Hemagglutinin Structure and Activities

Hemagglutinins (HAs) are the receptor-binding and membrane fusion glycoproteins of influenza viruses. They recognize sialic acid-containing, cell-surface glycoconjugates as receptors but have limited affinity for them, and, as a consequence, virus attachment to cells requires their interaction with several virus HAs. Receptor-bound virus is transferred into endosomes where membrane fusion by HAs is activated at pH between 5 and 6.5, depending on the strain of virus. Fusion activity requires extensive rearrangements in HA conformation that include extrusion of a buried "fusion peptide" to connect with the endosomal membrane, form a bridge to the virus membrane, and eventually bring both membranes close together. In this review, we give an overview of the structures of the 16 genetically and antigenically distinct subtypes of influenza A HA in relation to these two functions in virus replication and in relation to recognition of HA by antibodies that neutralize infection.

Hemagglutinin Receptor Binding of a Human Isolate of Influenza A(H10N8) Virus

Three cases of influenza A(H10N8) virus infection in humans have been reported; 2 of these infected persons died. Characterization of the receptor binding pattern of H10 hemagglutinin from avian and human isolates showed that both interact weakly with human-like receptors and maintain strong affinity for avian-like receptors.

Toxicity and potency evaluation of pertussis vaccines

Current methods for determining the potency and toxicity of pertussis vaccines are outdated and require improvement. The intracerebral challenge test is effective for determining the potency of whole-cell vaccines but is objectionable on animal welfare and technical grounds. The same applies to its modification for assaying acellular pertussis vaccines. Respiratory challenge methods offer an interim solution pending establishment of validated in vitro correlates of protection, for example nitric oxide induction. Their evaluation is being promoted by the World Health Organization through the Pertussis Vaccines Working Group. Current toxicity assays based on weight gain and histamine sensitization of mice are imprecise and need replacement. Limits need to be established for specific toxin content of both acellular and whole-cell vaccines and should be supported by specific assays. More precise methods based on determination of ribosyltransferase activity in tandem with receptor-binding assays are under evaluation. Genome sequence data and the use of gene microarrays to screen responses triggered by vaccine components may also provide leads to improved methods for assessing both toxicity and immunogenicity.

Both the unique and repeat regions of the Porphyromonas gingivalis hemagglutin A are involved in adhesion and invasion of host cells

Porphyromonas gingivalis is one of the major etiologic agents of adult periodontitis and has been associated with cardiovascular diseases. It expresses multiple hemagglutinins that are significant virulence factors and play an important role in bacterial attachment and invasion of host cells. The objective of this study was to determine the impact of P. gingivalis hemagglutinin A (HagA) on the attachment to and invasion of human coronary artery endothelial cells (HCAEC) and gingival epithelial cells (GEC). Bacterial strains expressing the HagA protein (or subunits), including Escherichia coli carrying plasmid pEKS5, E. coli carrying plasmid ST2, and Salmonella enterica serovar Typhimurium with plasmid pNM1.1 were used in this study. The strains were tested for their ability to attach to and invade HCAEC and GEC using antibiotic protection assays. In addition, the unique 5' N-terminal non-repeated segment of HagA was purified in recombinant form and a monoclonal antibody was created against the polypeptide. The monoclonal antibody against the unique portion of HagA was tested for inhibitory activity in these assays. The attachment of both E. coli strains expressing HagA fragment to host cells was significantly increased compared to their respective controls. However, they did not invade GEC or HCAEC. Interestingly, HagA expression in the Salmonella strain increased both adherence to and invasion of HCAEC, which may be due to the presence of the entire hagA ORF. A monoclonal antibody against the unique 5' N-terminal portion of HagA reduced invasion. Further experiments are needed to determine the role of the unique and the repeat segments of P. gingivalis HagA.

Human infection with highly pathogenic H5N1 influenza virus

Highly pathogenic H5N1 influenza A viruses have spread relentlessly across the globe since 2003, and they are associated with widespread death in poultry, substantial economic loss to farmers, and reported infections of more than 300 people with a mortality rate of 60%. The high pathogenicity of H5N1 influenza viruses and their capacity for transmission from birds to human beings has raised worldwide concern about an impending human influenza pandemic similar to the notorious H1N1 Spanish influenza of 1918. Since many aspects of H5N1 influenza research are rapidly evolving, we aim in this Seminar to provide an up-to-date discussion on select topics of interest to influenza clinicians and researchers. We summarise the clinical features and diagnosis of infection and present therapeutic options for H5N1 infection of people. We also discuss ideas relating to virus transmission, host restriction, and pathogenesis. Finally, we discuss vaccine development in view of the probable importance of vaccination in pandemic control.

Haemophilus paragallinarum haemagglutinin: role in adhesion, serotyping and pathogenicity

It is suggested that Haemophilus paragallinarum requires at least three haemagglutinins for adhesion during infection. This paper reports the partial purification and characterization of the HA-L haemagglutinin from H. paragallinarum strain 46-C3, a heat sensitive, trypsin sensitive haemagglutinin that has been shown to be the serovar specific haemagglutinin in this organism. Using the pl and molecular mass obtained, it was shown that this protein shares similarities with other types of adhesins found in Gram-negative bacteria. The haemagglutination assay conditions were optimized at pH 7.5 at 37 degrees C. It was also shown that activity is enhanced by the addition of Ca2+ and Mn2+ ions.

Carbohydrate recognition in neuronal development: structure and expression of surface oligosaccharides and beta-galactoside-binding lectins

The differentiation and development of vertebrate neurons is controlled in part by interactions with cell surface and extracellular matrix molecules, many of which are glycoproteins that mediate their developmental actions by homophilic or heterophilic binding to other glycoproteins. In addition there is increasing evidence that cell recognition and adhesion in some embryonic cell types involve interactions between cell surface oligosaccharides and complementary carbohydrate-binding proteins. Although a role for carbohydrate recognition in neuronal development has been proposed, the precise function of complex carbohydrate structures on neural cells has not been defined. To approach this problem, we have examined the structure and expression of cell surface oligosaccharides and carbohydrate-binding proteins by primary sensory neurons in the rat dorsal root ganglion (DRG). There are several functionally distinct subsets of DRG neurons, each of which conveys a different sensory modality to distinct target domains in the spinal cord. Monoclonal antibodies against defined oligosaccharide structures identify each of the major subsets of DRG neurons on the basis of their expression of a distinct set of complex oligosaccharides, derived from lacto-, globo- and ganglioseries backbone structures. In particular, small diameter DRG neurons involved in pain processing express beta-galactoside-based lactoseries oligosaccharides. DRG and spinal cord neurons also express two soluble beta-galactoside-binding proteins of relative molecular masses 14,500 and 29,000, termed RL-14.5 and RL-29, which represent potential ligands for lactoseries oligosaccharides. RL-14.5 is expressed by the majority of DRG neurons whereas RL-29 is restricted to the subset of small DRG neurons that express surface N-acetyllactosamine structures. RL-14.5 and RL-29 are expressed soon after the differentiation of DRG neurons and appear to be released from cultured DRG neurons. Rat brain cDNA clones encoding RL-14.5 have been isolated. The nucleotide and predicted amino acid sequence of RL-14.5 has confirmed that this lectin is highly homologous to soluble beta-galactoside-binding proteins in other vertebrate species. Northern blot analysis and in situ hybridization indicate that RL-14.5 mRNA is selectively expressed in sensory and motor neurons in the rat nervous system. The selective expression of lactoseries oligosaccharides and complementary beta-galactoside-binding lectins may contribute to the differentiation and/or development of these two classes of neurons.

