Characterization of coaggregation between Bacteroides gingivalis T22 and Fusobacterium nucleatum T18.

Bacterial adherence is a key factor in the colonization of the oral ecosystem, yet little is known about the mechanisms by which the pathogen Bacteroides gingivalis adheres in the periodontal environment. We examined the ability of strains of B. gingivalis to coaggregate with selected microorganisms isolated from the subgingival microbiota of the cynomolgus monkey. A strong interaction was demonstrated between strains of B. gingivalis and Fusobacterium nucleatum, whereas less pronounced or no interaction was observed with other oral isolates. Electron microscopic examination of coaggregates revealed large masses of bacteria, in which the fusiform F. nucleatum T18 and coccobacillary B. gingivalis T22 cells formed a woven pattern. To investigate this interaction and the nature of the bacterial cell surface molecules involved, we used a microcoaggregation assay. Galactose and galactose-related sugars blocked coaggregation, in contrast with the lack of effect of glucose or glucose-related sugars. The ability of F. nucleatum T18 cells to coaggregate was diminished by pretreatment with pronase. Pretreatment of B. gingivalis T22 cells with pronase resulted in an inhibition of coaggregation, whereas pretreatment with sodium metaperiodate completely abolished coaggregation. These data suggest that the coaggregation between B. gingivalis T22 and F. nucleatum T18 represents a carbohydrate-lectin interaction, mediated by a galactose-containing carbohydrate on B. gingivalis T22 and a protein on F. nucleatum T18.     

Interactions between periodontal bacteria and human oral epithelial cells: Fusobacterium nucleatum adheres to and invades epithelial cells

Bacteria are causative agents of periodontal diseases. Interactions between oral bacteria and gingival epithelial cells are essential aspects of periodontal infections. Using an in vitro tissue culture model, a selected group of gram-negative anaerobic bacteria frequently associated with periodontal diseases, including Bacteroides forsythus, Campylobacter curvus, Eikenella corrodens, Fusobacterium nucleatum, Porphyromonas gingivalis, and Prevotella intermedia, were examined for their ability to adhere to and invade primary cultures of human gingival epithelial cells (HGEC). The effects of these bacteria on the production of interleukin-8 (IL-8), a proinflammatory chemokine, were also measured. These studies provided an initial demonstration that F. nucleatum adhered to and invaded HGEC and that this was accompanied by high levels of IL-8 secretion from the epithelial cells. The attachment and invasion characteristics of F. nucleatum were also tested using KB cells, an oral epithelial cell line. The invasion was verified by transmission electron microscopy and with metabolic inhibitors. Invasion appeared to occur via a "zipping" mechanism and required the involvement of actins, microtubules, signal transduction, protein synthesis, and energy metabolism of the epithelial cell, as well as protein synthesis by F. nucleatum. A spontaneous mutant, lam, of F. nucleatum, isolated as defective in autoagglutination, was unable to attach to or invade HGEC or KB cells, further indicating the requirement of bacterial components in these processes. Sugar inhibition assays indicated that lectin-like interactions were involved in the attachment of F. nucleatum to KB cells. Investigation of these new virulence phenotypes should improve our understanding of the role of F. nucleatum in periodontal infections.     

Effect of Fusobacterium nucleatum on the T and B cell responses to Porphyromonas gingivalis in a mouse model

