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PubMed1987

Virus receptors on lymphoid cells.

The studies described above indicate the advances made in the isolation and characterization of virus receptors of lymphoreticular cells (Table I). Although the examples of lymphotropic virus receptors cited in this chapter indicate that single membrane glycoproteins can serve as receptors, other nonlymphoid viruses such as vesicular stomatitis virus (VSV) (Table I) appear to utilize glycolipid or phospholipid components for cell attachment. These molecules may be responsible for the broad specificity of host cell attachment by these viruses. The virus-binding moiety of phospholipid/glycolipid receptors remains to be fully analyzed. It is anticipated that biochemical techniques such as the use of chemical cross-linking reagents will aid in the identification of other virus receptors such as CMV and measles which have less restricted lymphotropism than EBV. In addition, X-ray crystallographic analysis of viruses such as the recent studies of human rhinovirus and poliovirus may provide insights on the complementary structure of cellular recognition sites for viruses.

B-Lymphocytes↗
PubMed2006

Enhancement of neutralizing activity of influenza virus-specific antibodies by serum components.

The role of serum components in enhancing virus neutralizing (VN) activity of influenza virus A/PR/8/34 hemagglutinin (HA)-specific MAbs in vitro was investigated. The degree of enhancement depended on the MAb's fine specificity and heavy chain isotype and on type of serum. Greatest enhancement (>100-fold) was seen with sera from immunodeficient mice that lacked serum immunoglobulin. At least two serum components were involved: C1q and a heat-resistant factor. C1q was mandatory for enhancement, and other components of the complement system were not required. C1q appeared to operate by improving MAb-mediated inhibition of virus attachment to host cells and was most effective with MAbs that inhibited virus attachment poorly on their own. The heat-resistant factor enhanced VN activity only in the presence of C1q and appeared to operate by enhancing VN activity at a post-attachment stage.

Animals↗
PubMed2002

Strategic targeting of essential host-pathogen interactions in chlamydial disease.

The chlamydiae are obligate intracellular gram-negative bacteria that are exquisitely adapted for exploitation of their hosts and contribute to a wide range of acute and chronic human diseases. Acute infections treated with non-cidal antibiotics can lead to the development of persistent, non-replicating bacteria with the corollary that these persistent (yet viable) chlamydiae can resist eradication by further antimicrobial treatment and cause chronic disease. These findings highlight an urgent need for therapeutics that are effective against persistent infections and call for creative approaches to identify potential drug targets. The C. pneumoniae and C. trachomatis genome projects have greatly expanded our knowledge of chlamydial pathogenesis and have provided an enormous potential for the identification and characterization of unknown genes and potential virulence factors in these bacteria. As intracellular pathogens, chlamydiae rely on host cells for all aspects of their survival, from the initial attachment with host cell membranes, to cellular invasion, acquisition of host cell metabolites and intracellular replication. As such, the molecules participating in interactions with the host could be attractive targets for therapeutic intervention. This review describes recent advances in chlamydial genomics, proteomics and cell biology that have cast light on host-pathogen relations that are essential for chlamydial survival. Using this knowledge, we discuss how strategically interfering with essential interactions between chlamydiae and the host cell could be exploited to develop an innovative, and potentially more relevant arsenal of therapeutic compounds.

Anti-Bacterial Agents↗
PubMed2003

The cytoskeleton of Giardia lamblia.

Giardia lamblia is a ubiquitous intestinal pathogen of mammals. Evolutionary studies have also defined it as a member of one of the earliest diverging eukaryotic lineages that we are able to cultivate and study in the laboratory. Despite early recognition of its striking structure resembling a half pear endowed with eight flagella and a unique ventral disk, a molecular understanding of the cytoskeleton of Giardia has been slow to emerge. Perhaps most importantly, although the association of Giardia with diarrhoeal disease has been known for several hundred years, little is known of the mechanism by which Giardia exacts such a toll on its host. What is clear, however, is that the flagella and disk are essential for parasite motility and attachment to host intestinal epithelial cells. Because peristaltic flow expels intestinal contents, attachment is necessary for parasites to remain in the small intestine and cause diarrhoea, underscoring the essential role of the cytoskeleton in virulence. This review presents current day knowledge of the cytoskeleton, focusing on its role in motility and attachment. As the advent of new molecular technologies in Giardia sets the stage for a renewed focus on the cytoskeleton and its role in Giardia virulence, we discuss future research directions in cytoskeletal function and regulation.

