Abstract
Avian-specific toll like receptor 15 (TLR15) is functionally equivalent to a group of TLR2 family proteins that the mammalian innate immune system utilizes to recognize a broad spectrum of microbe-associated molecular patterns, including bacterial lipoproteins. In this study we examined the role of chicken TLR2 family members in the innate immune response to the avian pathogenic bacterium, Mycoplasma synoviae. We found that Mycoplasma synoviae, and specifically the N-terminal diacylated lipopeptide (MDLP) representing the amino-terminal portion of its mature haemagglutinin protein, significantly induces the expression of TLR15, but not TLR1 and TLR2 in chicken macrophages and chondrocytes. TLR15 activation is specific and depends on diacylation of the lipopeptide. Activation of TLR15 after stimulation with Mycoplasma synoviae and MDLP triggers an increase in the expression of transcription factor nuclear factor kappa B and nitric oxide production. Moreover, transfection of avian macrophage cells with small interfering RNA reduces the expression of TLR15 after stimulation with MDLP. This leads to decreased activation of the innate immune response, as measured by nitric oxide production. Additionally, pretreatment of cells with neutralizing anti-TLR15 antibody results in a notable attenuation of MDLP-driven release of nitric oxide. This positive correlation may constitute a mechanism for stimulating the innate immune response against avian mycoplasmas in chicken cells via TLR15.
Highlights
Mycoplasmas are the smallest self-replicating organisms, and are distinguished from other bacteria by their small size and total lack of a cell wall
As with the Mycoplasma synoviae infection experiment, the mRNA expressions of TLR1 and TLR2 were significantly down-regulated after the treatment of the cells with MDLP (p < 0.01), whereas when treated with non acylated peptide analog (NAP), the expression remained the same compared to non-treated cells (Figure 1B, TLR1 and TLR2, respectively)
This study was designed to address if toll like receptor 15 (TLR15) is involved in the recognition of Mycoplasma synoviae lipoprotein MSPB
Summary
Mycoplasmas are the smallest self-replicating organisms, and are distinguished from other bacteria by their small size and total lack of a cell wall. As obligate parasites they usually exhibit strict host and tissue specificity. Mycoplasmas have been shown to interact with the host’s immune system on many levels, which includes modulating the host immune system and stimulating an inflammatory response. These abilities enable mycoplasmas to establish a chronic, persistent infection (reviewed in [1]). In the absence of a cell wall, the is the macrophage stimulatory lipopeptide MALP-2 from Mycoplasma fermentas, which is derived from a 43 kDa surface lipoprotein that is post-translationally cleaved into the mature 14-residue long N-terminal lipopeptide MALP-2 [8]
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