T cell cytokine profiles and specific serum antibody levels in five groups of BALB/c mice immunized with saline alone, viable Fusobacterium nucleatum ATCC 25586, viable Porphyromonas gingivalis ATCC 33277, F. nucleatum followed by P. gingivalis and P. gingivalis followed by F. nucleatum were determined. Splenic CD4 and CD8 cells were examined for intracytoplasmic interleukin (IL)-4, interferon (IFN)-gamma and IL-10 by dual colour flow cytometry and the levels of serum anti-F. nucleatum and anti-P. gingivalis antibodies determined by an ELISA. Both Th1 and Th2 responses were demonstrated by all groups, and while there were slightly lower percentages of cytokine positive T cells in mice injected with F. nucleatum alone compared with the other groups immunized with bacteria, F. nucleatum had no effect on the T cell production of cytokines induced by P. gingivalis in the two groups immunized with both organisms. However, the percentages of cytokine positive CD8 cells were generally significantly higher than those of the CD4 cells. Mice immunized with F. nucleatum alone had high levels of serum anti-F. nucleatum antibodies with very low levels of P. gingivalis antibodies, whereas mice injected with P. gingivalis alone produced anti-P. gingivalis antibodies predominantly. Although the levels of anti-F. nucleatum antibodies in mice injected with F. nucleatum followed by P. gingivalis were the same as in mice immunized with F. nucleatum alone, antibody levels to P. gingivalis were very low. In contrast, mice injected with P. gingivalis followed by F. nucleatum produced equal levels of both anti-P. gingivalis and anti-F. nucleatum antibodies, although at lower levels than the other three groups immunized with bacteria, respectively. Anti-Actinobacillus actinomycetemcomitans, Bacteroides forsythus and Prevotella intermedia serum antibody levels were also determined and found to be negligible. In conclusion, F. nucleatum immunization does not affect the splenic T cell cytokine response to P. gingivalis. However, F. nucleatum immunization prior to that of P. gingivalis almost completely inhibited the production of anti-P. gingivalis antibodies while P. gingivalis injection before F. nucleatum demonstrated a partial inhibitory effect by P. gingivalis on antibody production to F. nucleatum. The significance of these results with respect to human periodontal disease is difficult to determine. However, they may explain in part differing responses to P. gingivalis in different individuals who may or may not have had prior exposure to F. nucleatum. Finally, the results suggested that P. gingivalis and F. nucleatum do not induce the production of cross-reactive antibodies to other oral microorganisms.     

Differential regulation of cytokine genes in gingival epithelial cells challenged by Fusobacterium nucleatum and Porphyromonas gingivalis

IL-8 mRNA in human gingival epithelial cells (HGECs) is up-regulated by Fusobacterium nucleatum, and up-/down-regulated by Porphyromonas gingivalis in a complex interaction in the early stages (< or = 4 h) after infection. The mechanisms involved in this regulation in response to F. nucleatum and/or P. gingivalis infection, and identification of co-regulated cytokine genes, are the focus of this investigation. Heat, formalin or protease treatment of F. nucleatum cells attenuated the IL-8 mRNA up-regulation. NF-kappaB, mitogen-activated protein kinase (MAPK) p38 and MAPK kinase/extracellular signal-regulated kinase (MEK/ERK) pathways were involved in IL-8 mRNA induction by F. nucleatum. Pretreatment of P. gingivalis with heat, formalin or protease enhanced IL-8 mRNA induction. NF-kappaB, MARK p38, and MEK/ERK pathways were also involved in this induction. In contrast, down-regulation of IL-8 mRNA by P. gingivalis involved MEK/ERK, but not NF-kappaB or MAPK p38 pathways. cDNA arrays analysis revealed that mRNA down-regulation by P. gingivalis is a specific reaction that only a number of genes, e.g. IL-1beta, IL-8, macrophage inflammatory protein-2alpha, and migration inhibitory factor-related protein-14, are affected based on examination of 278 cytokine/receptor genes. These data indicate that F. nucleatum and P. gingivalis trigger specific and differential gene regulation pathways in HGECs.     

Interleukin-8 and intercellular adhesion molecule 1 regulation in oral epithelial cells by selected periodontal bacteria: multiple effects of Porphyromonas gingivalis via antagonistic mechanisms