Animals↗
PubMed1999

Have chondracanthid copepods co-speciated with their teleost hosts?

Chondracanthid copepods parasites many teleost species and have a mobile larval stage. It has been suggested that copepod parasites, with free-living infective stages that infect hosts by attaching to their external surfaces, will have co-evolved with their hosts. We examined copepods from the genus Chondracanthus and their teleost hosts for evidence of a close co-evolutionary association by comparing host and parasite phylogenies using TreeMap analysis. In general, significant co-speciation was observed and instances of host switching were rare. The prevalence of intra-host speciation events was high relative to other such studies and may relate to the large geographical distances over which hosts are spread.

Animals↗
PubMed2001

Role of Rusa deer Cervus timorensis russa in the cycle of the cattle tick Boophilus microplus in New Caledonia.

Two field experiments were conducted to evaluate the efficiency of Rusa deer in the development of the cattle tick Boaphilus microplus in comparison with that of steers in the same pastures and under the same conditions of infestation. No difference was noted between a mixed steer/deer herd and a pure steer or pure deer herd in the infestation pattern of each host, suggesting that attachment to the alternative host is mechanical and not affected by the simultaneous presence of the primary host on the pasture. Deer are capable of producing engorged viable females, with weight and reproductive performances similar to or even better than females fed on steers. For moderate levels (1 million larvae per hectare) and high levels (32 million larvae per hectare) of pasture infestation, tick burdens on steers were not very different (e.g. average 1,911 and 2,681 ticks per m2 skin, respectively, on day 24). This may be because of saturation of steer skin sites at the moderate larval dose. Deer harboured 2.7-33 times fewer ticks than steers and produce no engorged females at the moderate larval level and 32 times fewer engorged females than steers at the high larval level. Infestation of deer was dose-dependent with averages of 12 and 399 ticks per m2 skin on day 25 at the moderate and high larval levels, respectively. At a high infestation level of the environment, Rusa deer may contribute, but to a limited extent, to infestation of pastures and, consequently, of cattle. However, their role in sustaining a viable tick population requires further investigation.

Animals↗
PubMed1996

Varying temperature-dependence of post-attachment neutralization of human immunodeficiency virus type 1 by monoclonal antibodies to gp 120: identification of a very early fusion-independent event as a neutralization target.

Neutralization of human immunodeficiency virus type 1 by adding antibody after the virus has attached to the host cell (post-attachment neutralization:PAN) was investigated using three rat monoclonal antibodies (MAbs) directed against the outer domain of the membrane protein, gp 120. Two of the MAbs are specific for the CD4-binding site region and one for the V3 loop. MAb ICR39.13g (CD4-binding site region-specific; IgG2b) effected PAN efficiently at temperatures from 4 to 35 degree C. MAb ICR41.1i (V3 loop-specific; IgG2c) effected PAN only at temperatures of 24 degree C and below. This suggests that its V3 epitope is masked by a change in gp 120 which occurs at temperatures > or = 26 degree C, or that the virion function which is inhibited by ICR41.1i and is responsible for neutralization has already operated at > or = 26 degree C. Resistance to neutralization by ICR41.1i occurred within 20 min of shifting the temperature up to 35 degree C. Finally, MAb ICR39.3b (CD4-binding site region-specific; IgG2b) did not give PAN at any temperature, indicating that neutralization can only occur if this MAb binds virus before it attaches to the cell. Thus, these studies identify at least one novel fusion-independent event, the neutralization target of a V3 MAb, which occurs very early in the initial stages of virus-cell interaction.

