Cytokine production by human epithelial and endothelial cells following exposure to oral viridans streptococci involves lectin interactions between bacteria and cell surface receptors

In order to examine the possible implication of human epithelial and endothelial cells in the pathogenesis of various diseases associated with oral viridans streptococci, we tested the immunomodulatory effects of 11 representative strains of oral viridans streptococci on human epithelial KB cells and endothelial cells. We then examined the possible role of two major adhesins from oral viridans streptococci, protein I/II and rhamnose-glucose polymers (RGPs), in this process. In this study we demonstrate that oral viridans streptococci are potent stimulators of interleukin-8 (IL-8) production from KB cells and of IL-6 and IL-8 production from endothelial cells. The ability of protein I/II and RGPs to contribute to these effects was then examined. Using biotinylated protein I/IIf and RGPs from Streptococcus mutans OMZ 175, we showed that these adhesins bind to KB and endothelial cells through specific interactions and that the binding of these molecules initiates the release of IL-8 from KB cells and of IL-6 and IL-8 from endothelial cells. These results suggest that protein I/IIf and RGPs play an important role in the interactions between bacteria and KB and endothelial cells in that similar cytokine profiles are obtained when cells are stimulated with bacteria or surface components. We also provide evidence that protein I/IIf binds to and stimulates KB and endothelial cells through lectin interactions and that N-acetyl neuraminic acid (NANA) and fucose present on cell surface glycoproteins may form the recognition site since binding and cytokine release can be inhibited by dispase and periodate treatment of cells and by NANA and fucose. These results demonstrate that oral viridans streptococci, probably by engaging two cell surface adhesins, exert immunomodulatory effects on human KB and endothelial cells.

NF-kappaB and the MAP kinases/AP-1 pathways are both involved in interleukin-6 and interleukin-8 expression in fibroblast-like synoviocytes stimulated by protein I/II, a modulin from oral streptococci

As in rheumatoid arthritis (RA), it was demonstrated recently that bacterial fragments of DNA or rRNA are present in the joint and therefore could play a role in inducing or perpetuating the disease, this work was initiated to define mechanisms that account for the stimulatory activities of the oral streptococcal modulin, protein I/II, on fibroblast-like synoviocytes (FLSs) from RA patients. FLSs from RA patients were stimulated with protein I/II, and expression of interleukin (IL)-6 and IL-8 mRNA was evaluated by reverse transcription-polymerase chain reaction (RT-PCR). Immunoblotting by antibodies specific for activated forms of MAPKs and electrophoretic mobility shift assays (EMSAs) were performed to study downstream signalling, which allowed the synthesis of IL-6 and IL-8. We reported that protein I/II interactions with FLSs from RA patients trigger the synthesis and release of IL-6 and IL-8. We also demonstrated that protein I/II enhances the phosphorylation of ERK 1/2, p38 and JNKs and that ERK 1/2 and JNK MAPKs seem to play a more important role than p38 in protein I/II-mediated synthesis of IL-6 and IL-8. Our experiments also indicated that stimulation of FLSs with protein I/II induces nuclear translocation of NF-kappaB, AP-1-binding activity and that NF-kappaB plays a major role in IL-6 and IL-8 secretion from activated cells.

Conservation of salivary glycoprotein-interacting and human immunoglobulin G-cross-reactive domains of antigen I/II in oral streptococci

