Molecular characterization of receptor binding proteins and immunogens of virulent Treponema pallidum

How do phosphodiesterase-5 inhibitors affect cancer? A focus on glioblastoma multiforme

Since the discovery of phosphodiesterase-5 (PDE5) enzyme overexpression in the central nervous system (CNS) malignancies, investigations have explored the potential capacity of current PDE5 inhibitor drugs for repositioning in the treatment of brain tumors, notably glioblastoma multiforme (GBM). It has now been recognized that these drugs increase brain tumors permeability and enhance standard chemotherapeutics effectiveness. More importantly, studies have highlighted the promising antitumor functions of PDE5 inhibitors, e.g., triggering apoptosis, suppressing tumor cell growth and invasion, and reversing tumor microenvironment (TME) immunosuppression in the brain. However, contradictory reports have suggested a pro-oncogenic role for neuronal cyclic guanosine monophosphate (cGMP), indicating the beneficial function of PDE5 in the brain of GBM patients. Unfortunately, due to the inconsistent preclinical findings, only a few clinical trials are evaluating the therapeutic value of PDE5 inhibitors in GBM treatment. Accordingly, additional studies should be conducted to shed light on the precise effect of PDE5 inhibitors in GBM biology regarding the existing molecular heterogeneities among individuals. Here, we highlighted and discussed the previously investigated mechanisms underlying the impacts of PDE5 inhibitors in cancers, focusing on GBM to provide an overview of current knowledge necessary for future studies.

Viral, bacterial, and fungal infections of the oral mucosa: Types, incidence, predisposing factors, diagnostic algorithms, and management

For millions of years, microbiota residing within us, including those in the oral cavity, coexisted in a harmonious symbiotic fashion that provided a quintessential foundation for human health. It is now clear that disruption of such a healthy relationship leading to microbial dysbiosis causes a wide array of infections, ranging from localized, mild, superficial infections to deep, disseminated life-threatening diseases. With recent advances in research, diagnostics, and improved surveillance we are witnessing an array of emerging and re-emerging oral infections and orofacial manifestations of systemic infections. Orofacial infections may cause significant discomfort to the patients and unnecessary economic burden. Thus, the early recognition of such infections is paramount for holistic patient management, and oral clinicians have a critical role in recognizing, diagnosing, managing, and preventing either new or old orofacial infections. This paper aims to provide an update on current understanding of well-established and emerging viral, bacterial, and fungal infections manifesting in the human oral cavity.

Factors determining human-to-human transmissibility of zoonotic pathogens via contact

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There are several modes of contact transmission of pathogens amongst humans.

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Factors promoting contact transmission act at the pathogen, host or environmental levels.

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Common pathogen factors are immune evasion, high viral load and low infectious dose.

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Common host factors are crowding, promiscuity and the presence of co-infections.

The pandemic potential of zoonotic pathogens lies in their ability to become efficiently transmissible amongst humans. Here, we focus on contact-transmitted pathogens and discuss the factors, at the pathogen, host and environmental levels that promote or hinder their human-to-human transmissibility via the following modes of contact transmission: skin contact, sexual contact, respiratory contact and multiple route contact. Factors common to several modes of transmission were immune evasion, high viral load, low infectious dose, crowding, promiscuity, and co-infections; other factors were specific for a pathogen or mode of contact transmission. The identification of such factors will lead to a better understanding of the requirements for human-to-human spread of pathogens, as well as improving risk assessment of newly emerging pathogens.

Bifunctional role of the Treponema pallidum extracellular matrix binding adhesin Tp0751

Treponema pallidum, the causative agent of syphilis, is a highly invasive pathogenic spirochete capable of attaching to host cells, invading the tissue barrier, and undergoing rapid widespread dissemination via the circulatory system. The T. pallidum adhesin Tp0751 was previously shown to bind laminin, the most abundant component of the basement membrane, suggesting a role for this adhesin in host tissue colonization and bacterial dissemination. We hypothesized that similar to that of other invasive pathogens, the interaction of T. pallidum with host coagulation proteins, such as fibrinogen, may also be crucial for dissemination via the circulatory system. To test this prediction, we used enzyme-linked immunosorbent assay (ELISA) methodology to demonstrate specific binding of soluble recombinant Tp0751 to human fibrinogen. Click-chemistry-based palmitoylation profiling of heterologously expressed Tp0751 confirmed the presence of a lipid attachment site within this adhesin. Analysis of the Tp0751 primary sequence revealed the presence of a C-terminal putative HEXXH metalloprotease motif, and in vitro degradation assays confirmed that recombinant Tp0751 purified from both insect and Escherichia coli expression systems degrades human fibrinogen and laminin. The proteolytic activity of Tp0751 was abolished by the presence of the metalloprotease inhibitor 1,10-phenanthroline. Further, inductively coupled plasma-mass spectrometry showed that Tp0751 binds zinc and calcium. Collectively, these results indicate that Tp0751 is a zinc-dependent, membrane-associated protease that exhibits metalloprotease-like characteristics. However, site-directed mutagenesis of the HEXXH motif to HQXXH did not abolish the proteolytic activity of Tp0751, indicating that further mutagenesis studies are required to elucidate the critical active site residues associated with this protein. This study represents the first published description of a T. pallidum protease capable of degrading host components and thus provides novel insight into the mechanism of T. pallidum dissemination.

Endemic treponematosis: review and update

Despite major efforts to eradicate these disorders, yaws, bejel, and pinta (endemic treponematosis) remain serious health issues in many regions of the world. Aside from prominent skin manifestations, these diseases may also lead to significant osseous, neurologic, and ophthalmologic complications. Although progress has been made in differentiating the causative species in a research setting, a simple, specific, and sensitive diagnostic test remains elusive. Parenteral penicillin, in appropriate dosage, is the treatment of choice; alternative antibiotics such as tetracycline and erythromycin may also be effective.

