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Title: Dendritic cells respond differently to live and killed bacteria-molecular mechanisms of pathogen recognition by dendritic cells and implications for vaccine development
Keywords: Dendritic cells, differently, live and killed bacteria
Issue Date: 27-Aug-2009
Citation: CHAN EDMUND (2009-08-27). Dendritic cells respond differently to live and killed bacteria-molecular mechanisms of pathogen recognition by dendritic cells and implications for vaccine development. ScholarBank@NUS Repository.
Abstract: Escherichia coli (E.coli) is the most common enteric gram-negative bacteria to cause extraintestinal infections in the ambulatory, long term-care and hospital settings as well as severe food poisoning. Although vaccines against E.coli are being developed, with regard to the pathophysiology of E.coli infections, the involvement of dendritic cells (DCs) has not been clarified. DCs prime T cell activation and how DCs are activated affect T cell stimulation. Immune responses to live and killed organisms can differ markedly, and studies have shown that DCs respond differently to live and killed Neisseria meningitidis and Salmonella typhimurium. In this study, we compared the response of DC to live and killed E.coli. Heat-killed E.coli was indistinguishable from live and UV-killed bacteria in promoting DC expression of MHC II, CD40, CD54, CD83, CD80 and CD86. With respect to TNF-?, IL-6, IL-12p40, IL-10 and IL-23 induction, heat-killed E.coli was as potent as live and UV-killed E.coli. However, with respect to IL-12p70, heat-killed E.coli was found to be a poor inducer as compared to live and UV-killed E.coli. Interestingly, heat-killed E.coli induction of IL-12p70 is dominant over live or UV-killed E.coli stimulations in co-infections study. Investigation of the IL-10 profiles suggested that IL-10 could not be the cause of the poor IL-12p70 induction in response to heat-killed E.coli. Instead, results suggested that the cause of the poor IL-12p70 induction could be due to low IL-12p35 gene expression. In addition, results indicated that the low IL-12p70 production in heat killed E.coli infected DCs is LPS dependent and IFN-? can restore IL-12p70 level to a level comparable to live or UV-killed E.coli. Although heat-killed E.coli induced low IL-12p70 expression from DCs, MLR result indicated that like live and UV-killed E.coli, it was able to induce Th1 response. An analysis of nuclear translocation of NF-kappaB family members as well as IRF-1 and IRF-3 showed inhibitionof p65, c-Rel, RelB and IRF-1 nuclear translocation in heat-killed E.coli infected cells. This was not observed with live bacteria infection. In addition, we have also determined that both live and heat-killed E.coli strongly activates Toll-like receptors (TLRs) 2 and 4. Low TLR expression is frequently observed in published work and codon usage may explain the global expression of TLRs, thus, an analysis of the TLRs codons against the major human codons were carried out. Results showed that all TLRs except TLR9 have a reduced number of major codons in their genes. Replacement of the 302bp at the 5? end of the TLR2 gene sequence with the major human codons showed that TLR2 expression could be increased. Collectively, this study showed that the differential induction of IL-12p70 by live, UV and heat-killed E.coli could be due to differential regulation NF-?B and IRFs nuclear localization that affects IL-12p35 gene expression. This study also showed that despite low induction of IL-12p70 by heat-killed E.coli, they were able to induce a Th1 response similar to live and UV-killed E.coli. Finally, this study showed that the deviation of TLR sequences from using major codons dictates the low TLR expression and this may protect the host against excessive inflammation and tissue damage.
Appears in Collections:Ph.D Theses (Open)

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