No 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.

Major poultry pathogens M. gallisepticum and M. synoviae share a gene encoding a putative cysteine protease CysP similar to papain cysteine protease (C1A subfamily). Comparison of the cysP gene sequences of 18 M. synoviae and 10 M. gallisepticum strains sequenced in this study showed polymorphisms, including deletions. Seven M. synoviae strains, including the type strain WVU 1853, had a 39 bp deletion in the 39 end of the cysP gene. In the same cysP region, all M. gallisepticum strains showed a deletion of 66 bp. Immunoblot analysis with specific antibodies demonstrated that M. synoviae strains expressed CysP, which was approximately 65 kDa. Both M. synoviae and M. gallisepticum were able to digest chicken IgG (cIgG). Incubation of cIgG (~170 kDa) with M. synoviae or M. gallisepticum cells (~15 h at 37 6C) resulted in a papain-like cleavage pattern of cIgG and fragments corresponding to the antigen-binding fragment of IgG (Fab,~45 kDa) and the crystallizable region fragment (Fc) of the IgG heavy chain (dimer of 60 kDa). Iodoacetamide (50 mM) prevented cleavage of cIgG by both Mycoplasma species. Following site-directed mutagenesis (eight TGA codons were changed to TGG) the cysP gene of M. synoviae ULB 925 was expressed as a His-tagged protein in a cell-free system. Purified recombinant CysP (rCysP;~67 kDa, pI~8) cleaved cIgG into Fab and Fc fragments. This indicates that CysP is responsible for the cIgG cleavage caused by M. synoviae and, probably, by M. gallisepticum. This is the first evidence to our knowledge that mycoplasmas have enzymes that can cleave the host IgG and indicates a novel strategy used by M. gallisepticum and M. synoviae for prolonged survival despite the antibody response of their host.

The role of chondrocytes in the development of infectious arthritis is not well understood. Several examples of mycoplasma-induced arthritis in animals indicate that chondrocytes come into direct contact with bacteria. The objective of this study was to analyze the interaction of an arthrogenic Mycoplasma synoviae strain WVU 1853 with chicken chondrocytes. We found that M. synoviae significantly reduces chondrocyte respiration. This was accompanied by alterations in chondrocyte morphology, namely cell shrinkage and cytoplasm condensation, as well as nuclear condensation and formation of plasma membrane invaginations containing nuclear material, which appeared to cleave off the cell surface. In concordance with these apoptosis-like events in chondrocytes, transcription was increased in several pro-apoptotic genes. Twenty-four hours after infection, strong upregulation was assayed in NOS2, Mapk11, CASP8 and Casp3 genes. Twenty-four and 72 h incubation of chondrocytes with M. synoviae induced upregulation of AIFM1, NFκB1, htrA3 and BCL2. Casp3 and NOS2 remained upregulated, but upregulation ceased for Mapk11 and CASP8 genes. Increased production of nitric oxide was also confirmed in cell supernates. The data suggests that chicken chondrocytes infected with M. synoviae die by apoptosis involving production of nitric oxide, caspase 3 activation and mitochondrial inactivation. The results of this study show for the first time that mycoplasmas could cause chondrocyte apoptosis. This could contribute to tissue destruction and influence the development of arthritic conditions. Hence, the study gives new insights into the role of mycoplasma infection on chondrocyte biology and development of infectious arthritis in chickens and potentially in humans.

and rapid quantification results (Pfaffl, 2001; Yuan et al., 2006). Because of the lacking consensus on how to best perform qPCR, MIQE guidelines have been developed to uniform qPCR experiment setup, optimization and data analysis, making the protocols comparable between different research groups and organizations and ensuring the relevance, accuracy, correct interpretation and repeatability of the results (Bustin et al., 2009). When analyzing gene expression, qPCR data can be subjected to absolute or relative quantification (Livak and Schmittgen, 2001; Pfaffl, 2001; Yuan et al., 2006). Absolute quantification employs internal or external cali-Comparison of methods for relative quantification of gene expression using real-time PCR Quantitative real-time PCR (qPCR) has become a widely used tool for quantifying gene expression. Several methods for relative quantification have been developed, enabling rapid and reliable detection and quantification of specific nucleic acids. These methods, based on qPCR include: the standard curve method, the efficiency calibrated method and the 2 −ΔΔCq method. Here we analyzed if these three methods generate comparable results. To evaluate their performance, we analyzed the expression of the nuclease gene MS53_0284 from Mycoplasma synoviae type strain WVU 1853 during in vitro infection of CEC-32 cells, using qPCR. As determined, all three methods generated comparable and reliable results when all necessary conditions were fulfiled. Also, the efficiency calibrated and the standard curve methods were more suitable for quantifying small differences in relative gene expression than the 2 −ΔΔCq method. Key words: molecular genetics / genes / gene expression / quantitative real-time PCR / methods Primerjava metod za relativno kvantifikacijo genskega izražanja s PCR v realnem času Metoda kvantitativne verižne reakcije s polimerazo v realnem času (qPCR) je postala najpogosteje uporabljen način analize izražanja genov. Razvitih je bilo več metod za relativno kvantifikacijo genske ekspresije, ki omogočajo hitro in zanesljivo detekcijo ter kvantifikacijo specifičnih nukleinskih kislin. Mednje spadajo: metoda z umeritveno krivuljo, metoda z upoštevanjem učinkovitosti pomnoževanja in metoda po enačbi 2 −ΔΔCq. V tej študiji smo z analizirajem izražanja gena MS53_0284, ki kodira nukleazo pri bakteriji Mycoplasma synoviae WVU 1853, po okužbi celic CEC-32 in vitro s qPCR preverili primerljivost rezultatov, dobljenih z uporabo omenjenih metod. Pokazali smo, da z upoštevanjem potrebnih pogojev z omenjenimi metodami pridobimo primerljive rezultate ter da sta metoda z umeritveno krivuljo in metoda z upoštevanjem učinkovitosti pomnoževanja primernejši za ugotavljanje majhnih razlik v izražanju genov kot metoda po enačbi 2 −ΔΔCq .