In this study we localized more precisely the salivary glycoprotein-interacting and the human immunoglobulin G (hIgG)-cross-reacting domains on the SR molecule, an antigen I/II-related protein from S. mutans serotype f. Mapping of the SR molecule with polypeptides expressed by subclones covering the entire molecule and with synthetic peptides demonstrates that the salivary glycoprotein-binding domain is located in the N-terminal alanine-rich repeats of the SR molecule. In order to investigate the degree of conservation of both regions in various oral streptococci, we tested the reactivity of 8 representative strains of the mutans group and 11 nonmutans oral Streptococcus strains (S. anginosus, S. milleri, S. constellatus, S. intermedius, S. mitis, S. sanguis, S. gordonii, S. salivarius, and S. mitis strains) with antipeptide antibodies in a whole-cell enzyme linked immunosorbent assay together with colony hybridization analysis using DNA probes designed to map these two regions. All the mutans group strains except S. rattus and the 11 nonmutans streptococcal strains showed a high conservation of the C-terminal part of the SR molecule, especially the hIgG-cross-reacting domain, and less homology for the N-terminal salivary glycoprotein-binding region. Almost all of the sera from patients with rheumatic disease reacted strongly with SR from S. mutans serotype f, P1 from S. mutans serotype c, and four peptides located in the hIgG-cross-reacting region and not with peptides located at the C and N termini and in the proline-rich repeats. These results confirm that epitopes located within this region are immunogenic in humans and could lead to the synthesis of natural anti-IgG antibodies.

Serum and salivary antibody responses in rats orally immunized with Streptococcus mutans carbohydrate protein conjugate associated with liposomes

In this study we describe the preparation of a Streptococcus mutans vaccine consisting of a purified polysaccharide antigen, derived from S. mutans OMZ175 serotype f, covalently coupled through reductive amination to a previously isolated 74,000-molecular-weight (74K) cell wall protein which interacts with saliva proteins (74K-SR). We also investigated the local and systemic immune response to the poly-74K-SR conjugate after oral administration of the conjugate associated with liposomes. Intragastric administration of liposome-associated poly-74K-SR conjugate in rats produced a local immunoglobulin A (IgA) response directed against the polysaccharide and the cell surface protein, whereas liposome-associated polysaccharide was unable to induce any detectable local IgA response. The antigenicity of the polysaccharide in the conjugate was not affected by the coupling reaction, while that of the cell surface protein was reduced. We showed that the immunogenicity of S. mutans polysaccharide could be improved by chemical coupling with a carrier cell surface protein. If such a conjugate were orally administered with liposomes it could constitute a potential vaccine against dental caries.

Design of highly immunogenic liposomal constructs combining structurally independent B cell and T helper cell peptide epitopes

We have designed liposomal diepitope constructs that allow the physical combination, within the same vesicle, of B and Th epitopes as structurally separate entities. The immune response against such constructs was explored using TPEDPTDPTDPQDPSS (TPE), a B cell epitope originating from a Streptococcus mutans surface adhesin and QYIKANSKFIGITEL (QYI), a "universal" Th epitope from tetanus toxin. The two peptides were linked to the outer surface of small (diameter approximately 100 nm) unilamellar liposomes by covalent conjugation to two different anchors. To that end we have developed a strategy that allows the controlled chemical coupling of TPE and QYI, functionalized at their N terminus with a thiol, to preformed liposomes containing thiol-reactive derivatives of phosphatidylethanolamine and the lipopeptide S-[2,3-bis (palmitoyloxy)-(2-RS)-propyl]-N-palmitoyl-(R)-cysteinyl-alanyl-gly cine (Pam3CAG), respectively. This synthetic construct (administered i.p. to BALB/c mice) induced highly intense (titers > 20,000), anamnestic and long-lasting (over 2 years) immune responses, indicating that this strategy is successful. Two parameters were of prime importance to elicit this response with our liposomal diepitope constructs: (1) the simultaneous expression of B and Th epitopes on the same vesicle, and (2) the lipopeptide Pam3CAG anchor of the Th epitope QYI could not be replaced by a phosphatidylethanolamine anchor (a lesser immune response was observed). Analysis of the antibody response revealed a complex pattern; thus, besides the humoral response (production of IgG1, IgG2a, IgG2b) a superposition of a T-independent (TI-2 type) response was also found (IgM and IgG3). These results indicate that liposomal diepitope constructs could be attractive in the development of synthetic peptide-based vaccines.

