Pyroptosis and adaptive immunity mechanisms are promptly engendered in mesenteric lymph-nodes during pig infections with Salmonella enterica serovar Typhimurium

Abstract

In this study, we explored the transcriptional response and the morphological changes occurring in porcine mesenteric lymph-nodes (MLN) along a time course of 1, 2 and 6 days post infection (dpi) with Salmonella Typhimurium. Additionally, we analysed the expression of some Salmonella effectors in tissue to complete our view of the processes triggered in these organs upon infection. The results indicate that besides dampening apoptosis, swine take advantage of the flagellin and prgJ expression by Salmonella Typhimuriun to induce pyroptosis in MLN, preventing bacterial dissemination. Furthermore, cross-presentation of Salmonella antigens was inferred as a mechanism that results in a rapid clearance of pathogen by cytotoxic T cells. In summary, although the Salmonella Typhimurium strain employed in this study was able to express some of its major virulence effectors in porcine MLN, a combination of early innate and adaptive immunity mechanisms might overcome virulence strategies employed by the pathogen, enabling the host to protect itself against bacterial spread beyond gut-associated lymph-nodes. Interestingly, we deduced that clathrin-mediated endocytosis could contribute to mechanisms of pathogen virulence and/or host defence in MLN of Salmonella infected swine. Taken together, our results are useful for a better understanding of the critical protective mechanisms against Salmonella that occur in porcine MLN to prevent the spread of infection beyond the intestine.

Regulatory role of microRNA in mesenteric lymph nodes after Salmonella Typhimurium infection

“…Induction of the MHC-I gene expression was also evidenced in our experimental model of infection by over-expression of NLRC5 , a specific transcriptional activator of the MHC-I expression, induced by IFNγ through STAT1 activation [ 47 ], whose coding genes were observed also over-expressed in this study. Cross-presentation of exogenous antigens from Salmonella origin via MHC-I molecules in the porcine MLN had already been suggested by us [ 8 ]. The broad pathways by which cross-presentation occurs have not been clearly elucidated yet, although in the most likely scenario, phagocytosed proteins reach cytosol by chaperone retrotranslocation mechanisms, and are subsequently degraded by proteasomes, binding MHC-I molecules and activating CD8+ T-cells [ 48 – 50 ].…”

“…In pigs, MLN are key sites for antigen presentation in the adaptive immune response. However, in Salmonella infection, they also become niches of replication due to the ability of bacteria to survive in these organs [ 8 ]. Defense mechanisms in porcine MLN against Salmonella have been described by us previously.…”

“…In pigs, persistence of Salmonella Typhimurium in MLN has been reported up to 6 weeks after oral inoculation, sustaining these organs as major inductive sites for immune responses during porcine salmonellosis [ 7 ]. It has been shown that Salmonella Typhimurium expresses some of its major virulence effectors in porcine MLN [ 8 ]. In spite of that, a combination of early innate and adaptive immunity mechanisms overcome virulence strategies used by the pathogen, enabling the host to protect itself against bacterial spread beyond gut-associated lymph nodes [ 8 , 9 ].…”

“…It has been shown that Salmonella Typhimurium expresses some of its major virulence effectors in porcine MLN [ 8 ]. In spite of that, a combination of early innate and adaptive immunity mechanisms overcome virulence strategies used by the pathogen, enabling the host to protect itself against bacterial spread beyond gut-associated lymph nodes [ 8 , 9 ].…”

“…There are very few studies about the function of miRNA in innate and adaptive immunity of porcine lymph nodes, most of them related to viral infections [ 17 , 18 ]. Given the pivotal role of the MLN in the control of Salmonella Typhimurium infection in pigs [ 8 ], the aim of the present study was to characterize miRNA expression differences in porcine ileocecal MLN upon Salmonella challenge. In addition, to obtain a more accurate prediction of miRNA targets than those provided by bioinformatic tools, miRNA expression data were integrated with our previous large-scale protein expression data to identify immune response-related miRNA.…”