Date of Award

December 2015

Degree Type

Thesis

Degree Name

Master of Science

Department

Biomedical Sciences

First Advisor

Wail M. Hassan

Committee Members

Jeri-Anne Lyons, John Ndon

Keywords

AGM, HIV, RM, SIV

Abstract

Human immunodeficiency virus (HIV) is one of the most challenging infectious agents at the current time. To date, many vaccine trials have been conducted. However, there has not been a fully successful trial. This is due, in part, to the gap in knowledge of the protective immune response against HIV. African green monkeys (AGMs) serve as an interesting model to study immune protection in primate immunodeficiency virus infections due to their resistance to AIDS. Experimental SIV infection in rhesus macaques (RMs) resembles HIV infection in humans with chronic immune activation and progression to AIDS well characterized in both. Understanding the immune systems of AGMs and RMs and how they differ is likely to advance our knowledge of immune protection and immunopathogenesis in SIV/HIV disease. B cells are responsible for the humoral arm of acquired immunity, which results in the production of specific antibodies. In lentiviral infections, neutralizing antibodies block viral entry and are, therefore, essential for protective immunity. Other antibody-mediated functions, such as antibody-dependent cellular cytotoxicity, have gained increased interest after the recent demonstration of enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) in vaccinees in a vaccine trial commonly known as the Thai trial. T helper cells provide co-stimulatory signals that are essential for B cell activation and antibody production. Blocking CD40/CD40L interactions impairs antiviral humoral response, which emphasizes the importance of B and T helper interaction for protective humoral response. The current study aims to identify key B-cell and T-cell-related differences that separate African green monkeys and rhesus macaques in term of constitutive function (i.e. in the absence of infection) and in vitro, SIV-induced dysfunction. In this study, multiparametric flow cytometry approaches were used to identify any differences in the distribution of B and T cell subsets. B cells were stimulated with anti-IgM/G and T cells with phorbol myristate acetate and ionomycin (PMA/I) to assess the expression of their activation markers. These are unspecific stimuli that give an idea about the potential responses of the cells following specific stimulus. Also, B cells were evaluated for the expression and phosphorylation of intracellular signaling proteins. In addition, T cells were evaluated for the production of IFNɣ, TNFα, IL-2, expression of CD107a, and their ability to have more than one function. The results showed that AGMs have lower frequencies and absolute numbers of B and CD4+ T cells than RMs. Moreover, B cells of AGMs showed higher expression levels of CD40 than RMs, a molecule that plays an essential role in antibody production and Ig class switching. Furthermore, the analyses of B cell signaling proteins showed that AGMs express higher levels of these proteins and they get phosphorylated in higher levels than RMs. This may indicate a more robust signaling activity of AGMs’ B cells as compared to RMs, which may play a role in an early antibody response that controls the infection. T cells data analyses revealed that CD4 T cells of AGMs produce less IFNɣ, TNFα, and IL-2 than RM, which may indicate another immediate response, anti-inflammatory, rather than pro-inflammatory response. Also, this may explain the lack of chronic immune activation in AGM. DN T cells of AGM showed higher expression levels of CD107a than the DN T cells of RM. This may indicate the cytotoxic function of these cells in addition to their helper functions. DN T cells are resistant to SIV infection, and their multifunctionality give insights into new cellular therapeutic approaches.

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