Early immune response following Salmonella enterica subspecies enterica serovar Typhimurium infection in porcine jejunal gut loops

Abstract

Salmonella enterica subspecies enterica serovar Typhimurium, commonly called S. Typhimurium, can cause intestinal infections in humans and various animal species such as swine. To analyze the host response to Salmonella infection in the pig we used an in vivo gut loop model, which allows the analysis of multiple immune responses within the same animal. Four jejunal gut-loops were each inoculated with 3 x 10(8) cfu of S. Typhimurium in 3 one-month-old piglets and mRNA expressions of various cytokines, chemokines, transcription factors, antimicrobial peptides, toll like and chemokine receptors were assessed by quantitative real-time PCR in the Peyer's patch and the gut wall after 24 h. Several genes such as the newly cloned CCRL1/CCX-CKR were assessed for the first time in the pig at the mRNA level. Pro-inflammatory and T-helper type-1 (Th1) cytokine mRNA were expressed at higher levels in infected compared to non-infected control loops. Similarly, some B cell activation genes, NOD2 and toll like receptor 2 and 4 transcripts were more expressed in both tissues while TLR5 mRNA was down-regulated. Interestingly, CCL25 mRNA expression as well as the mRNA expressions of its receptors CCR9 and CCRL1 were decreased both in the Peyer's patch and gut wall suggesting a potential Salmonella strategy to reduce lymphocyte homing to the intestine. In conclusion, these results provide insight into the porcine innate mucosal immune response to infection with entero-invasive microorganisms such as S. Typhimurium. In the future, this knowledge should help in the development of improved prophylactic and therapeutic approaches against porcine intestinal S. Typhimurium infections.

Figure 1.

Schematic presentation of the jejunal segments used in the experiment (N = 3 piglets). Tissues (Peyer’s patch and Gut wall) were collected after 24 h. Two loops were used as control (Growth Media) and four loops were infected with Salmonella enterica subspecies enterica serovar Typhimurium SL1344 (Salmonella Typhimurium SL1344). IS: Interspace.

Figure 2.

(A) Schematic presentation of the T-helper type-1 (Th1) mediated immune response. (B) Relative mRNA expression of Th1 cytokines and transcription factors. Data were presented as mean ± S.E.M. for a total of 8 control and 12 infected loops. * P < 0.05, ** P < 0.01, ns: not significant (Student’s Paired t-test or Wilcoxon Signed Rank Test (Exact)). DC: Dendritic Cell; cPP: Control Peyer’s Patch (PP); iPP: Infected PP; cGW: Control Gut Wall (GW); iGW: Infected GW.

Figure 3.

Relative mRNA expression of CCL25 and its two receptors, CCR9 and CCRL1. Data were presented as mean ± S.E.M. for a total of 8 control and 12 infected loops. * P < 0.05, ** P < 0.01, ns: not significant (Student’s Paired t-test or Wilcoxon Signed Rank Test (Exact)).

Figure 4.

Relative mRNA expression of four pattern recognition receptors (NOD2, TLR2, TLR4 and TLR5) usually associated with Salmonella. Data were presented as mean ± S.E.M. for a total of 8 control and 12 infected loops. * P < 0.05, ** P < 0.01, ns: not significant (Student’s Paired t-test or Wilcoxon Signed Rank Test (Exact)).