Moraxella catarrhalis strain O35E expresses two filamentous hemagglutinin-like proteins that mediate adherence to human epithelial cells

Two-partner secretion (TPS) systems are a family of proteins being rapidly identified and characterized in a growing number of gram-negative bacteria. TPS systems mediate the secretion of proteins, many involved in virulence traits such as hemolysis, adherence to epithelial cells, inhibition of bacterial growth, and immunomodulation of the host. A TPS system typically consists of a transporter located in the bacterial outer membrane (OM) which is responsible for the recognition and secretion of at least one large exoprotein. Two of the better-characterized TPS systems specify the Bordetella pertussis FHA and Haemophilus influenzae HMW1/HMW2 proteins. We identified three gene products of Moraxella catarrhalis strain O35E that resemble TPS proteins and designated them MhaC (transporter), MhaB1 (exoprotein), and MhaB2 (exoprotein). Western blot analysis using anti-MhaC, or antibodies reacting to both MhaB1 and MhaB2 (MhaB-reactive), revealed that these antigens are expressed in the OM of 63% of isolates tested. Mutations in the mhaC gene specifying the putative transporter of the M. catarrhalis wild-type strains O35E, O12E, and McGHS1 resulted in the absence of MhaB1/MhaB2 in the OM of mutants. These results are therefore consistent with the Mha proteins functioning as a TPS system. Furthermore, we discovered that these mhaC mutants exhibit markedly decreased binding to human epithelial cells relevant to pathogenesis by M. catarrhalis (Chang, HEp2, A549, and/or 16HBE14o(-)). Expression of O12E MhaC and MhaB1 in a nonadherent strain of Escherichia coli was found to increase the adherence of recombinant bacteria to HEp2 monolayers by sevenfold, thereby demonstrating that this M. catarrhalis TPS system directly mediates binding to human epithelial cells. The construction of isogenic mutants in the mhaB1 and mhaB2 genes of strain O35E also suggests that the MhaB proteins play distinct roles in M. catarrhalis adherence.

Role of mitogen-activated protein kinases and NF-kappaB in the regulation of proinflammatory and anti-inflammatory cytokines by Porphyromonas gingivalis hemagglutinin B

Hemagglutinin B (HagB) is a nonfimbrial adhesin expressed on the surface of Porphyromonas gingivalis and has been implicated as a potential virulence factor involved in mediating the attachment of the bacteria to host cells. However, the molecular mechanisms underlying host responses to HagB and their roles in pathogenesis have yet to be elucidated. Mitogen-activated protein kinases (MAPKs) are activated following engagement of a variety of cell surface receptors via dual tyrosine and threonine phosphorylation and are thought to be involved in various cellular responses. The purpose of this study was to determine the role of intracellular signaling pathways including the MAPKs and NF-kappaB in regulating the production of proinflammatory and anti-inflammatory cytokines following stimulation of murine macrophages with recombinant HagB (rHagB). Stimulation of peritoneal macrophages with rHagB resulted in the production of the proinflammatory cytokines interleukin-12p40 (IL-12p40), gamma interferon (IFN-gamma), and tumor necrosis factor alpha, as well as the anti-inflammatory cytokine IL-10. We also demonstrated the activation of extracellular signal-related kinase (ERK), c-Jun NH2-terminal protein kinase (JNK), and p38 MAPKs by rHagB-stimulated macrophages. Furthermore, blocking of the ERK and p38 signaling pathways by using specific inhibitors revealed differential regulatory roles in the rHagB-mediated production of proinflammatory and anti-inflammatory cytokines. ERK and p38 were important in down-regulation of IL-12p40 and IFN-gamma production and up-regulation of IL-10 production. The enhanced levels of IL-12p40 in rHagB-stimulated macrophages by inhibition of ERK or p38 activity were partially attributable to the inhibition of IL-10 production. Moreover, NF-kappaB was found to be critical for up-regulation of IL-12p40 and down-regulation of IL-10 production in rHagB-stimulated macrophages. Taken together, our results demonstrate a role for the p38 and ERK pathways and the transcription factor NF-kappaB in modulating key immunoregulatory cytokines involved in the development of immune responses to P. gingivalis HagB.

Neuropeptide release from dental pulp cells by RgpB via proteinase-activated receptor-2 signaling

Dental pulp inflammation often results from dissemination of periodontitis caused mostly by Porphyromonas gingivalis infection. Calcitonin gene-related peptide and substance P are proinflammatory neuropeptides that increase in inflamed pulp tissue. To study an involvement of the periodontitis pathogen and neuropeptides in pulp inflammation, we investigated human dental pulp cell neuropeptide release by arginine-specific cysteine protease (RgpB), a cysteine proteinase of P. gingivalis, and participating signaling pathways. RgpB induced neuropeptide release from cultured human pulp cells (HPCs) in a proteolytic activity-dependent manner at a range of 12.5-200 nM. HPCs expressed both mRNA and the products of calcitonin gene-related peptide, substance P, and proteinase-activated receptor-2 (PAR-2) that were also found in dental pulp fibroblast-like cells. The PAR-2 agonists, SLIGKV and trypsin, also induced neuropeptide release from HPCs, and HPC PAR-2 gene knockout by transfection of PAR-2 antisense oligonucleotides inhibited significantly the RgpB-elicited neuropeptide release. These results indicated that RgpB-induced neuropeptide release was dependent on PAR-2 activation. The kinase inhibitor profile on the RgpB-neuropeptide release from HPC revealed a new PAR-2 signaling pathway that was mediated by p38 MAPK and activated transcription factor-2 activation, in addition to the PAR-2-p44/42 p38MAPK and -AP-1 pathway. This new RgpB activity suggests a possible link between periodontitis and pulp inflammation, which may be modulated by neuropeptides released in the lesion.

Bordetella bronchiseptica adherence to cilia is mediated by multiple adhesin factors and blocked by surfactant protein A

In the virulent state (Bvg+), Bordetella bronchiseptica expresses adhesins and toxins that mediate adherence to the upper airway epithelium, an essential early step in pathogenesis. In this study, we used a rabbit tracheal epithelial cell binding assay to test how specific host or pathogen factors contribute to ciliary binding. The host antimicrobial agent surfactant protein A (SP-A) effectively reduced ciliary binding by Bvg+ B. bronchiseptica. To evaluate the relative contributions of bacterial adhesins and toxins to ciliary binding, we used mutant strains of B. bronchiseptica in the binding assay. When compared to Bvg+ or Bvg- phase-locked B. bronchiseptica strains, single-knockout strains lacking one of the known adhesins (filamentous hemagglutinin, pertactin, or fimbriae) displayed an intermediate ciliary binding capacity throughout the coincubation. A B. bronchiseptica strain deficient in adenylate cyclase-hemolysin toxin also displayed an intermediate level of adherence between Bvg+ and Bvg- strains and had the lowest ciliary affinity of any of the Bvg+ phase strains tested. A B. bronchiseptica strain that was missing dermonecrotic toxin also displayed intermediate binding; however, this strain displayed ciliary binding significantly higher than most of the adhesin knockouts tested. Taken together, these findings suggest that virulent-state B. bronchiseptica expresses multiple adhesins with overlapping contributions to ciliary adhesion and that host production of SP-A can provide innate immunity by blocking bacterial adherence to the ciliated epithelium.

Effector functions of heparin-binding hemagglutinin-specific CD8+ T lymphocytes in latent human tuberculosis

BACKGROUND

Most individuals infected with Mycobacterium tuberculosis do not develop tuberculosis (TB) and can be regarded as being protected by an appropriate immune response to the infection. The characterization of the immune responses of individuals with latent TB may thus be helpful in the definition of correlates of protection and the development of new vaccine strategies. The highly protective antigen heparin-binding hemagglutinin (HBHA) induces strong interferon (IFN)- gamma responses during latent, but not active, TB. Because of the recently recognized importance of CD8(+) T lymphocytes in anti-TB immunity, we characterized the CD8(+) T lymphocyte responses to HBHA in subjects with latent TB.

RESULTS

HBHA-specific CD8(+) T lymphocytes expressed memory cell markers and synthesized HBHA-specific IFN- gamma . They also restricted mycobacterial growth and expressed cytotoxicity by a granule-dependent mechanism. This activity was associated with the intracellular expression of HBHA-induced perforin. Surprisingly, the perforin-producing CD8(+) T lymphocytes were distinct from the IFN- gamma -producing CD8(+) T lymphocytes.

CONCLUSION

During latent TB, the HBHA-specific CD8(+) T lymphocyte population expresses all 3 effector functions associated with CD8(+) T lymphocyte-mediated protective immune mechanisms, which supports the notion that HBHA may be protective in humans and suggests that markers of HBHA-specific CD8(+) T lymphocyte responses may be useful in the monitoring of protection.

