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Biomedical subjects

Christopher A Hunter

Publications and source records attributed to Christopher A Hunter.

At least 55 records · Page 3Linked to original sources
PubMed2004

Synthesis and photochemistry of a new class of photocleavable protein cross-linking reagents.

A new series of photocleavable protein cross-linking reagents based on bis(maleimide) derivatives of diaryl disulfides have been synthesised. They have been functionalised with cysteine and transient absorption spectra for the photolysis reaction have been recorded by using the pump-probe technique with a time resolution of 100 femtoseconds. Photolysis of the disulfide bond yields the corresponding thiyl radicals in less than a picosecond. There is a significant amount of geminate recombination, but some of the radicals escape the solvent cage and the quantum yield for photocleavage is 30 % in water.

Cross-Linking Reagents↗
PubMed2004

T cell-intrinsic expression of c-Rel regulates Th1 cell responses essential for resistance to Toxoplasma gondii.

The ability of many microbial and inflammatory stimuli to activate members of the Rel/NF-kappaB family of transcription factors is associated with the regulation of innate and adaptive responses required to control infection. Individual family members play distinct roles during different infectious and inflammatory responses. For example, c-Rel is essential for the production of IL-12 in response to LPS, but dispensable for IL-12 production in response to Toxoplasma Ag. To assess the role of c-Rel during immunity to the intracellular pathogen Toxoplasma gondii, wild-type (WT) and c-Rel(-/-) mice were infected with Toxoplasma and the immune response was analyzed. c-Rel(-/-) mice developed severe toxoplasmic encephalitis with increased numbers of parasites compared with WT controls and succumbed to infection within 5-8 wk. Although increased susceptibility of c-Rel(-/-) mice was associated with decreased T cell activation, proliferation, and production of IFN-gamma, these mice were able to generate Th1 effector cells that were present in the brain during chronic infection. In vitro mixing studies using WT and c-Rel(-/-) dendritic cells and WT and c-Rel(-/-) TCR transgenic T cells indicated that c-Rel(-/-) dendritic cells are defective in their ability to stimulate T cell responses. However, when c-Rel(-/-) T cells were transferred into T cell-deficient hosts, early defects in T cell activation, proliferation, and IFN-gamma production persisted, and these mice remained susceptible to infection. Together, these studies indicate that although c-Rel is an important regulator of innate immune responses, it also plays an important role in optimization and maintenance of adaptive T cell responses during infection.

Animals↗
PubMed2004

The NF-kappaB signaling pathway: immune evasion and immunoregulation during toxoplasmosis.

The NF-kappaB family of transcription factors is part of an evolutionarily conserved system that plays an important role in the regulation of genes associated with the development of innate and adaptive responses required for the recognition and immunologic control of pathogens [Clin. Microbiol. Rev. 15 (2002) 414; Annu. Rev. Immunol. 16 (1998) 225; Infect. Immun. 70 (2002) 3311]. In addition, NF-kappaB regulates other cellular processes required for a coordinated immune response, such as cellular growth and differentiation, cell adhesion, survival and apoptosis. Recent studies have highlighted the prominent role played by the NF-kappaB system in resistance to Toxoplasma gondii but it is becoming apparent that this intracellular parasite can directly modulate this signalling pathway. This article briefly reviews the biology of NF-kappaB, examines the complex interaction that takes place between T. gondii and these transcription factors in infected cells, and highlights the role of different NF-kappaB family members during the development of a protective immune response to this pathogen.

Animals↗
PubMed2004

Cutting edge: NF-kappa B2 is a negative regulator of dendritic cell function.

RelB, a member of the NF-kappaB family of transcription factors, is essential for dendritic cell (DC) maturation. Recent findings indicate that RelB is exclusively regulated through its interaction with cytoplasmic NF-kappaB2/p100. The studies presented in this report show that DCs lacking NF-kappaB2 have dramatically enhanced RelB activity, associated with increased MHC class II and costimulatory molecule expression and an enhanced ability to induce CD4(+) T cell responses. These studies identify a novel role for NF-kappaB2 in the negative regulation of RelB-induced DC maturation, with critical consequences for the regulation of adaptive immune responses.

Animals↗
PubMed2004

STAT1 plays a critical role in the regulation of antimicrobial effector mechanisms, but not in the development of Th1-type responses during toxoplasmosis.