Animals↗
PubMed1997

A third secreted protein that is encoded by the enteropathogenic Escherichia coli pathogenicity island is required for transduction of signals and for attaching and effacing activities in host cells.

Enteropathogenic Escherichia coli strains are able to signal host cells, cause dramatic cytoskeletal rearrangements, and adhere intimately to the cell surface in a process known as the attaching and effacing effect. A pathogenicity island of 35 kb known as the locus of enterocyte effacement (LEE) is necessary and sufficient for this effect. The LEE encodes an outer membrane adhesin called intimin, a type III secretion apparatus, and the EspA and EspB secreted proteins. The DNA sequence of the region between espA and espB revealed a new gene, espD. The product of espD was demonstrated by using a T7 expression system. We constructed a nonpolar mutation in espD and found that the mutant is incapable of the signal transduction events that lead to activation of the putative intimin receptor in host cells and that the mutant fails to induce the attaching and effacing effect. These phenotypes were restored to the mutant by complementation with a plasmid containing the cloned espD locus. We demonstrated by immunoblotting and microsequencing that the EspD protein is secreted via the type III apparatus. Thus, we describe a novel locus encoding a secreted protein that is required for attaching and effacing activity.

Animals↗
PubMed1986

Electron microscopy of Treponema pallidum (Nichols) cultivated in tissue cultures of Sf1Ep cells.

The in vitro interaction between Treponema pallidum and Sf1Ep cells during treponemal replication was investigated by using transmission electron microscopy. The Sf1Ep cells grown on Teflon-treated cover slips after 12 days of cocultivation were fixed in situ, overlaid with agar, embedded, and vertically sectioned. Large numbers of treponemes were found extracellularly not only at the upper cell surfaces but also in the narrow spaces between the cells and between the cells and the cover slips. These narrow spaces supported treponemal growth and survival, as did those at the upper cell surfaces. Although few in number, organisms were also seen in cell vacuoles either surrounded by a membrane or free in the cytoplasm. Some extracellular treponemes attached to host cells by body spirals or the terminal end and formed electron-dense layers at attachment sites. Some treponemes were often surrounded with amorphous, extracellular material which appeared to "connect" them to host cell surface. After 12 days of cocultivation, host cells showed excessive vacuolation and appeared to be damaged. This did not seem to be due to treponemal infection alone, because cells from uninfected cultures also showed similar vacuolation.

Animals↗
PubMed1990

Use of embryonic heart grafted in oculo to assess neurohumoral controls of cardiac development.

Culture of embryonic heart in the anterior eye chamber allows neurohumoral and genetic controls of cardiac development to be separated from the influence of hemodynamic load. Hearts from 12-day gestation rat embryos grafted into the anterior eye chamber of an adult host rat attach to the iris and become vascularized and innervated by collaterals from the host iris. The spontaneous beating of grafts is pacemaker-driven and under functional neural control. Grafts do not beat against a pressure load, allowing the influence of neurohumoral factors to be separated from altered hemodynamic load. In oculo, embryonic heart differentiates into mature myocardium by most morphologic and biochemical criteria. Mature intercalated disks and myofibrils with well-defined Z-lines and M-lines are observed. Mature grafts express the high levels of alpha-myosin heavy chain characteristic of young adult myocardium. Surgical sympathetic denervation of the anterior eye chamber prior to grafting of embryonic hearts compromises growth and increases the intrinsic pacemaker rate. Since the grafts are perfused by the host circulation, the hormonal milieu of the graft can be altered by treatment of the host. Thus, the interaction between hormones and innervation of grafts can be studied using the in oculo model system.

Animals↗
PubMed2000

Localization of saponin-sterol complexes and lectin-binding sites during interaction of Toxoplasma gondii with host cells.