Activation of human monocytes by Streptococcus mutans serotype f polysaccharide: immunoglobulin G Fc receptor expression and tumor necrosis factor and interleukin-1 production

Streptococcus mutans serotype f polysaccharide (poly f) was prepared from S. mutans whole cells by autoclaving. The poly f was purified by chromatography on DEAE Trisacryl M and Bio-Gel P100, treated with insoluble pronase, and resubjected to chromatography on DEAE Trisacryl M. Normal human blood monocytes, stimulated in vitro with purified poly f, produced extracellular tumor necrosis factor alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) in a dose-dependent fashion as determined by a heterologous two-site sandwich enzyme-linked immunosorbent assay. Poly f also increased the expression of monocyte cell surface receptors for the Fc part of human immunoglobulin G, activity which is correlated with an increase of the phagocytic activity of the stimulated monocytes. Polymyxin B had no effect on TNF-alpha and IL-1 beta release. Neutralization assays with anti-recombinant human TNF-alpha and anti-recombinant human IL-1 beta immunoglobulin G confirmed the fact that the cytotoxic and mitogenic mediators released by the poly f-stimulated monocytes were mainly TNF-alpha and IL-1 beta.

Involvement of alpha5beta1 integrins in interleukin 8 production induced by oral viridans streptococcal protein I/IIf in cultured endothelial cells

Using human endothelial cells, we define a mechanism that accounts for the induction of interleukin 8 (IL-8) by protein I/IIf, an adhesin from Streptococcus mutans serotype f. We report that protein I/IIf interactions with endothelial cells increased the tyrosine phosphorylation of three cellular components with relative mass of 145,000, 125,000 and 70,000 in endothelial cells. These proteins were identified as phospholipase Cgamma (PLCy), focal adhesion kinase (FAK) and paxillin after immunoprecipitation with monoclonal antibodies (mAbs) and immunoblotting with antiphosphotyrosine mAbs. These results suggested that beta1 integrins could be one of the components implicated in the modulin activity of protein I/IIf. By incubating protein I/IIf with either purified alpha5beta1 integrins or with alpha5beta1 integrins overexpressing CHO cells, we demonstrated that alpha5beta1 integrins act as cell receptors for protein I/IIf. We also showed that protein I/IIf interactions with alpha5beta1 integrins lead to IL-8 secretion. Using specific inhibitors, we demonstrated that protein I/IIf-induced IL-8 release involves mitogen-activated protein kinases (MAPKs), and that PLCgamma and PKC also seem to contribute to protein I/IIf stimulation. However, PI-3K activation is not involved in IL-8 release. Altogether, these results indicate that, after binding to alpha5beta1 integrins, protein I/IIf induces IL-8 release by activating the MAPKs signalling pathways.

Effects of Clostridium difficile toxin B on human monocytes and macrophages: possible relationship with cytoskeletal rearrangement

Toxin B from Clostridium difficile is cytopathic in vitro for various types of cells, including polymorphonuclear cells, lymphocytes, and monocytes. Since intestine lamina propria is rich in macrophages, we studied the effect of toxin B on human monocytes and on human macrophages generated in vitro by long-term culture of purified circulating blood monocytes. Upon addition of toxin B, human monocytes exhibited few modifications whereas macrophages adopted a stellate morphology, with rounding up of the perikaryon. Toxin B made microfilaments of actin disappear and induced an important reorganization of vimentin and a redistribution of tubulin. Membrane area increased by approximately 16%. Toxin B did not affect the viability of human mononuclear phagocytes and did not exert any significant lytic effect. It profoundly altered the phagocytic function of macrophages. When activated by gamma interferon in the presence of toxin B, monocytes were more cytotoxic for U-937 target cells than control monocytes activated in absence of toxin. Finally, the combined treatment of monocytes with gamma interferon and toxin B increased significantly the secretion of tumor necrosis factor alpha, whereas toxin B alone was unable to induce tumor necrosis factor production. These results suggest that morphological and functional alterations induced in human mononuclear phagocytes by toxin B from C. difficile are due to the disorganization of the cytoskeleton and the resulting impairment of the membrane traffic equilibrium.

