcinoma-associated ascites for investigation of paracrine versus autocrine effects

Many studies seek to explore the impact of extrinsic soluble factors present in serum, interstitial fluids or cell-conditioned media on cells in vitro. A convenient approach to elucidate the effects of a particular factor is its selective neutralization. However, intrinsic production of soluble factors such as cytokines by the cultured cells is common and can have an impact via autocrine mechanisms. The addition of cytokine-specific neutralizing antibodies leads to neutralization of the targeted factors irrespective of their source and affects paracrine and autocrine effects alike. Thus, neutralization assays are not suitable to irrevocably demonstrate that the examined factors exert their effect via a paracrine mechanism. We were interested in investigating the impact of immunosuppressive factors present in ovarian carcinoma-associated ascites by dissecting paracrine versus autocrine effects of interleukin 10 (IL-10) and prostaglandin E2 (PGE₂) on the activation of monocyte-derived dendritic cells (DC). We explored several methods of depletion based on introduction of the neutralizing antibodies bound to beads. Here we describe the pitfalls of the investigated depletion approaches and show the importance of monitoring the presence of residual neutralizing antibodies in the sample upon depletion, which impacts on the suitability of the approach to distinguish paracrine from autocrine effects. Only one of three investigated approaches showed no dislocation of neutralizing antibody from the beads into the sample. This method, which is based on covalently linking antibody to magnetic beads harbouring a reactive group allowed for the complete removal of the investigated factors from ascites and represents an elegant tool to elucidate immunoregulatory or -stimulatory cytokine networks in considerably more depth than the use of neutralizing antibodies in cell cultures alone can contribute.

Effects of the orientation of anti-BMP2 monoclonal antibody immobilized on scaffold in antibody-mediated osseous regeneration

Recently, we have shown that anti-BMP2 monoclonal antibodies (mAbs) can trap endogenous osteogenic BMP ligands, which can in turn mediate osteodifferentiation of progenitor cells. The effectiveness of this strategy requires the availability of the anti-BMP-2 monoclonal antibodies antigen-binding sites for anti-BMP-2 monoclonal antibodies to bind to the scaffold through a domain that will leave its antigen-binding region exposed and available for binding to an osteogenic ligand. We examined whether antibodies bound to a scaffold by passive adsorption versus through Protein G as a linker will exhibit differences in mediating bone formation. In vitro anti-BMP-2 monoclonal antibodies was immobilized on absorbable collagen sponge (ACS) with Protein G as a linker to bind the antibody through its Fc region and implanted into rat calvarial defects. The biomechanical strength of bone regenerated by absorbable collagen sponge/Protein G/anti-BMP-2 monoclonal antibodies immune complex was compared to ACS/anti-BMP-2 monoclonal antibodies or ACS/Protein G/isotype mAb control group. Results demonstrated higher binding of anti-BMP-2 monoclonal antibodies/BMPs to C2C12 cells, when the mAb was initially attached to recombinant Protein G or Protein G-coupled microbeads. After eight weeks, micro-CT and histomorphometric analyses revealed increased bone formation within defects implanted with absorbable collagen sponge/Protein G/anti-BMP-2 monoclonal antibodies compared with defects implanted with absorbable collagen sponge/anti-BMP-2 monoclonal antibodies (p < 0.05). Confocal laser scanning microscopy (CLSM) confirmed increased BMP-2, -4, and -7 detection in sites implanted with absorbable collagen sponge/Protein G/anti-BMP-2 monoclonal antibodies in vivo. Biomechanical analysis revealed the regenerated bone in sites with Protein G/anti-BMP-2 monoclonal antibodies had higher mechanical strength in comparison to anti-BMP-2 monoclonal antibodies. The negative control group, Protein G/isotype mAb, did not promote bone regeneration and exhibited significantly lower mechanical properties (p < 0.05). Altogether, our results demonstrated that application of Protein G as a linker to adsorb anti-BMP-2 monoclonal antibodies onto the scaffold was accompanied by increased in vitro binding of the anti-BMP-2 mAb/BMP immune complex to BMP-receptor positive cell, as well as increased volume and strength of de novo bone formation in vivo.

Inactivation of DNA-binding response regulator Sak189 abrogates beta-antigen expression and affects virulence of Streptococcus agalactiae

BACKGROUND

Streptococcus agalactiae is able to colonize numerous tissues employing different mechanisms of gene regulation, particularly via two-component regulatory systems. These systems sense the environmental stimuli and regulate expression of the genes including virulence genes. Recently, the novel two-component regulatory system Sak188/Sak189 was identified. In S. agalactiae genome, it was adjacent to the bac gene encoding for beta-antigen, an important virulence factor.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, the sak188 and sak189 genes were inactivated, and the functional role of Sak188/Sak189 two-component system in regulation of the beta-antigen expression was investigated. It was demonstrated that both transcription of bac gene and expression of encoded beta-antigen were controlled by Sak189 response regulator, but not Sak188 histidine kinase. It was also found that the regulation occurred at transcriptional level. Finally, insertional inactivation of sak189 gene, but not sak188 gene, significantly affected virulent properties of S. agalactiae.

CONCLUSIONS/SIGNIFICANCE

Sak189 response regulator is necessary for activation of bac gene transcription. It also controls the virulent properties of S. agalactiae. Given that the primary functional role of Sak188/Sak189 two-component systems is a control of bac gene transcription, this system can be annotated as BgrR/S (bacgene regulatory system).

Pathogenesis of poststreptococcal glomerulonephritis a century after Clemens von Pirquet

Considerable insight has been gained into the etiopathogenesis of poststreptococcal glomerulonephritis since the landmark theoretical construct of Clemens von Pirquet postulated that disease-causing immune complexes were responsible for the nephritis that followed scarlet fever. Over the years, molecular mimicry between streptococcal products and renal components, autoimmune reactivity and several streptococcal antigens have been extensively studied. Recent investigations assign a critical role to both in situ formation and deposition of circulating immune complexes that would trigger a variety of effector mechanisms. Glomerular plasmin-binding activity of streptococcal glyceraldehyde-3-phosphate-dehydrogenase may play a role in nephritogenicity and streptococcal pyrogenic exotoxin B and its zymogen precursor may be the long-sought nephritogenic antigen.