Roles of Arg- and Lys-gingipains in coaggregation of Porphyromonas gingivalis: identification of its responsible molecules in translation products of rgpA, kgp, and hagA genes

Arg- (Rgp) and Lys-gingipains (Kgp) are two individual cysteine proteinases produced by Porphyromonas gingivalis , an oral anaerobic bacterium, and are implicated as major virulence factors in a wide range of pathologies of adult periodontitis. Coaggregation of this bacterium with other oral bacteria is an initial and critical step in infectious processes, yet the factors and mechanisms responsible for this process remain elusive. Here we show that the initial translation products of the rgpA , kgp and hemagglutinin hagA genes are responsible for coaggregation of P. gingivalis and that the proteolytic activity of Rgp and Kgp is indispensable in this process. The rgpA rgpB kgp- and rgpA kgp hagA -deficient triple mutants exhibited no coaggregation activity with Actinomyces viscosus , whereas the kgp -null and rgpA rgpB -deficient double mutants significantly retained this activity. Consistently, the combined action of Rgp- and Kgp-specific inhibitors strongly inhibited the coaggregation activity of the bacterium, although single use of Rgp- or Kgp-specific inhibitor significantly retained this activity. We also demonstrate that the 47- and 43-kDa proteins produced from the translation products of the rgpA , kgp , and hagA genes by proteolytic activity of both Rgp and Kgp are responsible for the coaggregation of P. gingivalis.

The C-terminal domains of the gingipain K polyprotein are necessary for assembly of the active enzyme and expression of associated activities

The Porphyromonas gingivalis lysine-specific cysteine protease (gingipain K, Kgp) is expressed as a large precursor protein consisting of a leader sequence, a pro-fragment, a catalytic domain with a C-terminal IgG-like subdomain (IgSF) and a large haemagglutinin/adhesion (HA) domain. In order to directly study the role of these non-catalytic domains in pro-Kgp processing and maturation in P. gingivalis, the wild-type form of the gene was replaced with deletion variants encoding C-terminally truncated proteins, including KgpDeltaHA3/4 (Delta1292-1732 aa), KgpDeltaHA2-4 (Delta1157-1732 aa), KgpDeltaHA1-4 (Delta738-1732 aa), KgpDeltaC-term/HA (Delta681-1732 aa) and KgpDeltaIg/C-term/HA (602-1732 aa). Northern blot and reverse transcription polymerase chain reaction (RT-PCR) analysis revealed that all truncated variants of the kgp gene were transcribed in P. gingivalis. Despite high levels of kgpDeltaC-term/HA and kgpDeltaIg/C-term/HA transcripts, no Kgp-specific antigen was detected in cultures of these mutants as determined by Western blot analysis with monoclonal antibodies specific for the Kgp catalytic domain. Furthermore, only barely measurable amounts of Kgp-specific activity were detected in these two mutants. The remaining mutants expressed significant Kgp activity, however, at lower levels when compared with the parental strain. The decreased activity most probably resulted from altered folding and/or hindered secretion of the protein. The kgp gene truncation was also demonstrated to alter the distribution of the gingipain protein between membrane-associated and -secreted forms. While both gingipain K activity and the protein were cell membrane-associated in the parental strain, the mutants released significant amounts of both protein and activity into the media. Taken together, these results suggest that the C-terminal HA domains of Kgp are not only essential for full expression of gingipain activity, but also for proper processing of the multiprotein complex assembly on the P. gingivalis outer membrane. Moreover, our results indicate that the immunoglobulin-like subdomain is indispensable for proper folding and expression of the gingipains.

Protease-activated receptor signaling increases epithelial antimicrobial peptide expression

Epithelial tissues provide both a physical barrier and an antimicrobial barrier. Antimicrobial peptides of the human beta-defensin (hBD) family are part of the innate immune responses that play a role in mucosal defense. hBDs are made in epithelia including oral epithelium where the bacterial load is particularly great. hBD-2 and hBD-3 are up-regulated in response to bacterial stimuli. Previous studies show that hBD-2 expression in human gingival epithelial cells (GEC) is stimulated by both nonpathogenic and pathogenic bacteria, including Porphyromonas gingivalis, a Gram-negative pathogen associated with periodontitis. Present evidence suggests that hBD-2 expression in GEC uses several signaling pathways, including an NF-kappaB-mediated pathway but without apparent LPS-TLR4 signaling. Protease-activated receptors (PAR) are G-protein-coupled receptors that mediate cellular responses to extracellular proteinases. P. gingivalis secretes multiple proteases that contribute to its virulence mechanisms. To determine whether PAR signaling is used in hBD-2 induction, GEC were stimulated with wild-type P. gingivalis or mutants lacking one or more proteases. hBD-2 mRNA expression was reduced in GEC stimulated with single protease mutants (11-67% compared with wild type), strongly reduced in double mutants (0.1-16%), and restored to wild-type levels (93%) in mutant with restored protease activity. Stimulation by wild type was partially blocked by inhibitors of phospholipase C, a main signaling pathway for PARs. Expression of hBD-3 was unaffected. Peptide agonist of PAR-2, but not PAR-1 activator, also induced hBD-2 in GEC. Thus, P. gingivalis proteases are directly involved in regulation of hBD-2 in cultured GEC, and this induction partially uses the PAR-2 receptor and signaling pathway.

Coordinate expression of the Porphyromonas gingivalis lysine-specific gingipain proteinase, Kgp, arginine-specific gingipain proteinase, RgpA, and the heme/hemoglobin receptor, HmuR

Heme utilization inPorphyromonas gingivalisrequires the participation of an outer membrane hemin/hemoglobin receptor, HmuR, the lysine-specific gingipain proteinase (Kgp) and arginine-specific gingipain proteinase (Rgp). In this study, the expression ofhmuR,kgpandrgpAgenes in response to growth with different heme sources was examined by reverse transcription-polymerase chain reaction and enzyme-linked immunoassay. Coordinate regulation ofhmuR,kgpandrgpAgene expression was evaluated through utilization ofP. gingivalis hmuRandkgpmutants or by selective inactivation of proteinases with Kgp- and Rgp-specific inhibitors. We observed that expression of thekgpandrgpAgenes was not tightly regulated by heme, but rather by the growth phase. In contrast, expression of thehmuRgene was negatively regulated by heme, while growth ofP. gingivaliswith human serum resulted in increasedhmuRexpression. AP. gingivalis kgpisogenic mutant demonstrated significantly increasedhmuRgene expression, and inactivation of Kgp and Rgp activity by specific inhibitors up-regulatedhmuRgene transcription. Moreover, inactivation of Kgp up-regulatedrgpAtranscription. Finally, aP. gingivalis hmuRmutant exhibited repressedkgpgene expression and lysine-specific proteinase activity. Collectively, these results indicate thatkgp,rgpAandhmuRgene transcription is coordinately regulated and may facilitate greater efficiency of heme utilization inP. gingivalis.

Enhancement of the Endopeptidase Activity of Purified Botulinum Neurotoxins A and E by an Isolated Component of the Native Neurotoxin Associated Proteins

In botulism disease, neurotransmitter release is blocked by a group of structurally related neurotoxin proteins produced by Clostridium botulinum. Botulinum neurotoxins (BoNT, A-G) enter nerve terminals and irreversibly inhibit exocytosis via their endopeptidase activities against synaptic proteins SNAP-25, VAMP, and Syntaxin. Type A C. botulinum secretes the neurotoxin along with 5 other proteins called neurotoxin associated proteins (NAPs). Here, we report that hemagglutinin-33 (Hn-33), one of the NAP components, enhances the endopeptidase activity of not only BoNT/A but also that of BoNT/E, both under in vitro conditions and in rat synaptosomes. BoNT/A endopeptidase activity in vitro is about twice as high as that of BoNT/E under disulfide-reduced conditions. Addition of Hn-33 separately to nonreduced BoNT/A and BoNT/E (which otherwise have only residual endopeptidase activity) enhanced their in vitro endopeptidase activity by 21- and 25-fold, respectively. Cleavage of rat-brain synaptosome SNAP-25 by BoNTs was used to assay endopeptidase activity under nerve-cell conditions. Reduced BoNT/A and BoNT/E cleaved synaptosomal SNAP-25 by 20% and 15%, respectively. Addition of Hn-33 separately to nonreduced BoNT/A and BoNT/E enhanced their endopeptidase activities by 13-fold for the cleavage of SNAP-25 in synaptosomes, suggesting a possible functional role of Hn-33 in association with BoNTs. We believe that Hn-33 could be used as an activator in the formulation of the neurotoxin for therapeutic use.