Interaction of bacteria with mucosal surfaces can modulate the production of proinflammatory cytokines and adhesion molecules produced by epithelial cells. Previously, we showed that expression of interleukin-8 (IL-8) and intercellular adhesion molecule 1 (ICAM-1) by gingival epithelial cells increases following interaction with several putative periodontal pathogens. In contrast, expression of IL-8 and ICAM-1 is reduced after Porphyromonas gingivalis ATCC 33277 challenge. In the present study, we investigated the mechanisms that govern the regulation of these two molecules in bacterially infected gingival epithelial cells. Experimental approaches included bacterial stimulation of gingival epithelial cells by either a brief challenge (1.5 to 2 h) or a continuous coculture throughout the incubation period. The kinetics of IL-8 and ICAM-1 expression following brief challenge were such that (i) secretion of IL-8 by gingival epithelial cells reached its peak 2 h following Fusobacterium nucleatum infection whereas it rapidly decreased within 2 h after P. gingivalis infection and remained decreased up to 30 h and (ii) IL-8 and ICAM-1 mRNA levels were up-regulated rapidly 2 to 4 h postinfection and then decreased to basal levels 8 to 20 h after infection with either Actinobacillus actinomycetemcomitans, F. nucleatum, or P. gingivalis. Attenuation of IL-8 secretion was facilitated by adherent P. gingivalis strains. The IL-8 secreted from epithelial cells after F. nucleatum stimulation could be down-regulated by subsequent infection with P. gingivalis or its culture supernatant. Although these results suggested that IL-8 attenuation at the protein level might be associated with P. gingivalis proteases, the Arg- and Lys-gingipain proteases did not appear to be solely responsible for IL-8 attenuation. In addition, while P. gingivalis up-regulated IL-8 mRNA expression, this effect was overridden when the bacteria were continuously cocultured with the epithelial cells. The IL-8 mRNA levels in epithelial cells following sequential challenge with P. gingivalis and F. nucleatum and vice versa were approximately identical and were lower than those following F. nucleatum challenge alone and higher than control levels or those following P. gingivalis challenge alone. Thus, together with the protease effect, P. gingivalis possesses a powerful strategy to ensure the down-regulation of IL-8 and ICAM-1.     

Modulation of human neutrophil adherence by periodontopathic bacteria: reversal by specific monoclonal antibodies

Previous investigations by us have shown that direct interaction of Fusobacterium nucleatum with polymorphonuclear neutrophils (PMNs) results in the stimulation of PMN adherence whereas direct interaction with Bacteroides gingivalis results in PMN suppression. In the present study, panels of monoclonal antibodies (MAbs) raised against cell wall antigens of F. nucleatum and B. gingivalis were tested to determine their ability to block the modulatory effects of the bacteria in their interactions with PMNs. While no activity was demonstrated for any of the 9 MAbs raised against F. nucleatum, it was found that 2 of 16 MAbs raised against B. gingivalis were able to reverse the suppression of PMN adherence induced by the bacteria. Further studies on these 2 reactive MAbs showed that the effect of MAbs were abrogated by heat treatment as well as by trypsin proteolysis. Investigations into the nature of the reactive epitopes on the bacterial surface showed that they probably contain protein components susceptible to proteolytic attack by subtilisin. In addition, beta-galactose may be a component of the reactive epitopes for one of the MAbs, but sialic acid residues on the bacterial surface are probably not involved as their elimination by neuraminidase did not affect the binding of both MAbs. The results of the present study strongly validate our previous observations that direct specific interaction of B. gingivalis with human PMNs occurs, resulting in the suppression of PMNs.     

Nonspecific induction of immunoglobulin M antibodies to periodontal disease-associated microorganisms after polyclonal human B-lymphocyte activation by Fusobacterium nucleatum.

The production of antibodies to oral bacteria was determined in lymphocyte cultures stimulated with sonicated Fusobacterium nucleatum, a potent inducer of polyclonal B-cell activation. After 9 days the cultures were examined by a microenzyme-linked immunosorbent assay for immunoglobulin M (IgM) antibodies to F. nucleatum, Bacteroides gingivalis, Actinomyces viscosus, and Streptococcus sanguis. Antibodies to these four bacteria were detected in cultures stimulated with polyclonal B-cell activation-inducing concentrations of F. nucleatum. However, significant concentrations of antibodies to F. nucleatum, but not to the other three microorganisms, were produced in cultures that received suboptimal polyclonal B-cell activation-inducing doses of F. nucleatum. Absorption studies indicated the specificity of the antibodies to each of the bacteria tested. IgM antibody production induced by F. nucleatum was enhanced by the addition of T cells. The production of IgM antibodies to the bacteria was reproducible in cultures from a single person tested on 3 consecutive days. The concentration of antibodies in replicate cultures, however, fluctuated greatly. To obtain consistent responses on successive days, multiple replicate cultures were required. These results suggest that F. nucleatum, which is frequently present in subgingival plaque, could induce the production of antibodies not only to F. nucleatum, but also to other microorganisms associated with periodontal diseases.     

