Understanding the Impact of LPS and GLA on the Induction of Proinflammatory Cytokines Open Access
Ding, Tiffany (2016)
Abstract
Vaccines play a crucial role in the elimination of infectious disease by generating long-term protection against pathogens. Immunostimulatory adjuvants have currently been used in combination with vaccines to further enhance the body's immune response following infection. Toll-like receptor 4 (TLR4) agonist bacterial lipopolysaccharide (LPS) from Gram-negative bacteria is a potent adjuvant responsible for triggering an inflammatory response that results in the production of critical proinflammatory cytokines. Excessive release of these cytokines results in endotoxic shock in animals as characterized by systemic inflammation, organ failure and death. Monophosphoryl lipid A (MPL) is a low-toxicity derivative of LPS that is in development as a vaccine adjuvant due to its ability to retain the immunostimulatory properties of its parent molecule without the endotoxic effects associated with LPS. It is widely recognized that LPS is mediated by TLR4 t o initiate two principle signaling pathways: MyD88-dependent and MyD88-independent (TRIF-dependent) . MyD88-dependent signaling leads to the induction of proinflammatory cytokines while TRIF-dependent signaling activates Type 1 Interferons. Previous studies propose that TLR4 agonist MPL predominantly activates the TRIF-dependent pathway, a distinction that may be key to MPL's reduced toxicity. Thus, the present study investigates the affects of LPS and a synthetic form of MPL, Glucopyranosyl Lipid A (GLA), on the expression of critical proinflammatory cytokines in murine models using bone marrow derived macrophages in vitro. Stimulation with LPS results in increased cytokine expression in comparison to GLA over a time-dependent and concentration dependent response. In addition, cell death regulator Caspase-8 (Casp8) has been implicated as a critical factor in cytokine production downstream of TLR4. Our results reveal that gene expression is substantially reduced in Casp8-/-RIP3-/- mice compared to wild-type mice in vivo following LPS or GLA challenge. This data suggests that Casp8 is indispensable downstream of TLR4 receptor activation and an essential hose protease to be studied in vaccine development. Our results provide insight into TLR4 mediated gene expression by GLA that helps define the molecule as an ideal candidate in the design of vaccine adjuvants.
Table of Contents
INTRODUCTION P. 1
OBJECTIVES P. 12
MATERIALS AND METHODS P. 13
RESULTS P. 15
DISCUSSION P. 24
REFERENCES P. 28
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