The production of IFN-gamma by T cells and the ability of this cytokine to activate the transcription factor STAT1 are implicated in the activation of antimicrobial mechanisms required for resistance to intracellular pathogens. In addition, recent studies have suggested that the ability of STAT1 to inhibit the activation of STAT4 prevents the development of Th1 responses. However, other studies suggest that STAT1 is required to enhance the expression of T-bet, a transcription factor that promotes Th1 responses. To address the role of STAT1 in resistance to T. gondii, Stat1-/- mice were infected with this pathogen, and their response to infection was assessed. Although Stat1-/- mice produced normal serum levels of IL-12 and IFN-gamma, these mice were unable to control parasite replication and rapidly succumbed to this infection. Susceptibility to toxoplasmosis was associated with an inability to up-regulate MHC expression on macrophages, defects in NO production, and the inability to up-regulate some of the IFN-inducible GTPase family of proteins, molecules associated with antitoxoplasma activity. Analysis of T cell responses revealed that STAT1 was not required for the development of a Th1 response, but was required for the infection-induced up-regulation of T-bet. Together these studies suggest that during toxoplasmosis the major role of STAT1 is not in the development of protective T cell responses, but, rather, STAT1 is important in the development of antimicrobial effector mechanisms.

Animals↗
PubMed2004

The role of astrocytes in the immunopathogenesis of toxoplasmic encephalitis.

Challenge with the parasite Toxoplasma gondii eventually leads to persistent infection characterised by the presence of tissue cysts in the brain of the host. In immunocompetent individuals the parasite rarely leads to disease but in the immunocompromised host reactivation of these cysts can lead to toxoplasmic encephalitis. It is known that both CD4(+) and CD8(+) T cells are important in preventing reactivation of the parasite, however there is also evidence that astrocytes, a subset of glial cells dominant in the CNS, may be important in resistance to T. gondii. The aim of this paper is to review what is known about the immune functions of astrocytes, and the possible role they may play during toxoplasmic encephalitis.

Animals↗
PubMed2004

The regulation and activation of CD44 by natural killer (NK) cells and its role in the production of IFN-gamma.

Natural killer (NK) cells can express high levels of CD44, and signaling through CD44 has been shown to enhance NK cell cytotoxic activity. However, little is known about the factors that regulate CD44-mediated activation of NK cells. The studies reported here reveal that resting NK cells constitutively express CD44 that is in an inactive form that does not bind to hyaluronan (HA), the principal known ligand for CD44. After infection of mice with the intracellular parasite Toxoplasma gondii, however, a population of NK cells that expressed activated CD44 emerged. To determine how expression and activation of CD44 by resting NK cells were regulated, the role of cytokines in these events was assessed. These studies revealed that whereas stimulation of resting NK cells with interleukin-12 (IL-12) or IL-18 caused increased expression of CD44, only IL-2 or IL-15 led to the upregulation and activation of CD44. The cytokine-induced upregulation and activation of CD44 was independent of NK cell proliferation. To determine the functional consequences of CD44 activation, the effects of low molecular weight HA (LMWHA) on the production of interferon-gamma (IFN-gamma) by IL-2-activated NK cells were assessed. These studies showed that HA alone had little effect on the production of IFN-gamma, but when used in combination with IL-2, IL-12, or IL-18, LMWHA was a potent enhancer of IFN-gamma production. Together, these studies indicate an important role for proinflammatory cytokines in the activation of CD44 on NK cells and identify a novel pathway to enhance the ability of activated NK cells to produce IFN-gamma.

Animals↗
PubMed2004

New lessons from old pathogens: what parasitic infections have taught us about the role of nuclear factor-kappaB in the regulation of immunity.

The nuclear factor-kappaB (NF-kappaB) family of transcription factors is activated by many infectious and inflammatory stimuli. This family regulates the expression of multiple genes, whose products include cytokines, chemokines, adhesion molecules, and antiapoptotic factors that are important components of the innate and adaptive immune response. A prominent role of NF-kappaB transcription factors in resistance to a variety of infectious diseases was revealed by studies with mice that lack individual family members. However, little is known about the basis for these effects or about the role of individual family members during a coordinated immune response to infection. Diverse parasites such as Toxoplasma gondii, Leishmania major, and Trichuris muris provide a unique opportunity to understand the role of the NF-kappaB system in the development of innate and adaptive immunity to these infections. The basis for resistance and susceptibility to these parasites is well understood, and studies using these experimental systems have provided unique insights into the role of NF-kappaB in the regulation of T-helper 1 cell (Th1) and Th2 type responses. It has become clear that NF-kappaB family members have cell lineage-specific functions and that their relative importance varies with type of infection as well as route of pathogen entry. Thus, studies with models of parasitic infection have revealed that individual NF-kappaB family members perform distinct, nonoverlapping, and biologically significant functions in the regulation of immunity and inflammation.