Coaggregation of Candida dubliniensis with Fusobacterium nucleatum

The binding of microorganisms to each other and oral surfaces contributes to the progression of microbial infections in the oral cavity. Candida dubliniensis, a newly characterized species, has been identified in human immunodeficiency virus-seropositive patients and other immunocompromised individuals. C. dubliniensis phenotypically resembles Candida albicans in many respects yet can be identified and differentiated as a unique Candida species by phenotypic and genetic profiles. The purpose of this study was to determine oral coaggregation (CoAg) partners of C. dubliniensis and to compare these findings with CoAg of C. albicans under the same environmental conditions. Fifteen isolates of C. dubliniensis and 40 isolates of C. albicans were tested for their ability to coaggregate with strains of Fusobacterium nucleatum, Peptostreptococcus micros, Peptostreptococcus magnus, Peptostreptococcus anaerobius, Porphyromonas gingivalis, and Prevotella intermedia. When C. dubliniensis and C. albicans strains were grown at 37 degrees C on Sabouraud dextrose agar, only C. dubliniensis strains coaggregated with F. nucleatum ATCC 49256 and no C. albicans strains showed CoAg. However, when the C. dubliniensis and C. albicans strains were grown at 25 or 45 degrees C, both C. dubliniensis and C. albicans strains demonstrated CoAg with F. nucleatum. Heating the C. albicans strains (grown at 37 degrees C) at 85 degrees C for 30 min or treating them with dithiothreitol allowed the C. albicans strains grown at 37 degrees C to coaggregate with F. nucleatum. CoAg at all growth temperatures was inhibited by mannose and alpha-methyl mannoside but not by EDTA or arginine. The CoAg reaction between F. nucleatum and the Candida species involved a heat-labile component on F. nucleatum and a mannan-containing heat-stable receptor on the Candida species. The CoAg reactions between F. nucleatum and the Candida species may be important in the colonization of the yeast in the oral cavity, and the CoAg of C. dubliniensis by F. nucleatum when grown at 37 degrees C provides a rapid, specific, and inexpensive means to differentiate C. dubliniensis from C. albicans isolates in the clinical laboratory.     

Identification of a Fusobacterium nucleatum PK1594 galactose-binding adhesin which mediates coaggregation with periopathogenic bacteria and hemagglutination.

Attachment of Fusobacterium nucleatum to various oral surfaces is mediated by several adhesins anchored on its outer surface. Monoclonal antibodies (MAbs) were prepared and used to identify the putative galactose-binding adhesin of F. nucleatum PK1594. Four unique MAbs, 8G7, 26B9, 28G11, and 29D4, were isolated on the basis of their ability to inhibit coaggregation of F. nucleatum PK1594 with Porphyromonas gingivalis PK1924. All four MAbs were also capable of inhibiting galactose-inhibitable interactions of F. nucleatum PK1594 with other oral gram-negative bacteria and with erythrocytes. Preincubation of F. nucleatum PK1594 with MAb 26B9 or its Fab fragments at concentrations lower than 1 microg/ml resulted in complete inhibition of coaggregation with P. gingivalis PK1924 or hemagglutination. F. nucleatum PK1594 surface components prepared by mild sonication or by extracting whole cells with detergents were subjected to Western blot analysis. None of the MAbs were able to recognize any polypeptide in these experiments. Therefore, detergent extracts of F. nucleatum PK1594 surface components were subjected to three experimental procedures: (i) separation by ion-exchange chromatography and testing of fractions for reaction with MAb 26B9 in an enzyme-linked immunosorbent assay (ELISA), (ii) lactose-Sepharose affinity chromatography and testing of the lactose eluate in ELISA with MAb 26B9, and (iii) immunoseparation with either MAb 26B9 or 8G7. Collectively, the results suggest that the putative adhesin is a 30-kDa outer membrane polypeptide which mediates the coaggregation with P. gingivalis PK1924 as well as other galactose-sensitive interactions of F. nucleatum PK1594.     