Purification and structural characterization of lectins from the cnidarian Bunodeopsis antilliensis [corrected]

Purification and characterization of two different lectins from the Mexican anemone Bunodeopsis antilliensis are reported. These two lectins named Bunodeopsis antilliensis agglutinin-A (BAA-A) and -B (BAA-B) presented the following characteristics: BAA-A was resolved as a component, with haemagglutinating activity for human blood type A (N-acetylgalactosamine-galactose-fucose), with a molecular weight of 28,900 obtained by means of mass spectrometry, showed an isoelectric point of 5.04 with a higher carbohydrate specificity for N-acetylgalactosamine (GalNAc). The analysis of the N-terminal revealed it is related to phosphoesterase and GTP binding protein. BAA-B mainly active with human blood type B (galactose-galactose-fucose) was resolved into three fractions (BAA-B1-3). Their molecular weight were: BAA-B(1) 39,350, BAA-B(2) 28,300 and BAA-B(3) 17,550. The estimated isoelectric points were 8.05, 4.66 and 6.60, respectively. Only fraction 3 exhibited haemagglutinating activity with a higher carbohydrate specificity for galactose and mannose. The analysis of the N-terminal pointed out it is related with phospholipase A(2). We suggest these lectins could be related to a feeding strategy[corrected].

The surface (S-) layer is a virulence factor of Bacteroides forsythus

Bacteroides forsythus has emerged as a crucial periodontal pathogen with possible implications for systemic disease. The aim of this study was to isolate the S-layer from B. forsythus and examine its virulence potential as a part of efforts to characterize virulence factors of B. forsythus. The role of the S-layer in the haemagglutinating and adherent/invasive activities was evaluated. It was observed that the S-layer alone was able to mediate haemagglutination. In adherent and invasive studies, transmission electron microscopy clearly revealed that B. forsythus cells were able to attach to and invade KB cells, showing the formation of a microvillus-like extension around adherent and intracellular bacteria. The quantitative analysis showed that five different B. forsythus strains exhibited attachment (1.9-2.3 %) and invasion (0.4-0.7 %) capabilities. It was also observed through antibody inhibition assays that adherent/invasive activities of B. forsythus are mediated by the S-layer. Furthermore, an in vivo immunization study adopting a murine abscess model was used to prove that the S-layer is involved in the infectious process of abscess formation. While mice immunized with purified S-layer and B. forsythus whole cells did not develop any abscesses when challenged with viable B. forsythus cells, unimmunized mice developed abscesses. Collectively, the data obtained from these studies indicate that the S-layer of B. forsythus is a virulence factor.

The Vibrio cholerae O139 O-antigen polysaccharide is essential for Ca2+-dependent biofilm development in sea water

Vibrio cholerae is both an inhabitant of estuarine environments and the etiologic agent of the diarrheal disease cholera. Previous work has demonstrated that V. cholerae forms both an exopolysaccharide-dependent biofilm and a Ca2+-dependent biofilm. In this work, we demonstrate a role for the O-antigen polysaccharide of V. cholerae in Ca2+-dependent biofilm development in model and true sea water. Interestingly, V. cholerae biofilms, as well as the biofilms of several other Vibrio species, disintegrate when Ca2+ is removed from the bathing medium, suggesting that Ca2+ is interacting directly with the O-antigen polysaccharide. In the Bay of Bengal, cholera incidence has been correlated with increased sea surface height. Because of the low altitude of this region, increases in sea surface height are likely to lead to transport of sea water, marine particulates, and marine biofilms into fresh water environments. Because fresh water is Ca2+-poor, our results suggest that one potential outcome of an increase is sea surface height is the dispersal of marine biofilms with an attendant increase in planktonic marine bacteria such as V. cholerae. Such a phenomenon may contribute to the correlation of increased sea surface height with cholera.

Inhibition of phagocytosis by Haemophilus ducreyi requires expression of the LspA1 and LspA2 proteins

Haemophilus ducreyi previously has been shown to inhibit the phagocytosis of both secondary targets and itself by certain cells in vitro. Wild-type H. ducreyi strain 35000HP contains two genes, lspA1 and lspA2, whose encoded protein products are predicted to be 456 and 543 kDa, respectively. An isogenic mutant of H. ducreyi 35000HP with inactivated lspA1 and lspA2 genes has been shown to exhibit substantially decreased virulence in the temperature-dependent rabbit model for chancroid. This lspA1 lspA2 mutant was tested for its ability to inhibit phagocytosis of immunoglobulin G-opsonized particles by differentiated HL-60 and U-937 cells and by J774A.1 cells. The wild-type strain H. ducreyi 35000HP readily inhibited phagocytosis, whereas the lspA1 lspA2 mutant was unable to inhibit phagocytosis. Similarly, the wild-type strain was resistant to phagocytosis, whereas the lspA1 lspA2 mutant was readily engulfed by phagocytes. This inhibitory effect of wild-type H. ducreyi on phagocytic activity was primarily associated with live bacterial cells but could also be found, under certain conditions, in concentrated H. ducreyi culture supernatant fluids that lacked detectable outer membrane fragments. Both the wild-type strain and the lspA1 lspA2 mutant attached to phagocytes at similar levels. These results indicate that the LspA1 and LspA2 proteins of H. ducreyi are involved, directly or indirectly, in the antiphagocytic activity of this pathogen, and they provide a possible explanation for the greatly reduced virulence of the lspA1 lspA2 mutant.

Influenza virus hemagglutinin concentrates in lipid raft microdomains for efficient viral fusion

Lipid raft microdomains are enriched in sphingomyelin and cholesterol and function as platforms for signal transduction and as the site of budding of several enveloped viruses, including influenza virus. The influenza virus hemagglutinin (HA) glycoprotein, which mediates both viral-cell attachment and membrane fusion, associates intrinsically with lipid rafts. Residues in the HA transmembrane (TM) domain are important for raft association as sequence substitutions in the HA TM domain ablate HA association with rafts (nonraft HA). Cells expressing either WT or nonraft HA cause complete fusion (lipid mixing and content mixing) over widely varying HA expression levels. However, the number of fusion events measured for nonraft HA mutant protein at all HA surface densities was reduced to approximately 55% of the events for WT HA protein. Mutant influenza viruses were generated that contain the nonraft HA TM domain alterations. Electron microscopy experiments showed that WT HA was distributed at the cell surface in clusters of 200-280 nm in diameter, whereas nonraft HA was distributed mostly randomly at the plasma membrane. Nonraft HA virus showed reduced budding, contained reduced amounts of HA protein, was greatly reduced in infectivity, and exhibited decreased virus-membrane fusion activity. Cholesterol depletion of virus did not affect the ability of virions to cause either virus-cell lipid mixing or virus-mediated hemolysis, a surrogate for content mixing. Taken together, the data suggest that HA clusters in rafts to provide a sufficient concentration of HA in budding virus to mediate efficient virus-cell fusion.

The Hag protein of Moraxella catarrhalis strain O35E is associated with adherence to human lung and middle ear cells

Previous studies have demonstrated that the Moraxella catarrhalis surface antigen UspA1 is an adhesin for Chang human conjunctival cells. The present report demonstrates that lack of UspA1 expression does not affect the adherence of strain O35E to A549 human lung cells or primary cultures of human middle ear epithelial (HMEE) cells. These results imply that another molecule mediates the adherence of M. catarrhalis to these two cell lines. To identify this adhesin, strain O35E was mutagenized with a transposon and 1,000 mutants were screened in a microcolony formation assay using A549 cells. Nine independent isolates exhibited an 8- to 19-fold reduction in adherence and contained a transposon in the same locus. Nucleotide sequence data and PCR analysis indicated that the transposons were inserted in different locations in the gene encoding the surface protein Hag. Quantitative assays using one representative transposon mutant, O35E.TN2, showed considerably decreased binding to A549 as well as HMEE cells. However, this mutant adhered at wild-type levels to Chang conjunctival cells. These findings suggest that the M. catarrhalis Hag protein is an adhesin for cell lines derived from human lung and middle ear tissues.