Biological basis for syphilis

Syphilis is a chronic sexually transmitted disease caused by Treponema pallidum subsp. pallidum. Clinical manifestations separate the disease into stages; late stages of disease are now uncommon compared to the preantibiotic era. T. pallidum has an unusually small genome and lacks genes that encode many metabolic functions and classical virulence factors. The organism is extremely sensitive to environmental conditions and has not been continuously cultivated in vitro. Nonetheless, T. pallidum is highly infectious and survives for decades in the untreated host. Early syphilis lesions result from the host's immune response to the treponemes. Bacterial clearance and resolution of early lesions results from a delayed hypersensitivity response, although some organisms escape to cause persistent infection. One factor contributing to T. pallidum's chronicity is the paucity of integral outer membrane proteins, rendering intact organisms virtually invisible to the immune system. Antigenic variation of TprK, a putative surface-exposed protein, is likely to contribute to immune evasion. T. pallidum remains exquisitely sensitive to penicillin, but macrolide resistance has recently been identified in a number of geographic regions. The development of a syphilis vaccine, thus far elusive, would have a significant positive impact on global health.

Genome scale identification of Treponema pallidum antigens

Antibody responses for 882 of the 1,039 proteins in the proteome of Treponema pallidum were examined. Sera collected from infected rabbits were used to systematically identify 106 antigenic proteins, including 22 previously identified antigens and 84 novel antigens. Additionally, sera collected from rabbits throughout the course of infection demonstrated a progression in the breadth and intensity of humoral immunoreactivity against a representative panel of T. pallidum antigens.

Treponema pallidum fibronectin-binding proteins

Putative adhesins were predicted by computer analysis of the Treponema pallidum genome. Two treponemal proteins, Tp0155 and Tp0483, demonstrated specific attachment to fibronectin, blocked bacterial adherence to fibronectin-coated slides, and supported attachment of fibronectin-producing mammalian cells. These results suggest Tp0155 and Tp0483 are fibronectin-binding proteins mediating T. pallidum-host interactions.

Identification of a Treponema pallidum laminin-binding protein

Host extracellular matrix (ECM) components represent ideal microbial adhesion targets that many pathogens use for colonization of tissues and initiation of infection. This study investigated the interaction of the spirochete Treponema pallidum with the ECM component laminin. To identify candidate laminin-binding adhesins, the T. pallidum genome was analyzed to predict open reading frames that encode putative outer membrane proteins, as these proteins interact directly with host ECM components. Subsequent recombinant expression of these proteins and analysis of their laminin-binding potential identified one protein, Tp0751, that demonstrated specific attachment to laminin. Tp0751 attached to laminin in a dose-dependent, saturable manner but did not attach to the ECM component collagen type I or IV or to the negative control proteins fetuin or bovine serum albumin. Sodium metaperiodate treatment of laminin reduced the Tp0751-laminin interaction in a concentration-dependent manner, suggesting that oligosaccharides play a role in this interaction. In addition, Tp0751-specific antibodies were detected in serum samples collected from both experimental and natural syphilis infections, indicating that Tp0751 is expressed in vivo during the course of infection. Collectively, these experiments identified Tp0751 as a laminin-binding protein that is expressed during infection and may be involved in attachment of T. pallidum to host tissues.

Syphilis: review with emphasis on clinical, epidemiologic, and some biologic features

Syphilis is a chronic disease with a waxing and waning course, the manifestations of which have been described for centuries. It occurs worldwide, and the incidence varies significantly with geographic location. Transmission is mainly by sexual contact. The causative organism, Treponema pallidum, was first described in 1905, but because of the inability to culture the organism and the limitations of direct microscopy, serologic testing is the mainstay of laboratory diagnosis. The disease has been arbitrarily divided into several stages. The primary stage is defined by a chancre at the site of inoculation. The secondary stage is characterized by a polymorphic rash, lymphadenopathy, and other systemic manifestations. A variable asymptomatic latent period follows, which for epidemiologic purposes is divided into early (<1 year) and late (>1 year) stages. The early stages (primary, secondary, and early latent) are potentially infectious. The tertiary stage is the most destructive and is marked by cardiovascular and neurologic sequelae and gummatous involvement of any organ system. Congenital infection may result in protean early or late manifestations. Unlike many other bacteria causing infectious diseases, the organism remains sensitive to penicillin, and this remains the mainstay of therapy.

Fibronectin-binding activity in Borrelia burgdorferi1

Recently, the term MSCRAMM (microbial surface components recognizing adhesive matrix molecules), has been introduced to describe microbial molecules that recognize extracellular matrix (ECM) [1]. Here we present evidence for the presence of fibronectin-binding molecules in Borrelia burgdorferi and several other Borrelia species. Immunofluorescence studies show that plasma fibronectin is bound uniformly over the cell surface of free swimming B. burgdorferi. In addition, the spirochetes are able to bind to plasma fibronectin-coated microwell plates, an interaction that is inhibited by anti-fibronectin antibody as well as exogenous plasma fibronectin. Taken together, the data suggest that fibronectin binds to the surface of the spirochete. On Western blot-like assays, B. burgdorferi and some B. afzelii strains express a major fibronectin-binding protein (Fn-BA) with an approximate molecular mass of 52 kDa. In addition, several other major Fn-BAs were found in B. hermsii (26, 31, 33, 39, 46, 54 and 58 kDa) and B. turicatae (39, 41, 45, 50, 56, 59 and 66 kDa). Preliminary evidence suggests that fibronectin (and Fn-BA) may play a role as a molecular bridge between the spirochete and other components of the extracellular matrix.

Differential attachment of oral treponemes to monolayers of epithelial cells

This in vitro study describes the attachment properties of several oral treponemes to monolayers of epithelial cells and the effect of epithelial cell confluence on treponeme attachment. Four serotypes of Treponema denticola, Treponema scoliodontum, three subspecies of Treponema socranskii, and Treponema vincentii were tested with monolayers of epithelial cells of human and canine origin. Attachment of oral treponemes were compared to attachment by T. pallidum subsp. pallidum, and by the non-pathogen Treponema phagedenis. Results indicated that different serotypes of T. denticola had similar abilities to attach to epithelial cells. However, subspecies of T. socranskii differed in their ability to attach to epithelial cells. The proportion of epithelial cells susceptible to attachment by oral spirochetes was strongly related to the confluence level of the monolayer. In contrast, T. pallidum attached equally well to both epithelial cell lines at all confluence levels. T. phagedenis attached to < 1% of all epithelial cells. In general, attachment of oral treponemes to canine cells was lower than to human cells, suggesting species-specificity for adherence. Attachment of oral treponemes to epithelial cells may promote colonization of the periodontal pocket, as well as retention of treponeme colonies within plaque. The preference of oral treponemes to attach to cells of low confluence fields may translate in vivo to an increased ability to attach to cells which are actively dividing. Such cells are found in areas of repair, a common status within inflamed periodontal pockets. Furthermore, attachment of oral treponemes to epithelial cell barriers may promote or potentiate cytopathic processes.

