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Biomedical subjects

A Gallimore

Publications and source records attributed to A Gallimore.

At least 19 recordsLinked to original sources
PubMed2001

Normal pathogen-specific immune responses mounted by CTLA-4-deficient T cells: a paradigm reconsidered.

CTLA-4 is a critical negative regulator of T cell responses and CTLA-4-deficient (CTLA-4(-/-)) mice die of a lymphproliferative disease. Nevertheless, RAG-2-deficient mice reconstituted with a mixture of CTLA-4(-/-) and normal (CTLA-4(+/+)) bone marrow survive in the absence of any signs of disease, although 50% of their T cells do not express CTLA-4. Using such mixed chimeras, we analyzed the role of CTLA-4 in specific T cell responses to lymphocytic choriomeningitis virus, Leishmania major and mouse mammary tumor virus, which cause acute, chronic and persistent infections, respectively. The populations of antigen-specific CTLA-4(-/-)CD4(+) and CTLA-4(-/-)CD8(+) T cells became activated, expanded and contracted indistinguishably from CTLA-4(+/+)CD4(+) and CTLA-4(+/+)CD8(+) T cells after infection with all three pathogens. Thus, CTLA-4 is not involved in the down-regulation of specific T cell responses and peripheral deletion in a T cell-autonomous fashion.

Abatacept↗
PubMed2001

Deletion of the CD4 silencer element supports a stochastic mechanism of thymocyte lineage commitment.

The mechanism of T cell lineage commitment remains controversial; to examine it we deleted the CD4-silencer element in the germ line of a mouse using a combination of gene targeting and Cre/LoxP-mediated recombination. We found that these mice were unable to extinguish CD4 expression either in immature thymocytes or mature CD8+ cytotoxic T cells (CTLs), which resulted in the development of major histocompatibility complex class II-restricted double-positive CTLs in the periphery. This finding strongly supports a stochastic over an instructive mechanism of coreceptor down-regulation.

Animals↗
PubMed2000

Induction of antigen-specific CD8+ T cells, T helper cells, and protective levels of antibody in humans by particle-mediated administration of a hepatitis B virus DNA vaccine.

A DNA vaccine against the hepatitis B virus (HBV) was evaluated for safety and induction of immune responses in 12 healthy, hepatitis-naïve human volunteers using the needle-free PowderJect system to deliver gold particles coated with DNA directly into cells of the skin. Three groups of four volunteers received three administrations of DNA encoding the surface antigen of HBV at one of the three dose levels (1, 2, or 4 microg). The vaccine was safe and well tolerated, causing only transient and mild to moderate responses at the site of administration. HBV-specific antibody and both CD4+ and CD8+ T cell responses were measured before and after each immunization. All the volunteers developed protective antibody responses of at least 10 mIU/ml. In volunteers who were positive for the HLA class I A2 allele, the vaccine also induced antigen-specific CD8+ T cells that bound HLA-A2/HBsAg(335-343) tetramers, secreted IFN-gamma, and lysed target cells presenting a hepatitis B surface antigen (HBsAg) CTL epitope. Enumeration of HBsAg-specific T cells producing cytokine indicated preferential induction of a Type 1 T helper cell response. These results provide the first demonstration of a DNA vaccine inducing protective antibody titers and both humoral and cell-mediated immune responses in humans.

Adult↗
PubMed2000

Inducible costimulator protein (ICOS) controls T helper cell subset polarization after virus and parasite infection.

It has been shown that certain pathogens can trigger efficient T cell responses in the absence of CD28, a key costimulatory receptor expressed on resting T cells. Inducible costimulator protein (ICOS) is an inducible costimulator structurally and functionally related to CD28. Here, we show that in the absence of CD28 both T helper cell type 1 (Th1) and Th2 responses were impaired but not abrogated after infection with lymphocytic choriomeningitis virus (LCMV), vesicular stomatitis virus (VSV), and the nematode Nippostrongylus brasiliensis. Inhibition of ICOS in CD28-deficient mice further reduced Th1/Th2 polarization. Blocking of ICOS alone had a limited but significant capacity to downregulate Th subset development. In contrast, cytotoxic T lymphocyte (CTL) responses, which are regulated to a minor and major extent by CD28 after LCMV and VSV infection, respectively, remained unaffected by blocking ICOS. Together, our results demonstrate that ICOS regulates both CD28-dependent and CD28-independent CD4(+) subset (Th1 and Th2) responses but not CTL responses in vivo.

Animals↗
PubMed2000

Functionally distinct CD8+ memory T cell subsets in persistent EBV infection are differentiated by migratory receptor expression.