The attachment of tachyzoites of Toxoplasma gondii to the surface of host cells induces the formation of a vacuole known as the parasitophorous vacuole (PV). In the present study we used lectins labeled with either fluorescein or colloidal gold particles to follow the fate of lectin-binding sites on the host-cell surface during the process of parasite/host-cell interaction. The results obtained indicate that few, if any, lectin-binding sites are internalized together with the tachyzoites to make part of the PV membrane. However, these sites are internalized and observed in small vesicles that are seen close to the PV. We also used the freeze-fracture technique in cells treated with saponin, which reveals cholesterol-containing sites as easily identifiable elongated sulculi and depressions. Intramembranous particles, which represent membrane integral proteins, were seen in the membrane lining the PV. However, saponin-cholesterol complexes were not observed in the membrane lining the PV, although they were seen in the parasite membranes. These observations, in association with data from previous studies, show that some, but not all, membrane components of the host cell contribute to the formation of the PV membrane.

Animals↗
PubMed2000

Human immunodeficiency virus type 1 hijacks host cyclophilin A for its attachment to target cells.

Our laboratory has identified a new facet of human immunodeficiency virus type 1 (HIV-1) entry. We demonstrated that the incorporation of host cyclophilin A (CypA) into nascent viruses is absolutely required for HIV-1 attachment to target cells. Although CypA is initially incorporated into the interior of the virus, we found that during maturation CypA relocates to the viral surface. Our work indicates that exposed CypA mediates HIV-1 attachment to target cells via heparans. We believe that this interaction between CypA and heparan represents the initial step in HIV-1 entry.

Acquired Immunodeficiency Syndrome↗
PubMed2001

TgM2AP participates in Toxoplasma gondii invasion of host cells and is tightly associated with the adhesive protein TgMIC2.

Like other members of the medically important phylum Apicomplexa, Toxoplasma gondii is an obligate intracellular parasite that secretes several classes of proteins involved in the active invasion of target host cells. Proteins in apical secretory organelles known as micronemes have been strongly implicated in parasite attachment to host cells. TgMIC2 is a microneme protein with multiple adhesive domains that bind target cells and is mobilized onto the parasite surface during parasite attachment. Here, we describe a novel parasite protein, TgM2AP, which is physically associated with TgMIC2. TgM2AP complexes with TgMIC2 within 15 min of synthesis and remains associated with TgMIC2 in the micronemes, on the parasite surface during invasion and in the culture medium after release from the parasite plasma membrane. TgM2AP is proteolytically processed initially when its propeptide is removed during transit through the golgi and later while it occupies the parasite surface after discharge from the micronemes. We show that TgM2AP is a member of a protein family expressed by coccidian parasites including Neospora caninum and Eimeria tenella. This phylogenic conservation and association with a key adhesive protein suggest that TgM2AP is a fundamental component of the T. gondii invasion machinery.

Amino Acid Sequence↗
PubMed2003

Shiga toxin producing Escherichia coli infection: current progress & future challenges.

Shiga toxin producing Escherichia coli (STEC) is a newly emerged pathogen that has been the focus of immense international research effort driven by its recognition as a major cause of large scale epidemics and thousands of sporadic cases of gastrointestinal illness. It produces a severe bloody diarrhoea that is clinically distinct from other types of diarrhoeal diseases caused by other enteric pathogens. One of the most important areas of current exploration concerns how STEC enters our food chain, an investigational avenue that begins with the ecology of STEC in animals and in the environment. A variety of foods have been identified as vehicles of STEC-associated illness and this makes the organism one of the most serious threats to the food industry in recent years. The pathogenesis of STEC is multifactorial and involves several levels of interaction between the bacterium and the host. STEC strains carry a set of virulence genes that encode the factors for attachment to host cells, elaboration of effective molecules and production of two different types of Shiga toxins. These genes are found in the locus of enterocyte effacement (LEE), lamboid phages, and a large virulence associated plasmid. The publication of the complete genome sequence of Esch. coli O157:H7 chromosome offers a unique resource that will help to identify additional virulence genes, to develop better methods of strain detection and in the understanding of the evolution of Esch. coli through comparison with the genome of the non-pathogenic laboratory strain Esch. coli K-12. These research efforts in turn, should lead to development of new potent and cost effective anti-Stx therapies or vaccines and thereby major improvement in human health world-wide.

