Biomedical subjects

Christopher A Hunter

Publications and source records attributed to Christopher A Hunter.

88 records · Page 5Linked to original sources

PubMed2002

A role for inducible costimulator protein in the CD28- independent mechanism of resistance to Toxoplasma gondii.

Long-term resistance to Toxoplasma gondii is dependent on the development of parasite-specific T cells that produce IFN-gamma. CD28 is a costimulatory molecule important for optimal activation of T cells, but CD28(-/-) mice are resistant to T. gondii, demonstrating that CD28-independent mechanisms regulate T cell responses during toxoplasmosis. The identification of the B7-related protein 1/inducible costimulator protein (ICOS) pathway and its ability to regulate the production of IFN-gamma suggested that this pathway may be involved in the CD28-independent activation of T cells required for resistance to T. gondii. In support of this hypothesis, infection of wild-type or CD28(-/-) mice with T. gondii resulted in the increased expression of ICOS by activated CD4(+) and CD8(+) T cells. In addition, both costimulatory pathways contributed to the in vitro production of IFN-gamma by parasite-specific T cells and when both pathways were blocked, there was an additive effect that resulted in almost complete inhibition of IFN-gamma production. Although in vivo blockade of the ICOS costimulatory pathway did not result in the early mortality of wild-type mice infected with T. gondii, it did lead to increased susceptibility of CD28(-/-) mice to T. gondi associated with reduced serum levels of IFN-gamma, increased parasite burden, and increased mortality compared with the control group. Together, these results identify a critical role for ICOS in the protective Th1-type response required for resistance to T. gondii and suggest that ICOS and CD28 are parallel costimulatory pathways, either of which is sufficient to mediate resistance to this intracellular pathogen.

Animals↗

PubMed2002

Substituent effects on edge-to-face aromatic interactions.

Chemical double mutant cycles have been used to measure the magnitude of edge-to-face aromatic interactions in hydrogen-bonded zipper complexes as a function of substituents on both aromatic rings. The interaction energies vary depending on the combination of substituents from +1.0 kJ mol-1 (repulsive), to -4.9 kJ mol-1 (attractive). The results correlate with the Hammett substituent constants which indicates that electrostatic interactions are responsible for the observed differences in interaction energy. The experiments can be rationalised based on local electrostatic interactions between the protons on the edge ring and the pi-electron density on the face ring as well as global electrostatic interactions between the overall dipoles on the two aromatic groups.

Amides↗

PubMed2002

An evaluation of force-field treatments of aromatic interactions.

Experimental measurements of edge-to-face aromatic interactions have been used to test a series of molecular mechanics force fields. The experimental data were determined for a range of differently substituted aromatic rings using chemical double mutant cycles on hydrogen-bonded zipper complexes. These complexes were truncated for the purposes of the molecular mechanics calculations so that problems of conformational searching and the optimisation of large structures could be avoided. Double-mutant cycles were then carried out in silico using these truncated systems. Comparison of the experimental aromatic interaction energies and the X-ray crystal structures of these truncated complexes with the calculated data show that conventional molecular mechanics force fields (MM2, MM3, AMBER and OPLS) do not perform well. However, the XED force field which explicitly represents electron anisotropy as an expansion of point charges around each atom reproduces the trends in interaction energy and the three-dimensional structures exceedingly well. Collapsing the XED charges onto atom centres or the use of semi-empirical atom-centred charges within the XED force field gives poor results. Thus the success of XED is not related to the methods used to assign the atomic charge distribution but can be directly attributed to the use of off-atom centre charges.

Amides↗

PubMed2002

NF-kappa B2 is required for optimal CD40-induced IL-12 production but dispensable for Th1 cell Differentiation.

NF-kappa B is a ubiquitously expressed transcription factor involved in the regulation of innate and adaptive immunity. As part of studies to define the role of various NF-kappa B family members in Th cell development and maintenance, we infected NF-kappa B2(-/-) and control mice with Leishmania major and followed disease progression. NF-kappa B2(-/-) mice on a normally resistant background develop chronic nonhealing lesions associated with uncontrolled parasite replication and a failure to develop an IFN-gamma response. We show that there are no intrinsic defects in Th cell differentiation in the absence of NF-kappa B2. Indeed, NF-kappa B2(-/-) T cells are able to develop a Th1 phenotype and protect recombination-activating gene(-/-) mice from progressive cutaneous leishmaniasis. We demonstrate instead that the susceptibility of NF-kappa B2(-/-) mice to L. major is the result of an IL-12 deficiency, and we provide evidence for a specific impairment in CD40-induced IL-12 production by macrophages lacking this transcription factor.