Immunogenicity of polysaccharides conjugated to peptides containing T- and B-cell epitopes

To develop a general model of polysaccharide-peptide vaccine, we have investigated the efficiency of linear peptides derived from protein SR, and adhesin of the I/II protein antigen family of oral streptococci, to act as carriers for two T cell-independent polysaccharides: serogroup f polysaccharide from Streptococcus mutans OMZ 175 (poly f) and Saccharomyces cerevisiae mannan. Peptide 3 (YEKEPTPPTRTPDQ) and peptide 6 (TPEDPTDPTDPQDPSS), accessible on the native SR protein as demonstrated by their reactivity in enzyme-linked immunosorbent assays with rat antisera raised against protein SR, correspond to immunodominant regions of SR. Peptide 3 contains at least one B- and one T-cell epitope, as demonstrated by its ability to induce peptide- and SR-specific antibody responses without any carrier and to stimulate the proliferation of rat lymph node cells primed either with free peptide or native SR, whereas peptide 6 contains only B-cell epitope(s). Peptide 3 was then covalently coupled though reductive amination to either poly f or mannan, and peptide 6 was coupled to poly f. Subcutaneous immunizations of rats with poly f-peptide 3 or mannan-peptide 3 conjugates produced a systemic immunoglobulin M (IgM) and IgG antibody response, and the elicited antibodies reacted with free poly f or mannan, peptide 3, protein SR, and S. mutans or S. cerevisiae whole cells. Rats immunized with poly f-peptide 6 did not develop any antipeptide or anti-SR response. Furthermore, a booster immunization of animals with poly f-peptide 3 or mannan-peptide 3 conjugates induced high titers of anti-peptide 3, anti-poly f, and antimannan antibodies, which occurred quickly. The response is anamnestic for the peptide and the polysaccharides and is characterized by an Ig switch from IgM to IgG. The data presented here confirm that the presence of B- and T-cell epitopes is necessary to induce an anamnestic antipeptide response and that a peptide containing relevant B- and T-cell epitopes can act as a good carrier in improving an antipolysaccharide anamnestic immune response.

Local response in rat to liposome-associated Streptococcus mutans polysaccharide-protein conjugate

The effect of gastric intubation with soluble or liposome-associated Streptococcus mutans serovar polysaccharide, 74-kDa saliva receptor (74K SR protein) or polysaccharide-74K SR protein conjugate on the locally induced salivary IgA response and memory in rats was investigated. Animals immunized on four successive days with soluble antigens showed a weak salivary anti-74K SR protein or anti-polysaccharide IgA response. Rats primed and boosted by a single injection of liposome-associated 74K SR protein or polysaccharide-74K SR protein conjugate developed a salivary anti-74K SR protein IgA and IgG primary and secondary response. A primary anti-polysaccharide response was only observed in saliva of animals immunized with either high concentration of liposome-associated polysaccharide or liposome-associated polysaccharide-74K SR protein conjugate. However, a secondary local anti-polysaccharide IgA response was detected in animals boosted with liposome-polysaccharide-74K SR protein conjugate. No such anamnestic response was seen when high dose of liposome-associated polysaccharide was used to boost the animals. Furthermore, the salivary anti-polysaccharide IgA response paralleled the anti-74K SR protein IgA response. These studies showed that intragastric immunization of rats with liposome-associated polysaccharide-74K SR protein conjugate produced a local anti-polysaccharide IgA memory.

Protein I/II of oral viridans streptococci increases expression of adhesion molecules on endothelial cells and promotes transendothelial migration of neutrophils in vitro

As accumulation of leukocytes in perivascular tissues is a key step in inflammatory disorders, we have analyzed in the present work the up-regulation of expression of adhesion molecules, such as E-selectin, ICAM-1, and VCAM-1, on human endothelial cells, in response to protein I/II, a modulin from Streptococcus mutans OMZ 175. Using cultured human saphenous vein endothelial cells (HSVEC), we demonstrated that protein I/II directly and specifically up-regulated E-selectin, ICAM-1, and VCAM-1 expression. We confirmed also that the up-regulation of adhesion molecules in HSVEC is mediated by lectin activity for NANA- and fucose-containing receptors. The ability of protein I/II to promote the transendothelial migration of neutrophils was then examined. Using Transwell inserts, we found that protein I/II, in promoting the up-regulation of adhesion molecule expression, stimulates neutrophil migration through endothelial cells. These events may play a role in the etiology of inflammatory responses leading to the various pathologies associated with oral viridans streptococci.

