Detection of interferon-γ response to tuberculosis in blood collected at commencement of exsanguination at slaughter from cattle sensitized with Mycobacterium bovis

Transcriptome analysis of porcine PBMCs reveals lipopolysaccharide-induced immunomodulatory responses and crosstalk of immune and glucocorticoid receptor signaling

The current level of knowledge on transcriptome responses triggered by endotoxins and glucocorticoids in immune cells in pigs is limited. Therefore, in the present study, we treated porcine peripheral blood mononuclear cells (PBMCs) with lipopolysaccharide (LPS) and dexamethasone (DEX) separately or combined for 2 hours. The resultant transcriptional responses were examined by mRNA sequencing. We found that the LPS treatment triggered pronounced inflammatory responses as evidenced by upregulation of pro-inflammatory cytokines, chemokines, and related signaling pathways like NF-κB. Concurrently, a series of downregulated pro-inflammatory and upregulated anti-inflammatory molecules were identified. These are involved in the inhibition of TLR, NF-κB, and MAPK cascades and activation of signaling mediated by Tregs and STAT3, respectively. These findings suggested that LPS initiated also an anti-inflammatory process to prevent an overwhelming inflammatory response. The transcriptome responses further revealed substantial crosstalk of immune responses and glucocorticoid receptor (GR) signaling. This was apparent in four aspects: constitutive inhibition of T cell signaling by DEX through a subset of genes showing no response to LPS; inhibition of LPS-induced inflammatory genes by DEX; attenuation of DEX action by LPS paralleled by the regulation of genes implicated in cytokine and calcium signaling; and DEX-induced changes in genes associated with the activation of pro-inflammatory TLR, NF-κB, iNOS, and IL-1 signaling. Consequently, our study provides novel insights into inflammatory and GR signaling in pigs, as well as an understanding of the application of glucocorticoid drugs for the treatment of inflammatory disorders.

Evaluation of the interferon-γ assay on blood collected at exsanguination of cattle under field conditions for surveillance of bovine tuberculosis

Development of point of concentration (POC) surveillance strategies for bovine tuberculosis (bTB) would facilitate global efforts to eradicate bTB. The interferon-gamma (IFNγ) assay can detect IFNγ responses to Mycobacterium bovis in blood collected at commencement of exsanguination (COE) of experimentally challenged cattle but has not been evaluated under field conditions. The current study was aimed at determining (i) whether blood collected at COE of cattle at slaughter, under field conditions, is practical to obtain and useful for identifying cattle as IFNγ positive for bTB, (ii) whether the results of the IFNγ assay obtained at COE reliably compare with results obtained from live animals in the field, and (iii) whether the identified animal(s) originated from bTB-infected or bTB-exposed herds. Cattle from three risk groups were used: the highest risk group consisted of 49 cattle from 3 bTB-infected herds; the medium risk group consisted of 24 cattle from a potentially exposed herd; and the lowest risk group consisted of 60 cattle from herds with no known history of bTB exposure. The IFNγ assay was performed on blood collected both before stunning and at COE of cattle at slaughter. An enhanced slaughter inspection for gross lesions consistent with bTB was performed on all cattle. In addition, lymph nodes were cultured for M. bovis for cattle that tested positive for bTB via the IFNγ assay and for most cattle that tested negative for bTB. Cattle, both with and without lesions consistent with bTB, were identified as positive for bTB by the IFNγ assay using blood collected at COE, but none of the positive cattle originated from the lowest risk group. The current study demonstrates that blood collected at COE of cattle is both a practical and moderately reliable sample for accessing bTB infection using the IFNγ assay.

Effect of transportation, time of sampling, and lymphocyte numbers on gamma interferon response to Mycobacterium bovis in cattle at time of slaughter

Adapting the gamma interferon (IFNγ) assay for tuberculosis screening at points-of-concentration of cattle would improve global efforts to eradicate bovine tuberculosis. Two separate studies were conducted to evaluate if transportation of cattle, the time of blood collection, and total lymphocyte count affects the retention of a positive IFNγ assay result during slaughter of cattle experimentally sensitized with inactivated Mycobacterium bovis. Study 1 evaluated IFNγ assay responses to M. bovis and Mycobacterium avium stimulations in 5 cows (4 sensitized and 1 control) at the housing facility, after a 30-min transport to the slaughter facility, immediately before stunning, at commencement of exsanguination, and at 5 min after exsanguination commenced. Study 2 evaluated IFNγ assay responses to Mycobacterium antigen stimulations and total lymphocyte count in blood collected from 5 steers (4 sensitized and 1 control) at the housing facility, at commencement of exsanguination and at 2 successive 1-min intervals. The results indicated that blood obtained from sensitized cattle at commencement of exsanguination was more likely to remain positive than blood collected at successive time points; hence the time of blood collection is crucial to obtaining a useful IFNγ assay result for bovine tuberculosis at slaughter. The lymphocyte count progressively declined following exsanguination, and this decline might contribute to the reduction in the measured IFNγ. To compensate for the reduction in IFNγ production, a different set of positive cutoff values might be needed for blood collected at exsanguination. The current findings provide useful preliminary information necessary for making changes to the interpretation of the IFNγ assay on blood collected during exsanguination.