Interaction of outer envelope proteins of Chlamydia psittaci GPIC with the HeLa cell surface

The chlamydial life cycle involves the intimate interaction of components of the infectious elementary body (EB) surface with receptors on the susceptible eukaryotic cell plasma membrane. We have developed an in vitro ligand binding assay system for the identification and characterization of detergent-extracted EB envelope proteins capable of binding to glutaraldehyde-fixed HeLa cell surfaces. With this assay, the developmentally regulated cysteine-rich envelope protein Omp2 of Chlamydia psittaci strain guinea pig inclusion conjunctivitis was shown to bind specifically to HeLa cells. HeLa cells bound Omp2 selectively over other cell wall-associated proteins, including the major outer membrane protein, and the binding of Omp2 was abolished under conditions which alter its conformation. Furthermore, trypsin treatment, which reduces EB adherence, resulted in the proteolytic removal of a small terminal peptide of Omp2 at the EB surface and inactivated Omp2 in the ligand binding assay, while having a negligible effect on the major outer membrane protein. Collectively, our results suggest that Omp2 possesses the capacity to engage in a specific interaction with the host eukaryotic cell. We speculate that, since Omp2 is present only in the infectious EB form, the observed in vitro interaction may be representative of a determining step of the chlamydial pathogenic process.

Nonvenereal treponematoses: yaws, endemic syphilis, and pinta

The nonvenereal treponematoses--yaws, endemic syphilis, and pinta--constitute a major health concern for many third world countries. These diseases are caused by an organism that is morphologically and antigenically identical to the causative agent of venereal syphilis, Treponema pallidum. Nonvenereal treponematoses differ significantly in their modes of transmission, epidemiology, and clinical presentation from venereal syphilis. Like venereal syphilis, they have a chronic relapsing course and have prominent cutaneous manifestations. Recently, several cases of imported yaws and endemic syphilis have been described in Europe. With the escalating U.S. military presence in many remote areas of the world and ever-increasing world-wide travel, the diagnosis of the nonvenereal treponematoses must be considered in appropriate clinical and historical situations.

Polypeptides of Treponema pallidum: progress toward understanding their structural, functional, and immunologic roles. Treponema Pallidum Polypeptide Research Group

Treponema pallidum subsp. pallidum, the spirochete that causes syphilis, is unusual in a number of respects, including its small genome size, inability to grow under standard in vitro culture conditions, microaerophilism, apparent paucity of outer membrane proteins, structurally complex periplasmic flagella, and ability to evade the host immune responses and cause disease over a period of years to decades. Many of these attributes are related ultimately to its protein content. Our knowledge of the activities, structure, and immunogenicity of its proteins has been expanded by the application of recombinant DNA, hybridoma, and structural fractionation techniques. The purpose of this monograph is to summarize and correlate this new information by using two-dimensional gel electrophoresis, monoclonal antibody reactivity, sequence data, and other properties as the bases of polypeptide identification. The protein profiles of the T. pallidum subspecies causing syphilis, yaws, and endemic syphilis are virtually indistinguishable but differ considerably from those of other treponemal species. Among the most abundant polypeptides are a group of lipoproteins of unknown function that appear to be important in the immune response during syphilitic infection. The periplasmic flagella of T. pallidum and other spirochetes are unique with regard to their protein content and ultrastructure, as well as their periplasmic location. They are composed of three core proteins (homologous to the other members of the eubacterial flagellin family) and a single, unrelated sheath protein; the functional significance of this arrangement is not understood at present. Although the bacterium contains the chaperonins GroEL and DnaK, these proteins are not under the control of the heat shock regulon as they are in most organisms. Studies of the immunogenicity of T. pallidum proteins indicate that many may be useful for immunodiagnosis and immunoprotection. Future goals in T. pallidum polypeptide research include continued elucidation of their structural locations and functional activities, identification and characterization of the low-abundance outer membrane proteins, further study of the immunoprotective and immunodiagnostic potential of T. pallidum proteins, and clarification of the roles of treponemal proteins in pathogenesis.

Chemical and biological activities of a 64-kilodalton outer sheath protein from Treponema denticola strains

This study examined the distribution of the major outer sheath proteins (MOSP) in several Treponema denticola strains and reports the isolation of a 64-kDa protein from the outer sheath of human clinical isolate T. denticola GM-1. The outer sheath was isolated by freeze-thaw procedures, and the distribution of outer sheath proteins was examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). T. denticola GM-1, MS25, SR-5, and three low-passage clinical isolates possessed an MOSP with a relative molecular mass of 60 to 64 kDa. This MOSP was absent in T. denticola ATCC 35404 (TD-4) and clinical isolate SR-4. The latter possessed an MOSP of 58 kDa. 125I labeling revealed both MOSP to be dissociated forms of higher-molecular-mass oligomeric units between 116 and 162 kDa. Two-dimensional SDS-PAGE confirmed the modifiability of these MOSP. Isoelectric focusing of the 64-kDa MOSP indicated a pI of 6.7. Immunoblots with antiserum to GM-1 whole cells revealed the 64-kDa protein to be immunogenic and not cross-reactive with the MOSP of TD-4 or SR-4, and monospecific antibody to the 64-kDa protein recognized common epitopes on the high-molecular-weight oligomeric protein. These antibodies did not react with any component of TD-4 whole cells in immunoblots or in immunogold electron microscopy. Fab fragments inhibited the adherence of T. denticola GM-1 to human gingival fibroblasts by 78% (1:1,600; 0.72 micrograms of protein per ml), while TD-4 adherence was not inhibited. Amino acid analysis revealed a slightly acidic protein, devoid of cysteine, with 36% hydrophobic residues. Cyanogen bromide fragmentation of the 64-kDa protein revealed that a 42-kDa fragment contained a T-L-D-L-A-L-D segment which was 100% homologous with an integrin alpha subunit of a human leukocyte adhesion glycoprotein p 150,95.