Mucosal immunogenicity of polysaccharides conjugated to a peptide or multiple-antigen peptide containing T- and B-cell epitopes

In this study we investigated the mucosal and systemic responses to two T-cell-independent polysaccharides, a serogroup f polysaccharide (formed of rhamnose glucose polymers [RGPs]) from Streptococcus mutans OMZ 175 and a mannan from Saccharomyces cerevisiae, covalently conjugated either to a linear peptide (peptide 3) or to a multiple-antigen peptide (MAP), both derived from S. mutans protein SR, an adhesin of the I/II protein antigen family of oral streptococci. Peptide 3 and MAP, which contained at least one B- and one T-cell epitope, were tested as carriers for the polysaccharides and as protective immunogens. Intragastric intubation of rats with the conjugates (RGPs-peptide 3, RGPs-MAP, mannan-peptide 3, and mannan-MAP) associated with liposomes produced salivary immunoglobulin A (IgA) antibodies which reacted with RGPs or mannan, peptide 3 or MAP, protein SR, and S. mutans or S. cerevisiae cells. Administration of conjugate boosters to the animals showed that both carriers conjugated to the polysaccharides were able to induce, in immunized animals, a salivary antipolysaccharide IgA memory. In contrast, animals primed and challenged with unconjugated polysaccharide showed no anamnestic response. Rats orally immunized with the conjugates also developed systemic primary antipolysaccharide and antipeptide IgM antibody responses which were characterized by a switch from IgM to IgG during the course of the secondary response. Data presented here demonstrated that both peptide 3 and the MAP construct can act as good carriers for orally administered polysaccharides. Unexpectedly, the use of a MAP did not further improve the immunogenicity of polysaccharides at the mucosal level; nevertheless, such a construct should be of great interest in overcoming the problem of genetic restriction induced by linear peptides.

Anti-IgG antibodies in rheumatic diseases cross-react with Streptococcus mutans SR antigen

We have previously shown that SR protein, a S. mutans major cell wall protein, as well as the recombinant protein SR (rSR) share common epitopes with human IgG. Since this antigenic mimicry could play a role in the induction of anti IgG, we have examined, in k-ELISA, the presence of antibodies reacting with S. mutans SR proteins and S. mutans whole cells in sera from 36 patients with rheumatic diseases. The majority of the 36 sera showed a high reactivity with rSR when compared with control sera. Eight highly positive sera were further purified on rSR and human IgG sorbents and tested against both rSR and IgG in ELISA and Western blotting. The affinity-purified antibodies reacted strongly with rSR, IgG and IgG Fab fragments but failed to react with IgG Fc fragment. In Western blotting the addition of unlabelled IgG abolished the reactivity of affinity-purified biotinylated antibodies with all antigens, confirming the existence of a common epitope shared by rSR and human IgG heavy chain. We show the existence in rheumatic diseases of high titres of anti-human IgG antibodies cross-reactive with S. mutans SR proteins. Those antibodies are principally IgG and react with the Fd part of the Fab fragment. We can hypothesize from the above data that this antigenic mimicry existing between S. mutans SR-related antigens and human IgG could play a role in the synthesis of at least a part of the anti-IgG antibodies present in rheumatic diseases sera.

