Master of Science (MS)
Microsporidia are ubiquitous, obligate intracellular eukaryotes that cause chronic diarrhea and disseminated diseases in humans, especially in immunocompromised individuals. Macrophages, cellular components of the innate immune system, are believed to be the source of dissemination of this pathogen throughout the body. Little is known about the innate immune response to microsporidia. Macrophages are a source of interleukin (IL)-12 and IL-23 and play an essential role in the link between innate and adaptive immunity. The focus of this thesis is the investigation of the p38 mitogen-activated protein kinase (MAPK) signaling mechanisms and IL-12 and IL-23 production regulated by Toll-like receptor (TLR) 2 and TLR4 engagement with pathogenic and nonpathogenic species of microsporidia. IL-12 and IL-23 production by primary human macrophage were induced in response to challenge with avirulent but not virulent species from 12 to 24 hour time points. Using western blot, we found that activated p38á MAPK is continuous from three to 24 hours post infection of human macrophages with avirulent species. Activation of p38á MAPK is transient when infected with pathogenic species as we only detected phosphorylation at three hours and six hours post infection. These data suggest that activation of p38 MAPK may be necessary for the proper innate immune response to microsporidia to control infection. Using small interfering RNA, p38á, ã, and ä MAPK were knocked down in primary human macrophages and resulted in a decrease in IL-12/IL-23 p40 production when infected with nonpathogenic species. Thus, additional isoforms of p38 MAPK may regulate the production of IL-12 and/or IL-23 which is a novel finding to the field of microsporidian research and immunology as a whole. MAPK phosphatases (MKP) 1 and/or MKP5 may be negative regulators of this IL-12 and/or IL-23 response. Increased expression of MKP5, but not MKP1, was observed in MDMs challenged with pathogenic species for six hours. The deactivation of p38 MAPK by MKPs may result in the diminished levels of IL-12 and IL-23 observed in virulent infections and thus leading to host susceptibility to microsporidian infection.
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Mathews, Amber Lynn, "Comparative studies of innate host defense mechanisms against virulent and avirulent species of microsporidia" (2010). LSU Master's Theses. 2366.