Animals↗
PubMed2004

The role of IL-27 in the development of T-cell responses during parasitic infections.

The recognition that CD4+ T-cell responses could be divided into at least two functional subsets either dominated by production of interferon (IFN)-gamma and associated with cell-mediated immunity (Th1) or characterized by production of interleukin (IL)-4 and IL-5 and associated with humoral immunity (Th2) provided a basis to understand the role of T cells in resistance or susceptibility to different types of pathogens. As a consequence, many studies have focused on the identification of cytokines that influence these events. For example, the development of Th1-type responses is largely dependent on IL-12. However, other cytokines also affect this process, and initial studies revealed that IL-27, a cytokine with close structural and functional similarity to IL-12, can promote Th1 responses required for immunity to Leishmania major. Subsequent work with IL-27R (WSX-1)-deficient mice infected with Toxoplasma gondii or Trypanosoma cruzi revealed that the IL-27/IL-27R system can act as a negative regulator of inflammatory T-cell responses. The aim of this review is to discuss recent studies from these laboratories on the role of IL-27 in immunity to parasitic infections in the context of previous work and to highlight the pleiotropic effects of the IL-27/IL-27R system in the development and regulation of Th1 and Th2 responses.

Animals↗
PubMed2004

TRAF6-dependent mitogen-activated protein kinase activation differentially regulates the production of interleukin-12 by macrophages in response to Toxoplasma gondii.

The production of interleukin-12 (IL-12) is critical to the development of innate and adaptive immune responses required for the control of intracellular pathogens. Many microbial products signal through Toll-like receptors (TLR) and activate NF-kappaB family members that are required for the production of IL-12. Recent studies suggest that components of the TLR pathway are required for the production of IL-12 in response to the parasite Toxoplasma gondii; however, the production of IL-12 in response to this parasite is independent of NF-kappaB activation. The adaptor molecule TRAF6 is involved in TLR signaling pathways and associates with serine/threonine kinases involved in the activation of both NF-kappaB and mitogen-activated protein kinase (MAPK). To elucidate the intracellular signaling pathways involved in the production of IL-12 in response to soluble toxoplasma antigen (STAg), wild-type and TRAF6(-/-) mice were inoculated with STAg, and the production of IL-12(p40) was determined. TRAF6(-/-) mice failed to produce IL-12(p40) in response to STAg, and TRAF6(-/-) macrophages stimulated with STAg also failed to produce IL-12(p40). Studies using Western blot analysis of wild-type and TRAF6(-/-) macrophages revealed that stimulation with STAg resulted in the rapid TRAF6-dependent phosphorylation of p38 and extracellular signal-related kinase, which differentially regulated the production of IL-12(p40). The studies presented here demonstrate for the first time that the production of IL-12(p40) in response to toxoplasma is dependent upon TRAF6 and p38 MAPK.

Animals↗
PubMed2004

Interleukin-15-deficient mice develop protective immunity to Toxoplasma gondii.

Previous studies have suggested an important role for interleukin-15 (IL-15) in resistance to and memory for Toxoplasma gondii infection. The studies presented here reveal that IL-15 is not required for infection-induced expansion of NK or CD8+ T cells. Furthermore, IL-15-/- mice develop long-term protective immunity to this pathogen.

Animals↗
PubMed2004

Development of a system to study CD4+-T-cell responses to transgenic ovalbumin-expressing Toxoplasma gondii during toxoplasmosis.

