tuberculosis infected bone marrow derived macrophages as well as Salmonella infected RAW264. 7 macrophages. Here we report for the first time that B. pseudomallei up regulates both arginase 1 and arginase 2 isoforms in the host with arginase 2 being more dominant. The expression profiles demonstrate both full article host nitric oxide synthase 2 and arginase 2 were elevated at a similar magnitude at 24 hpi. This suggests that arginase competes with NOS2 to produce NO from arginine during the infection, leading to the suboptimal antibacterial effect of NOS2 in the B. pseu domallei infected host. Certain pathogens evade the host defence by trigger ing the TLR2 mediated biased anti inflammatory effects or prevent recognition by TLRs. For example, Yer sinia and Candida induced TLR2 signalling leads to the release of IL 10, which can lead to immunosuppression.

However, the response following recognition of B. pseu domallei via the TLR2 signalling pathway is contrary to the evasion mechanism exploited by Yersina spp. and Candida spp. In addition, some pathogens have devel oped strategies to either block or avoid their recognition by TLRs and subsequent activation of the innate defence. This study suggests that B. pseudomallei may use specific TLR mediated signals to escape from the host defence. Future studies will be aimed at determin ing whether B. pseudomallei utilizes these signals to evade TLR clearance mechanisms. Tissue injury leads to extracellular matrix breakdown, including the degradation of hyaluronic acid and resulting oligosaccharides.

In this study, the gene encod ing hyaluronan synthase 2, the enzyme that pro duces HA, was induced. In contrast, the genes encoding hyaluronoglucosaminidases, the enzymes that degrade HA, were repressed, indicating that perhaps HA is not degraded during a B. pseudomal lei infection. These endogenous signals can also trigger TLR2 and or TLR4 activation and signals distinct from microbial stimulators, for instance HA but not LPS, sig nal through TLR4, MD2, and CD44. Up regulation of TLR2, TLR4 and TLR7 as well as MD2 could indicate B. pseudomallei infected host responses to endogenous signals released during tissue damage. However, the ability of the engaged TLRs to distinguish between microbial and endogenous signals and subsequently trig ger appropriate responses, remains unclear.

These observations reflect that the inflammatory response may cause more damage to the host than the microbe. In summary, our work has provided an exten sive description of host defence responses to B. pseudo mallei during an acute infection. Changes in host cell metabolism as a consequence of nutrient scavenging by intracellular B. pseudomallei have never been studied. Batimastat The microarray data presented here provides the first description of changes in the B.