Enzyme immunoassay for the diagnosis of brucellosis: chimeric Protein A–Protein G as a common enzyme labeled detection reagent for sera for different animal species

A recombinant protein combining the immunoglobulin binding sites of Proteins A and G, conjugated with horseradish peroxidase was used as a universal detection reagent for the assessment of antibodies against Brucella spp. The reagent was applied in an indirect enzyme immunoassay for detection of antibodies to smooth lipopolysaccharide antigen in sera from Brucella spp. exposed and non-exposed cattle, sheep, goats and pigs and to antibodies to rough lipopolysaccharide in sheep, dogs and cattle. The results were similar to those obtained when murine monoclonal antibody-enzyme conjugates were used. An added advantage was that a universal cut-off for all tests using the proteins A and G detection reagent could be established, simplifying diagnostic interpretation of the data.

Role of group A streptococcal IgG-binding proteins in triggering experimental glomerulonephritis in the rabbit

Our previous studies have indicated that the IgG-binding M-family proteins (IgGBP) of group A streptococci may be involved in eliciting experimental acute poststreptococcal glomerulonephritis (APSGN) in the rabbit. These surface proteins were also found to trigger production of anti-IgG, which might conceivably act to enhance renal deposition of immune complexes (IC). In the present study, a clinical isolate of serotype M22 (strain AL168), an isogenic double mutant deficient for both the IgGBPs Mrp and Emm, as well as mutants deficient in only one of the proteins were tested for capacity to induce glomerulonephritis. Streptococci to be used for injecting rabbits were heat-killed. Surface-bound IgG was removed by 1 M KSCN and cells were then repeatedly washed in PBS before use. Rabbits were injected intravenously with 109 cells three times a week for 8 weeks and, following one month of rest, for another 6 weeks. Deposits of IgG and C3 as well as induced chemokines TNF-alpha, IL-1beta and IL-6 were traced in cryostat sections using specific antibodies and appropriate peroxidase-labelled anti-antibodies. In four rabbits immunized with the double mutant strain, no deposits were found, and as examined by TEM, only subtle and transient renal changes were observed. In contrast, the original strain AL168 induced pronounced inflammatory and degenerative glomerular changes in all four rabbits injected, and deposits of TNF-alpha, IL-1beta and IL-6 were found in mesangial and endothelial cells. Similar deposits and glomerular changes were seen in all eight rabbits injected with the mrp-emm+ mutant and in four out of seven animals receiving the mrp+emm- mutant. There was a highly significant correlation between high levels of circulating anti-IgG and development of APSGN. These results confirm an important role of streptococcal IgGBP in triggering experimental APSGN as earlier proposed by our group.

Influence of growth conditions on expression of immunoglobulin G binding in group A streptococci

Many group A streptococci (GAS) bind the Fc part of IgG. In the present work, the possible influence of growth time and incubation atmosphere on the expression of the IgG binding activity by GAS of various serotypes was studied. Among 13 GAS reference strains, two categories were distinguished on aerobic incubation at 37 degrees C, one expressing similar IgG binding activity at 6 h and 18 h (types M1, M4, M13, M15), and a second one which showed higher binding at 6 h than at 18 h (M9, M14, M22, M25, M48, M49). Only one strain (M36) bound less IgG at 6 h than at 18 h. Seven of the strains (M5, M6, M22, M25, M36, M48, M49) showed higher binding of IgG when grown in a 5% CO2 atmosphere than in air, whereas one strain (M14) showed a reverse pattern and in the remaining five strains, no influence was found. Protease activity was detected in the growth supernatant of most of the strains. For five selected strains, the time of appearance of supernatant protease activity coincided with a decay of surface IgG binding activity. Purified streptococcal cysteine protease was found to reduce or abolish the binding of IgG by each of three studied strains (M1, M13 and M15) and of type M1 or M15 purified IgG binding material. When tested in the stationary phase, a majority of 62 clinical GAS isolates belonging to 6 different M types showed high protease activity but low binding of IgG. We conclude that streptococcal IgG binding is often better expressed on growth in 5% CO2 atmosphere than in air. Furthermore, due to its sensitivity to streptococcal protease, the IgG binding activity is mostly higher during the logarithmic than during the stationary phase of growth.

Streptococcal cysteine proteinase releases biologically active fragments of streptococcal surface proteins

Streptococcus pyogenes are important pathogenic bacteria which produce an extracellular cysteine proteinase contributing to their virulence and pathogenicity. S. pyogenes also express surface molecules, M proteins, that are major virulence determinants due to their antiphagocytic property. In the present work live S. pyogenes bacteria of the M1 serotype were incubated with purified cysteine proteinase. Several peptides were solubilized, and analysis of their protein-binding properties and amino acid sequences revealed two internal fibrinogen-binding fragments of M1 protein (17 and 21 kDa, respectively), and a 36-kDa IgG-binding NH2-terminal fragment of protein H, an IgGFc-binding surface molecule. M protein also plays a role in streptococcal adherence, and removal of this and other surface proteins could promote bacterial dissemination, whereas the generation of soluble complexes between immunoglobulins and immunoglobulin-binding streptococcal surface proteins could be an etiological factor in the development of glomerulonephritis and rheumatic fever. Thus, in these serious complications to S. pyogenes infections immune complexes are found in affected organs. The cysteine proteinase also solubilized a 116-kDa internal fragment of C5a peptidase, another streptococcal surface protein. Activation of the complement system generates C5a, a peptide stimulating leukocyte chemotaxis. C5a-mediated granulocyte migration was blocked by the 116-kDa fragment. This mechanism, by which phagocytes could be prevented from reaching the site of infection, may also contribute to the pathogenicity and virulence of S. pyogenes.