Molecular characterization of the gene sr of the saliva interacting protein from Streptococcus mutans OMZ175

The saliva interacting protein (74KSR) from Streptococcus mutans serotype f, which is immunologically related to antigen I/II from serotype c, also termed B, P1, PAc, is probably involved in the adherence process of Strep. mutans to the tooth surface. A solid-phase adherence assay showed that 38% of the binding of salivary glycoproteins to Strep. mutans OMZ175 was due to this protein. We have cloned and sequenced the 74KSR gene (sr), which produces a recombinant protein (rec195K) with a relative molecular mass of 195,000, as estimated by SDS-PAGE. The strong immunological relationship and functional identity of the 74KSR and rec195K indicate that the Mr 195K protein is probably a precursor form, post-translationally processed, of the 74KSR produced in Strep. mutans. The gene sr consists of 4667 bp and codes for a 171,177 Mr protein. Biochemical features of the protein (density in proline residues and hydrophobicity) may explain the difference observed between the SDS-PAGE estimated molecular mass of the immature protein and the one deduced from the nucleotide sequence. Intra-species hybridization experiments using three contiguous restriction fragments isolated from gene sr as probes showed that the sequence is highly similar in strains from serotypes c and e. We have also shown that a fraction of the heart specific antibodies induced in rabbits during immunization with the 74KSR or rec195K reacts predominantly with human IgG and suggest the hypothesis of antigen mimicry as an explanation for the production of anti-IgG autoantibodies. It will be of great importance to identify the cross-reactive epitopes within the molecule before considering its use in protective immunization against oral streptococci.

Pro-inflammatory cytokine production by synoviocytes following exposure to protein I/II, a modulin from oral streptococci

We have tested the ability of protein I/II, an adhesin from oral streptococci, to stimulate the production of pro-inflammatory cytokines by synovial cells isolated from both rheumatoid arthritis and control patients. Protein I/II triggers synovial fluid cells to produce interleukin (IL)-6 and IL-8 while secretion of tumor necrosis factor-alpha (TNF-alpha) was less enhanced. Using fibroblast-like synoviocytes, we found that protein I/II also exerts an immunomodulatory effect (IL-6 and IL-8 release) on these cells. These findings indicate that, if it gains access to the joint cavity, protein I/II could participate in the initiation and/or perpetuation of rheumatic diseases, by stimulating pro-inflammatory cytokine release from various synovial cells.

Purification and partial characterization of rat macrophage Fc receptor and binding factor for IgA

By using a biotinylated ligand and Western blotting techniques, a receptor (RFc alpha) and a binding factor (BF) for IgA were detected, respectively, on membrane and in the cell-free culture supernatant of rat peritoneal macrophages. Extraction of the RFc alpha was obtained by solubilization of macrophages with Nonidet P-40, and purification was performed by HPLC affinity chromatography on a column derivatized with IgA. RFc alpha is formed of two subunits, with molecular masses of 56 and 70 kDa, which are both involved in the IgA binding ability of rat peritoneal macrophages. IgABF was recovered from the cell-free supernatant of a short-term culture of rat macrophages and was affinity-purified in the same manner as RFc alpha. Like RFc alpha, IgABF retained its IgA binding activity in its native, as well as denatured form. Since the molecular masses of RFc alpha and IgABF are similar, and IgABF competes with RFc alpha for IgA binding, one can assume that IgABF probably represents a shed RFc alpha.

Activation of human monocytes by streptococcal rhamnose glucose polymers is mediated by CD14 antigen, and mannan binding protein inhibits TNF-alpha release