Role for mannose-sensitive hemagglutinin in promoting interactions between Vibrio cholerae El Tor and mussel hemolymph

The role of mannose-sensitive hemagglutinin (MSHA) in Vibrio cholerae O1 El Tor interactions with hemolymph of the mussel Mytilus galloprovincialis was studied. Bacterial adherence to and association with hemocytes were evaluated at 4 and 18 degrees C, respectively. In hemolymph serum, the wild-type strain N16961 adhered to and associated with hemocytes about twofold more efficiently than its mutant lacking MSHA. In artificial seawater (ASW), no significant differences between the two strains were observed. N16961 was also more sensitive to hemocyte bactericidal activity than its MSHA mutant; in fact, the percentages of killed bacteria after 120 min of incubation were 60 and 34%, respectively. The addition of D-mannose abolished the serum-mediated increase in adherence, association, and sensitivity to killing of the wild-type strain without affecting the interactions of the mutant. A similar increase in N16961 adherence to hemocytes was observed when serum was adsorbed with MSHA-deficient bacteria. In contrast, serum adsorbed with either wild-type V. cholerae El Tor or wild-type Escherichia coli carrying type 1 fimbriae was no longer able to increase adherence of N16961 to hemocytes. The results indicate that hemolymph-soluble factors are involved in interactions between hemocytes and mannose-sensitive adhesins.

Activation of human matrix metalloproteinase 2 by gingival crevicular fluid and Porphyromonas gingivalis

AIM

To assess the potential of gingival crevicular fluid (GCF) from adult periodontitis patients and Porphyromonas gingivalis proteases to activate matrix metalloproteinase 2 (MMP-2) in vitro.

MATERIAL AND METHODS

GCF samples were collected from each of 15 adult periodontitis patients, from a clinically healthy site, a deep (>6 mm) bleeding site, and a deep nonbleeding site. The GCF samples were examined for general proteolytic activity, gelatinolytic activity and ability to activate pro-MMP-2 by zymography. Ultrasonic extracts of a range of clinical isolates of P. gingivalis cells and purified arg- and lys-gingipains were also assessed for their ability to activate pro-MMP-2.

RESULTS

GCF from deep nonbleeding sites showed higher general proteolytic activity than samples from deep bleeding and healthy sites but this did not reach statistical significance. Pefabloc, a general serine protease inhibitor, inhibited the majority (92%) of the proteolytic activity. GCF samples contained neutrophil MMP-9 in its latent form in 93% of the samples, and in its activated form in 40% of the samples. In contrast, MMP-2 was present in only trace amounts in 9% of the samples. When latent MMP-2 was added to these GCF samples, it was converted to the activated form (59 kDa) in 68% of the samples. Lower molecular weight (55 and 45 kDa) activated forms also appeared in 53% of the samples, particularly those from deep sites. Activation to the 55 and 45 kDa forms was inhibited by MSAAPket (a neutrophil elastase inhibitor), whereas Pefabloc completely inhibited the activation of latent MMP-2. All ultrasonic extracts of P. gingivalis activated latent MMP-2 in a concentration- and time-dependent manner. Also, latent MMP-2 was activated by purified arg-gingipain but less efficiently by lys-gingipain.

CONCLUSION

These findings suggest that P. gingivalis arg-gingipain and neutrophil elastase present in GCF can activate latent MMP-2, which may contribute in vivo to local periodontal tissue destruction.

Mutations in the lspA1 and lspA2 genes of Haemophilus ducreyi affect the virulence of this pathogen in an animal model system

Haemophilus ducreyi 35000HP contains two genes, lspA1 and lspA2, whose predicted protein products have molecular weights of 456,000 and 543,000, respectively (C. K. Ward, S. R. Lumbley, J. L. Latimer, L. D. Cope, and E. J. Hansen, J. Bacteriol. 180:6013-6022, 1998). We have constructed three H. ducreyi 35000HP mutants containing antibiotic resistance cartridges in one or both of the lspA1 and lspA2 open reading frames. Western blot analysis using LspA1- and LspA2-specific monoclonal antibodies indicated that the wild-type parent strain 35000HP expressed LspA1 protein that was readily detectable in culture supernatant fluid together with a barely detectable amount of LspA2 protein. The lspA2 mutant 35000HP.2 expressed LspA1 protein that was detectable in culture supernatant fluid and no LspA2 protein. In contrast, the H. ducreyi lspA1 mutant 35000HP.1, which did not express the LspA1 protein, expressed a greater quantity of the LspA2 protein than did the wild-type parent strain. The lspA1 lspA2 double mutant 35000HP.12 expressed neither LspA1 nor LspA2. The three mutant strains adhered to human foreskin fibroblasts and to a human keratinocyte cell line in vitro at a level that was not significantly different from that of the wild-type strain 35000HP. Lack of expression of the LspA1 protein by both the lspA1 mutant and the lspA1 lspA2 double mutant was associated with an increased tendency to autoagglutinate. When evaluated in the temperature-dependent rabbit model for chancroid, the lspA1 lspA2 double mutant was substantially less virulent than the wild-type strain 35000HP. The results of these studies indicated that H. ducreyi requires both the LspA1 and LspA2 proteins to be fully virulent in this animal model for experimental chancroid.

Hemagglutinating factor (HAF) associated with adhesiveness in enteroinvasive Escherichia coli (EIEC)

A cell-associated mannose-resistant hemagglutinating factor (HAF) was extracted from enteroinvasive Escherichia coli (EIEC) serotype O124:H- by sonication. Ultrastructural analysis of EIEC and immunocytochemical assays with the cell-free HAF and EIEC bacterial cells on HeLa cells, suggested that the HAF is a non-fimbrial putative adhesive factor that mediates in vivo adherence of EIEC to human epithelial cells.

The role of gingipains in the pathogenesis of periodontal disease

Gingipains are trypsin-like cysteine proteinases produced by Porphyromonas gingivalis, a major causative bacterium of adult periodontitis. HRgpA (95 kDa) and RgpB (50 kDa), products of 2 distinct but related genes, rgpA and rgpB, respectively, are specific for Arg-Xaa peptide bonds. Kgp, a product of the kgp gene, is specific for Lys-Xaa bonds. HRgpA and Kgp are non-covalent complexes containing separate catalytic and adhesion/ hemagglutinin domains, while RgpB has only a catalytic domain with a primary structure essentially identical to that of the catalytic subunit of HRgp. HRgpA and RgpB induce vascular permeability enhancement through activation of the kallikrein/kinin pathway and activate the blood coagulation system, which, respectively, are potentially associated with gingival crevicular fluid production and progression of inflammation leading to alveolar bone loss in the periodontitis site. Kgp is the most potent fibrinogen/fibrin degrading enzyme of the 3 gingipains in human plasma and is involved in the bleeding tendency at the diseased gingiva. HRgpA activates coagulation factors and degrades fibrinogen/fibrin more efficiently than RgpB due to the adhesion/hemagglutinin domains, which have affinity for phospholipids and fibrinogen. Gingipains degrade macrophage CD14, thus inhibiting activation of the leukocytes through the lipopolysaccharide (LPS) receptor, and thereby facilitating sustained colonization of P. gingivalis. Gingipains play a role in bacterial housekeeping and infection, including amino acid uptake from host proteins and fimbriae maturation. Based on the important activities of gingipains in the bacterial infection and the pathogenesis of periodontitis, the bacterial proteinases can be targets for periodontal disease therapy. Immunization with RgpB, HRgpA, or a portion of HRgpA catalytic domain attenuated P. gingivalis induced disorders in mice. In addition, a trypsin-like proteinase inhibitor retarded P. gingivalis growth specifically. Gingipains are potent virulence factors of P. gingivalis, and are likely to be associated with the development of periodontitis. It is, therefore, suggested that gingipain inhibition by vaccination and gingipain-specific inhibitors is a useful therapy for adult periodontitis caused by P. gingivalis infection.