Human memory T lymphocytes have recently been re-defined as central or effector memory cells (Sallusto, F., Lenig, D., Forster, R., Lipp, M. and Lanzavecchia, A., Nature 1999. 401: 708-712). Effector memory cells (T(em)) are targeted to the peripheral tissues and show rapid effector function in response to antigenic stimulation. Central memory (T(cm)) cells are targeted to the lymph nodes and cannot be immediately activated. In this report HLA-A2-Epstein-Barr virus (EBV) peptide tetramers have been used to characterize the EBV-specific CD8+ T cell subsets in persistent EBV infection. In short-term activation studies two populations of tetramer-positive T cells were identified. One group resembled T(em) cells in that they rapidly produced IFN-gamma and lacked the lymph node homing receptor, CD62L, the second was similar to T(cm) cells since they were CD62L+ but could not be immediately induced to express IFN-gamma.

Antigens, CD↗
PubMed2000

MHC class I-restricted killing of neurons by virus-specific CD8+ T lymphocytes is effected through the Fas/FasL, but not the perforin pathway,.

Induction of MHC class I genes in neurons of the central nervous system requires signals by pro-inflammatory cytokines, in particular IFN-gamma, and the blockade of electric activity, which is known to suppress induction of MHC related genes in a highly ordered, but unusual fashion [1], [2]. The present experiments explore the immunological function of neuronal MHC class I antigens expressed under permissive conditions. MHC class I proteins were induced in electrically silenced murine hippocampal neurons by treatment with the sodium channel blocker tetrodotoxin and recombinant IFN-gamma, conditions which also resulted in the induction of Fas molecules. The MHC class I positive neurons were challenged with CD8+ cytotoxic T lymphocytes (CTL) specific for the H2-Db binding peptide GP33, a dominant epitope of the lymphocytic choriomeningitis virus envelope glycoprotein, or with alloreactive CTL. Single primed neurons, attacked by GP33-specific CTL, were continuously monitored for changes in intracellular calcium ([Ca2+]i), an indicator of cytotoxic damage. MHC class I-induced neurons pulsed with the GP33 peptide, but not a control peptide, showed a gradual and sustained increase in [Ca2+]i within 3 h following attack by GP33-specific CTL, while in astrocytes [Ca2+]i elevation was rapid. The slow course of the neuronal response was consistent with a delayed apoptotic killing mechanism rather than rapid granule-mediated plasma membrane lysis. Indeed, the attacked neurons bound annexin V, indicating membrane alterations preceding apoptotic cell death. In further support of apoptotic cell death, this sustained increase of [Ca2+]i levels was also observed following attack by perforin-deficient CTL, but was not detected in neurons derived from mutant lpr mice, which lack functional Fas molecules.

Animals↗
PubMed1999

Developmental regulation of Lck targeting to the CD8 coreceptor controls signaling in naive and memory T cells.

The question of whether enhanced memory T cell responses are simply due to an increased frequency of specific cells or also to an improved response at the single cell level is widely debated. In this study, we analyzed T cell receptor (TCR) transgenic memory T cells and bona fide memory T cells isolated from virally infected normal mice using the tetramer technology. We found that memory T cells are qualitatively different from naive T cells due to a developmentally regulated rearrangement of the topology of the signaling machinery. In naive cytotoxic T cells, only a few CD8 molecules are associated with Lck and the kinase is homogeneously distributed inside the cell. However, in vivo priming of naive T cells induces the targeting of Lck to the CD8 coreceptor in the cell membrane and the consequent organization of a more efficient TCR signaling machinery in effector and memory cells.

Acetyltransferases↗
PubMed1999

Effect of epitope flanking residues on the presentation of N-terminal cytotoxic T lymphocyte epitopes.

We here demonstrate that placing two distinct influenza virus nucleoprotein epitopes at the N terminus of a cytosolic protein selectively blocks their presentation to specific cytotoxic T lymphocytes. The block is a cytosolic phenomenon, which can be overcome by distancing the epitope from the protein N terminus by two or more amino acids. Shortening the protein's C terminus fails to relieve the antigen presentation block. These results demonstrate that events at the N terminus of the target protein, rather than at its C terminus, are responsible for the lack of presentation of N-terminal epitopes. We also show that lack of presentation of N terminal epitopes is associated with a modification of the target protein which affects its electrophoretic mobility and isoelectric focusing point. This modification can be prevented by mutating the epitope's N-terminal flanking sequence, which results in an efficient presentation of the N-terminal epitope. Lack of presentation of the N-terminal epitopes results in a reduced ability of influenza-primed mice to clear acute infection with vaccinia virus encoding an N-terminal nucleoprotein epitope. Our results demonstrate that presentation of epitopes localized at the N terminus of cytosolic proteins can be modulated by events occurring at early stages of antigen processing.

