Differential Gene Expression Profiles of Lung Epithelial Cells Exposed to Burkholderia pseudomallei and Burkholderia thailandensis during the Initial Phase of Infection

Department of Immunology, Faculty of Medicine, Siriraj Hospital, Bangkok, Thailand.
Asian Pacific journal of allergy and immunology / launched by the Allergy and Immunology Society of Thailand (Impact Factor: 0.97). 04/2009; 27(1):59-70.
Source: PubMed


Burkholderia pseudomallei is the causative agent of melioidosis, and its infection usually affects patients' lungs. The organism is a facultative intracellular Gram-negative bacillus commonly found in soil and water in endemic tropical regions. Another closely related Burkholderia species found in soil and water is B. thailandensis. This bacterium is a non-pathogenic environmental saprophyte. B. pseudomallei is considerably more efficient than B. thailandensis in host cell invasion and adherence. A previous study by our group demonstrated that after successfully invading cells, there was no difference in the ability to survive and to replicate between both Burkholderia species in cultured A549 human lung epithelial cells. In this study, Human Affymetrix GeneChips were used to identify the difference in gene expression profiles of A549 cells after a 2-h exposure to B. pseudomallei and B. thailandensis. A total of 280 of 22,283 genes were expressed at higher levels in the B. pseudomallei-infected cells than in the B. thailandensis-infected cells, while 280 genes were expressed at lower levels in the B. pseudomallei-infected cells. Approximately 9% of these genes were involved in immune response and apoptosis. Those genes were further selected for gene expression analysis using reverse transcription PCR and/or real-time RT-PCR. The results of RT-PCR and real-time RT-PCR are in accordance with data from the microarray data in that bcl2 gene expression in the B. pseudomallei-infected cells was 2-fold higher than the level in the B. thailandensis-infected cells even though no apoptosis was seen in the infected cells. The levels of E-selectin, ICAM-1, IL-11, IRF-1, IL-6, IL-1beta and LIF genes expression in the B. pseudomallei-infected cells were 1.5-5 times lower than in the B. thailandensis-infected cells. However, both species stimulated the same level of IL-8 production from the tested epithelial cell line, and no difference in the ratio of adherent polymorphonuclear cells (PMNs) to infected A549 cells of both species was observed. Taken together, our results suggest that B. pseudomallei manipulates host response in favor of its survival in the host cell, which may explain the more virulent characteristics of B. pseudomallei when compared with B. thailandensis.

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    • "Many researchers have demonstrated that infections by intracellular pathogens alter the expression of genes encoding pro-inflammatory cytokines and chemokines, which have been implicated as principal mediators during infections of the host in both in vitro and in vivo systems [6,7,33]. These cytokines and chemokines also function as central mediators in stimulating various host defences systems such as the cytokine-cytokine receptor interactions pathway, signalling pathways and apoptosis and eventually elicit appropriate adaptive immune system. "
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    • "In vitro studies have established that B. pseudomallei is capable of surviving and multiplying intracellularly within professional phagocytes, including macrophages, monocytes and neutrophils (Jones et al., 1996; Stevens and Galyov, 2004) or non-phagocytic cells, including respiratory epithelial cells (Brown et al., 2002; Wongprompitak et al., 2009) although the exact mechanism of invasion and colonization remains unknown. When B. pseudomallei is taken up by macrophage-like cells, it is capable of escaping from endocytic vacuoles into the cytoplasm, where it can replicate by lysing the endosome membrane (Harley et al., 1998). "
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