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R C Duke

Publications and source records attributed to R C Duke.

12 recordsLinked to original sources
PubMed1992

Apoptosis and programmed cell death in immunity.

Death of some cells in the mammalian body is clearly programmed. In the immune system there are many examples of programmed cell death, during development of lymphocytes as well as at later stages, after interaction with antigen. Many of these examples display the morphology of apoptosis: They undergo shrinkage and zeiosis, the nucleus collapses, and chromatin is cleaved into nucleosomal fragments. The cell is rapidly recognized by phagocytes and disposed of without releasing its contents. In some but not all cases of apoptosis, new macromolecular synthesis is required. Cytotoxic T cells induce changes in their targets that are morphologically apoptotic. The mechanism of apoptosis is currently under active investigation.

Animals↗
PubMed1992

Apoptosis in cytotoxic T lymphocytes and their targets.

Cytotoxic T lymphocytes have been useful not only in understanding immune responses but also in providing valuable insights into the biology and mechanism of apoptosis. In this article two examples of apoptosis directly related to cytotoxic T lymphocyte biology are discussed. These are apoptosis of activated cytotoxic T cells as a result of antigen clearance and subsequent growth factor deprivation and apoptosis of target cells following interaction with cytotoxic T lymphocytes.

Animals↗
PubMed1989

Purified perforin induces target cell lysis but not DNA fragmentation.

Rapid and extensive target cell DNA fragmentation is a unique characteristic of CTL-mediated killing. We studied the role of the granule pore-forming protein (PFP/perforin/cytolysin) of CTL in mediating lysis and DNA fragmentation of target cells. Perforin was isolated from murine CTL by sequential application of perforin-enriched granule fractions to four chromatographic columns: DEAE-Sepharose, Q-Sepharose, Polyanion SI, and Superose 12. Purified perforin was eluted as a single band of 70 kD in SDS-PAGE. While purified perforin produced potent lysis of a variety of target cells tested, it did not induce any measurable amount of DNA fragmentation. In parallel experiments, intact CTL produced marked DNA fragmentation of the same target cell populations. Our results suggest that perforin alone is not responsible for the DNA fragmentation observed during CTL-mediated killing and that other, as yet unknown, mediators or mechanisms are likely to be involved in the induction of target cell nuclear damage.

Animals↗
PubMed1989

Self recognition by T cells. I. Bystander killing of target cells bearing syngeneic MHC antigens.

Activated CTL can kill any cell to which they bind or by which they are bound. This observation has been used to determine whether alloreactive CTL can recognize cells bearing self-MHC. When activated by their specific targets, 19 CTL clones of 4 different specificities and origins killed bystander targets bearing syngeneic but not third-party MHC antigens. Using target cells derived from MHC-recombinant animals, syngeneic bystander killing was shown to be restricted to a single self MHC-encoded molecule. These results provide the first clear demonstration that T cells, or more precisely CTL, are capable of self recognition in the absence of their specific antigen. Our findings support the model that T cell repertoire selection occurs as a result of positive selection during maturation in the thymus of precursor cells whose antigen receptors have low but real affinity for self-MHC.

Animals↗
PubMed1988

Cytotoxic lymphocyte-derived lytic granules do not induce DNA fragmentation in target cells.

When target cells are exposed to CTL, they very quickly sustain nuclear damage, including DNA cleavage, and then they lyse. Nuclear damage of this type is not seen when cells are killed by antibody and C. The role of nuclear damage in the T cell-mediated killing process as well as the mechanism by which the killer cell induces this damage are unknown; however, accumulating evidence suggests that cytolysis may depend on induction of nuclear damage. The exocytosed contents of CTL granules are thought by many workers to mediate target cell lysis. We have now determined whether lytic granules also induce nuclear damage (DNA fragmentation) in cells which they lyse. They do not. In addition, no DNA fragmentation was detected in nuclei incubated with lytic granules or activated CTL. In summary, our results suggest that target cell DNA fragmentation induced by CTL is mediated neither by lytic granules nor by a CTL-derived endonuclease and support the view that the target cell is itself responsible for the internal damage it sustains.

Animals↗
PubMed1986

Differences in target cell DNA fragmentation induced by mouse cytotoxic T lymphocytes and natural killer cells.

Fragmentation of YAC-1 target cell DNA during cytolysis mediated by mouse natural killer (NK) cells and cytotoxic T lymphocytes (CTL) was compared. Cleavage of nuclear chromatin was always an extensive and early event in CTL-mediated cytolysis, whereas with NK cell-mediated killing the degree of DNA fragmentation showed an unexpected relationship to the effector:target (E:T) ratio. At low NK:YAC-1 ratios, DNA fragmentation and 51Cr release were equivalent and increased proportionately until a ratio of about 50:1 was reached; at higher ratios, 51Cr release increased as expected but DNA fragmentation decreased dramatically. Comparison of time course data at E:T ratios producing similar rates of 51Cr release showed that the target cell DNA fragmentation observed in NK killing was not nearly as rapid nor as extensive as that observed with CTL effectors. These results suggest that NK cells induce target cell injury via two different mechanisms. One mechanism would involve lysis mediated by cell-to-cell contact, while the other may induce DNA fragmentation via a soluble mediator. In support of this notion, cell-free culture supernatants containing NK cytotoxic factor (NKCF) induced DNA fragmentation in YAC-1 cells. The DNA fragments induced by NK cells and NKCF-containing supernatants consisted of oligonucleosomes indistinguishable from those induced by CTL. The results presented here show distinct differences in target cell DNA fragmentation induced by CTL and NK cells, and suggest that these two effectors use different mechanisms to achieve the same end. CTL seem to induce DNA fragmentation in their targets by direct signaling, whereas NK cells may do so by means of a soluble factor.

Animals↗
PubMed1986

IL-2 addiction: withdrawal of growth factor activates a suicide program in dependent T cells.

IL-2-dependent T effector cells usually die when deprived of growth factor. Cell death (as measured by plasma membrane breakdown) requires protein synthesis because it is inhibited by cycloheximide or emetine. When the DNA in several IL-2-dependent cell lines was examined following removal of IL-2, it was found that extensive chromatin cleavage precedes plasma membrane breakdown by several hours. The DNA fragments observed were not randomly generated but consisted of oligonucleosomes. This suggests that IL-2 deprivation led to activation of an endonuclease with specificity for linker DNA. DNA fragmentation, like cell death, did not occur in the presence of protein synthesis inhibitors. The protein(s) synthesized in response to IL-2 deprivation may, therefore, be the endonuclease or its activator; none of the IL-2-dependent T cells examined contain detectable endogenous endonuclease prior to IL-2 removal. DNA fragments were also found in vivo in lymph node cells draining a site of antigen administration. These results suggest that one aspect of the termination of immune responses involves activation of a cell suicide program in the expanded effector T cell clones. In this program an endonuclease is activated and chromatin is cleaved; as a result macromolecular synthesis begins to wind down so that repair synthesis stops; within a few hours, the cell lyses.

Animals↗