Toll-Like Receptor Responses in Peripheral Blood Mononuclear Cells of HIV Exposed Seronegative Female Commercial Sex Workers from Nairobi Kenya
Omange, Robert Were
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The innate immune system is at the interface between the host's immune system and the initial contact with HIV. Understanding the correlates of innate immune protection against Human Immunodeficiency Virus is an important goal for development of effective anti-HIV therapies or vaccines. Not all exposures to HIV end in infection. The innate immune system has been linked to the reduced susceptibility of HIV-exposed seronegative (HESN) female commercial sex workers in Kenya by a number of studies. This thesis is a comparison of Toll-like receptor (TLR) responses in different immune cells in peripheral blood mononuclear cells (PBMCs) from HESN and HIV negative (susceptible) female commercial sex workers (CSWs). This study tested the hypothesis that higher TLR8 responsiveness in PBMCs of HESN to ssRNA analogous to HIV's genetic material, would result in higher effector responses capable of making HIV target cells more refractory in vitro, compared to susceptible controls. The results showed that PBMCs of HESN were often hypo-responsive to TLR4 and TLR7 stimulations evidenced by often reduced cytokine responses to the corresponding ligands, but hyper-responsive to TLR8 following stimulation with ssRNA analogous to HIV's genetic material. The 'dichotomy' in TLR responsiveness of HESN PBMCs was associated with differential expression of cognate TLRs in PBMCs, and altered activation of TLR signalling pathways. The opposing pattern of TLR7 and TLR8 responsiveness corresponded to the ability of HIV to infect target cells in vitro; where pre-treatment of PBMCs with TLR7 enhanced HIV replication whereas TLR8 stimulation inhibited HIV replication. The differences in outcomes of the HIV infection assays were associated with distinct cytokine profiles, where TLR7 stimulation induced robust type I IFNs responses without proinflammatory TNF-α and IL-12 cytokine responses,while TLR8 stimulations produced type II IFN responses accompanied by robust proinflammatory responses in both groups. The cytokine milieu of HESN PBMCs prior to and following TLR4 and TLR8 stimulations was more tightly regulated, but was associated with higher activation of CD8+, NK cells, monocytes but not blood DCs. These results demonstrate that the lower activation or 'quiescent' state of HESN PBMCs did not limit the ability of their cells to recognize ssRNA analogous to HIV derived genetic material and mount potent responses capable of limiting HIV infection in vitro, supporting the overall hypothesis tested. This thesis contributes to the growing knowledge on the dichotomous outcomes between TLR7 and TLR8 treatments with respect to HIV infection that could be instrumental in the design of novel HIV inventions such as vaccines or microbicides.