Animals↗
PubMed1999

OX40-deficient mice are defective in Th cell proliferation but are competent in generating B cell and CTL Responses after virus infection.

OX40, a member of the TNF receptor superfamily, is expressed on activated T cells and implicated in stimulation of T cells and T-dependent humoral responses. We generated OX40-/- mice and found that the formation of extrafollicular plasma cells, germinal centers, and antibody responses was independent of OX40. After infection with LCMV and influenza virus, OX40-/- mice retain primary and memory cytotoxic T cell responses with normal expansion and decline of specific CTL. In contrast, CD4+ T cell proliferation and the number of IFN-gamma-producing CD4+ T cells were reduced in OX40-/- mice. Moreover, the number of CD4+ T cells infiltrating the lungs of influenza virus-infected OX40-/- mice was reduced. These results define a unique role of OX40 in the generation of optimal CD4+ T cell responses in vivo.

Animals↗
PubMed1998

Protective immunity does not correlate with the hierarchy of virus-specific cytotoxic T cell responses to naturally processed peptides.

Infection of C57BL/6 mice with lymphocytic choriomeningitis virus (LCMV) stimulates major histocompatibility complex class I-restricted cytotoxic T cells (CTLs), which normally resolve the infection. Three peptide epitopes derived from LCMV have been shown to bind the mouse class I molecule H-2 Db and to stimulate CTL responses in LCMV-infected mice. This report describes the identity and abundance of each CTL epitope after their elution from LCMV-infected cells. Based on this information, peptide abundance was found to correlate with the magnitude of each CTL response generated after infection with LCMV. Subsequent experiments, performed to determine the antiviral capacity of each CTL specificity, indicate that the quantitative hierarchy of CTL activity does not correlate with the ability to protect against LCMV infection. This report, therefore, indicates that immunodominant epitopes should be defined, not only by the strength of the CTL response that they stimulate, but also by the ability of the CTLs to protect against infection.

Adoptive Transfer↗
PubMed1998

Induction and exhaustion of lymphocytic choriomeningitis virus-specific cytotoxic T lymphocytes visualized using soluble tetrameric major histocompatibility complex class I-peptide complexes.

This study describes the construction of soluble major histocompatibility complexes consisting of the mouse class I molecule, H-2Db, chemically biotinylated beta2 microglobulin and a peptide epitope derived from the glycoprotein (GP; amino acids 33-41) of lymphocytic choriomeningitis virus (LCMV). Tetrameric class I complexes, which were produced by mixing the class I complexes with phycoerythrin-labeled neutravidin, permitted direct analysis of virus-specific cytotoxic T lymphocytes (CTLs) by flow cytometry. This technique was validated by (a) staining CD8+ cells in the spleens of transgenic mice that express a T cell receptor (TCR) specific for H-2Db in association with peptide GP33-41, and (b) by staining virus-specific CTLs in the cerebrospinal fluid of C57BL/6 (B6) mice that had been infected intracranially with LCMV-DOCILE. Staining of spleen cells isolated from B6 mice revealed that up to 40% of CD8(+) T cells were GP33 tetramer+ during the initial phase of LCMV infection. In contrast, GP33 tetramers did not stain CD8+ T cells isolated from the spleens of B6 mice that had been infected 2 mo previously with LCMV above the background levels found in naive mice. The fate of virus-specific CTLs was analyzed during the acute phase of infection in mice challenged both intracranially and intravenously with a high or low dose of LCMV-DOCILE. The results of the study show that the outcome of infection by LCMV is determined by antigen load alone. Furthermore, the data indicate that deletion of virus-specific CTLs in the presence of excessive antigen is preceded by TCR downregulation and is dependent upon perforin.

Animals↗
PubMed1998

A protective cytotoxic T cell response to a subdominant epitope is influenced by the stability of the MHC class I/peptide complex and the overall spectrum of viral peptides generated within infected cells.