Sequencing of genes within the vir regulon of Streptococcus pyogenes type M15--an opacity factor-positive serotype with low opacity factor expression

Major virulence determinants of group A streptococci, such as M-protein, immunoglobulin Fc-receptors (FcRA, EmmL) and C5a peptidase, appear to be genetically co-regulated, their genes being located within a vir regulon. We studied the organization of these genes in a group A, type M15 strain of Streptococcus pyogenes, previously defined as OF-, by hybridization analysis of chromosomal DNA and of an S. pyogenes gene library in Escherichia coli, and by gene sequencing. Within the vir regulon, in addition to the virR and scpA genes, three so-called emm-related genes were found: fcrA, emmL and enn. Whereas IgG Fc-binding proteins were encoded by fcrA and emmL, the product of enn was not identified. The presence of three emm-related genes in this region is reminescent of vir regulon organization in OF+ rather than OF- strains as earlier defined by others. Furthermore, analysis of the deduced product of the emmL gene showed deletions and amino acid substitutions within the PGTS-rich domain and membrane anchor, which thus resembles corresponding products of OF+ rather than OF- strains. In view of these findings, the opacity factor (OF) activity of the strain was tested using growth supernatant, with negative outcome. However, a concentrated SDS cell extract revealed definite OF activity. One of two other type M15 reference strains also showed definite OF activity in SDS extracts. We therefore propose that type M15 strains belong to the OF+ category but often show low levels of expression of OF.

Streptococcus pyogenes type M12 protein shows selective binding to some human immunoglobulin G3 myeloma proteins

Purified, recombinant M12 protein from Streptococcus pyogenes CS24 has recently been demonstrated to bind human immunoglobulin G3 (IgG3). The binding site for IgG has been localized to an internal peptide encoded by a PvuII fragment of the gene emm12. We have investigated the ability of an isolated recombinant M12 protein consisting of the peptide encoded by the PvuII fragment to bind various monoclonal human IgG3 myeloma proteins representing a number of both Caucasian and Oriental IgG3 Gm(allotypic) phenotypes. Of nine Caucasian IgG3 myeloma proteins, only two bound strongly to the recombinant M12 protein in enzyme-linked immunosorbent assays. The allotypic phenotypes of the reactive proteins were IgG3m(b+)(g-) and IgG3m(b-)(g+). No binding was seen for seven IgG3 myeloma proteins of Oriental origin with G3m(st+)(u-)(b+)(g-), G3m(st-)(u+)(b+)(g-), G3m(st-)(u+)(b-)(g+), and G3m(st-)(u-)(b-)(g+) phenotypes. The binding of human IgG3 to M12 protein seems to be related to features other than its Gm allotypic markers. Selective reactivity of IgG3 myeloma proteins with M12 protein may provide another way to subclassify human IgG3 molecules. The biological significance of the selective reactivity is not known.

M-like, immunoglobulin-binding protein of Streptococcus pyogenes type M15

An M-like protein from Streptococcus pyogenes type M15 strain EF1949 (EMML15) was cloned in Escherichia coli and sequenced. Recombinant EMML15 protein revealed a unique binding pattern for human IgG subclasses not described previously. Comparative analysis of the EMML15 amino acid sequence with those of other M-like proteins of opacity factor positive (OF+) serotypes and protein H, and IgG receptor from OF- serotype M1, showed that IgG-binding proteins with common binding of IgG3 were closely related and distinct from streptococcal IgG receptors not binding IgG3. Thus, the Ig-binding proteins from S. pyogenes were subdivided into two main categories according to binding pattern, protein structure, and gene location.

M1 protein and protein H: IgGFc- and albumin-binding streptococcal surface proteins encoded by adjacent genes

M1 protein and Protein H are surface proteins simultaneously present at the surface of certain strains of Streptococcus pyogenes, important pathogenic bacteria in humans. The present study concerns the structure, protein-binding properties and relationship between these two molecules. The gene encoding M1 protein (emm1) was found immediately upstream of the Protein H gene (sph). Both genes were preceded by a promoter region. Comparison of the sequences revealed a high degree of similarity in the signal peptides, the C repeats located in the central parts of the molecules and in the C-terminal cell-wall-attached regions, whereas the N-terminal sequences showed no significant similarity. Protein H has affinity for the Fc region of IgG antibodies. Also M1 protein, isolated from streptococcal culture supernatants or from Escherichia coli expressing emm1, was found to bind human IgGFc. When tested against polyclonal IgG from eight other mammalian species, M1 protein and Protein H both showed affinity for baboon, rabbit and pig IgG. M1 protein also reacted with guinea-pig IgG, whereas both streptococcal proteins were negative in binding experiments with rat, mouse, bovine and horse IgG. The two proteins were also tested against other members of the immunoglobulin super family: human IgM, IgA, IgD, IgE, beta 2-microglobulin, and major histocompatibility complex (MHC) class-I and class-II antigens. M1 protein showed no affinity for any of these molecules whereas Protein H reacted with MHC class-II antigens. M1 protein is known to bind albumin and fibrinogen also. The binding sites for these two plasma proteins and for IgGFc were mapped to different sites on M1 protein. Thus albumin bound to the C repeats and IgGFc to a region (S) immediately N-terminal of the C repeats. Finally, fibrinogen bound further towards the N-terminus but close to the IgGFc-binding site. On the fibrinogen molecule, fragment D was found to mediate binding to M1 protein. The IgGFc-binding region of M1 protein showed no similarity to that of Protein H. Still, competitive binding experiments demonstrated that the two streptococcal proteins bound to overlapping sites on IgGFc.

Prevalence of IgA receptors in clinical isolates of Streptococcus pyogenes and Streptococcus agalactiae: serologic distinction between the receptors by blocking antibodies

Group A and B streptococci (Streptococcus pyogenes and Streptococcus agalactiae) are the only known bacterial pathogens expressing IgA Fc-receptors. However, the IgA binding proteins of the two species have been found genetically unrelated. In the present investigation the binding of human IgA among clinical isolates of group A and group B streptococci was studied and the respective IgA-binding epitopes were compared serologically. Surface binding of radiolabelled, monoclonal human IgA1 occurred in 38% of 115 unselected group A streptococcal isolates. Comparing four predominant T-types, IgA-binding was found in 77% and 85%, respectively, of types T4 and T28 strains but only in 5% and 25%, respectively, of T1 and T12 strains. In group B streptococci, 70% of 58 type Ib strains but only 2% of 399 strains of other serotypes bound IgA. Using rabbit immune sera raised to the two streptococcal species it was found that strains exhibiting IgA Fc-receptors often induced antibodies blocking the binding of IgA to bacteria. Furthermore, the blocking shown by an individual serum was restricted to the streptococcal group used for immunization showing that also the IgA-binding eptiopes in group A and B streptococci are conformationally distinct. Though infections with serotypes often binding IgA, compared to other types, are not known to differ, it is assumed that the non-immune binding of IgA might favour mucosal colonization of the organisms.