A heat-labile protein of Chlamydia trachomatis binds to HeLa cells and inhibits the adherence of chlamydiae

From highly purified elementary bodies (EBs) of Chlamydia trachomatis, we have identified a protein of 38 kDa that selectively binds to monolayer cultures of HeLa cells. This protein, which we have named the chlamydial cytadhesin (CCA), is present on the surface of the EBs of three C. trachomatis serovars (B, E, and L1) that were examined. Localization of the CCA at the surface was confirmed by its ability to be labeled when viable EBs were iodinated and by its absence in preparations from trypsin-treated EBs. Viable EBs, but not heated or trypsin-treated EBs, inhibited the binding of the CCA to HeLa cells, indicating competition for a common receptor on the host cell membrane. A dose-dependent inhibition of adherence of radioactive EBs to HeLa cells was effected by extracts containing the CCA. This inhibition occurred even with extracts prepared from the EB of heterologous serovars. However, no inhibition could be demonstrated with extracts prepared from heat-treated EBs. Heat treatment of the extract resulted in the loss of ability of the CCA to bind to the host cells. HeLa cells preincubated with CCA-containing chlamydial extract showed reduced ability to bind labeled EBs and to develop cytoplasmic inclusions after infection. This protective activity was lost after exposure of the extract to heat. These findings indicate that the CCA is a thermolabile surface-exposed chlamydial adhesin; it may be useful in the development of vaccines for diseases caused by the pathogenic bacterium.

A new attempt to distinguish serologically the subspecies of Treponema pallidum causing syphilis and yaws

In an effort to serologically differentiate syphilis from yaws, 69 monoclonal antibody species raised against Treponema pallidum subsp. pallidum were tested by immunoblotting for their reactivity with Treponema pallidum subsp. pertenue. All monoclonal antibodies reacted with antigens with the same molecular weight of both subspecies. Furthermore, no differences in reactivity between sera from yaws patients and from syphilis patients were found by Western blot (immunoblot) analysis of cell lysates of T. pallidum subsp. pallidum and T. pallidum subsp. pertenue. We tried to exploit the only known molecular difference between the subspecies. The subunits of the 190-kilodalton multimeric proteins TpF1 and TyF1 of T. pallidum subsp. pallidum and T. pallidum subsp. pertenue, respectively, have previously been shown to differ in one amino acid residue at position 40. In this study, no difference was found in immunoreactivity of TpF1 or TyF1 with either syphilis sera or yaws sera. Synthetic peptides based on the sequence of TpF1 and of TyF1 were used in an enzyme-linked immunosorbent assay with syphilis sera and yaws sera. Again, no difference in reactivity between the T. pallidum subsp. pallidum- and T. pallidum subsp. pertenue-derived peptides was observed.

Immune T cells sorted by flow cytometry confer protection against infection with Treponema pallidum subsp. pertenue in hamsters

The role of cell-mediated immunity against infection with Treponema pallidum subsp. pertenue in humans or experimental animals is unclear. Hamsters injected subcutaneously in the hind paws with 4 x 10(6) unfractionated lymph node cells or enriched lymph node T cells (immunoglobulin negative, Ia negative) from T. pallidum subsp. pertenue-immune hamsters were resistant to challenge with T. pallidum subsp. pertenue. The popliteal lymph nodes of hamsters that received immune cells weighed less and had significantly fewer treponemes than did lymph nodes from hamsters infused with cells from nonimmune donors. Furthermore, recipients of immune T cells failed to develop antitreponemal antibodies 21 days after challenge. Enriched T cells were obtained by flow cytometric separation by using monoclonal anti-Ia antibody 14-4-4s, which identified hamster B cells. Flow cytometric analysis by two-color immunofluorescent staining with anti-hamster-immunoglobulin and monoclonal anti-Ia antibody 14-4-4s confirmed that monoclonal anti-Ia antibody 14-4-4s recognized B cells. In addition, lymph node cells obtained after treatment with anti-Ia monoclonal antibody 14-4-4s and complement were 97% T cells, as determined by monoclonal antibody 20, a hamster T-cell marker. These results demonstrated that highly enriched T cells (immunoglobulin negative, Ia negative) from T. pallidum subsp. pertenue-immune hamsters conferred partial protection on hamsters against infection with T. pallidum subsp. pertenue.

Molecular and antigenic analysis of treponemes

The treponemes comprise the essentially non-cultivable Treponema pallidum subspecies (agents of syphilis, yaws and other human trepanematoses), the gut pathogen of pigs, T. hydysenteriae, and a group of antigenically related, cultivable species, some of which are strongly implicated in human periodontal or gastrointestinal disease. Technical developments during the last decade have made possible the molecular analysis of components of this diverse group of organisms. Polypeptides and other macromolecular components have been characterized by techniques including electron microscopy, gel electrophoresis and immunoblotting. Antigenic analysis has been greatly enhanced by the use of monoclonal antibodies. Finally, DNA cloning and genetic manipulation have enabled the detailed investigation of important antigens at a genetic, structural and functional level. We examine these developments and provide a current overview of the data now available, which is an important foundation for applications in diagnosis, therapy, and, potentially, immunization against disease.

Characterization of lipid-modified immunogenic proteins of Treponema pallidum expressed in Escherichia coli

This study describes the sequence of the immunodominant Treponema pallidum surface protein TpD and its expression in Escherichia coli. The translated TpD DNA sequence revealed the presence of a putative site for lipid-modification downstream from the signal sequence of this membrane protein. Growth of TpD-expressing E. coli in the presence of radioactive palmitic acid revealed that TpD was lipid-modified. Three other, previously characterized cloned proteins of T. pallidum were also lipid-modified. The N-termini of two of three sequenced T. pallidum proteins contain a tetrapeptide sequence characteristic for lipoproteins in Gram-negative bacteria: Leu-X-Y-Cys. Only TpD differed from this consensus sequence in the substitution of the first residue by Phe. The apparent high incidence of lipoproteins among E. coli recombinants expressing T. pallidum antigens suggest an important role of lipoproteins in the induction of humoral immunity during syphilitic infection.