Animals↗

PubMed2002

Substituent effects on cation-pi interactions: a quantitative study.

A synthetic supramolecular complex has been adapted to quantify cation-pi interactions in chloroform by using chemical double-mutant cycles. The interaction of a pyridinium cation with the pi-face of an aromatic ring is found to be very sensitive to the pi-electron density. Electron-donating substituents lead to a strong attractive interaction (-8 kJ/mol(-1)), but electron-withdrawing groups lead to a repulsive interaction (+2 kJ/mol(-1)).

Cations↗

PubMed2002

Cutting edge: identification of c-Rel-dependent and -independent pathways of IL-12 production during infectious and inflammatory stimuli.

The production of IL-12 is required for immunity to many intracellular pathogens. Recent studies have shown that c-Rel, a member of the NF-kappaB family of transcription factors, is essential for LPS-induced IL-12p40 production by macrophages. In this study, we demonstrate that c-Rel is also required for IL-12p40 production by macrophages in response to Corynebacterium parvum, CpG oligodeoxynucleotides, anti-CD40 and low molecular weight hyaluronic acid. However, c-Rel(-/-) mice infected with Toxoplasma gondii produce comparable amounts of IL-12p40 to infected wild-type mice and have an IL-12-dependent mechanism of resistance to this infection. Furthermore, c-Rel was not required for IL-12p40 production by macrophages or dendritic cells in response to soluble Toxoplasma Ag, and neutrophils from c-Rel(-/-) mice contain normal amounts of preformed IL-12p40. Together these studies reveal the presence of c-Rel-dependent pathways critical for IL-12p40 production in response to inflammatory stimuli and demonstrate a novel c-Rel-independent pathway of IL-12p40 production during toxoplasmosis.

Animals↗

PubMed2002

Dendritic cells and immunity to leishmaniasis and toxoplasmosis.

There is increased recognition that dendritic cells (DCs) are an important source of the IL-12 required to initiate protective immunity to protozoa, such as Leishmania and Toxoplasma. This article reviews the advances made in the last two years in understanding the pathways that lead to DC activation after infection with these organisms. Interestingly, there appear to be differences in the DC activation pathways utilized by these two intracellular protozoa which also may differ from the pathways utilized by bacteria.

Animals↗

PubMed2002

Regulatory pathways involved in the infection-induced production of IFN-gamma by NK cells.

The production of interferon gamma (IFN-gamma) by natural killer (NK) cells provides an innate mechanism of resistance to many intracellular pathogens. These events are regulated by multiple cytokines and transcription factors which have both positive and negative effects. This article reviews the role of cytokines, as well as costimulatory and signaling pathways, involved in NK cell responses associated with resistance to infection.

Animals↗

PubMed2002

NF-kappaB family of transcription factors: central regulators of innate and adaptive immune functions.

Transcription factors of the Rel/NF-kappaB family are activated in response to signals that lead to cell growth, differentiation, and apoptosis, and these proteins are critical elements involved in the regulation of immune responses. The conservation of this family of transcription factors in many phyla and their association with antimicrobial responses indicate their central role in the regulation of innate immunity. This is illustrated by the association of homologues of NF-kappaB, and their regulatory proteins, with resistance to infection in insects and plants (M. S. Dushay, B. Asling, and D. Hultmark, Proc. Natl. Acad. Sci. USA 93:10343-10347, 1996; D. Hultmark, Trends Genet. 9:178-183, 1993; J. Ryals et al., Plant Cell 9:425-439, 1997). The aim of this review is to provide a background on the biology of NF-kappaB and to highlight areas of the innate and adaptive immune response in which these transcription factors have a key regulatory function and to review what is currently known about their roles in resistance to infection, the host-pathogen interaction, and development of human disease.

Animals↗

PubMed2002

Contribution of interleukin-12 (IL-12) and the CD28/B7 and CD40/CD40 ligand pathways to the development of a pathological T-cell response in IL-10-deficient mice.