Antigenic diversity of IgA receptors in Streptococcus pyogenes

In a previous study, group A and group B streptococcal IgA receptors were shown to differ serologically, in agreement with their known structural unrelatedness. The present study was undertaken to serologically compare the IgA binding epitopes of group A streptococcal strains representing various serotypes by the use of antisera to this species. It was found that blocking antibodies occurred in antisera to IgA binding but not to non-binding strains and that binding of IgA to a streptococcal strain was generally blocked by antiserum to the homologous type. However, cross-testing of a panel of 11 IgA binding strains, representing various M and T serotypes, with 10 different antisera to group A streptococci, demonstrated that IgA receptors were inhibited to a highly variable degree and that inhibition patterns were unique for each type. Comparing solubilized IgA receptors of various strains in immunoblot experiments, a variation in the molecular mass, between approximately 35 and 45 kDa, emerged. The IgA binding epitopes, analogous to protective sites of streptococcal M-protein, thus exhibited hypervariability which may suggest that IgA binding also plays a key role for evading host immune defence mechanisms.

Many group A streptococcal strains express two different immunoglobulin-binding proteins, encoded by closely linked genes: characterization of the proteins expressed by four strains of different M-type

Most group A streptococcal strains are able to bind immunoglobulin (Ig) in a non-immune manner, and the majority of these strains bind both IgA and IgG. Using molecular cloning and immunochemical techniques, we have purified and characterized the Ig Fc-receptors expressed by four such strains. Two of the strains express a novel type of receptor, designated protein Sir, which binds IgA and IgG of all subclasses, and therefore has broader reactivity than any Fc-receptor previously described. The other two strains express protein Arp, a receptor that binds IgA of both subclasses, and also binds polyclonal IgG weakly. Characterization of the weak IgG-binding ability of protein Arp shows that it binds only some monoclonal IgG proteins, in particular those of the IgG3 subclass. The four strains studied here were unexpectedly found to also express a second Ig-receptor, called protein Mrp, encoded by a gene closely linked to the gene for the first receptor. The Mrp protein does not bind IgA, but it binds IgG molecules of the IgG1, IgG2 and IgG4 subclasses, and it also binds fibrinogen. Binding of fibrinogen has been reported to be a characteristic property of streptococcal M proteins, which suggests that the Mrp protein may be an M protein that also binds Ig. Taken together, all available evidence now indicates that most strains of group A streptococci express two different Ig-binding proteins, encoded by closely linked genes.

Distribution of protein D, an immunoglobulin D-binding protein, in Haemophilus strains

Protein D, a novel surface protein of the bacterial species Haemophilus influenzae with specific affinity for human immunoglobulin (Ig) D was detected in all 127 H. influenzae strains studied. All strains representing different serotypes of encapsulated strains and different biotypes of nonencapsulated strains bound 125I-labeled IgD to a high degree (38 to 74%). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot (immunoblot) analysis showed that protein D from all H. influenzae strains had the same apparent molecular weight (i.e., 42,000) and reacted with all three different anti-protein D monoclonal antibodies. By Scatchard analysis, the number of protein D residues on a nontypeable H. influenzae strain was estimated to be approximately 2,800 per organism. The equilibrium constant for the reaction between a human IgD myeloma protein and IgD was found to be 5.8 x 10(8) M-1. Also, all strains of H. haemolyticus and H. aegypticus strains tested bound IgD, 21 to 28% and 41 to 48%, respectively. In extracts of those bacteria, a 42,000-molecular-weight protein reactive with IgD and all three anti-protein D monoclonal antibodies was found. In H. parainfluenzae, H. aphrophilus, H. paraphrophilus, and Actinobacillus actinomycetemcomitans, a 42,000-molecular-weight protein that was reactive with one to three of three anti-protein D monoclonal antibodies but not reactive with human IgD was detected with Western blot analysis. Other Haemophilus species (H. ducreyi, H. parasuis, H. parahaemolyticus, H. segnis, and H. haemoglobinophilus) did not react with human monoclonal IgD or anti-protein D antibodies. On the basis of the wide distribution of protein D among H. influenzae strains, we suggest that protein D could be a vaccine candidate.

Recombinant fusion proteins of protein A and protein G with glutathione S-transferase as reporter molecules

The regions encoding the IgG-binding domains of protein A (PA) and protein G (PG) were cloned into the bacterial expression vector pGEX. Both proteins were expressed in Escherichia coli as fusion proteins with glutathione S-transferase (PA-GST and PG-GST) and were found to be soluble, abundant and easily purified in one step from the bacterial lysate by affinity chromatography on immobilized glutathione. Yields of 50 mg/litre of cultures were obtained. Both purified fusion proteins were shown to be functional in a variety of immunochemical procedures. In radial diffusion tests, PA-GST precipitated IgG from human, squirrel monkey, rabbit, dog, cat and pig but not mouse, sheep, goat, cow, horse or chicken. PG-GST formed precipitin bands with IgG from human, rabbit, mouse, pig, sheep, goat, cow and horse but not squirrel monkey, dog, cat and chicken IgG. The fusion proteins were shown to function as effective detection reagents in ELISA and Western blotting. Glutathione agarose beads with bound fusion protein were shown to be useful for immunoprecipitation.

Protein D, an immunoglobulin D-binding protein of Haemophilus influenzae: cloning, nucleotide sequence, and expression in Escherichia coli

The gene for protein D, a membrane-associated protein with specific affinity for human immunoglobulin D, was cloned from a nontypeable strain of Haemophilus influenzae. The gene was expressed in Escherichia coli from an endogenous promoter, and the gene product has an apparent molecular weight equal to that of H. influenzae protein D (42,000). The complete nucleotide sequence of the gene for protein D was determined, and the deduced amino acid sequence of 364 residues includes a putative signal sequence of 18 amino acids containing a consensus sequence, Leu-Ala-Gly-Cys, for bacterial lipoproteins. The sequence of protein D shows no similarity to those of other immunoglobulin-binding proteins. Protein D is the first example of immunoglobulin receptors from gram-negative bacteria that has been cloned and sequenced.

