Rapid expression of chemokines and proinflammatory cytokines in newly hatched chickens infected with Salmonella enterica serovar typhimurium

Abstract

Poultry meat and eggs contaminated with Salmonella enterica serovar Enteritidis or Salmonella enterica serovar Typhimurium are common sources of acute gastroenteritis in humans. However, the exact nature of the immune mechanisms protective against Salmonella infection in chickens has not been characterized at the molecular level. In the present study, bacterial colonization, development of pathological lesions, and proinflammatory cytokine and chemokine gene expression were investigated in the liver, spleen, jejunum, ileum, and cecal tonsils in newly hatched chickens 6, 12, 24, and 48 h after oral infection with Salmonella serovar Typhimurium. Very high bacterial counts were found in the ileum and cecal contents throughout the experiment, whereas Salmonella started to appear in the liver only from 24 h postinfection. Large numbers of heterophils, equivalent to neutrophils in mammals, and inflammatory edema could be seen in the lamina propria of the intestinal villi and in the liver. Interleukin 8 (IL-8), K60 (a CXC chemokine), macrophage inflammatory protein 1 beta, and IL-1 beta levels were significantly upregulated in the intestinal tissues and in the livers of the infected birds. However, the spleens of the infected birds show little or no change in the expression levels of these cytokines and chemokines. Increased expression of the proinflammatory cytokines and chemokines (up to several hundred-fold) correlated with the presence of inflammatory signs in those tissues. This is the first description of in vivo expression of chemokines and proinflammatory cytokines in response to oral infection with Salmonella in newly hatched chickens.

FIG. 1.

Histopathology of the ileum (A) and liver (B) of chickens infected with Salmonella serovar Typhimurium. Paraffin-embedded sections from the control (1) and at 48 h p.i. (2) were conventionally stained with hematoxylin and eosin. Note the heterophil extravasation, thickening of the villi, and increased vascular permeability leading to edema in the ileal villi. The presence of small foci filled with heterophils (circled) and of scattered heterophils was evident in the liver 48 h p.i.

FIG. 2.

Quantification of chemokine and proinflammatory cytokine mRNA extracted from jejuna of chickens after experimental infection with Salmonella serovar Typhimurium. Only statistically significant (P < 0.05) results are expressed as fold changes in chemokine mRNA levels for infected birds compared to those for age-matched, mock-infected controls. The error bars show standard error for triplicate samples from five birds in two separate experiments.

FIG. 3.

Quantification of chemokine and proinflammatory cytokine mRNA extracted from ilea of chickens after Salmonella serovar Typhimurium experimental infection. Only statistically significant (P < 0.05) results are expressed as fold changes in chemokine mRNA levels for infected birds compared to those for age-matched, mock-infected controls. The error bars show standard error for triplicate samples from five birds in two separate experiments.

FIG. 4.

Quantification of chemokine and proinflammatory cytokine mRNA extracted from cecal tonsils of chickens after experimental infection with Salmonella serovar Typhimurium. Only statistically significant (P < 0.05) results are expressed as fold changes in chemokine mRNA levels for infected birds compared to those for age-matched, mock-infected controls. The error bars show standard error for triplicate samples from five birds in two separate experiments.

FIG. 5.

Quantification of chemokine and proinflammatory cytokine mRNA extracted from livers of chickens after experimental infection with Salmonella serovar Typhimurium. Only statistically significant (P < 0.05) results are expressed as fold changes in chemokine mRNA levels for infected birds compared to those for age-matched, mock-infected controls. The error bars show standard error for triplicate samples from five birds in two separate experiments.

FIG. 6.

Quantification of chemokine and proinflammatory cytokine mRNA extracted from spleens of chickens after experimental infection with Salmonella serovar Typhimurium. Only statistically significant (P < 0.05) results are expressed as fold changes in chemokine mRNA levels for infected birds compared to those for age-matched, mock-infected controls. The error bars show standard error for triplicate samples from five birds in two separate experiments.