The ability of interleukin-10 (IL-10) to suppress accessory cell functions required for optimal T-cell activation makes it an important inhibitor of cell-mediated immunity. Thus, after infection with the protozoan parasite Toxoplasma gondii, IL-10 knockout (KO) mice develop a CD4(+)-T-cell-dependent shock-like reaction with high levels of IL-12 and gamma interferon (IFN-gamma) in serum, leading to death of mice during the acute phase of infection. Previous studies from this laboratory have shown that simultaneous blockade of CD28 and CD40 can prevent this lethal reaction by inhibiting the production of IFN-gamma. However, the blockade of costimulation did not affect systemic levels of IL-12. To better understand the relationship between IL-12 and the CD28 and CD40 pathways in mediating immune hyperactivity, antagonists of these factors were used to determine their effects on the development of a pathological T-cell response in IL-10 KO mice. Blockade of IL-12 or the CD28/B7 interaction alone did not affect survival; however, the combined blockade of both pathways resulted in decreased production of IFN-gamma and the survival of IL-10 KO mice. To assess the role of the two ligands for CD28, B7.1 and B7.2, IL-10 KO mice were treated with alphaIL-12 plus alphaB7.1 or alphaB7.2 or the combination of all three antibodies. These studies revealed that blockade of both B7 molecules is required for decreased production of IFN-gamma and survival of infected IL-10 KO mice, suggesting that B7.1 and B7.2 can contribute to the lethal shock-like reaction in IL-10 KO mice. In contrast, neutralization of IL-12 and blockade of the CD40/CD40 ligand (CD40L) interaction in vivo did not alter the production of IFN-gamma and only resulted in a small delay in time to death of mice. Together, these data suggest that the CD28/B7 interaction has a central role in the development of a pathological T-cell response in IL-10 KO mice, which is distinct from the role of the CD40/CD40L and IL-12 pathways.

Animals↗

PubMed2002

Early enhanced Th1 response after Leishmania amazonensis infection of C57BL/6 interleukin-10-deficient mice does not lead to resolution of infection.

C3H and C57BL/6 mice are resistant to Leishmania major but develop chronic lesions with persistent parasite loads when they are infected with Leishmania amazonensis. These lesions develop in the absence of interleukin-4 (IL-4), indicating that susceptibility to this parasite is not a result of development of a Th2 response. Expression of the cytokine IL-10 during infection could account for the lack of IL-12 expression and poor cell-mediated immunity towards the parasite. Therefore, we tested the hypothesis that IL-10 plays a central role in downmodulating the Th1 response after L. amazonensis infection. Infection of C57BL/6 IL-10-deficient mice indicated that in the absence of IL-10 there was early enhancement of a Th1 response, which was downregulated during the more chronic stage of infection. In addition, although there were 1- to 2-log reductions in the parasite loads within the lesions, the parasites continued to persist, and they were associated with chronic lesions whose size was similar to that of the control lesions. These experiments indicated that L. amazonensis resistance to killing in vivo is only partially dependent on expression of host IL-10. However, IL-10-deficient mice had an enhanced delayed-type hypersensitivity response during the chronic phase of infection, indicating that there were Th1 type effector cells in vivo at this late stage of infection. These results indicate that although IL-10 plays a role in limiting the Th1 response during the acute infection phase, other immunomodulatory factors are responsible for limiting the Th1 response during the chronic phase.

Animals↗

PubMed2002

Susceptibility of interleukin-2-deficient mice to Toxoplasma gondii is associated with a defect in the production of gamma interferon.

Costimulation through the B7-CD28 interaction is an important second signal for T-cell activation, and previous studies have shown that CD28(-/-) mice infected with Toxoplasma gondii generate suboptimal CD4(+) T-cell responses, associated with a defect in production of the T-cell growth factor interleukin-2 (IL-2). To address the role of IL-2 in the expansion of T cells during toxoplasmosis, IL-2(-/-) mice were infected with T. gondii and their ability to generate a protective T-cell response was assessed. Although IL-2(-/-) mice produced normal levels of IL-12p40, they had reduced levels of gamma interferon (IFN-gamma) in serum, had an increased parasite burden, and succumbed to infection with T. gondii within 20 days. Fluorescence-activated cell sorter analysis revealed that, although uninfected IL-2(-/-) mice had an increased number of activated T cells compared with uninfected IL-2(+/+) mice, following infection they were unable to further upregulate this population. Examination of the ability of splenocytes from uninfected and infected mice to produce IFN-gamma revealed that IL-2(-/-) mice were hyporesponsive to stimulation with anti-CD3 or parasite antigen compared with wild-type mice, and the addition of IL-2 alone or in combination with IL-12 or stimulation with phorbol myristate acetate and ionomycin did not restore the production of IFN-gamma. Together, these studies reveal that IL-2(-/-) mice are unable to generate a protective IFN-gamma response following infection with T. gondii and suggest that IL-2(-/-) mice have an intrinsic defect in their ability to activate and expand IFN-gamma-producing T cells required for resistance to T. gondii.