In vitro model of Treponema pallidum invasiveness

The purpose of this investigation was to develop an in vitro model with which invasion of tissues by pathogenic Treponema pallidum could be studied. Double-sided culture chambers were created by mounting abdominal walls excised from mice between two halves of small dialysis cells. The integrity of tissue barriers was confirmed by dye exclusion. T. pallidum subsp. pallidum, including intrinsically radiolabeled organisms, was introduced into one side of each chamber, and fractions from the other side were evaluated over time by dark-field microscopy and scintillation counting. Tissues were evaluated by scanning electron microscopy and immunologic staining. Motile T. pallidum, but not nonpathogenic, host-indigenous Treponema phagedenis biotype Reiter, was able to pass from one side of the chamber to the other side within 10 h. Up to 12% of the inoculum crossed the chamber within 24 h. Spirochetes were found within tissue in the greatest numbers between 6 and 8 h postinoculation. The murine abdominal wall has epithelium only on the peritoneum side, and results showed that T. pallidum required an epithelial surface on the entry side of the double-chambered cell in order to traverse the tissue barrier. This new in vitro technique may be of value in studying spirochete virulence and host resistance.

Interaction of Lyme disease spirochetes with cultured eucaryotic cells

The association of the Lyme disease spirochete, Borrelia burgdorferi, with cultured human endothelial cells was investigated. Attachment was time and temperature dependent, with optimal adherence occurring after 4 h of incubation at 37 degrees C. Pretreatment of borreliae with heat, immune human serum, or monoclonal antibodies directed against outer surface protein B (OspB) reduced the attachment of organisms to host cell monolayers. These results suggest that the adherence of B. burgdorferi may be mediated, at least in part, by borrelial surface proteins.

Trypanosoma cruzi trypomastigote clones differentially express a parasite cell adhesion molecule

We have cloned blood trypomastigotes from infected mice and found that Trypanosoma cruzi strains are composed of heterogeneous populations that dramatically vary (more than 100 fold) in their abilities to attach to and enter rat heart myoblasts. Trypomastigote clones were distinctively separated into highly and weakly infective groups presenting higher and lower rates of attachment to myoblasts, respectively. Each trypomastigote clone maintained the same profile of attachment and internalization into heart myoblasts when tested at different periods of time. This pattern did not change when the parasites were incubated in fresh medium before being exposed to heart myoblasts. Highly and weakly infective clones show differences at the cell surface level, particularly with regard to a 83 kDa glycoprotein. We have identified this 83 kDa glycoprotein as the parasite membrane ligand that specifically binds to rat heart myoblasts. The binding of the biotinylated 83 kDa to myoblasts is inhibited by cold excess in Western blots, as indicated by laser densitometry. In addition, the specific binding of this molecule to myoblasts is saturable and is greater in highly than in weakly infective trypomastigote clones. Highly invasive trypomastigote clones express this glycoprotein in more abundance on their surface than weakly infective trypomastigote clones. These results indicate that the 83 kDa glycoprotein present on the surface of T. cruzi trypomastigotes mediates the attachment of the parasite to heart myoblasts.

Interactions of Treponema pallidum with endothelial cell monolayers

Syphilis is a chronic disease characterized by hematogenous dissemination of Treponema pallidum into tissues such as the cardiovascular and central nervous systems. In order to test whether these aspects of the pathogenesis of syphilis reflect an ability of T. pallidum to invade vascular endothelial surfaces, we explored the association of T. pallidum with human and rabbit endothelial cells in vitro. Using radiolabeled motile organisms, we found that treponemal attachment was two times greater to rabbit aortic endothelial cells and human umbilical endothelial cells than to HeLa cells. Mild trypsinization of attached treponemes resulted in release from cells of all organisms detectable by darkfield microscopy without visible damage to the monolayer. Nevertheless, 25% of the counts representing T. pallidum remained associated with the cell monolayers. Further trypsin treatment to release the monolayer and differential centrifugation showed that 80% of the remaining cell-associated counts were not within the cells. These results suggest that some treponemes had associated with the monolayer in a trypsin resistant niche. Additionally, motile T. pallidum passed through tight-junctioned endothelial cell monolayers on membrane filters under conditions were heat-killed T. pallidum and the host indigenous nonpathogen. T. phagedenis biotype Reiter failed to do so. Electron micrographs of transverse sections through the monolayers showed many T. pallidum in junctions between endothelial cells. These studies suggest that T. pallidum may leave the circulation by passing between endothelial cells.

Treponema pallidum subspecies pallidum (Nichols) and Treponema pallidum subspecies pertenue (CDC 2575) differ in at least one nucleotide: comparison of two homologous antigens

In an attempt to identify antigenic differences between Treponema pallidum subsp. pallidum (T. pallidum) and Treponema pallidum subsp. pertenue (T. pertenue) a gene bank of T. pertenue was constructed in lambda vector EMBL3. Clones carrying the T. pertenue gene encoding a 190 kDa protein, TyF1, were selected and the DNA was expressed in E. coli. TyF1 was shown to be closely related, but slightly different from the previously cloned T. pallidum antigen TpF1. TyF1 and TpF1 are high molecular weight antigens of about 190 kDa, which dissociate into 19 kDa subunits after heat treatment in presence of SDS. The difference between the two proteins is most obvious after treatment with proteinase K, which yields a 115 kDa component from TyF1 and a 95 kDa component from TpF1, as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). The structural genes encoding TyF1 and TpF1 were sequenced and the predicted amino acid sequences differed in a single amino acid residue at position 40, which is arginine in TyF1 and glutamine in TpF1. Similarities TyF1 and TpF1 with the previously described 4D antigen are discussed. The antibody response to TyF1 and TpF1 seems higher in syphilis patients than in yaws patients. The possibility of using the difference between these T. pallidum and the T. Pertenue antigens for serological discrimination of syphilis and yaws is discussed.

Affinities of Treponema pallidum for human lactoferrin and transferrin

The acquisition of lactoferrin and transferrin by live Treponema pallidum organisms was examined. Saturation binding kinetics were obtained for virulent treponemes with increasing amounts of radioiodinated lactoferrin but not with transferrin. Furthermore, lactoferrin bound up to 100 times more effectively than transferrin. Only unlabelled lactoferrin stoichiometrically completed with iodinated lactoferrin binding. Time course kinetics showed maximum lactoferrin acquisition within the first five minutes at 34 degrees C. Optimum iron accumulation, however, was achieved by T pallidum in 30 minutes at 34 degrees C, and amounts of iron were six times greater than the equivalent amount of lactoferrin bound. Interestingly, iron uptake was also detected in the presence of transferrin, despite the minimal amounts of transferrin acquired by live treponemes. These observations reinforce the possibility that the associations of T pallidum with host molecules, such as plasma proteins, are essential for survival of the parasite within host environments.