The present work was initiated to define mechanisms that account for the binding on human monocytes of streptococcal cell wall polysaccharides formed by rhamnose glucose polymers (RGPs), and subsequent stimulatory activities. We show here that RGPs bind to and stimulate human monocytes to produce TNF-alpha in a dose-dependent manner. To detect cell surface RGPs binding proteins, intact monocytes were biotinylated before lysis with Nonidet P-40 and solubilized proteins were incubated with RGPs Affi-Prep beads. One major membrane protein of 55 kDa was specifically detected and identified as CD14 because it reacted with anti-CD14 mAbs. Furthermore, anti-CD14 mAbs were able to perform a dose-dependent inhibition of RGPs binding, and suppressed TNF-alpha release from RGPs-stimulated monocytes. Moreover, we demonstrated that RGPs also bind to CD11b; however, this binding is not implicated in synthesis of TNF-alpha. Interestingly, RGPs binding to monocytes was enhanced by human normal serum (HNS) whereas HNS inhibits the TNF-alpha-stimulating activity of RGPs. Western blotting analysis of HNS proteins purified on RGPs Affi-prep beads revealed three specific bands of 75, 55, and 32 kDa reactive with anti-C3 Abs, anti-CD14 mAbs (TUK4), and anti-human mannan binding protein (hMBP)-derived peptide IgG, respectively. These results suggest that C3, soluble CD14, and hMBP form complexes that are probably active in enhancing the binding of RGPs to monocytes. Additional studies have shown that hMBP that recognizes RGPs prevents, unlike the LPS binding protein, TNF-alpha release by inhibiting the binding of RGPs to CD14 Ag. By incubating cells with a constant amount of RGPs-hMBP complexes in the presence or absence of increasing concentrations of C1q, we also demonstrated that C1q receptor mediates the binding and probably the uptake of RGPs-hMBP complexes by human monocytes.

Human interferons-alpha inhibit the production of immunoglobulin M by secreting and nonsecreting lymphoblastoid cell lines

It is well known that human lymphoblastoid interferon-alpha [HuIFN-alpha(ly)] may either increase or decrease antibody production by B cells, in vivo as well as in vitro, depending on the experimental conditions and the system used. We compare here the effect of HuIFN-alpha(ly) and human recombinant interferon-alpha (rHuIFN-alpha) on immunoglobulin M (IgM) production by secreting and nonsecreting human B-like lymphoblastoid cells, respectively, ST8246, and Daudi cells. Under our experimental conditions, Daudi cells were less sensitive to the antiproliferative effect of IFN than previously reported by other authors, and ST8246 cells were insensitive to this antiproliferative effect. In contrast, IgM production was profoundly affected in both cell lines. Thus, we could discriminate between the effect on cell growth from the effect on the immune response. Using high-pressure liquid chromatography (HPLC) separation, mu chains and monomeric and pentameric IgM were distinguished from cytosolic and membrane-associated fractions and from culture medium (extracellular IgM). Pentameric extracellular IgM and monomeric membrane IgM were diminished by HuIFN-alpha(ly) treatment, respectively, in ST8246 cells and in Daudi cells. We conclude that HuIFN-alpha(ly) induces regression of B-like lymphoblastoid cells toward a less mature phenotype.

Activation of human monocytes by streptococcal rhamnose glucose polymers is mediated by CD14 antigen, and mannan binding protein inhibits TNF-alpha release

The present work was initiated to define mechanisms that account for the binding on human monocytes of streptococcal cell wall polysaccharides formed by rhamnose glucose polymers (RGPs), and subsequent stimulatory activities. We show here that RGPs bind to and stimulate human monocytes to produce TNF-alpha in a dose-dependent manner. To detect cell surface RGPs binding proteins, intact monocytes were biotinylated before lysis with Nonidet P-40 and solubilized proteins were incubated with RGPs Affi-Prep beads. One major membrane protein of 55 kDa was specifically detected and identified as CD14 because it reacted with anti-CD14 mAbs. Furthermore, anti-CD14 mAbs were able to perform a dose-dependent inhibition of RGPs binding, and suppressed TNF-alpha release from RGPs-stimulated monocytes. Moreover, we demonstrated that RGPs also bind to CD11b; however, this binding is not implicated in synthesis of TNF-alpha. Interestingly, RGPs binding to monocytes was enhanced by human normal serum (HNS) whereas HNS inhibits the TNF-alpha-stimulating activity of RGPs. Western blotting analysis of HNS proteins purified on RGPs Affi-prep beads revealed three specific bands of 75, 55, and 32 kDa reactive with anti-C3 Abs, anti-CD14 mAbs (TUK4), and anti-human mannan binding protein (hMBP)-derived peptide IgG, respectively. These results suggest that C3, soluble CD14, and hMBP form complexes that are probably active in enhancing the binding of RGPs to monocytes. Additional studies have shown that hMBP that recognizes RGPs prevents, unlike the LPS binding protein, TNF-alpha release by inhibiting the binding of RGPs to CD14 Ag. By incubating cells with a constant amount of RGPs-hMBP complexes in the presence or absence of increasing concentrations of C1q, we also demonstrated that C1q receptor mediates the binding and probably the uptake of RGPs-hMBP complexes by human monocytes.