Fusobacterium nucleatum increases collagenase 3 production and migration of epithelial cells

Fusobacterium nucleatum is closely associated with human periodontal diseases and may also be a causative agent in other infections, such as pericarditis, septic arthritis, and abscesses of tonsils and liver. Initiation and outcome of infective diseases depend critically on the host cell signaling system altered by the microbe. Production of proteinases by infected cells is an important factor in pericellular tissue destruction and cell migration. We studied binding of F. nucleatum to human epithelial cells (HaCaT keratinocyte line) and subsequent cell signaling related to collagenase 3 expression, cell motility, and cell survival, using a scratch wound cell culture model. F. nucleatum increased levels of 12 protein kinases involved in cell migration, proliferation, and cell survival signaling, as assessed by the Kinetworks immunoblotting system. Epithelial cells of the artificial wound margins were clearly preferential targets of F. nucleatum. The bacterium colocalized with lysosomal structures and stimulated migration of these cells. Of the 13 anaerobic oral bacterial species, F. nucleatum and Fusobacterium necrophorum were among the best inducers of collagenase 3 mRNA levels, a powerful matrix metalloproteinase. Production of collagenase 3 was detected in fusobacterium-infected cells and cell culture medium by immunocytochemistry, immunoblotting, and zymography. The proteinase production involved activation of p38 mitogen-activated protein kinase in the infected cells. The study suggests that F. nucleatum may be involved in the pathogenesis of periodontal diseases (and other infections) by activating multiple cell signaling systems that lead to stimulation of collagenase 3 expression and increased migration and survival of the infected epithelial cells.     

Specificity of monoclonal antibodies reactive with Fusobacterium nucleatum: effect of formalin fixation

Monoclonal antibody specific for Fusobacterium nucleatum was reacted with untreated and formalin fixed F. nucleatum cells by an enzyme-linked immunosorbent assay (ELISA) and by indirect immunofluorescence. Treatment of bacterial cells with formalin destroyed the antigenic determinant responsible for reactivity with this monoclonal antibody in both assays. Formalin fixation had no effect on hemagglutination activity (HA) of F. nucleatum cells or reactivity with polyvalent rabbit antiserum in double diffusion in agar. Scanning electron microscopy demonstrated that formalin fixation did not affect binding of F. nucleatum cells to microtiter plates. When developing monoclonal antibodies to be used as diagnostic reagents, the antigenic form utilized for immunization should be identical to the antigenic form which will eventually be used in the diagnostic assay.     

Identification of proteases from periodontopathogenic bacteria as activators of latent human neutrophil and fibroblast-type interstitial collagenases.

Activation of latent human fibroblast-type and neutrophil interstitial procollagenases as well as degradation of native type I collagen by supra- and subgingival dental plaque extracts, an 80-kDa trypsinlike protease from Porphyromas gingivalis (ATCC 33277), a 95-kDa chymotrypsinlike protease from Treponema denticola (ATCC 29522), and selected bacterial species commonly isolated in periodontitis was studied. The bacteria included were Prevotella intermedia (ATCC 25261), Prevotella buccae (ES 57), Prevotella oris (ATCC 33573), Porphyromonas endodontalis (ES 54b), Actinobacillus actinomycetemcomitans (ATCC 295222), Fusobacterium nucleatum (ATCC 10953), Mitsuokella dentalis (DSM 3688), and Streptococcus mitis (ATCC 15909). None of the bacteria activated latent procollagenases; however, both sub- and supragingival dental plaque extracts (neutral salt extraction) and proteases isolated from cell extracts from potentially periodontopathogenic bacteria P. gingivalis and T. denticola were found to activate latent human fibroblast-type and neutrophil interstitial procollagenases. The fibroblast-type interstitial collagenase was more efficiently activated by bacterial proteases than the neutrophil counterpart, which instead preferred nonproteolytic activation by the oxidative agent hypochlorous acid. The proteases were not able to convert collagenase tissue inhibitor of metalloproteinase (TIMP-1) complexes into active form or to change the ability of TIMP-1 to inhibit interstitial collagenase. None of the studied bacteria, proteases from P. gingivalis and T. denticola, or extracts of supra- and subgingival dental plaque showed any significant collagenolytic activity. However, the proteases degraded native and denatured collagen fragments after cleavage by interstitial collagenase and gelatinase. Our results indicate that proteases from periodontopathogenic bacteria can act as direct proteolytic activators of human procollagenases and degrade collagen fragments. Thus, in concert with host enzymes the bacterial proteases may participate in periodontal tissue destruction.     