Host-cell attachment by Trypanosoma cruzi: identification of an adhesion molecule

We have identified an 83 kDa surface glycoprotein in T. cruzi trypomastigotes which specifically binds to rat heart myoblasts. The binding of this molecule to myoblasts is inhibited by excess unlabeled material and saturable. Antibodies against the cell surface of insect trypomastigotes, blood trypomastigotes and produced during human infection recognize the 83 kDa glycoprotein adhesion molecule by immunoblotting, indicating that this molecule that mediates this critical step is immunogenic and is a candidate for vaccination against Chagas' disease.

Biological activity of Borrelia burgdorferi antigens

OSP-A (approximately 31 kDa) and flagellins (approximately 41 kDa) are prominent antigens of Borrelia burgdorferi. Both OSP-A and flagellins are immunogenic in patients and in experimentally infected mice and hamsters, but the kinetics of antibody formation to each vary considerably between the species. The role of eluted OSP-A and flagellins in the cellular immune response, chemotaxigenesis, and cytoadherence was measured. Eluted OSP-A and flagellins stimulated the proliferation of normal and infected mouse splenocytes but only the peripheral mononuclear cells of patients. Both OSP-A and flagellins induced human neutrophil chemotaxis, but at significantly reduced levels as compared to other known chemotactic peptides. Live B. burgdorferi adhere to HEp-2 cells in culture. OSP-A and the flagellins are involved in adherence; monoclonal antibodies to determinants in these proteins partially inhibited adherence. Cytoadherence was also partially inhibited by treatment of the cells with tunicamycin and sialidase.

Role of the RGD sequence in parasite adhesion to host cells

For many protozoan parasites, one of the first events in the process of infection is attachment to the surface of host cells. This adhesion phase usually involves ligand-receptor interactions, and has stimulated interest in the biochemical characterization of those host cell and parasite surface components involved. In this article, Ali Ouaissi discusses the strategy employed by pathogens such as Trypanosoma cruzi, Trichomonas, Leishmania and Treponema pallidum, in binding to their host cells' fibronectin receptors. Two systems appear available - to bind to the dimeric cell surface fibronectin through the Arginine-Glycine-Aspartic acid (RGD) sequence that is not occupied by the host cell surface receptors, or to present a surface antigen representing a 'fibronectin-like' molecule containing the RGD sequence directly to the host cell fibronectin receptors.

Treponema pallidum invades intercellular junctions of endothelial cell monolayers

The pathogenesis of syphilis reflects invasive properties of Treponema pallidum, but the actual mode of tissue invasion is unknown. We have found two in vitro parallels of treponemal invasiveness. We tested whether motile T. pallidum could invade host cells by determining the fate of radiolabeled motile organisms added to a HeLa cell monolayer; 26% of treponemes associated with the monolayer in a trypsin-resistant niche, presumably between the monolayer and the surface to which it adhered, but did not attain intracellularity. Attachment of T. pallidum to cultured human and rabbit aortic and human umbilical vein endothelial cells was 2-fold greater than to HeLa cells. We added T. pallidum to aortic endothelial cells grown on membrane filters under conditions in which tight intercellular junctions had formed. T. pallidum was able to pass through the endothelial cell monolayers without altering tight junctions, as measured by electrical resistance. In contrast, heat-killed T. pallidum and the nonpathogen Treponema phagedenis biotype Reiter failed to penetrate the monolayer. Transmission electron micrographs of sections of the monolayer showed T. pallidum in intercellular junctions. Our in vitro observations suggest that these highly motile spirochetes may leave the circulation by invading the junctions between endothelial cells.

Identification and properties of Trichomonas vaginalis proteins involved in cytadherence

Trichomonas vaginalis NYH286 surface proteins which are candidates for mediating parasite cytadherence (adhesins) were identified. At least four trichomonad protein ligands ranging in relative molecular mass from 65 to less than or equal to 21 kilodaltons were found to selectively bind to chemically stabilized HeLa cells. The proteins were present on the surfaces of 10 different isolates of T. vaginalis examined; however, the nonpathogenic trichomonad T. tenax did not possess similar HeLa cell-binding proteins under identical experimental conditions, suggesting that these proteins are unique to the pathogenic human trichomonads. The surface nature of the candidate adhesins was confirmed by the ability of the proteins on intact, live organisms to be radioiodinated and to be removed with trypsin treatment. Rabbit antiserum (immunoglobulin G fraction) generated against adhesin proteins electroeluted from acrylamide preparations inhibited cytadherence compared with control immunoglobulin G. An adherence-negative subpopulation of T. vaginalis NYH286 organisms was also isolated. These nonadherent trichomonads did not synthesize the adhesin proteins. Interestingly, absence of adhesins from these parasites paralleled expression of a major immunogen known to undergo phenotypic variation. Revertant organisms derived from the adherence-minus subpopulation synthesized the adhesins and attached to HeLa cells. The emergence of revertant adherent T. vaginalis organisms also corresponded with the appearance of parasites which were without the major immunogen on their surface. Finally, it was determined that only those parasites lacking the major surface immunogen were capable of adherence and toxicity to HeLa cells.

Molecular cloning of Treponema pallidum outer envelope fibronectin binding proteins, P1 and P2

Phages directing the synthesis of Treponema pallidum fibronectin binding adhesin proteins, P1 and P2, were isolated from an EMBL-3 bacteriophage lambda library of T pallidum deoxyribonucleic acid (DNA). The recombinant phages were identified using antisera generated to treponemal proteins purified in fibronectin-Sepharose. Recombinant P1 and P2 proteins possessed the same relative molecular weights as the native surface polypeptides of spirochaetes. The structural genes for these proteins were subcloned into the plasmid vector pUC19, and transformed Escherichia coli expressed and translocated recombinant P1 and P2 to their outer membranes. Finally, the recombinant adhesin proteins, P1 and P2, were purified from detergent solubilised E coli outer membrane preparations using fibronectin-Sepharose affinity chromatography, which confirmed that the fibronectin binding properties of the cloned proteins were retained.