Isolated DNA repeat region from fcrA76, the Fc-binding protein gene from an M-type 76 strain of group A streptococci, encodes a protein with Fc-binding activity

The DNA repeat region of fcrA76, the gene encoding a group A streptococcal Fc-binding protein, was subcloned in-frame into an Escherichia coli plasmid expression vector. The expressed protein product displayed the same Fc-binding properties as the full-length Fc-binding protein expressed from fcrA76. The affinity-purified, full-length Fc-binding protein was found to compete with staphylococcal protein A or streptococcal protein G for binding to beads coated with human IgG. These results are consistent with earlier studies suggesting that the binding sites on human IgG for protein A, protein G and the type II Fc-binding protein from group A streptococci are located at the interface of the CH2 and CH3 domains of the Fc region.

A secreted receptor related to M1 protein of Streptococcus pyogenes binds to fibrinogen, IgG, and albumin

An extracellular protein (eMP) of Streptococcus pyogenes M type 1 was isolated by affinity chromatography on albumin- and IgG-Sepharose. The protein was found to bind to the human plasma proteins, fibrinogen, IgG, and albumin. Analysis of eMP by Western blotting demonstrated a major band with a molecular weight of 49 kD which was responsible for binding of the three plasma proteins. The purified protein was found to bind selectively to human and primate polyclonal IgG, human and mouse albumin, as well as human fibrinogen which has been the only fibrinogen tested. Serological investigations revealed a close relation of eMP to streptococcal M1 protein. It showed a reaction of identity with cell-extracted M1 protein in immunodiffusion. Moreover, the 49 kD peptide responsible for binding, was recognized with an antiserum directed against the 20 amino acids comprising synthetic peptide (42VAL-61GLU) of the N-terminal part of the M1 protein sequence. The affinity of M protein to plasma proteins other than fibrinogen opens new approaches to its purification by affinity chromatography.

Protein H--a novel IgG binding bacterial protein

Forty-eight group A streptococcal strains of different M types were screened for binding of human radiolabeled IgG. Three of the strains bound more than 80% of the added radioactivity and one of them, an M protein type 1 strain designated AP1, was selected for further analysis. Attempts were made to solubilize the IgG binding bacterial molecule, and small amounts of an IgG binding protein with a mol. wt of 40 kDa could be solubilized with mutanolysin, a muramolytic agent. The gene encoding this streptococcal protein was cloned and expressed in E. coli, and the E. coli-produced protein was purified in a single step by affinity chromatography on IgG-Sepharose. When tested with IgGs from different species, the molecule was found to bind human IgG almost exclusively. The N-terminal amino acid sequence was determined and showed no homology with previously isolated Ig binding proteins, and the name protein H (as in human IgG) is suggested for this novel Ig binding bacterial protein. Protein H showed preferential affinity for heavy chains and Fc fragments of human IgG, and did not bind Ig light chains. The affinity constant, determined by Scatchard plots, between protein H and human polyclonal IgG was 1.6 x 10(9). No binding was observed between protein H and IgM, IgA, IgD, or IgE. Finally, when tested against several additional proteins and human plasma, protein H only showed weak binding to alpha 2-macroglobulin, a proteinase inhibitor.

Possible role of microbial IgG Fc-binding proteins in rheumatoid arthritis

IgG Fc binding substances (receptors) are widespread among pathogenic microorganisms. The receptors from Staphylococcus aureus, streptococci of group A, C and G as well as Herpes-infected cells bind to the interface between the CH2 and CH3 domains i.e. to His 435, Tyr 436 and possibly also His 433 and/or 310. Most rheumatoid factors (RF) from patients with rheumatoid arthritis show a similar binding pattern. Hence, it has been shown that antibodies to microbial IgG Fc receptors (S. aureus and group A streptococci type M15) and RF are idiotypic-anti-idiotypic antibody "partners" i.e. that RF are the "internal images" of microbial IgG Fc binding proteins. Group A streptococci possessing IgG Fc receptors elicit higher titres of RF when injected in rabbits as compared to group A streptococci without IgG Fc receptors. The streptococcal IgG Fc receptors exhibit a diversity of preferences for subclasses of human IgG, some of them showing allotype preferences. Such allotypes are also recognized by certain RF. IgG RF are able to self-associate thereby forming immune complexes which can activate the complement cascade as well as stimulate release of prostaglandins and (probably) interleukin-1. Since these factors have been assigned an important pathogenic role in rheumatoid arthritis, self-aggregating IgG RF, proposed to be induced by microbial IgG Fc receptors might be an important pathogenic factor in rheumatoid arthritis because rheumatoid arthritis is the only known condition where synthesis of RF takes place in the synovia.

Role of group A streptococcal IgG Fc-receptor in induction of anti-IgG by immunization in the rabbit

Previous work has demonstrated that streptococcal IgG Fc-receptors (FcR) may trigger production of anti-IgG after immunization of rabbits with group A streptococci. This effect seemed dependent on in vitro binding of IgG, derived from the growth medium, to the vaccine strains. In the experiments presented here, IgG was eluted from streptococcal strains to be used for immunization of rabbits by 1 M KSCN and washing, a treatment which did not affect the capacity of the strains to bind newly added IgG. Using two IgG FcR-positive group A streptococcal strains (M-types 1 and 22) for intravenous immunization, anti-IgG was found in the sera of 26 out of 28 rabbits, examined 8 weeks after immunization. In contrast, anti-IgG was not induced in 16 rabbits receiving either group A, type T27 or group B, type Ia streptococci both of which lack surface FcR activity. Finally, immunization with purified streptococcal IgG FcR (0.35 mg, given subcutaneously combined with Freund's complete adjuvant and two weeks later intraconjunctivally without adjuvant) also induced anti-IgG. In all rabbits, anti-human rather than anti-rabbit IgG was detected. It is proposed that in vivo interaction between the bacterial FcR and rabbit IgG, resulting in conformation changes in IgG, is a prerequisite for the induction of anti-IgG. Thus, streptococcal triggering of anti-IgG, ascribable to IgG Fc-receptor activity and not requiring presence of foreign IgG, has been demonstrated in the rabbit.

