Publication Date

2015-09-02

Availability

Open access

Embargo Period

2015-09-02

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Microbiology and Immunology (Medicine)

Date of Defense

2015-08-20

First Committee Member

Mario Stevenson

Second Committee Member

Geoffrey W. Stone

Third Committee Member

David I. Watkins

Fourth Committee Member

Savita G. Pahwa

Fifth Committee Member

Michal J. Toborek

Sixth Committee Member

Enrique A. Mesri

Seventh Committee Member

Susana T. Valente

Abstract

SIV–specific CD8+ T cells kill SIV–infected CD4+ T cells in an MHC Class I (MHC–I) dependent manner. However, they are reportedly less efficient at killing SIV–infected macrophages. Since the viral accessory protein, Nef, has been shown to down–regulate MHC–I molecules and enhance CTL evasion in HIV–1 infected CD4+ T cells, we examined whether Nef played a role in protecting SIV–infected macrophages from killing by SIV–specific CD8+ T cells. To explore the role of Nef in CD8+ T cell evasion, we compared the ability of freshly sorted SIV–specific CD8+ T cells to readily suppress viral replication or eliminate CD4+ T cells or monocyte–derived macrophages infected with SIV variants containing wild–type (WT) or mutated nef genes. In Chapter 3, we show that SIV–specific CD8+ T cells suppressed viral replication and eliminated the majority of SIV–infected CD4+ T cells. Additionally, suppression of viral replication was enhanced in CD4+ T cells infected with a SIV harboring a nef variant containing a point mutation (Y223F) that has been shown to impair MHC–I down–regulation. However, infection with the Y223F Nef variant did not promote killing of macrophages by freshly sorted SIV–specific CD8+ T cells. Furthermore, we show elimination of WT–infected macrophages by CD8+ T cells lines in a MHC–I dependent manner. These results suggest that mechanisms other than Nef–mediated MHC–I down–regulation govern the resistance of SIV–infected macrophages to killing by freshly sorted CD8+ T cells. Chapter 4 evaluates the ability of freshly sorted SIV–specific CD8+ T cells to kill macrophages infected with a nef deletion mutant (∆nef). Despite the fact that ∆nef restored the MHC–I expression, it did not sensitize infected macrophages to CD8+ T cell elimination or suppression of viral replication after 24 h of co–culture. Thus, we show that although macrophages infected with SIV nef mutants that increase MHC–I expression, and entirely disrupt Nef function, this is not sufficient to impact their sensitivity to CD8+ T cell killing, as observed in infected CD4+ T cells. Therefore, these results suggest that Nef appears neither necessary nor sufficient for the resistance of infected macrophages to elimination or suppression of viral replication by “unstimulated” freshly sorted SIV–specific CD8+ T cells. This study has implications for viral persistence and suggests that macrophages may afford primate lentiviruses some degree of protection from immune surveillance.

Keywords

macrophages; SIV; CD8; Suppression

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