This study identifies instability of MHC class I/peptide complexes and intermolecular competition for MHC class I presentation as factors responsible for the subdominance of cytotoxic T lymphocyte (CTL) epitopes. This evidence is based on the characterization of a new CTL epitope derived from the glycoprotein (GP) of lymphocytic choriomeningitis virus (LCMV). This epitope, peptide GP117-125 (GP117) is presented to T cells by the mouse MHC class I molecule, H-2Db. In short-term experiments induction of GP117-specific CTL by vaccination rendered C57BL/6 mice only partially resistant to infection with wild-type LCMV (LCMV-WE) but completely resistant to challenge with a previously described LCMV variant. The variant virus, LCMV-8.7B23, bears point mutations within both known LCMV-GP, H-2 Db-restricted epitopes GP33-41 (GP33) and GP276-286 (GP276) resulting in a valine to leucine change at position 35 in peptide GP33 (V35L) and an asparagine to serine change at position 280 in peptide GP276 (N280S). Although variant peptide GP33/V35L stimulates a weak CTL response, GP276/N280S does not. Elution of peptide GP117 from both LCMV-WE- and LCMV-8.7B23-infected cells revealed that the difference in the capacity of GP117-specific CTL to protect against LCMV-WE and the virus variant LCMV-8.7B23 was due to differences in the level of GP117 presentation on the surface of both types of cells. Thus, it appears that the protective capacity of CTL specific for the subdominant epitope GP117 is influenced by the extent of presentation of other immunodominant peptide epitopes present within infected cells.

Animals↗
PubMed1998

The proteasome inhibitor lactacystin prevents the generation of an endoplasmic reticulum leader-derived T cell epitope.

The presentation of viral antigens on MHC class I molecules requires their intracellular fragmentation into peptides of appropriate length and anchor residue positions. Evidence has accumulated that the proteasome is the endoprotease in charge of the generation of MHC class I ligands in the cytoplasm. The generation of T cell epitopes derived from the leader peptides of endoplasmic reticulum (ER) targeted proteins, however. has been reported to be independent of the proteasome. Here we show that the H-2Db restricted antigen presentation of the immunodominant T cell epitope derived from the ER leader of the glycoprotein of lymphocytic choriomeningitis virus (LCMV) is completely abolished by administration of the proteasome inhibitor lactacystin. Thus our data support the role of the proteasome in class I restricted antigen processing and extend it to an ER leader derived epitope from a viral glycoprotein.

Acetylcysteine↗
PubMed1998

Hierarchies of antigen-specific cytotoxic T-cell responses.

Studies carried out using either mice or humans have shown that cytotoxic T-lymphocyte (CTL) responses to many different pathogenic organisms often comprise CTL specific for multiple class I-restricted peptide epitopes. Differences in the magnitude of epitope-specific CTL responses appear to arise mainly from differences in the expression level of the corresponding class I/peptide complex on the surface of the antigen-presenting cell. The size of the CTL response may be limited by the frequency and possibly by the affinity of specific CTL precursors in the naive T-cell pool. Thus, both the efficiency of antigen processing and the composition of the peripheral T-cell pool impose direct limitations on the extent of a T-cell response to a given peptide epitope. Studies of CTL hierarchies have resulted in the identification of immunodominant epitopes i.e. peptide epitopes which stimulate the largest number of specific CTL and which are therefore generally believed to offer the best level of protection against the pathogen from which they were derived. It is also thought that CTL responses to non-dominant epitopes mediate protection against pathogenic challenge. These ideas are considered here with respect to experimental data collected following infection of mice with lymphocytic choriomeningitis virus.

Animals↗
PubMed1996

Cytotoxic T cells--protection from disease progression--protection from infection.

We briefly review current evidence which indicates that major histocompatibility complex (MHC)-restricted, virus-specific cytotoxic T cells may be of immunological importance in protection from infection with immunodeficiency virus or with protection from disease progression which would finally result in acquired immunodeficiency syndrome (AIDS) and death. We suggest that prophylactic vaccines should elicit cytotoxic T lymphocyte (CTL) activity in naive individuals. Further, immunotherapy in infected individuals could be aimed at ensuring that levels of virus-specific CTL are kept high, broadening and redirecting their specificity towards conserved parts of the viral genome.

Acquired Immunodeficiency Syndrome↗
PubMed1995

The MHC E locus in macaques is polymorphic and is conserved between macaques and humans.

Although the functions of the molecules encoded by the classical MHC class I loci are well defined, no function has been ascribed to the molecules encoded by the non-classical MHC class I loci. To investigate the evolution and conservation of the non-classical loci, we cloned and sequenced HLA-E homologues in macaques. We isolated four E locus alleles from five rhesus monkeys and two E locus alleles from one cynomolgus monkey, which indicated that the E locus in macaques is polymorphic. We also compared the rate of nucleotide substitution in the second intron of the macaque and human E locus alleles with that of exons two and three. The rate of nucleotide substitution was significantly higher in the introns, which suggested that the E locus has evolved under selective pressure. Additionally, comparison of the rates of synonymous and non-synonymous substitutions in the peptide binding region versus the remainder of the molecule suggested that the codons encoding the amino acids in the peptide binding region had been conserved in macaques and humans over the 36 million years since macaques and humans last shared a common ancestor.

Amino Acid Sequence↗