Cloning structural genes for Treponema pallidum immunogens and characterisation of recombinant treponemal surface protein, P2 (P2 star)

A genomic library consisting of partially digested 10 to 20 kilobase pair fragments of Treponema pallidum deoxyribonucleic acid (DNA) was constructed using bacteriophage lambda EMBL-3 as the vector. Positive clones expressing T pallidum antigens were detected with sera from experimentally infected rabbits. Treponemal proteins ranging in molecular weight from 37,000 daltons to 120,000 daltons were identified by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and immunoblotting of phage lysate proteins. One recombinant phage was examined further and contained an insert encoding a prominent treponemal 37,000 dalton protein. The recombinant protein was not recognised by antiserum directed against a fibronectin binding treponemal adhesion that contained the same electrophoretic mobility. Neither did antibody to the recombinant 37,000 dalton protein react with any treponemal proteins purified by fibronectin affinity chromatography. The recombinant protein in Escherichia coli lysates was labelled P2 (P2 star) to differentiate it from the comigrating adhesin protein called P2. Native P2 protein was present on T pallidum surfaces as shown by radioimmunoprecipitation assays with extrinsically labelled organisms. A cross reactive molecule like P2 was not synthesised by the avirulent spirochaete, T phagedenis biotype Reiter, which indicated that P2 is a protein specific to virulent T pallidum organisms. Finally, only sera of patients with primary syphilis possessed appreciable concentrations of antibody to recombinant P2 protein.

Identification and purification of a recombinant Treponema pallidum basic membrane protein antigen expressed in Escherichia coli

A recombinant plasmid designated pLVS3 previously was described that harbored a 14-kilobase insert of Treponema pallidum genomic DNA. Escherichia coli maxicells programmed with this plasmid synthesized three treponemal protein antigens of molecular weights 39,000, 35,000, and 25,000 (39K, 35K, and 25K proteins, respectively). In this study, a detailed deletion analysis of pLVS3 demonstrated that the genetic information for all three protein antigens is contained within a 1.5-kilobase EcoRI-HpaI restriction fragment. The DNA sequence of this fragment revealed a single open reading frame of 361 codons that most likely encodes a signal peptide-bearing precursor to the 39K protein that can be transiently detected in E. coli maxicells. Evidence indicated that the 35K and 25K protein antigens are derivatives of the larger protein and are only produced in maxicells. A significant elevation in expression of the 39K treponemal protein antigen in E. coli was obtained by using the E. coli lpp and lac promoters and a genetic construction in which the signal peptide and first four residues of the "mature" 39K protein were replaced by six amino acids encoded by the vector. This hybrid protein exhibited an unusually high pI, which greatly facilitated its purification to homogeneity. By using antibody prepared against the hybrid protein, the native treponemal protein counterpart, also of molecular weight 39,000, was identified as a membrane component of T. pallidum. Since the native protein also exhibited a net positive charge, it has been designated the T. pallidum basic membrane protein.

Factors that inhibit adherence of Treponema pallidum (Nichols strain) to a human fibroblastic cell line: development in serum of patients with syphilis

Serum samples from 25 patients at five different stages of syphilis were investigated for their ability to inhibit the adherence of pathogenic Nichols treponemes to cultured human fibroblasts. Serum taken from patients at the end of the primary stage showed an appreciable inhibition of treponemal adherence, and maximum inhibition of adherence was produced by serum from patients with secondary syphilis. Some freshly harvested treponemal suspensions were resistant to the adherence inhibition factors in serum from patients with syphilis; after incubation in vitro for 24 hours this resistance was lost. In vitro incubation almost doubled the number of adherent treponemes/fibroblast. These phenomena are discussed in terms of loss and reconstruction of the treponemal outer envelope. This leads to the suggestion that adherence occurs not only at the tips of the treponemes, but that surface components are also implicated, possibly as an initial contact mechanism. The composition of the outer envelope may in this way determine localisation versus dissemination of the treponemes.

Antigenic interrelationship between endoflagella of Treponema phagedenis biotype Reiter and Treponema pallidum (Nichols): molecular characterization of endoflagellar proteins

Purified endoflagella from nonpathogenic Treponema phagedenis biotype Reiter were characterized biochemically and compared antigenically with the endoflagellar proteins of Treponema pallidum. T. phagedenis biotype Reiter endoflagella were dissociated into constituent polypeptides by incubation under conditions which disrupt noncovalent bonds. Chymotrypsin peptide maps of T. phagedenis biotype Reiter endoflagellar proteins revealed that the 37- and 33-kilodalton (kDa) major components shared significant homology with the 27- and 30-kDa minor components, respectively. The peptide maps also suggested that the major components shared a lesser degree of structural similarity with each other. These relationships were confirmed by Western blots of T. phagedenis biotype Reiter endoflagellar proteins employing antibodies that were purified against the individual endoflagellar polypeptides. Western blots of T. pallidum with the purified antibodies also demonstrated strong cross-reactivity between the T. phagedenis biotype Reiter endoflagellar proteins and T. pallidum proteins of identical or similar molecular weights. A unique Western blotting technique that we called epitope bridging was used to determine that the 37-kDa subunit contains most of the external epitopes on T. phagedenis biotype Reiter endoflagella. Immunoelectron microscopy with human syphilitic serum and rabbit T. phagedenis biotype Reiter endoflagellar antiserum confirmed the presence of cross-reactive epitopes on the surface of intact T. phagedenis and T. pallidum endoflagella.

Antibody-independent interactions of fibronectin, C1q, and human neutrophils with Treponema pallidum

Although recent evidence suggests that fibronectin may be involved in the attachment of treponemes to mammalian cells, its possible role in promoting phagocytosis of Treponema pallidum has not been investigated. In the present study, we examined the antibody-independent interactions of fibronectin, C1q, and human polymorphonuclear leukocytes with T. pallidum. Binding of [125I]fibronectin was specific and saturable with an affinity constant of approximately 2 X 10(7) M-1. The number of binding sites per treponeme at 37 degrees C, irrespective of the mammalian source of fibronectin, was between 2,500 and 7,500, with a mean of approximately 4,700. Binding of [125I]C1q to T. pallidum, in the absence of antibodies to the organism, also was saturable and specific. Pretreatment of treponemes with C1q enhanced binding of soluble [125I]fibronectin two- to threefold and also increased attachment of 125I-surface-labeled treponemes to fibronectin-coated surfaces. Treatment of 125I-labeled T. pallidum with fibronectin alone, or together with C1q, however, did not enhance surface phagocytosis by neutrophils.