Animals↗
PubMed2005

Defining the interaction of the Treponema pallidum adhesin Tp0751 with laminin.

Various invasive pathogens attach to host tissues via the extracellular matrix component laminin, the major glycoprotein found within basement membranes. Previous investigations identified the laminin-binding adhesin Tp0751 within the spirochete bacterium Treponema pallidum. In the current study, Tp0751 was shown to attach to a variety of laminin isoforms that are widely distributed throughout the host, including laminins 1, 2, 4, 8, and 10. Such universal attachment is conducive for an adhesin present within a highly invasive pathogen that encounters a variety of tissue sites during the course of infection. Additional studies systematically identified the amino acid residues within Tp0751 that contribute to laminin binding using synthetic peptides designed from the mature protein sequence. The minimum laminin-binding region of the adhesin was localized to 10 amino acids; peptides containing these residues inhibited attachment of Tp0751 and T. pallidum to laminin. Further, Tp0751-specific antibodies inhibited attachment of T. pallidum to laminin. This study furthers our knowledge of the interaction of T. pallidum with laminin, an association that is proposed to facilitate bacterial traversal of basement membranes and subsequent entry into the circulation and tissue invasion. As such, these investigations will reveal new targets for possible prevention of bacterial dissemination and establishment of chronic infection.

Adhesins, Bacterial↗
PubMed2001

Migration of cells into and out of peripheral nerve isografts in the peripheral and central nervous systems of the adult mouse.

Peripheral nerve (PN) isografts provide a favourable environment for axon regeneration after peripheral and central nervous system (CNS) injury, but definitive information on the extent of cellular intermixing between donor and host tissues is lacking. We wished to compare migration patterns in fresh and predegenerate PN grafts, and also compare the extent of cell migration after transplantation to peripheral nervous system (PNS) versus CNS. To discern how host and donor cells interact after PN transplantation, sciatic nerve segments were transplanted from inbred adult mice into PN defects (PN-PN grafts) or into lesioned cerebral cortex of opposite gender siblings. Migrating male cells were identified using a Y-chromosome-specific probe and in situ hybridization methods, and characterized immunohistochemically. The extent of donor and host cellular intermixing was similar in fresh and predegenerate PN-PN isografts. There was substantial intermixing of donor and host cells by 8 days. Many host cells migrating into epineurial regions of grafts were immunopositive for F4/80 (macrophages). The endoneurium of grafted PN was also colonized by host cells; some were F4/80+ but many were immunostained with S-100 (Schwann cell marker). Donor S-100+ Schwann cells rapidly migrated out into proximal and distal host PN and by 12 weeks were found at least 2 mm from the grafts. Endoneurial microvessels in grafts were mostly donor-derived. By comparison, in male PN grafts to female CNS, even after 6 weeks few donor cells had migrated out into surrounding host cortex, despite the observation that almost all grafts contained regenerating axons and were thus attached to host CNS tissue.

Animals↗
PubMedDate not supplied

Adhesins as targets for vaccine development.

Blocking the primary stages of infection, namely bacterial attachment to host cell receptors and colonization of the mucosal surface, may be the most effective strategy to prevent bacterial infections. Bacterial attachment usually involves an interaction between a bacterial surface protein called an adhesin and the host cell receptor. Recent preclinical vaccine studies with the FimH adhesin (derived from uropathogenic Escherichia coli) have confirmed that antibodies elicited against an adhesin can impede colonization, block infection, and prevent disease. The studies indicate that prophylactic vaccination with adhesins can block bacterial infections. With recent advances in the identification, characterization, and isolation of other adhesins, similar approaches are being explored to prevent infections, from otitis media and dental caries to pneumonia and sepsis.

Adhesins, Bacterial↗