Human IgG and Streptococcus mutans SR protein contain cross-reactive epitopes

Antigen B, a glycoprotein present on the cell surface of "mutans streptococci," mediates bacterial adherence to teeth surfaces and has been implicated in cross-reactivity with human heart components. Elevated levels of anti-IgG antibodies were generally found in sera of rabbits immunized with protein SR, a B-related protein from Streptococcus mutans serogroup f, or recombinant protein SR (rSR). These anti-IgG antibodies could be involved in the previously mentioned heart cross-reactivities. Results from immunoblots and ELISA analyses demonstrate that these anti-IgG antibodies recognize common epitopes on SR, rSR, and human IgG2 and IgG4 probably located on the Fab region. Furthermore, control experiments with biotinylated human IgG show that the cross-reactions between IgG and SR were not mediated by an FcR mechanism. Direct competition between rSR and human IgG in binding to anti-IgG or anti-SR antibodies confirm that S. mutans SR protein possesses Ag mimicry with human IgG. Our studies provide some evidence that S. mutans SR protein and human IgG H chains share autoimmune epitopes which could play a role in the induction of anti-IgG antibodies and therefore could explain the enhancement of anti-IgG antibody levels observed in rabbits immunized with either S. mutans whole cells or purified B-related Ag.

Local and systemic immune response to orally administered liposome-associated soluble S. mutans cell wall antigens

The aim of the present study was to develop an immunization procedure which preferentially stimulated the IgA system of rats, with release of IgA in secretions. Rats immunized by intragastric route with liposome-associated soluble antigen extracted from Streptococcus mutans cell wall, showed a significantly higher IgA (and IgG) response than did rats injected with the soluble antigen alone. In saliva, maximal antibody titres were obtained 11 days after the beginning of intubations for IgA, and 16 days for IgG. After a booster immunization, the secondary response occurred very quickly in saliva and, like the primary response, it was almost exclusively of the IgA class. This demonstrates, on one hand the existence of immunological memory in the IgA system and, on the other, the efficiency of liposomes as insoluble adjuvants in eliciting an immunological response.

Human IgG and Streptococcus mutans SR protein contain cross-reactive epitopes

Antigen B, a glycoprotein present on the cell surface of "mutans streptococci," mediates bacterial adherence to teeth surfaces and has been implicated in cross-reactivity with human heart components. Elevated levels of anti-IgG antibodies were generally found in sera of rabbits immunized with protein SR, a B-related protein from Streptococcus mutans serogroup f, or recombinant protein SR (rSR). These anti-IgG antibodies could be involved in the previously mentioned heart cross-reactivities. Results from immunoblots and ELISA analyses demonstrate that these anti-IgG antibodies recognize common epitopes on SR, rSR, and human IgG2 and IgG4 probably located on the Fab region. Furthermore, control experiments with biotinylated human IgG show that the cross-reactions between IgG and SR were not mediated by an FcR mechanism. Direct competition between rSR and human IgG in binding to anti-IgG or anti-SR antibodies confirm that S. mutans SR protein possesses Ag mimicry with human IgG. Our studies provide some evidence that S. mutans SR protein and human IgG H chains share autoimmune epitopes which could play a role in the induction of anti-IgG antibodies and therefore could explain the enhancement of anti-IgG antibody levels observed in rabbits immunized with either S. mutans whole cells or purified B-related Ag.