Fusobacterium nucleatum transports noninvasive Streptococcus cristatus into human epithelial cells

Analysis of human buccal epithelial cells frequently reveals an intracellular polymicrobial consortium of bacteria. Although several oral bacteria have been demonstrated to invade cultured epithelial cells, several others appear unable to internalize. We hypothesized that normally noninvasive bacteria may gain entry into epithelial cells via adhesion to invasive bacteria. Fusobacterium nucleatum is capable of binding to and invading oral epithelial cells. By contrast, Streptococcus cristatus binds weakly to host cells and is not internalized. F. nucleatum and S. cristatus coaggregate strongly via an arginine-sensitive interaction. Coincubation of KB or TERT-2 epithelial cells with equal numbers of F. nucleatum and S. cristatus bacteria led to significantly increased numbers of adherent and internalized streptococci. F. nucleatum also promoted invasion of KB cells by other oral streptococci and Actinomyces naeslundii. Dissection of fusobacterial or streptococcal adhesive interactions by using sugars, amino acids, or antibodies demonstrated that this phenomenon is due to direct attachment of S. cristatus to adherent and invading F. nucleatum. Inhibition of F. nucleatum host cell attachment and invasion with galactose, or fusobacterial-streptococcal coaggregation by the arginine homologue l-canavanine, abrogated the increased S. cristatus adhesion to, and invasion of, host cells. In addition, polyclonal antibodies to F. nucleatum, which inhibited fusobacterial attachment to both KB cells and S. cristatus, significantly decreased invasion by both species. Similar decreases were obtained when epithelial cells were pretreated with cytochalasin D, staurosporine, or cycloheximide. These studies indicate that F. nucleatum may facilitate the colonization of epithelial cells by bacteria unable to adhere or invade directly.     

A study of the activation of fibrin-bound plasminogen by tissue-type plasminogen activator,single chain urokinase and sequential combinations of the activators

The efficacy of tissue-type plasminogen activator (t-PA) and single chain urokinase-type plasminogen activator (scu-PA) to activate fibrin-bound plasminogen was determined. With the use of a solid-phase model of intact and plasmin-degraded fibrin, the initial rate, Vi (fmol of plasmin/min), of plasmin generation by t-PA, scu-PA and two chain u-PA (tcu-PA) and the ratio, R (mol of plasmin generated/mol of activator) were determined as indicators of the efficiency of plasminogen activation. [Glu)t-plasminogen bound to intact fibrin was most efficiently activated by t-PA (Vi=0.843 and R=4.08), while scu-PA and tcu-PA produced markedly lower activation coefficients (Vi=0.011 and 0.023, and R=0.13 and 0.50 respectively). In contrast, when [Glu]¹-plasminogen was bound to the degraded surface, it became activatable with equivalent efficiencies by both t-PA and scu-PA (R=4.95 and 4.72, respectively). No evidence of Lys-plasminogen formation was observed. Rather, the selective activation of plasminogen bound to degraded fibrin by scu-PA is consistent with a particular interaction of Glu-plasminogen with carboxy-terminal lysine residues on the degraded surface. The consequences of this interaction of scu-PA with plasminogen bound to degraded fibrin on sequential activations of plasminogen by both t-PA and scu-PA were further explored. While the activation by scu-PA and then t-PA produced only an additive effect on plasmin generation, the opposite combination induced a greater than additive affect; the concentration of activators needed to produce 50% of plasmin generation was 70pM for the scu-PA/t-PA combination; in contrast, the amount required to produce a similar degree of activation with the opposite combination (t-PA/scu-PA) was only 17 pM. These results indicate that the potentiation of the scu-PA activity requires both the previous generation of plasmin by t-PA, and plasminogen bound to carboxy-terminal lysine residues of the degraded fibrin surface as a substrate.     

