Author ORCID Identifier

https://orcid.org/0000-0003-4668-4367

Date Available

12-18-2025

Year of Publication

2024

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy (PhD)

College

Medicine

Department/School/Program

Molecular and Cellular Biochemistry

Advisor

Sidney W. Whiteheart

Abstract

Aside from their classical role in maintaining hemostasis, platelets are considered first-line vascular guardians that influence both the innate and adaptive immune systems. This is mediated by either direct interactions with immune cells or through the release of pre-stored cytokines and chemokines upon interacting with pathogens such as viruses. While this establishes platelets as potential players in the response to pathogens, it remains unclear what platelets can do with pathogens and how important that is to immune responses, especially against viruses. Most systemic viremias, such as HIV-1, present with mild thrombocytopenia, which is mediated through several mechanisms such as a decrease in platelet production, increased platelet activation, and/or platelet destruction through the formation of immune complexes. However, the literature is contradictory, with some reports claiming that platelets are essential for the immune responses, while others imply that platelets are viral reservoirs that release virions at later stages of infection. Our lab has shown that murine platelets endocytose HIV-1 pseudo particles (HIVpp) in a dynamin-dependent process and are activated in vivo and in vitro. However, what platelets do with the endocytosed HIVpp, or which receptor(s) are responsible for this interaction is unclear. HIVpp cannot be used to study chronic viremia as they are incapable of replicating in vivo. Therefore, there is a need for a mouse model that recapitulates the HIV-1 life cycle in mice to identify the key mechanisms of HIV-1 interaction with platelets. In 2005, Potash et al. developed a mouse infective HIV-1 model, aka. EcoHIV, which expresses all of the HIV-1 genome except the gp120 gene, which is replaced with the murine leukemia virus’ gp80. Thus, EcoHIV is capable of infecting rodents only and not humans. This substitution does not change the normal cell targets of EcoHIV as the WBCs express the murine Cationic Amino acid Transporter-1 (mCAT-1), which is needed for the EcoHIV to infect cells. We hypothesized that platelets could similarly interact with the EcoHIV as with HIVpp, being endocytosed and leading to activation. Hence, by using the EcoHIV several questions could be answered, such as: what is the importance of platelet HIV-1 endocytosis on the HIV-1 progression in later stages of infection; what do platelets do with the endocytosed HIV-1; and do platelets act as viral reservoirs, viral disposers, or both? Our results indicate that EcoHIV is different in many aspects from HIVpp and HIV-1 during the acute and chronic stages of infection. EcoHIV uses the spleen as a viral reservoir for replication for up to one week before the virus goes into a latent phase after six weeks of infection. Moreover, EcoHIV is rapidly cleared from the blood circulation after 48 hr of injection, which is not the case with HIV-1, which is only cleared (on the protein level) from the blood circulation after infected patients start their combined antiretroviral therapy (cART). Furthermore, EcoHIV is not endocytosed, nor does it activate platelets in vivo or ex vivo as its uptake is exclusively limited to cells with the mCAT-1 receptor, which is not present on the surface of the platelets. Our data do not support the concept that platelet surface molecules, such as Dendritic Cell-Specific Intercellular adhesion molecule-3- Grabbing Non-integrin (DC-SIGN), C-type lectin-like receptor 2 (CLEC-2), or the integrins, have a wide recognition for many different viruses or pathogens and suggest that platelet/pathogens interactions must be more specific. In the process of our studies, we developed, for the first time, a detailed step-by-step protocol for generating purified EcoHIV and established essential quality controls to evaluate viral preparations. We also established more accurate methods to calculate the viral titers and measure different aspects of the progression of EcoHIV infection in mice to allow better assessments of both acute and chronic phases of infection. Our research is innovative as it sheds light on the differences between EcoHIV and HIV-1 in terms of infection dynamics and clearance mechanisms

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2024.462

Funding Information

This work is supported by grants from the National Institutes of Health, National Heart, Lung and Blood Institute (HL56652, HL138179, and HL150818 to S.W.W.). 2020-2024

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Available for download on Thursday, December 18, 2025

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