| In this dissertation, I investigate the methods employed by HIV-1 to cause depletion of CD4+ cells within the lymphoid organ. Human ex-vivo tissue models for infection provide a relevant microenvironment for studying acute infection and subsequent pathogenesis, with only the influence of an innate immune response. Two viral isolates obtained from a rapid progressor patient with significantly different pathogenic phenotypes have been used to identify mechanisms of HIV-1-mediated cell death. The two isolates have significant sequence homology, particularly in the envelope (Env) region. However, isolate R3A demonstrates enhanced fusion as well as enhanced pathogenesis in both relevant in-vivo and ex-vivo organ model systems when compared to isolate R3B. Interestingly, when fusion is inhibited, R3A demonstrates pathogenic abilities through a bystander killing method as well.;Analysis of Env proteins both in vitro and ex vivo demonstrates that enhanced Env-mediated fusion (determined by the C-terminal Heptad Repeat off gp41) contributes significantly to the distinct pathogenicity observed by the pathogenic R3A Env isolate, while CXCR4-binding affinity does not correlate with pathogenicity. In the absence of Env-mediated fusion, however, it is also observed that the pathogenic HIV Env continues to deplete cells. Further analysis of these findings demonstrated the role of the HIV Env V1/V2 domain upon activation of plasmacytoid dendritic cells (presumably due to enhanced CD4 binding affinity), which then induce bystander killing of uninfected lymphocytes.;Finally, I examine the role that the HIV-1 Nef protein plays (in concert with an Env of high CD4 binding affinity) to activate the host innate immune response, which likely contributes to the observed bystander cell death phenotype. This analysis suggests that the Nef protein may enhance HIV Env expression on the surface of virus-producing cells and hence on budded virions, which can then more robustly activate pDCs.;The findings from these studies aim to elucidate the mechanisms of pathogenicity utilized by a particularly pathogenic HIV Env isolated from a rapid progressor patient. These mechanisms shed light upon the nature of pathogenic viruses in total, and will hopefully aid in the development of therapy options for HIV-infected patients in the future. |