Tissue-type plasminogen activator-mediated activation of plasminogen on the surface of group A, C, and G streptococci.

The interaction of Glu-plasminogen with group A, C, and G streptococci and subsequent formation of surface-associated plasminogen by tissue-type plasminogen activator (t-PA) were studied. Binding of 125I-Glu-plasminogen to streptococci greatly facilitated its activation to 125I-Glu-plasmin by exogenous t-PA, whereas activation in the absence of bacteria took place only slowly. Glu-plasmin formed on the streptococcal surface was further converted to the Lys form. Similar activation and modification took place also in the presence of plasminogen-depleted plasma, containing functional t-PA and plasmin inhibitors, indicating that the surface-associated enzymes were protected against these inhibitors. Lys-plasminogen was 10- to 30-fold more potent than Glu-plasminogen or Glu-plasmin in inhibiting the binding of 125I-Glu-plasminogen to streptococci. This indicated a higher affinity of the Lys form towards plasminogen-binding molecule(s) on the streptococcal surface. The surface-associated plasmin was also enzymically active as judged by digestion of chromogenic substrate S-2251. Surface-associated plasmin activity was observed only when the incubations were carried out in the presence of t-PA and Glu-plasminogen or human plasma as the source of plasminogen. Under these conditions, soluble enzymatic activity was also recovered in the supernatant of group A streptococci. This favors the idea that plasmin can be released from the bacterial surface. The findings provide a mechanism for streptococci to adopt proteolytic activity by binding a host-derived enzyme zymogen on their surface, where the subsequent activation then takes place. The results suggest a role for surface-associated plasmin activity in tissue tropism and tissue invasiveness of streptococci.     

Mapping of the human plasmin domain recognized by the unique plasmin receptor of group A streptococci.

A high-affinity surface receptor for human plasmin has been reported on certain group A streptococci. To map the region of the plasmin molecule that binds to the bacterial receptor, isolated domains of plasmin were tested for their ability to inhibit the binding of intact radiolabeled plasmin to receptor-positive bacteria. Complete inhibition of binding of labeled plasmin to bacteria by isolated heavy chains was achieved, but this inhibition was not as efficient on a molar basis when compared with that of unlabeled plasmin. By contrast, a conformationally altered form of native plasminogen was found to bind to bacteria and was as efficient a competitive inhibitor as intact plasmin was. The results of this study indicate that the selective binding of human plasmin to a group A streptococcus is dependent on structures present in the conformationally altered form of native plasminogen or plasmin that are not found on the native zymogen, the plasminogen with NH2-terminal glutamic acid.     

Lectinlike interactions of Fusobacterium nucleatum with human neutrophils.