Discrete proteolysis of focal contact and adherens junction components in Porphyromonas gingivalis-infected oral keratinocytes: a strategy for cell adhesion and migration disabling

Adhesive interactions of cells are critical to tissue integrity. We show that infection with Porphyromonas gingivalis, a major pathogen in the periodontal disease periodontitis, interferes with both cell-matrix and cell-cell adhesion in the oral keratinocyte cell line HOK-16. Thus, infected cells showed reduced adhesion to extracellular matrix, changes in morphology from spread to rounded, and impaired motility on purified matrices in Transwell migration assays and scratch assays. Western blot analysis of P. gingivalis-challenged HOK-16 cells revealed proteolysis of focal contact components (e.g., focal adhesion kinase), adherens junction proteins (e.g., catenins), and adhesion signaling molecules (e.g., the tyrosine kinase SRC). Proteolysis was selective, since important components of adherens junctions (E-cadherin) or signaling molecules (extracellular signal-regulated kinases ERK1/2) were not degraded. The virulence factors gingipains, cysteine proteinases expressed by P. gingivalis, are likely responsible for this proteolytic attack, since they directly digested specific proteins in pull-down experiments, and their proteolytic activity was blocked by the cysteine proteinase inhibitor N-alpha-p-tosyl-L-lysine chloromethyl ketone and also by a caspase inhibitor. Proteolysis was strain dependent, such that ATCC 33277 and 381 had high proteolytic potential, whereas W50 showed almost no proteolytic activity. These findings may help explain the formation of gingival pockets between cementum and periodontal epithelium, a hallmark of periodontitis. Furthermore, they illustrate a new pathogenetic paradigm of infection whereby bacteria may disrupt the integrity of epithelia.

Galectins and cancer

The galectins are a family of proteins that are distributed widely in all living organisms. All of them share galactose-specificity. At present, 14 members of the family are characterized in mammals. The galectins have been implicated in many essential functions including development, differentiation, cell-cell adhesion, cell-matrix interaction, growth regulation, apoptosis, RNA splicing, and tumor metastasis. Although efforts have mostly focused on the possible function of galectins in tumor development and invasiveness, their precise role in this field is still debated. This review discusses the recent way in which the expression of galectins and galectin-binding sites may affect the behavior of a variety of human neoplastic tissues.

Animal lectins: a historical introduction and overview

Some proteins we now regard as animal lectins were discovered before plant lectins, though many were not recognised as carbohydrate-binding proteins for many years after first being reported. As recently as 1988, most animal lectins were thought to belong to one of two primary structural families, the C-type and S-type (presently known as galectins) lectins. However, it is now clear that animal lectin activity is found in association with an astonishing diversity of primary structures. At least 12 structural families are known to exist, while many other lectins have structures apparently unique amongst carbohydrate-binding proteins, although some of those "orphans" belong to recognised protein families that are otherwise not associated with sugar recognition. Furthermore, many animal lectins also bind structures other than carbohydrates via protein-protein, protein-lipid or protein-nucleic acid interactions. While animal lectins undoubtedly fulfil a variety of functions, many could be considered in general terms to be recognition molecules within the immune system. More specifically, lectins have been implicated in direct first-line defence against pathogens, cell trafficking, immune regulation and prevention of autoimmunity.

Binding and cross-linking properties of galectins

The galectins are a family of animal lectins that possess similar carbohydrate binding specificities and conserved consensus sequences. The biological properties of mammalian galectins include the regulation of inflammation, cell adhesion, cell proliferation and cell death. Evidence suggests that the biological activities of the galectins are related to their multivalent binding properties since most galectins possess two carbohydrate recognition domains and are therefore bivalent. For example, galectin-1, which is dimeric, binds and cross-links specific glycoprotein counter-receptors on the surface of human T-cells leading to apoptosis [J. Immunol. 163 (1999) 3801]. Different galectin-1 counter-receptors associated with specific phosphatase or kinase activities formed separate clusters on the surface of the cells as a result of the lectin binding to the carbohydrate chains of the respective glycoproteins. Importantly, monovalent galectin-1 is inactive in this system. This indicates that the separation and organization of signaling molecules that result from galectin-1 binding is involved in the apoptotic signal. The separation of specific glycoprotein receptors induced by galectin-1 binding was modeled on the basis of molecular and structural studies of the binding of lectins to multivalent carbohydrates resulting in the formation of specific two- and three-dimensional cross-linked lattices [Biochemistry 36 (1997) 15073]. In this article, the binding and cross-linking properties of galectin-1 and other lectins are reviewed as a model for the biological signal transduction properties of the galectin family of animal lectins.

Role of galectins in inflammatory and immunomodulatory processes

Galectins are members of a highly conserved family of beta-galactoside-binding animal lectins. Presently, more than 14 members have been identified and additional homologues are likely to be discovered. Given their conservation throughout animal evolution, it is not surprising that they could play key roles in innate and adaptive immune responses, through sugar-dependent and -independent mechanisms. Recently, it has become increasingly clear that galectins can differentially affect cellular activation and function. These biological effects attracted attention of researchers in cell biology, biochemistry, glycobiology and immunology, not only in the mode of action of galectins, but also in their role as putative modulators of immune surveillance, apoptosis, cell adhesion and chemotaxis. Here we will summarize the state-of-the-art of the effects of galectins in inflammatory and immunomodulatory processes. In addition, we will discuss in-depth the current knowledge about the effects of this enigmatic family of animal lectins and their glycoligands in the progression, diagnosis and treatment of different pathological processes such as autoimmunity, allergy, infection and chronic inflammation.

Intracellular functions of galectins

Many galectin family members are detected primarily intracellularly in most of the systems studied, although certain members can be found both inside and outside of cells. Specific functions that are consistent with their intracellular localization have now been documented for some of the galectins. Galectin-1 and -3 have been identified as redundant pre-mRNA splicing factors. Galectin-3, -7, and -12 have been shown to regulate cell growth and apoptosis, being either anti-apoptotic or pro-apoptotic. Galectin-3 and -12 have been shown to regulate the cell cycle. In some cases, the mechanisms by which galectins exert their functions have been partially delineated in relation to known intracellular pathways associated with these processes. In addition, a number of intracellular proteins involved in these processes have been identified as the interacting ligands of certain galectins. This review summarizes the intracellular activities displayed by several galectins and discusses the possible underlying mechanisms.

Roles for Arg- and Lys-gingipains in the disruption of cytokine responses and loss of viability of human endothelial cells by Porphyromonas gingivalis infection

Accumulating evidence indicates that periodontal disease is associated with human cardiovascular diseases. The periodontal pathogen Porphyromonas gingivalis was shown to be present in atherosclerotic plaques in addition to periodontal pockets. This bacterium is known to produce two individual cysteine proteinases, Arg-gingipain (Rgp) and Lys-gingipain (Kgp). Here we show that these two enzymes are responsible for either the disruption of cytokine responses in human umbilical vein endothelial cells (HUVEC) to the bacterium infection or the loss of cell viability. The expression of interleukin-8 and monocyte chemoattractant protein-1 mRNA in HUVEC was greatly induced when infected with the wild-type strain, nevertheless, their protein levels in the culture medium were markedly decreased. This decrease was completely abolished in the cells infected with the Rgp/Kgp-null mutant, but not in either the Rgp- or Kgp-null mutants. Loss of the adhesion activity and viability of HUVEC were greatly induced by the culture supernatant of the wild-type strain and strongly inhibited by either a combination of the Rgp- and the Kgp-specific inhibitors or the deficiency of the Rgp- and Kgp-encoding genes. These findings indicate that P. gingivalis modulates the cytokine response in the cells and disrupts the adhesion activity and the viability through the cooperative action of Rgp and Kgp and thereby may contribute to pathogenesis of cardiovascular diseases as well as periodontal disease.

Galectins and their ligands: amplifiers, silencers or tuners of the inflammatory response?

