Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/19034
Title: The study of pulmonary innate immune responses against Burkholderia pseudomallei
Authors: SIM SIEW HOON
Keywords: Pseudomallei, intracellular, epithelial, innate, peptides, cathelicidin
Issue Date: 27-Jul-2009
Source: SIM SIEW HOON (2009-07-27). The study of pulmonary innate immune responses against Burkholderia pseudomallei. ScholarBank@NUS Repository.
Abstract: Burkholderia pseudomallei, a facultative intracellular pathogen, causes systemic infection in humans with high mortality. Although the lung was a common targeted organ for the bacteria, to date, information on how pulmonary epithelial cells respond to B. pseudomallei is limited. In this study, using a murine lung epithelial cell line, primary lung epithelial cells and an inhalational murine infection model, we characterize for the first time the immune factors that are involved in epithelial-mediated immune reaction against B. pseudomallei. Among a wide panel of immune components studied, increased levels of major pro-inflammatory cytokines (IL-6 and TNFa) which are important markers of disease severity in melioidosis and chemokine (MCP-1) were observed. In addition, we also detected differential regulation of the antimicrobial peptides chemokine (C-C motif) ligand 20 (CCL20), secretory leukocyte protease inhibitor (SLPI), and lysozyme; and showed the involvement of NF-kB and p38 MAPK pathways in regulating the expression of these antimicrobial peptides (CCL20, SLPI and lysozyme). This is the first study demonstrating the involvement of peptides in murine melioidosis and results from our study suggest that the epithelium could play an important role in host innate immune response against B. pseudomallei. The BALB/c and C57Bl/6 mice have differential susceptibilities to B. pseudomallei infection. To further determine this differential susceptibility was due to differential expression of pulmonary antimicrobial peptides, we used quantitative real-time PCR to determine the expression of a panel of antimicrobial peptides (murine cathelicidin-related antimicrobial peptide CRAMP, lysozyme, CCL20, SLPI, Surfactant A, Surfactant D, ?-Defensin14) in the lungs of B. pseudomallei-infected BALB/c and C57Bl/6 mice. ?-Defensin14 gene was xi significantly more down-regulated in BALB/c mice when compared to C57Bl/6 mice. However, further in vitro experiments with functionally similar human equivalent hBD-3 revealed the lack of direct killing or intracellular killing against B. pseudomallei. Although results from this study showed the lack of bactericidal effect of hBD-3 against B. pseudomallei, further studies will need to unravel if there is any difference in the immunomodulatory role of hBD-3 in BALB/c and C57Bl/6 mice that could lead to their differential susceptibility to the bacteria. Due to the reported antimicrobial and immunomodulatory roles of cathelicidin on other bacteria as well as the observed association between ?-defensin and susceptibility to pulmonary melioidosis in BALB/c mice, the roles of human cathelicidin, LL-37 in B. pseudomallei infection was also investigated. LL-37 does not have any direct antimicrobial effect on B. pseudomallei. Paradoxically, pre-incubation of cells with LL-37 (as low as 3?g/ml) resulted in an increase in bacterial invasion. In B. thailandenesis, a much higher concentration of LL-37 (50?g/ml) was required. In vivo, pretreatment of BALB/c mice with LL-37 resulted in increased bacterial load in the lungs and enhanced production of pulmonary cytokines (IL-6, MCP-1 and TNF-alpha). Results from this study suggest that besides an immunomodulatory role, LL-37 could enhance bacterial uptake into the host cells. Taken collectively, this study underscores the need for improved understanding between the interaction of innate immune response in the respiratory tract to B. pseudomallei, the interplay of which could result in either reduced or increased susceptibility to melioidosis.
URI: http://scholarbank.nus.edu.sg/handle/10635/19034
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