Biomedical subjects

John T Harty

Publications and source records attributed to John T Harty.

9 recordsLinked to original sources

PubMed2024

Immunopeptidomics Mapping of Listeria monocytogenes T Cell Epitopes in Mice.

Listeria monocytogenes is a foodborne intracellular bacterial model pathogen. Protective immunity against Listeria depends on an effective CD8+ T cell response, but very few T cell epitopes are known in mice as a common animal infection model for listeriosis. To identify epitopes, we screened for Listeria immunopeptides presented in the spleen of infected mice by mass spectrometry-based immunopeptidomics. We mapped more than 6000 mouse self-peptides presented on MHC class I molecules, including 12 high confident Listeria peptides from 12 different bacterial proteins. Bacterial immunopeptides with confirmed fragmentation spectra were further tested for their potential to activate CD8+ T cells, revealing VTYNYINI from the putative cell wall surface anchor family protein LMON_0576 as a novel bona fide peptide epitope. The epitope showed high biological potency in a prime boost model and can be used as a research tool to probe CD8+ T cell responses in the mouse models of Listeria infection. Together, our results demonstrate the power of immunopeptidomics for bacterial antigen identification.

Animals↗

PubMed2003

Regulation of CD8+ T cells undergoing primary and secondary responses to infection in the same host.

Naive Ag-specific CD8(+) T cells expand, contract, and become memory cells after infection and/or vaccination. Memory CD8(+) T cells provide faster, more effective secondary responses against repeated exposure to the same pathogen. Using an adoptive transfer system with low numbers of trackable nontransgenic memory CD8(+) T cells, we showed that secondary responses can be comprised of both primary (naive) and secondary (memory) CD8(+) T cells after bacterial (Listeria monocytogenes) and/or viral (lymphocytic choriomeningitis virus) infections. The level of memory CD8(+) T cells present at the time of infection inversely correlated with the magnitude of primary CD8(+) T cell responses against the same epitope but directly correlated with the level of protection against infection. However, similar numbers of Ag-specific CD8(+) T cells were found 8 days postinfection no matter how many memory cells were present at the time of infection. Rapid contraction of primary CD8(+) T cell responses was not influenced by the presence of memory CD8(+) T cells. However, contraction of secondary CD8(+) T cell responses was markedly prolonged compared with primary responses in the same host mice. This situation occurred in response to lymphocytic choriomeningitis virus or L. monocytogenes infection and for CD8(+) T cell responses against multiple epitopes. The delayed contraction of secondary CD8(+) T cells was also observed after immunization with peptide-coated dendritic cells. Together, the results show that the level of memory CD8(+) T cells influences protective immunity and activation of naive precursors specific for the same epitope but has little impact on the magnitude or program of the CD8(+) T cell response.

Adoptive Transfer↗

PubMed2003

Viral infection results in massive CD8+ T cell expansion and mortality in vaccinated perforin-deficient mice.

Perforin-mediated cytotoxicity is essential for clearance of primary LCMV infection. BALB/c-perforin-deficient (PKO) mice survived LCMV infection by deleting NP(118)-specific CD8(+) T cells whereas vaccination of PKO mice with Listeria expressing NP(118) generated a stable memory CD8(+) T cell population. However, >85% of vaccinated BALB/c-PKO mice died after LCMV infection. Mortality was associated with enormous expansion of NP(118)-specific CD8(+) T cells in both lymphoid and nonlymphoid tissues and aberrant CD8(+) T cell cytokine production. Depletion of CD8(+) T cells or treatment with anti-IFNgamma antibody rescued vaccinated mice from mortality. Thus, perforin was essential for resistance to secondary LCMV infection, and, in the absence of perforin, vaccination resulted in lethal disease mediated by dysregulated CD8(+) T cell expansion and cytokine production.

Animals↗

PubMed2003

Memory lanes.

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Animals↗

PubMed2002

Quantitation of CD8+ T cell expansion, memory, and protective immunity after immunization with peptide-coated dendritic cells.