Interaction of type II IgG Fc-receptors from streptococci of serological group A with murine IgG

A group A streptococcal strain demonstrated binding activities for 125I-murine IgG3 and 125I-human IgG. This 125I-murine IgG3 binding could be inhibited by unlabelled equine IgG but not by IgG from cattle, chickens and dogs, indicating binding properties of IgG Fc-receptors of type II. In contrast to binding sites of Streptococcus dysgalactiae (serogroup C) carrying type III IgG Fc-receptors, the binding sites of the group A streptococcus appeared to be antigenically different, extremely sensitive to trypsin and did not show any cross reactions with human albumin. The group A and group C streptococcal binding sites could be solubilized by lysozyme treatment of the bacteria and subsequently isolated by affinity chromatography on human IgG-Sepharose. Further analysis of the group A and group C streptococcal binding proteins by SDS-PAGE and Western blotting revealed numerous, almost identical protein bands with binding activities for 125I-murine IgG3.

Fc-receptor and M-protein genes of group A streptococci are products of gene duplication

The partial nucleotide sequence for an Fc-receptor gene from an M-type 76 group A streptococcus was determined. DNA sequence analysis revealed considerable sequence similarity between the Fc-receptor and M-protein genes in their proposed promoter regions, signal sequences, and 3' termini. Additional analysis indicated that the deduced Fc-receptor protein contains a proline-rich region and membrane anchor region highly similar to that of M protein. In view of these results, we postulated that Fc-receptor and M-protein genes of group A streptococci are the products of gene duplication from a common ancestral gene. It is proposed that DNA sequence similarity between these two genes may allow for extragenic homologous recombination as a means of generating antigenic diversity in these two surface proteins.

Identification of non-immunoglobulin A-Fc-binding forms and low-molecular-weight secreted forms of the group B streptococcal beta antigen

The beta antigen expressed on the surfaces of certain strains of group B streptococci has been reported to bind to the Fc region of human immunoglobulin A (IgA). In this study, we screened 100 isolates of group B streptococci for expression of both beta antigen and IgA-Fc-binding activity. We identified two isolates which expressed the beta antigen but could not bind human IgA Fc fragments and also observed variability in IgA-Fc-binding activity among other beta-antigen-expressing strains. Novel low-molecular-weight forms of beta antigen were secreted by four beta-antigen surface-negative isolates and included IgA-Fc-binding (Mrs, 55,000 and 53,000) and non-IgA-Fc-binding (Mr, 38,000) molecules. These results suggest that the IgA-Fc-binding site represents a unique domain of the beta antigen. The 55,000- and 53,000-Mr forms of secreted beta antigen were functionally and antigenically representative of the size-heterogeneous (Mr, up to 145,000) beta-antigen molecules expressed by surface-positive strains. The cell surface-localized IgA-Fc-binding molecules could bind only human serum IgA efficiently; however, once solubilized, these molecules could bind both human serum and secretory IgAs.

Receptor for IgA in group A streptococci: cloning of the gene and characterization of the protein expressed in Escherichia coli

The gene for an IgA-binding protein from a group A streptococcal strain was cloned and expressed in Escherichia coli. The IgA-binding protein, called protein Arp, was purified on IgA-Sepharose, allowing complete purification in a single step. Analysis of protein Arp by Western immunoblotting demonstrated a major IgA-binding band, with an apparent molecular weight of 42 kD. The purified protein was shown to bind serum IgA and secretory IgA, as well as monoclonal IgA of both subclasses. There was no binding to IgM, IgD or IgE, but a weak binding to IgG. Inhibition experiments with whole bacteria indicated that IgA and IgG bind at separate sites. Experiments with immunoglobulin fragments showed that protein Arp binds to the Fc region of both IgA and IgG. The equilibrium constant of the reaction between protein Arp and polyclonal human IgA was determined to be 5.6 x 10(8) M-1. Amino acid sequencing of protein Arp demonstrated a direct repeat of 7 amino acids in the NH2-terminal region, a feature previously found in several streptococcal M proteins. This suggests that protein Arp, like M proteins, may be a streptococcal virulence factor.

Development of rheumatoid factor research through 50 years

The discovery of Waaler in 1937 initiated fruitful research on RFs. It was not until the early 1960s that investigators in the field agreed that RFs are antibodies to Fc fragment of IgG. Separate factors combining with human and rabbit IgG and a factor combining with both these IgGs were at first demonstrated by mixed agglutination and then by separation through IgG-conjugated columns. Only RF combining with native autologous IgG should be considered an autoantibody. Other RFs are allo- or heteroantibodies. Cross-reacting RFs that combine with IgG of various species or with IgG and antigens of cell nuclei are of considerable interest. This cross-reactivity may be due to a combining site interacting with shared epitopes or otherwise to multispecificity of the RF molecule in that it has separate or partially overlapping combining sites acting on different epitopes. Experimental studies conducted since the mid-1950s showed that formation of RFs may be elicited by altered autologous IgG. Under natural conditions such alteration was shown to result from interaction of IgG antibody with its corresponding antigen and RF in many infectious diseases and possibly also in rheumatoid arthritis appeared to result from stimulation by immune complexes. More recently alterations of IgG by its reaction with microbial Fc receptors as well as non-specific polyclonal stimulation of B cells were shown to play a role in RF formation. RFs have been implemented in the pathogenicity of rheumatoid arthritis. Recent studies on dispersion of immune complexes in tissue sections by aggregated IgG showed that self-polymerization of IgG RFs results in formation of glomerular deposits in various nephropathies.

Extraction of group C streptococcal IgG-binding receptor and characterization of the active peptides by Western blotting and isoelectric focusing

Three different enzymatic extraction procedures were tested for their effectivity in releasing IgG-binding peptides from the streptococcal cell wall. Streptococcus equisimilis strain 12628 isolated from pig was incubated with phage-associated lysin, trypsin and Streptomyces globisporus lytic enzyme and the extracts were investigated by Western blotting, indirect erythrocyte agglutination and Ouchterlony diffusion for IgG-binding activity. With all treatments IgG-binding peptides were extracted. However, no homogenous IgG-binding material was released by the enzymes tested. In each case a multiple peptide pattern with IgG-binding activity was found. The molecular weights of the active peptides released also differed between the extraction procedures. The isoelectric points between 4.0 and 4.3 of IgG-binding components were found to be similar for all three extracts.