Recent evidence has implicated galectins and their ligands as master regulators of immune cell homeostasis. Whereas some members of this family, such as galectin-3, behave as amplifiers of the inflammatory cascade, others, such as galectin-1, trigger homeostatic signals to shut off T-cell effector functions. These carbohydrate-binding proteins, identified by shared consensus amino acid sequences and affinity for beta-galactoside-containing sugars, participate in the homeostasis of the inflammatory response, either by regulating cell survival and signaling, influencing cell growth and chemotaxis, interfering with cytokine secretion, mediating cell-cell and cell-matrix interactions or influencing tumor progression and metastasis. The current wealth of new information promises a future scenario in which individual members of the galectin family or their ligands will be used as powerful anti-inflammatory mediators and selective modulators of the immune response.

Role of Treponema denticola in periodontal diseases

Among periodontal anaerobic pathogens, the oral spirochetes, and especially Treponema denticola, have been associated with periodontal diseases such as early-onset periodontitis, necrotizing ulcerative gingivitis, and acute pericoronitis. Basic research as well as clinical evidence suggest that the prevalence of T denticola, together with other proteolytic gram-negative bacteria in high numbers in periodontal pockets, may play an important role in the progression of periodontal disease. The accumulation of these bacteria and their products in the pocket may render the surface lining periodontal cells highly susceptible to lysis and damage. T. denticola has been shown to adhere to fibroblasts and epithelial cells, as well as to extracellular matrix components present in periodontal tissues, and to produce several deleterious factors that may contribute to the virulence of the bacteria. These bacterial components include outer-sheath-associated peptidases, chymotrypsin-like and trypsin-like proteinases, hemolytic and hemagglutinating activities, adhesins that bind to matrix proteins and cells, and an outer-sheath protein with pore-forming properties. The effects of T. denticola whole cells and their products on a variety of host mucosal and immunological cells has been studied extensively (Fig. 1). The clinical data regarding the presence of T. denticola in periodontal health and disease, together with the basic research results involving the role of T. denticola factors and products in relation to periodontal diseases, are reviewed and discussed in this article.

Activation of the neutrophil nicotinamide adenine dinucleotide phosphate oxidase by galectin-1

Galectins are a group of lactose-binding proteins widely distributed in nature. Twelve mammalian galectins have so far been identified, but their functions are to a large extent unknown. In this work we study galectin-1 in its interaction with human neutrophils, with regard to both cell surface binding and activation of the superoxide-producing NADPH-oxidase. We show that galectin-1 is able to activate the neutrophil NADPH-oxidase, provided that the cells have been primed by extravasation from the blood into the tissue, an activation pattern that is similar to that of galectin-3. Using in vitro priming protocols, the galectin-1 responsiveness was found to correlate to granule mobilization and galectin-1 binding to the cells, suggesting the presence of granule-localized receptors that are up-regulated to the cell surface upon priming. By galectin-1 overlay of fractionated neutrophils we identified potential galectin-1 receptor candidates localized in the membranes of the secretory vesicle and gelatinase granules. The binding of galectin-1 and galectin-3 to neutrophil proteins was compared, as were the dose dependencies for activation by the two lectins. The results suggest that, although similarities are found between the two galectins, they appear to activate the NADPH-oxidase using different receptors. In conclusion, galectin-1 appears to have proinflammatory functions, mediated through activation of the neutrophil respiratory burst.

Galectin-1 is overexpressed in nasal polyps under budesonide and inhibits eosinophil migration

Because of the importance of galectins for various cellular activities, the influence of the glucocorticoid budesonide on the level of expression of galectins-1 and -3 was investigated in human nasal polyposis. Ten nasal polyps obtained from surgical resection were maintained for 24 hours in the presence of various concentrations of budesonide. As quantitatively demonstrated by means of computer-assisted microscopy, 250 ng/ml (the highest dose tested) induced a pronounced increase of galectin-1 expression. This feature was observed in nasal polyps from allergic patients but not in those from nonallergic patients. Since eosinophils represent the main inflammatory cell population in nasal polyps, we investigated the effect of galectin-1 on their migration levels by means of quantitative phase-contrast computer-assisted videomicroscopy. Our results show that galectin-1 (coated on plastic supports) markedly reduced the migration levels of eosinophils in comparison to P-selectin. On the cellular level, marked modifications in the polymerization/depolymerization dynamics of the actin cytoskeleton (as revealed by means of computer-assisted fluorescence microscopy) and, to a much lesser extent, an increase in the adhesiveness of eosinophils to tested substrata were detectable. The present study therefore reveals a new galectin-1-mediated mechanism of action for glucocorticoid-mediated anti-inflammatory effects.

Cysteine proteases of Porphyromonas gingivalis

The cysteine proteases of Porphyromonas gingivalis are extracellular products of an important etiological agent in periodontal diseases. Many of the in vitro actions of these enzymes are consistent with the observed deregulated inflammatory and immune features of the disease. They are significant targets of the immune responses of affected individuals and are viewed by some as potential molecular targets for therapeutic approaches to these diseases. Furthermore, they appear to represent a complex group of genes and protein products whose transcriptional and translational control and maturation pathways may have a broader relevance to virulence determinants of other persistent bacterial pathogens of human mucosal surfaces. As a result, the genetics, chemistry, and virulence-related properties of the cysteine proteases of P. gingivalis have been the focus of much research effort over the last ten years. In this review, we describe some of the progress in their molecular characterization and how their putative biological roles, in relation to the in vivo growth and survival strategies of P. gingivalis, may also contribute to the periodontal disease process.

Role of ADP-ribosyltransferase activity of pertussis toxin in toxin-adhesin redundancy with filamentous hemagglutinin during Bordetella pertussis infection

Pertussis toxin (PT) and filamentous hemagglutinin (FHA) are two major virulence factors of Bordetella pertussis. FHA is the main adhesin, whereas PT is a toxin with an A-B structure, in which the A protomer expresses ADP-ribosyltransferase activity and the B moiety is responsible for binding to the target cells. Here, we show redundancy of FHA and PT during infection. Whereas PT-deficient and FHA-deficient mutants colonized the mouse respiratory tract nearly as efficiently as did the isogenic parent strain, a mutant deficient for both factors colonized substantially less well. This was not due to redundant functions of PT and FHA as adhesins, since in vitro studies of epithelial cells and macrophages indicated that FHA, but not PT, acts as an adhesin. An FHA-deficient B. pertussis strain producing enzymatically inactive PT colonized as poorly as did the FHA-deficient, PT-deficient strain, indicating that the ADP-ribosyltransferase activity of PT is required for redundancy with FHA. Only strains producing active PT induced a local transient release of tumor necrosis factor alpha (TNF-alpha), suggesting that the pharmacological effects of PT are the basis of the redundancy with FHA, through the release of TNF-alpha. This may lead to damage of the pulmonary epithelium, allowing the bacteria to colonize even in the absence of FHA.

Isolation and characterization of galectins in the mammalian retina

PURPOSE

Previous studies have suggested that galectins may be involved in retinal adhesion and photoreceptor cell survival. To elucidate the underlying mechanisms, the authors isolated retinal galectins, determined their types and distributions, and investigated the validity of the hypothesis, using rat models.

METHODS

An antibody was prepared against a bovine retinal lectin that was isolated by use of a lactose-agarose column. cDNA of the lectin was isolated by screening of a bovine retinal cDNA library, using the antibody, and then was sequenced. The cDNAs of rat retinal galectins were also isolated by means of polymerase chain reaction and used to produce an antibody against recombinant galectin-3. Using the described antibodies, the authors examined the distributions of galectins in bovine and rat retinas, morphologic changes of rat retinas induced by the antibodies, and distributional changes of galectins in constant-light-exposed rat retinas.

RESULTS

The cDNAs of bovine galectin-1, rat galectin-1, and rat galectin-3 were isolated. Galectin-1 was found in various regions, including the retinal pigment epithelium, outer limiting membrane, and outer plexiform layer in bovine and rat retinas. Galectin-3 was increasingly detected in the cytoplasm of Müller cells after constant light exposure after an increase in its transcript. Retinal detachment and vacuolation of the outer plexiform layer were induced in rat eyes by intravitreous injection of the anti-galectin-1 antibody.

CONCLUSIONS

Galectin-1 may be involved in adhesion of the photoreceptor and outer plexiform layers by interacting with glycoconjugates with beta-galactoside residues in the interphotoreceptor matrix and synaptic cleft matrix. Galectin-3 may increase in Müller cells of a degenerative rat retina, probably through endogenous anti-apoptosis.