Animals↗

PubMedDate not supplied

Genomic data analysis using DNA structure: an analysis of conserved nongenic sequences and ultraconserved elements.

Recent comparative studies of the human and mouse genomes have revealed sets of conserved nongenic sequences (CNGs) and sets of ultraconserved elements (UCEs). Both sets of sequences, which exhibit extremely high levels of conservation, extend over hundreds of bases and have no known function. Since there is no detectable sequence homology between paralogous CNGs or UCEs in either of the species, an alignment-free technique is needed for their analysis. We have previously compiled a database of the structural properties of all 32,896 unique DNA octamers, including information on stability, the minimum energy conformation, and flexibility. We have used Fourier techniques to analyze the UCEs and CNGs in terms of their octamer structural properties, to reveal structural correlations which may indicate possible functions for some of these sequences.

Animals↗

PubMedDate not supplied

Structural DNA profiles: single sequence queries.

Structural DNA profiles use the structural properties of the constituent octamers either to observe any characteristics of a single sequence that are unusual (a single sequence query) or to visualize a pattern common to a set of sequences (a multiple sequence query). They are an aid in understanding structural reasons for functional DNA activity. Profiles that answer single sequence queries are introduced and Profile Manager (a software application developed to automate profile generation) is presented. Two sequences that are similar by their nucleotide composition but are known to be very different by structure are analyzed, resulting in useful illustrations that agree with the experimental nuclear magnetic resonance structures.

Animals↗

PubMedDate not supplied

The role of cytokines and their signaling pathways in the regulation of immunity to Toxoplasma gondii.

The development of a strong cellular immune response is critical for the control of the intracellular pathogen Toxoplasma gondii. This occurs by activation of a complex, integrated immune response, which utilizes cells of the innate and adaptive immune systems. In the last two decades there have been major advances in our understanding of the role of cytokines in the initiation and maintenance of protective immunity to T. gondii, and IFN-gamma has been identified as the major mediator of resistance to this pathogen. This article provides an overview of the biology of toxoplasmosis and focuses on the pivotal role of cytokines and their signaling pathways during infection. It also addresses the role of cytokines in modulating other immune functions that are critical in determining the balance between a protective and a pathological immune response.

Animals↗

PubMedDate not supplied

An essential role of Th1 responses and interferon gamma in infection-mediated suppression of neoplastic growth.

We had previously demonstrated that in mice acute toxoplasmosis leads to systemic inhibition of angiogenesis and, consequently, strong suppression of neoplastic growth. Here we investigated the role of Th1 cytokines, in particular interferon gamma (IFN-gamma), in this phenomenon. Besides toxoplasma, neoplastic growth was readily blocked during acute infection with other Th1 response-inducing pathogens such as Listeria monocytogenes and lymphocytic choriomeningitis virus (LCMV). In contrast, chronic infection with LCMV (when Th1 responses were strongly suppressed) and acute infection with Schistosoma mansoni (when Th2 responses predominated) afforded no anti-tumor protection. To corroborate the involvement of Th1 cytokines in infection-mediated suppression of neoplastic growth, we utilized mice deficient in interleukin-10 (IL10), a suppressor of Th1 responses. When challenged with B16 cells concomitantly with toxoplasma infection, both IL10-null and wild type mice exhibited resistance to neoplastic growth. However, tumors borne by IL10-null animals were even smaller than those borne by their wild type counterparts. This enhanced resistance correlated with dramatically elevated levels of circulating IFN-gamma, a principal Th1 cytokine. Furthermore, while interleukin-12 and tumor necrosis factor a were dispensable for tumor suppression, in animals deficient in IFN-gamma production or signaling, tumor growth and neovascularization were markedly enhanced. Interestingly, the enhancement was also apparent in uninfected animals suggesting that IFN-gamma and its anti-angiogenic effects underlie both infection-dependent and -independent tumor surveillance.

Acute Disease↗