Cloning and expression of the gene for an immunoglobulin G Fc receptor protein from a group A streptococcus

DNA containing the 5' end of the M-12 structural gene was used as a probe in colony hybridizations in an attempt to clone the M-76 gene from an M-type 76 group A streptococcal strain. A single positive colony was detected, and Southern hybridization analysis of plasmid DNA isolated from this colony indicated that the insert DNA had homology to the 5' end of the M-12 structural gene. Subclones were constructed to define the limits of the M-76 gene, and sonicates of these subclones were reacted with M-76-specific antiserum in immunodiffusion. A sonicate of one subclone, JM83(pDH56), reacted strongly with the M-76-specific antiserum but also reacted with preimmune rabbit serum. Protein expressed from this subclone bound immunoglobulin from horse and pig, as well as human myeloma immunoglobulin G (IgG) representing all four subclasses and purified human IgG Fc fragments. This indicated that JM83(pDH56) expressed a protein with characteristics previously attributed to the IgG Fc receptor protein from group A streptococci. Western blot analysis indicated that the cloned IgG Fc receptor protein had a molecular weight of approximately 29,000. Binding studies showed that the Fc receptor gene is expressed by the M-type 76 strain from which it was cloned and by an M- variant.

Isolation and characterization of type IIa and type IIb Fc receptors from a group A streptococcus

Certain group A streptococcal strains have been reported to express two distinct type II receptors that bind to the Fc region of human IgG. In this study, we have isolated and characterized these two type II Fc receptors and characterized their reactivity with differing species of IgG. The type IIa receptor was found to be a 56,000 molecular weight protein which binds human IgG1, IgG2 and IgG4, in addition to pig and rabbit IgG. The type IIb receptor was found to be a 38,000 molecular weight protein that bound exclusively to human IgG3. Neither the type IIa nor the type IIb receptor bound to goat, cow, dog, rat, or sheep IgG. Monospecific polyclonal antibodies were prepared against both the type IIa and type IIb Fc receptors. These antibodies demonstrated that the type IIa and type IIb were antigenically closely related and could not be distinguished from each other on the basis of their reactivity with either antibody. The distribution of type IIa and type IIb Fc receptors on a variety of different nephritogenic and non-nephritogenic group A streptococcal strains was documented.

Independent binding of native and aggregated IgG in group A streptococci

Irrespective of IgG Fc-receptor activity, earlier characterized, many group A streptococci were recently found to bind aggregated IgG Fab and/or light chains. In the present study, binding of glutaraldehyde-aggregated, radiolabelled, intact human IgG (a*IgG) to group A streptococci was tested, and strains representing several M-types were found reactive. In particular, high binding was observed among type M12 strains, earlier found devoid of Fc-receptors for monomeric IgG; accordingly, unlabelled, native IgG had little influence on the binding. The sites binding a*IgG were highly sensitive to trypsin and relatively resistant to heat treatment. The binding to M12 was inhibited by human fibrinogen and, to a lesser extent, by heat-aggregated serum albumin. Rabbit antiserum to M12 was more inhibitory than antiserum to a heterologous type of group A streptococci or normal rabbit serum. Our results indicate that streptococcal M-protein binds a*IgG by a multipoint requiring interaction of low specificity and that previously described Fc-receptors binding native IgG are not involved. For comparison, in Cowan I staphylococci and one strain of group G streptococci tested, high binding of a*IgG was also observed; however, this binding was inhibited by native IgG, indicating that protein A and group G streptococcal Fc-receptor, earlier known to bind untreated IgG, also bound a*IgG.

Isolation and partial characterization of a type II Fc receptor from a group A streptococcus

A group A streptococcal strain rich in Fc receptors was selected by an immunoblotting technique and used as the source for isolation of a functionally active Fc receptor. A variety of extraction techniques were compared including (1) heat extraction at neutral, acid or alkaline pH, (2) treatment with the enzymes mutanolysin, hyaluronidase, trypsin, papain or phage lysin, or (3) autoclaving or heating in the presence of sodium dodecyl sulfate. The most homogeneous receptor was recovered following heat extraction and contained two molecular weight forms. The major form had a molecular weight of 56 000 daltons and the minor form had a molecular weight of 38 000 daltons. These two proteins could be isolated without loss of activity by binding to and elution from a column of immobilized human IgG. An antibody prepared against a single form of the affinity purified receptor demonstrated reactivity with both molecular weight forms of the heat extracted receptor. The group A receptor was found to be both antigenically and physicochemically distinct from either the type I receptor found on the majority of Staphylococcus aureus strains or the type III Fc receptors found on the majority of group C streptococcal strains.

Influence of dipeptides on the interaction of immunoglobulins with bacterial Fc receptors

Binding of radiolabeled human IgG to bacteria expressing type I, type II, or type III Fc receptors in the presence of glycyl-glycine, glycyl-tyrosine, glycyl-histidine, glycyl-leucine, or glycyl-phenylalanine was studied. No inhibition of labeled human IgG binding to type I or type III Fc receptor positive bacteria was observed by any of the dipeptides. Inhibition of binding of labeled human IgG1, IgG2, and IgG4, but not IgG3, indicated the presence of two distinct Fc receptors associated with the type II Fc receptor-positive group A streptococcal strain.