Treponemal infection specifically enhances node T-cell regulation of macrophage activity

Hamsters experimentally inoculated in the inguinal region with Treponema pallidum subsp. endemicum develop considerable pathology at that site. We examined the cell populations from these inguinal lymph nodes to determine their intercellular responses to infection. In vitro, syphilitic-node T cells markedly suppressed C3b receptor-mediated ingestion (C3bMI) in syphilitic macrophages derived from sites both proximal and distal to the inoculation. This activity was more pronounced when node T cells rather than peritoneal T cells were used. When treponemal preparations or live treponemes were added to the coculture system, the suppression was specifically enhanced, whereas the addition of heterologous agents did not promote this effect. Syphilitic macrophages from either compartment cultured alone showed no significant inhibition of C3bMI. In parallel studies on syphilitic macrophages, we observed that the expression of Ia quickly became elevated and was sustained throughout the infection. Moreover, in vitro culturing of the syphilitic-node T cells with these macrophages did not alter this function. These observations suggest that the syphilitic node contains a subpopulation of T cells that can selectively suppress macrophage C3bMI activity and concurrently regulate their cellular response to treponemal infection.

Isolation of a Treponema pallidum gene encoding immunodominant outer envelope protein P6, which reacts with sera from patients at different stages of syphilis

A phage directing the synthesis of an abundant 45-kD Treponema pallidum surface protein was isolated from an EMBL-4 bacteriophage lambda library of T. pallidum DNA. The recombinant phage was identified using an mAb that was directed toward an immunodominant, outer envelope T. pallidum protein designated P6. The recombinant P6 protein possessed the same mol mass as the native treponemal antigen detected from total T. pallidum protein preparations, confirming the cloning of the structural gene for this molecule. Furthermore, E. coli was transformed by a 4.5-kb Eco RI lambda insert fragment subcloned into the plasmid vector pUC19. These transformed cells expressed and translocated the 45-kD protein to their outer membranes. Finally, all sera from patients with different stages of syphilis (primary, secondary, and latent) contained antibody reactive to this protein.

Monoclonal antibodies directed against major histocompatibility complex antigens bind to the surface of Treponema pallidum isolated from infected rabbits or humans

Evidence is presented for the association of class I major histocompatibility complex (MHC) antigens with the surface of Treponema pallidum during infection. A monoclonal antibody (IgG2a) directed against a murine H-2Kb epitope of public specificity reacted with the cell surface of T. pallidum, as assayed by the binding of protein A-colloidal gold in immunoelectron microscopy. Monoclonal antibodies directed against class I rabbit MHC antigens also reacted in immunofluorescence assays with material on the surface of rabbit-cultivated T. pallidum. In addition, impression smears of human syphilitic genital ulcers that were darkfield-positive for the presence of spirochetes were tested in immunofluorescence assays with monoclonal antibodies directed against human MHC antigens; antibody directed against HLA-ABC (class I) was reactive whereas antibody directed against HLA-DR (class II) was nonreactive. Results of the study suggest that the association of host-derived class I MHC antigens or molecular mimicry may play a role in T. pallidum evasion of host immune defenses.

Enhanced levels of attachment of fibronectin-primed Treponema pallidum to extracellular matrix

Freshly extracted Treponema pallidum organisms treated with exogenous human fibronectin (Fn) (Fn-primed treponemes) showed a 6- to 15-fold increased level of attachment to Fn-coated cover slips and to extracellular matrix (ECM) when compared with unprimed treponemes. Treponemes primed with collagen or laminin showed no similar enhanced binding to immobilized Fn or ECM. Preexposure of immobilized Fn and ECM to anti-Fn serum but not to anti-collagen or anti-laminin serum prevented treponemal adherence. Also, the presence of proteoglycanlike molecules such as dextran sulfate or heparan sulfate inhibited Fn-primed treponemal attachment to Fn or ECM. In contrast Fn-primed treponemes did not exhibit elevated levels of attachment to eucaryotic cell monolayers. To understand the increased tropism of Fn-primed T. pallidum organisms for Fn and ECM-like surfaces, we radiolabeled freshly extracted treponemes with [35S]methionine and examined them for the presence of surface immunoreactive Fn. Magnetic protAspheres and glass beads coated with monospecific anti-Fn serum bound only 20 to 30% of radiolabeled treponemes. Nonadherent treponemes failed to bind to gelatin-agarose, further confirming the absence of surface Fn or Fn-like material. Fn-free organisms, however, did attach to Fn-coated cover slips and to cell monolayers like treponemes of the original population. Incubation of Fn-free treponemes with human Fn resulted in almost total binding of organisms to anti-Fn antibody on glass beads and also produced increased attachment to Fn-coated cover slips and ECM. These results suggest that enhanced interactions between T. pallidum and the host are dependent on the presence of Fn on syphilis spirochetes and the specific location and orientation of Fn in vivo.

The surface of virulent Treponema pallidum: resistance to antibody binding in the absence of complement and surface association of recombinant antigen 4D

The binding of immunoglobulin G present in syphilitic immune rabbit serum, syphilitic human serum, and rabbit antiserum to purified recombinant Treponema pallidum antigen 4D by T. pallidum, Nichols strain, was studied by immunoelectron microscopy. Treponemes were incubated with antiserum under the conditions of the T. pallidum immobilization test, in which T. pallidum-specific antibody renders the organism nonmotile and avirulent only in the presence of complement after a 16-h incubation period in an anaerobic environment. Antibody was not demonstrable on the surface of T. pallidum incubated with nonimmune rabbit serum or normal human serum in the presence of complement. Similarly, in the absence of complement, little or no antibody was found on the treponemal surface after incubation with syphilitic immune rabbit serum, syphilitic human serum, or rabbit antiserum directed against the recombinant 4D antigen. The addition of complement to syphilitic immune rabbit serum, syphilitic human serum, and anti-4D antibody resulted in immobilization and the deposition of antibody on the entire surface of the immobilized organisms. These results corroborate earlier work by other investigators demonstrating the resistance of freshly isolated T. pallidum to antibody binding in a variety of serological tests. Detection of 4D antigen on the surface of immobilized T. pallidum strongly implies that the use of T. pallidum immobilization test conditions provides a means to demonstrate the association of individual surface antigens on virulent T. pallidum. The resistance of T. pallidum to antibody binding may be relevant to the pathogenesis of syphilis.