Flagellin expression enhances Salmonella accumulation in TLR5-positive macrophages (original) (raw)

Recently, it has been reported that Salmonella secrete flagellin in response to host produced lysophospholipids. However, this monomer of the bacterial flagella activates Toll-like receptor 5 (TLR5) in the innate immune system. The objective of this study was to examine the role of flagellin expression during infection of species-specific macrophages (M) which either expressed or lacked TLR5. Initially, TLR5activity was confirmed in bovine M using Salmonella typhimurium derived-flagellin. Within these cells, recombinant FliC induced a potent CXCL8 response when compared to the heterogeneous (FliC/FljB) form of purified flagellin. Furthermore, neither form of flagellin induced nitrite secretion which was subsequently detected after exposing bovine M to LPS in the presence of IFN-␥. Flagellin enhanced the accumulation of Salmonella enteritidis in TLR5-positive bovine and human M which was independent of adhesion in bovine M. In contrast, murine M s which lacked TLR5 were equally susceptible to hosting S. enteritidis, with or without flagellin. However, lack of flagellin in S. typhimurium marginally inhibited bacterial accumulation in bovine M , where FljB and FliC compensated for the lack of each other. This study suggests that flagellin may be inducing TLR5-dependent internalisation mechanisms in MФ which vary qualitatively between different species and Salmonella serotypes.