Galectin-8 Functions as a Matricellular Modulator of Cell Adhesion

The interaction of cells with the extracellular matrix regulates cell adhesion and motility. Here we demonstrate that different cell types adhere and spread when cultured in serum-free medium on immobilized galectin-8, a mammalian beta-galactoside-binding protein. At maximal doses, galectin-8 is equipotent to fibronectin in promoting cell adhesion and spreading. Cell adhesion to immobilized galectin-8 is mediated by sugar-protein interactions with integrins, and galectin-8 triggers integrin-mediated signaling cascades including Tyr phosphorylation of focal adhesion kinase and paxillin. Cell adhesion is potentiated in the presence of Mn(2+), whereas it is interrupted in the presence of soluble galectin-8, integrin beta(1) inhibitory antibodies, EDTA, or thiodigalactoside but not by RGD peptides. Furthermore, cells readily adhere onto immobilized monoclonal galectin-8 antibodies, which are equipotent to integrin antibodies in promoting cell adhesion. Cell adhesion to immobilized galectin-8 is partially inhibited by serum proteins, suggesting that complex formation between immobilized galectin-8 and serum components generates a matrix that is less supportive of cell adhesion. Accordingly, cell motility on immobilized galectin-8 readily takes place in the presence of serum. Truncation of the C-terminal half of galectin-8, including one of its two carbohydrate recognition domains, largely abolishes its ability to modulate cell adhesion, indicating that both carbohydrate recognition domains are required to maintain a functional form of galectin-8. Collectively, our findings implicate galectin-8 as a physiological modulator of cell adhesion. When immobilized, it functions as a matrix protein equipotent to fibronectin in promoting cell adhesion by ligation and clustering of cell surface integrin receptors. In contrast, when present in excess as a soluble ligand, galectin-8 (like fibronectin) forms a complex with integrins that negatively regulates cell adhesion. Because of its dual effects on the adhesive properties of the cells and its association with fibronectin, galectin-8 might be considered a novel type of matricellular protein.

Role of gingipains in growth of Porphyromonas gingivalis in the presence of human serum albumin

Porphyromonas gingivalis, a bacterium associated with active chronic periodontitis lesions, produces several proteolytic enzymes that are thought to be involved in host colonization, perturbation of the immune system, and tissue destruction. The aim of the present study was to investigate the contribution of Arg- and Lys-gingipains produced by P. gingivalis to its growth. Although all of the proteins studied were degraded by P. gingivalis, only human serum albumin and transferrin supported growth during serial transfers in a chemically defined medium (CDM). Growth studies with site-directed gingipain-deficient mutants of P. gingivalis revealed that inactivation of both gingipains prevents growth, whereas inactivation of either Arg- or Lys-gingipain activity extended the doubling times to 33 or 13 h, respectively, compared to 9 h for the parent strain. Growth of the mutants and the parent strain was similar when the CDM was supplemented with a protein hydrolysate instead of human serum albumin. Incubation of resting P. gingivalis ATCC 33277 cells with fluorophore-labeled albumin indicated that the proteolytic fragments generated by the gingipains were internalized by the bacterial cells. Internalization of fluorophore-labeled albumin fragments was reduced or completely inhibited in the proteinase-deficient mutants. Interestingly, gingival crevicular fluid samples from diseased periodontal sites contained low-molecular-mass albumin fragments, whereas samples from healthy sites did not. The critical role of proteinases in the growth of P. gingivalis was further investigated using specific Arg- and Lys-gingipain inhibitors. Adding the inhibitors to CDM containing albumin revealed that leupeptin (Arg-gingipain A and B inhibitor) was more efficient at inhibiting growth than cathepsin B inhibitor II (Lys-gingipain inhibitor). Our study suggests that Arg-gingipains and, to a lesser extent, Lys-gingipain play an important role in the growth of P. gingivalis in a defined medium containing a human protein as the sole carbon and nitrogen source.

The heparin-binding haemagglutinin of M. tuberculosis is required for extrapulmonary dissemination

Tuberculosis remains the world's leading cause of death due to a single infectious agent, Mycobacterium tuberculosis, with 3 million deaths and 10 million new cases per year. The infection initiates in the lungs and can then spread rapidly to other tissues. The availability of the entire M. tuberculosis genome sequence and advances in gene disruption technologies have led to the identification of several mycobacterial determinants involved in virulence. However, no virulence factor specifically involved in the extrapulmonary dissemination of M. tuberculosis has been identified to date. Here we show that the disruption of the M. tuberculosis or Mycobacterium bovis Bacille Calmette-Guérin (BCG) hbhA gene encoding the heparin-binding haemagglutinin adhesin (HBHA) markedly affects mycobacterial interactions with epithelial cells, but not with macrophage-like cells. When nasally administered to mice, the mutant strains were severely impaired in spleen colonization, but not in lung colonization. Coating wild-type mycobacteria with anti-HBHA antibodies also impaired dissemination after intranasal infection. These results provide evidence that adhesins such as HBHA are required for extrapulmonary dissemination, and that interactions with non-phagocytic cells have an important role in the pathogenesis of tuberculosis. They also suggest that antibody responses to HBHA may add to immune protection against tuberculosis.

Galectins as modulators of cell adhesion

The galectins are a family of carbohydrate-binding proteins that are distributed widely in metazoan organisms. Each galectin exhibits a specific pattern of expression in various cells and tissues, and expression is often closely regulated during development. Although these proteins are found mainly in the cell cytoplasm, some are secreted from cells and interact with appropriately glycosylated proteins at the cell surface or within the extracellular matrix. These receptors include cell-adhesion molecules such as integrins, and matrix glycoproteins such as laminin and fibronectin isoforms. Recent studies have increased understanding of the roles of the galectins in regulating cell-cell and cell-matrix adhesion. These interactions are critically involved in modulation of normal cellular motility and polarity and during tissue formation, and loss of adhesive function is implicated in several disease states including tumour progression, inflammation and cystic development in branching epithelia such as kidney tubules. This review discusses recent progress in defining the specificities and mechanisms of action of secreted galectins as multifunctional cell regulators.

[Galectins: a novel family of proteins involved in the regulation of the immune response. Implications in immunopathological processes]

Galectins have emerged as a new family of closely related carbohydrate-binding proteins, which exert their functions by virtue of their ability to decipher glycocodes on complex glycoconjugates. They have been implicated in different immunological processes, such as lymphocyte adhesion, cytokine production, cell growth regulation, apoptosis and central and peripheral immune tolerance. In the present article we analyze the implications of this protein family in different immune pathologies with up- or down-regulated immune responses, such as autoimmune disorders, acute and chronic inflammation, allergic diseases, infection and metastases. The use of recombinant galectins or their antagonists will have future implications in the diagnosis, prognosis and treatment of these diseases, widening the horizons of molecular immunopathology.

Porphyromonas gingivalis gingipains and adhesion to epithelial cells

Porphyromonas gingivalis is one of the principal organisms associated with adult periodontitis. Bacterial surface proteins such as fimbriae and gingipain hemagglutinin domains have been implicated as adhesins that actuate colonization of epithelium lining the gingival sulcus. We investigated the genetics of P. gingivalis adhesion to monolayers of epithelial cells using wild-type and gingipain mutant strains. These experiments suggested that arginine-specific gingipain (Rgp) catalytic activity modulated adhesion. From the data obtained with rgp mutants, we constructed a working hypothesis predicting that attachment and detachment of P. gingivalis to epithelial cells were mediated by gingipain adhesin and Rgp catalytic domains, respectively. A membrane-based epithelial cell binding assay, used to locate adhesins in extracellular fractions of wild-type and mutant strains, recognized gingipain peptides as adhesins rather than fimbriae. We developed a capture assay that demonstrated the binding of gingipain adhesin peptides to oral epithelial cells. The adherence of fimbrillin to epithelial cells was detected after heat denaturation of cell fractions. The prediction that Rgp catalytic activities mediated detachment was substantiated when the high level of attachment of an rgp mutant was reduced in the presence of wild-type cell fractions that contained gingipain catalytic activities.