The study of the immune response to Toxoplasma gondii has provided numerous insights into the role of T cells in resistance to intracellular infections. However, the complexity of this eukaryote pathogen has made it difficult to characterize immunodominant epitopes that would allow the identification of T cells with a known specificity for parasite antigens. As a consequence, analysis of T-cell responses to T. gondii has been based on characterization of the percentage of T cells that express an activated phenotype during infection and on the ability of these cells to produce cytokines in response to complex mixtures of parasite antigens. In order to study specific CD4(+) T cells responses to T. gondii, recombinant parasites that express a truncated ovalbumin (OVA) protein, in either a cytosolic or a secreted form, were engineered. In vitro and in vivo studies reveal that transgenic parasites expressing secreted OVA are able to stimulate T-cell receptor-transgenic OVA-specific CD4(+) T cells to proliferate, express an activated phenotype, and produce gamma interferon (IFN-gamma). Furthermore, the adoptive transfer of OVA-specific T cells into IFN-gamma(-/-) mice provided enhanced protection against infection with the OVA-transgenic (but not parental) parasites. Together, these studies establish the utility of this transgenic system to study CD4(+)-T-cell responses during toxoplasmosis.

Adoptive Transfer↗
PubMed2003

Molecular acrobatics: self-assembly of calixarene-porphyrin cages.

Calix[4]arenes equipped with two and four zinc porphyrins have been prepared, and they show remarkable flexibility in their self-assembly properties with the bidentate ligand DABCO. The calix-bisporphyrin forms a 2:2 complex with DABCO, generating a large cavity that has the potential to act as a supramolecular host. The calix-tetraporphyrin, on the other hand, forms four different complexes with DABCO depending on the stoichiometry and concentration. During the course of a titration, all four complexes are populated, leading to large conformational changes and the formation of both intramolecular and intermolecular calix-tetraporphyrin-DABCO sandwich complexes. The system was fully characterized using a combination of UV-visible and (1)H NMR spectroscopy to identify the complexes. At a calix-tetraporphyrin:DABCO ratio of 2:4, the major species is dimeric cage assembly that features a large internal cavity for guest complexation.

Journal Article↗
PubMed2003

Control of effector CD8+ T cell function by the transcription factor Eomesodermin.

Activated CD8+ T cells play a critical role in host defense against viruses, intracellular microbes, and tumors. It is not clear if a key regulatory transcription factor unites the effector functions of CD8+ T cells. We now show that Eomesodermin (Eomes), a paralogue of T-bet, is induced in effector CD8+ T cells in vitro and in vivo. Ectopic expression of Eomes was sufficient to invoke attributes of effector CD8+ T cells, including interferon-gamma (IFN-gamma), perforin, and granzyme B. Loss-of-function analysis suggests Eomes may also be necessary for full effector differentiation of CD8+ T cells. We suggest that Eomesodermin is likely to complement the actions of T-bet and act as a key regulatory gene in the development of cell-mediated immunity.

Amino Acid Sequence↗
PubMed2003

Sequence-dependent DNA structure: a database of octamer structural parameters.

We have constructed the potential energy surfaces for all unique tetramers, hexamers and octamers in double helical DNA, as a function of the two principal degrees of freedom, slide and shift at the central step. From these potential energy maps, we have calculated a database of structural and flexibility properties for each of these sequences. These properties include: the values of each of the six step parameters (twist roll, tilt, rise, slide and shift), for each step of the sequence; flexibility measures for both decrease and increase in each property value from the minimum energy conformation for the central step; and the deviation from the path of a hypothetical straight octamer. In an analysis of structural change as a function of sequence length, we observe that almost all DNA tends to B-DNA and becomes less flexible. A more detailed analysis of octamer properties has allowed us to determine the structural preferences of particular sequence elements. GGC and GCC sequences tend to confer bistability, low stability and a predisposition to A-form DNA, whereas AA steps strongly prefer B-DNA and inhibit A-structures. There is no correlation between flexibility and intrinsic curvature, but bent DNA is less stable than straight. The most difficult deformation is undertwisting. The TA step stands out as the most flexible sequence element with respect to decreasing twist and increasing roll. However, as with the structural properties, this behavior is highly context-dependent and some TA steps are very straight.

DNA↗
PubMed2003

New building blocks for the assembly of sequence selective molecular zippers.

Synthetic H-bonded molecular zippers contain no sequence information that can be used to engineer the selective binding interactions characteristic of biopolymers; reversing the sense of the amide bonds in the two binding partners generates a new orthogonal recognition motif and the mutually complementary binding partners form complexes an order of magnitude more stable than the corresponding mismatch complexes.

Amino Acid Motifs↗