Defective cytotoxic T lymphocyte function in HIV infection

Kottilil, Shyamasundaran (1999) Defective cytotoxic T lymphocyte function in HIV infection. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (25MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The primary objective of this thesis is to determine whether cytotoxic T lymphocytes (CTL) detectable against CD4⁻ lymphocytes in vitro act in vivo to promote CD4⁻ depletion and thereby contributing to immune dysfunction and disease progression in HIV-I infected individuals. During this study, the relationship between the level of CTL activity against CD4 lymphocytes and disease progression was assessed by carrying out a series of in vitro experiments in a HIV-positive cohort of ∼70 individuals. -- It is well established that CTL use clonotypic T cell receptors (TCR) associated with the invariant CD3 signalling complex, to recognize antigenic peptides bound to major histocompatibility complex (MHC) molecules on the target cells. Since P815 cells express an FcR and Fas antigen, IgG anti-CD3 antibodies can trigger non-specific killing of P815 cells by a variety of effector cells. Comparable inhibition of cellular cytotoxicity against P815 cells by Jo-2 or by cycloheximide, a protein synthesis inhibitor preventing Fas ligand induction, confirmed that the different levels of killing of Jo-2 treated and untreated P815s reflected the extent that perforin and Fas ligand, respectively, were utilized in target cell killing. -- Abnormally high numbers of T cells from HIV-infected individuals undergo spontaneous and activation-induced cell death (AICD), and also are especially sensitive to Fas-mediated apoptosis, suggesting that Fas/Fas ligand (FasL) interactions might contribute to AICD in HIV infection. We used treatment with PMA and ionomycin to investigate the possible role of Fas/FasL interactions in AICD in HIV infection. PMA/ionomycin-induced AICD measured using Cr release, DNA analysis and electron microscopy, demonstrated that PMA and ionomycin acted synergistically to induce up to 70% release of incorporated Cr from fresh PBMC of HIV-infected individuals compared with up to 26% release by healthy volunteers. Cell death required cell-cell contact and extracellular calcium, while it did not involve Fas/FasL interactions or DNA fragmentation, but showed plasma membrane disruption with intact nuclear membranes of damaged cell. We describe a novel form of AICD in T lymphocytes from HIV-infected individuals. -- The presence, number and proportion of activated CD8+ T lymphocytes in the peripheral blood of HIV-infected individuals correlates with disease progression. We examined the associations between autoreactive CTL in the peripheral blood of HIV-infected individuals and disease progression. A significant percentage of HIV-seropositive persons (>50%) in our study cohort, in contrast to healthy individuls showed cytolysis of PHA-activated uninfected lymphocytes. These autoreactive CTL were found to be CD28⁻ CD8⁺ T cells which expanded with disease progression. A high proportion of CD28⁻ CD8⁺ T cells was seen in all HIV-infected individuals with demonstrable levels of circulating CTL. -- We have shown direct association between the autoreactivity and other markers of disease progression such as plasma viral load, CD4⁺ T-cell count, CD8⁺ T cell count, and plasma levels of β₂ microglobulin. The data is in agreement with the proposed hypothesis that these CTL actually contribute to immunodeficiency and clinical progression to AIDS. Based on our data, CTL appear to be a major contributor to disease progression. Further studies based on longitudinal follow-up of these patients may help uncover the functional significance of autoreactive CTL.

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