Dendritic cells (DCs) are potent APCs for naive CD8(+) T cells and are being investigated as vaccine delivery vehicles. In this study, we examine the CD8(+) T cell response to defined peptides from Listeria monocytogenes (LM), lymphocytic choriomeningitis virus, and murine CMV coated singly and in combination onto mature bone marrow-derived DCs (BMDCs). We show that immunization of mice with 2 x 10(5) mature BMDCs coated with multiple MHC class I peptides generates a significant Ag-specific CD8(+) T cell response in both the spleen and nonlymphoid organs. This immunization resulted in a peptide-specific hierarchy in the magnitude of CD8(+) T cell priming and noncoordinate kinetics in response to different peptide epitopes. Kinetics were not exclusively due to specific characteristics of the MHC class I molecule, and were not altered in an Ag-independent manner by concurrent LM infection. Mice immunized with listeriolysin O 91-99-coated BMDCs are protected against high dose challenge with virulent LM. This protection was enhanced by diversifying the memory CD8(+) T cell compartment, even in the absence of a large increase in Ag-specific CD8(+) memory T cells.

Animals↗

PubMed2002

Programmed contraction of CD8(+) T cells after infection.

The extent of infection and rate of pathogen clearance are thought to determine both the magnitude of antigen-specific CD8(+) T cell expansion and the ensuing contraction to a stable number of memory cells. We show that CD8(+) T cell expansion after Listeria monocytogenes infection was primarily dependent on the initial infection dose or amount of antigen displayed, and was also influenced by the rate of pathogen clearance. However, the onset and kinetics of CD8(+) T cell contraction after L. monocytogenes and lymphocytic choriomeningitis virus infections were independent of the magnitude of expansion, dose and duration of infection or amount of antigen displayed. Thus, major features of antigen-specific CD8(+) T cell homeostasis, including the contraction phase of an immune response, may be programmed early after infection.

Animals↗

PubMed2002

Influence of effector molecules on the CD8(+) T cell response to infection.

Expansion and contraction of antigen-specific CD8(+) T cells after infection or vaccination results in stable memory. Recent evidence demonstrates that anti-microbial effector molecules such as perforin and IFN-gamma regulate specific aspects of CD8(+) T cell homeostasis by mechanisms that may be dependent or independent of pathogen clearance.

Animals↗

PubMed2002

CD8(+) T-cell homeostasis after infection: setting the 'curve'.

Antigen (Ag)-specific CD8(+) T-cell responses exhibit remarkably similar kinetics after different types of infection. Starting from levels that are virtually undetectable in vivo, pathogen-specific naïve CD8(+) T cells are precisely regulated to go through rapid expansion and contraction (death) phases, achieving memory levels of Ag-specific CD8(+) T cells that are maintained for the life of the host. However, the exact mechanisms used to achieve appropriate and reproducible CD8(+) T-cell homeostasis in response to diverse pathogens remain to be determined. The possibility that early events after infection regulate major features of Ag-specific CD8(+) T-cell homeostasis will be discussed here.

Animals↗

PubMed2002

CD8(+)-T-cell response to secreted and nonsecreted antigens delivered by recombinant Listeria monocytogenes during secondary infection.

Understanding how existing antivector immunity impacts live vaccine delivery systems is critical when the same vector system may be used to deliver different antigens. We addressed the impact of antivector immunity, elicited by immunization with attenuated actA-deficient Listeria monocytogenes, on the CD8(+)-T-cell response to a well-characterized lymphocytic choriomeningitis virus epitope, NP118-126, delivered by infection with recombinant L. monocytogenes. Challenges of immune mice with actA-deficient and with wild-type recombinant L. monocytogenes generated similar numbers of CD8(+) T cells specific for the NP118-126 epitope. High-dose immunization with actA-deficient L. monocytogenes resulted in substantial numbers of CD8(+) T cells specific for the L. monocytogenes LLO91-99 epitope in the effector and memory stages of the T-cell response. Challenge of these immune mice with recombinant L. monocytogenes resulted in rapid control of the infection and decreased CD8(+)-T-cell responses against both the secreted and nonsecreted form of the recombinant antigen compared to the response of naïve mice. In contrast, mice immunized with a low dose of actA-deficient L. monocytogenes had approximately 10-fold fewer effector and memory T cells specific for LLO91-99 and a substantially higher CD8(+)-T-cell response against the recombinant antigen after challenge with recombinant L. monocytogenes. Although mice immunized with low-dose actA-deficient L. monocytogenes had a substantial recall response to LLO91-99, which reached the same levels by 5 to 7 days postchallenge as that in high-dose-immunized mice, they exhibited decreased ability to control L. monocytogenes replication. Thus, the level of antivector immunity impacts the control of infection and efficiency of priming responses against new antigens introduced with the same vector.

Animals↗