Date of Award

2013

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Microbiology and Immunology

Abstract

Liposomes are lipid particles formed by self-aggregated phospholipids. They are clinically used both as delivery vectors and immune adjuvants to treat many human infectious and cancerous diseases. However, how liposomes interact with host immune system remains poorly understood. Particularly, little is known about whether an innate immune receptor exists to sense liposomes. I hypothesize that liposomes activate NLRP3 inflammasome in macrophages, which results in the release of interleukin 1β (IL-1β), a proinflammatory cytokine that plays a key role in innate and adaptive immune responses.

To test my hypothesis, I determined the ability of inducing IL-1β secretion from macrophages by differentially charged liposomes. Furthermore, I tested whether the intact NLRP3 inflammasome machinery is required for liposomes-induced IL-1β secretion. Notably, similar to liposomes, accumulating evidence has indicated that exposure to other particulates, such as crystals, can activate the NLRP3 inflammasome in phagocytes. To delineate the mechanism by which particulates (liposomes/crystals) activate the NLRP3 inflammasome, I further hypothesize that particulates induce oxidative stress, resulting in the production of mitochondrial reactive oxygen species (ROS). Accumulation of ROS can then induce calcium influx via the transient receptor potential melastatin 2 (TRPM2) ion channel, which results in the drastic increase of intracellular calcium concentration. The change in the ionic environment would create a favorable condition for activation of the NLRP3 inflammasome. To test this, I used combinations of chemical and genetic approaches. First, I determined whether liposomes can induce mitochondrial ROS production and subsequent ROS-dependent calcium influx via TRPM2 in vitro. Next, by taking advantage of the TRPM2 gene knockout mice, I further determined if genetic ablation of TRPM2 could impair liposomes/crystals-induce NLRP3 inflammasome activation both in vitro and in vivo. Lastly, because IL-1β-IL-1 receptor signaling axis is critical for inducing humoral immune responses, I tested if blocking this signaling pathway would affect liposomal adjuvant effect in vivo. Briefly, I determined if, in comparison with wild-type animals, IL-1RI deficient mice would have any defect in mounting target-antigen specific antibody responses. Taken together, this project identifies the previously unknown innate immune sensor for liposomes and provides novel insights of the molecular mechanism underlying particle-induced NLRP3 inflammasome activation.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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