Related bindings of aggregated beta 2-microglobulin, IgG Fab, kappa and lambda light chains to group A streptococci

Aggregates of various mammalian beta 2-microglobulin (beta 2m) homologues were tested in binding experiments with group A streptococcal strains of different M types. The binding patterns obtained were similar, suggesting that evolutionarily conserved parts of the beta 2m molecule are responsible for the interaction with group A streptococci. An N-terminally abnormal beta 2m showed binding characteristics similar to those of normal human beta 2m, indicating that the amino-terminal does not participate in this interaction. Aggregates of human IgG Fab fragments, kappa chains and lambda chains, were also analyzed. Whereas several of the beta 2m-reactive M types did not interact with any of these aggregates, all strains binding aggregated Fab, kappa or lambda, also bound aggregated beta 2m. Strains of M types 4, 12, 23 and 53 bound all the tested proteins; M type 1 bound all but IgG Fab, whereas M types 46, 49 and 53 showed affinity for beta 2m and lambda chains only. In inhibition experiments, unlabelled aggregated beta 2m in excess completely blocked the uptake of radiolabelled aggregated IgG Fab, kappa and lambda chains. Conversely, Fab, kappa and lambda aggregates inhibited the binding of radiolabelled beta 2m aggregates. Our results indicate that the differences in reactivity recorded between beta 2m and IgG Fab, kappa and lambda chains, all structurally related, are quantitative rather than qualitative. Thus, a common binding structure for these aggregated proteins on group A streptococci appears probable.

Blocking of antibody complement-dependent effector functions by streptococcal IgG Fc-receptor and staphylococcal protein A

Using haemolysis in gel, two bacterial IgG-binding substances, an Fc-receptor isolated from group A streptococci type M15, and protein A from Staphylococcus aureus, were shown to inhibit complement-mediated lysis of sheep erythrocytes sensitized with rabbit IgG. When the crude alkaline extracts of ten types of group A streptococci were tested to see whether streptococcal components other than Fc-binding material might affect lysis, the degree of inhibition was found to be correlated with Fc-binding activity. In no case was the lysis of IgM-coated cells inhibited. Opsonophagocytosis experiments showed that both purified streptococcal Fc-receptor and protein A impaired antibody complement-dependent killing by human polymorphonuclear leukocytes of each of two strains of group B streptococci (lacking IgG Fc-receptors). Furthermore, the impairment was ascribable to interference with the fixation of complement to the antibodies, as demonstrated in pre-opsonization experiments with one of the strains. Our results suggest that blocking of the binding of complement to IgG is an important virulence mechanism in Fc-receptor-bearing streptococci and staphylococci.

Binding of aggregated human serum albumin to M12 and some other types of group A streptococci

In radiobinding tests many group A, C and G streptococci react with IgG and IgA, irrespective of the antigen-combining sites, as well as with various other serum proteins, e.g. human serum albumin (HSA). The present study demonstrated that glutaraldehyde-aggregated, radiolabelled HSA (a*HSA), in comparison to monomeric HSA, binds more avidly to streptococci. Of group A streptococci, strains representing types M6, M12, M18, M46, M55 and M57 displayed pronounced binding of a*HSA whereas a number of other serotypes were non-reactive. The streptococcal sites involved proved to be relatively heat-resistant and highly sensitive to trypsin treatment. Human fibrinogen counteracted the binding of a*HSA. The uptake by M12 was inhibited strongly by rabbit antiserum raised against M12, whereas other antisera were less active. The results suggest that the bacterial structure binding a*HSA is a protein and that, in at least one serotype, M12, the binding occurs to the M-protein.

Effect of mouse passage on Fc receptor expression by group A streptococci

The expression and stability of receptors for the Fc region of human IgG on the surface of group A streptococci was studied. Two strains were sequentially passed in mice 22 times. The Fc-receptor expression on one group A strain, 529, was unaltered while the expression of Fc receptor on a second, 64, was enhanced and approached the level of Fc-receptor expression of the protein A-rich Staphylococcus aureus Cowan strain. The level of Fc-receptor expression on this organism remained stable for over 18 months of laboratory subculture. Mouse passage did not result in the production of a soluble Fc receptor from either of the streptococcal strains. Heat extraction of the Fc-receptor-positive group A strain resulted in solubilization of an Fc-receptor activity which was functionally distinct from either staphylococcal protein A or the Fc receptor isolated from a group C streptococcus.

Binding of aggregated IgG Fab-fragments and light chains to some group A, C and G streptococci

Receptors for IgG Fc in many group A, C and G streptococci have been reported previously. We now describe a reaction between group A, C and G streptococci and IgG Fab-parts, not involving the antigen combining sites. The bacteria proved to bind aggregated, but not monomeric, IgG Fab-fragments, indicating that multivalent interaction was a prerequisite for the binding to occur. Most of the strains exhibiting affinity for aggregated IgG Fab could also interact with aggregated K and/or lambda light chains. The capacity of the single strains to bind aggregated IgG Fab did not correlate with presence of IgG Fc-receptor activity. Furthermore, in contrast to streptococcal Fc-receptors, the streptococcal structure reacting with Fab was highly sensitive to trypsin as well as phosphatase treatment. The binding of aggregated lambda-chains to each of two strains tested was inhibited by liquoid and aggregated human albumin, suggesting that lipoteichoic acid and/or M protein are responsible for the binding of IgG Fab-fragments. A pronounced binding of aggregated IgG Fab, but not light chains, to Staphylococcus aureus, strain Cowan I, was also found. Various other bacterial species were tested for binding of the aggregates, with negative results.

Differential susceptibility of cell-bound streptococcal immunoglobulin Fc-receptors to autolytic degradation

The susceptibility of IgA and IgG Fc-receptors of different streptococci to autolytic degradation was tested by incubating washed bacteria in phosphate-buffered saline at 37 degrees C for 24-72 h. Before incubation, strain M1 bound 74 per cent of 2.5 micrograms radio-labelled IgG added to 200 microliter of the suspension, and strain M4 bound 85 per cent of 2.5 micrograms radio-labelled IgA; both types of binding decreased to less than 15 per cent. Evidence was obtained that the decrease in binding was caused by digestion of the respective receptors, and not by degradation of the immunoglobulins or through inhibition by solubilized Fc-receptors. The autolytic process was inhibited by EDTA, iodoacetic acid, benzamidinium chloride, phenylmethylsulfonyl fluoride and diisopropylfluorophosphate. The IgG Fc-receptors in other types of group A streptococci (including type M4) and a group C and a group G strain were not affected by such prolonged incubation, also when strains were mixed with M-type 1 streptococci from the start of incubation. These findings, which thus revealed certain differences in stability between streptococcal Fc-receptors, are discussed in relation to the intracellular degradation of streptococci.