Fusobacterium nucleatum expresses lectinlike adherence factors which mediate binding to a variety of human tissue cells. Adherence is selectively inhibited by galactose, lactose, and N-acetyl-D-galactosamine. In this study, adherence of F. nucleatum to human peripheral blood polymorphonuclear neutrophils (PMNs) was investigated. The results indicated that the fusobacteria adhered to live and metabolically inactivated or fixed PMNs. Adherence of F. nucleatum resulted in activation of PMNs as determined by PMN aggregation, membrane depolarization, increased intracellular free Ca2+, superoxide anion production, and lysozyme release. Transmission electron micrographs showed that F. nucleatum was phagocytized by the PMNs. Microbicidal assays indicated that greater than 98% of F. nucleatum organisms were killed by PMNs within 60 min. Adherence to and activation of PMNs by F. nucleatum were inhibited by N-acetyl-D-galactosamine or lactose greater than galactose, whereas equal concentrations of glucose, N-acetyl-D-glucosamine, mannose, and fucose had little or no effect on F. nucleatum-PMN interactions. Pretreatment of the fusobacteria with heat (80 degrees C, 20 min) or proteases inhibited adherence to and activation of PMNs, but superoxide production was also stimulated by heated bacteria. The results indicate that interaction of F. nucleatum with PMNs is lectinlike and is probably mediated by fusobacterial proteins which bind to other human tissue cells. Adherence of F. nucleatum to PMNs in the absence of serum opsonins, such as antibodies and complement, may play an important role in PMN recognition and killing of F. nucleatum in the gingival sulcus and in the subsequent release of PMN factors associated with tissue destruction.     

Taxonomy, biology, and periodontal aspects of Fusobacterium nucleatum.

The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has the potential to be pathogenic because of its number and frequency in periodontal lesions, its production of tissue irritants, its synergism with other bacteria in mixed infections, and its ability to form aggregates with other suspected pathogens in periodontal disease and thus act as a bridge between early and late colonizers on the tooth surface. Second, of the microbial species that are statistically associated with periodontal disease, F. nucleatum is the most common in clinical infections of other body sites. Third, during the past few years, new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins (OMPs). OMPs are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility. This review covers what is known to date about F. nucleatum in general, such as taxonomy and biology, with special emphasis on its pathogenic potential. Its possible relationship to other periodontal bacteria in the development of periodontal diseases and the possible roles played by OMPs are considered.     

The multifaceted roles of Leptospira enolase

A previous study had demonstrated that Leptospira enolase is secreted extracellularly by a yet unknown mechanism and reassociates with the bacterial membrane. Surface-anchored leptospiral enolase displays plasminogen binding activity. In this work, we explored the consequences of this interaction and also assessed whether Leptospira enolase might display additional moonlighting functions by interacting with other host effector proteins. We first demonstrated that enolase-bound plasminogen is converted to its active form, plasmin. The protease plasmin targets human fibrinogen and vitronectin, but not the complement proteins C3b and C5. Leptospira enolase also acts as an immune evasion protein by interacting with the negative complement regulators C4b binding protein and factor H. Once bound to enolase, both regulators remain functional as cofactors of factor I, mediating cleavage of C4b and C3b. In conclusion, enolase may facilitate leptospiral survival and dissemination, thus contributing to bacterial virulence. The identification and characterization of moonlighting proteins is a growing field of bacterial pathogenesis, as these multifaceted proteins may represent potential future therapeutic targets to fight bacterial infections.     

Plasmin as a proinflammatory cell activator

The serine protease plasmin generated from its zymogen plasminogen is best known for its function as a key enzyme of the fibrinolytic cascade. However, beyond fibrinolysis, plasmin has a number of crucial functions in a variety of processes, including inflammation. Various cells can bind plasminogen and plasmin via plasminogen-binding sites exposing a C-terminal lysine. Plasmin, generated as a result of plasminogen activation at the cell surface, is protected from its physiological inhibitors. Apart from its ability to facilitate cell migration in tissues, plasmin is capable of triggering signaling, which depends on cellular binding via its lysine-binding sites and its proteolytic activity. Plasmin-induced signaling affects various functions of monocytes, macrophages, DCs, and others, with the list of affected cells still growing. In vitro and in vivo studies have demonstrated the ability of plasmin to stimulate the production of cytokines, ROS, and other mediators, thereby contributing to inflammation. Plasmin-induced chemotaxis of monocytes and DCs indicates that it is also a potent chemoattractant for immune cells. Therefore, excessive activation of plasmin in chronic inflammatory or autoimmune diseases might exacerbate the activation of inflammatory cells and the pathogenesis of the disease. This review focuses on the available evidence for physiological and pathophysiological roles the serine protease plasmin in inflammatory processes.