Impact of TGEV infection on the pig small intestine

Abstract

Background: Pig diarrhea causes high mortality and large economic losses in the swine industry. Transmissible gastroenteritis virus (TGEV) causes pig diarrhea, with 100% mortality in piglets less than 2 weeks old. No investigation has yet been made of the small intestine of piglets that survived infection by TGEV.

Methods: In this study, we evaluated the impact of TGEV infection on the small intestine of recovered pigs.

Results: Histological analyses showed that TGEV infection led to villi atrophy, and reduced villous height and crypt depth. The number of SIgA positive cells, CD3⁺T cells, and dendritic cells (DCs) in jejunum decreased after TGEV infection in vivo. In contrast, microfold cell (M cell) numbers and cell proliferation increased in infected pigs. TGEV infection also significantly enhanced the mRNA expression levels of cytokine IL-1β, IL-6, TNF-α, IL-10, and TGF-β. Additionally, lower gene copy numbers of Lactobacillus, and higher numbers of Enterobacteriaceae, were detected in mucosal scraping samples from TGEV-infected pigs.

Conclusions: TGEV infection damages the small intestine, impairs immune functions, and increases pathogenic bacterial loading, all of which may facilitate secondary infections by other pathogens. These findings help quantify the impact of TGEV infection and clarify the pathogenic mechanisms underlying its effects in pigs.

Keywords: Infection; Pig; Small intestine; Transmissible gastroenteritis virus.

Fig. 1

Persistent TGEV infection in recovered pigs. Detection of TGEV infection by immunohistochemistry staining in the jejunum. The TGEV antigen stains brown in the cytoplasm of epithelial cells

Fig. 2

Histological and morphometrical analyses of pig small intestine. a HE-stained sections of the duodenum, jejunum and ileum. b–d Villus height and crypt depth for the small intestine. e Area measurements for PPs in ileum. Scale bars: 50 μm. Differences were considered significant at (*) 0.01 < p < 0.05, (**) p < 0.01

Fig. 3

Expression of SIgA positive cells, CD3⁺T cells, DC's. Immunohistochemical staining of SIgA positive cells and CD3⁺T cells, and immunofluorescent staining of DCs in the jejunum. a Changes in SIgA positive cells after TGEV infection. b Changes in CD3⁺T cells. Positive cells were quantified by densitometry analysis, and were calculated in 10 random fields. IOD: Integrated optical density. c Number of SLA-II-DR⁺SWC3a⁺DCs. Scale bars: 50 μm. Differences were considered significant at (*) 0.01 < p < 0.05, (**) p < 0.01

Fig. 4

Quantification of M cells and PCNA. Expression of cytokeratin 18, and measurements of intestinal epithelial cell proliferation. a Ileal sections were immunostained with anti-cytokeratin 18 monoclonal antibodies. b Immunofluorescence staining of proliferation marker PCNA from jejunum tissue. Scale bars: 50 μm in (a) and 100 μm in (b). Differences were considered significant at (*) 0.01 < p < 0.05, (**) p < 0.01

Fig. 5

mRNA level of the cytokines. Effect of TGEV infection on cytokines in the jejunum. Relative mRNA levels were measured for the proinflammatory cytokine IL-1β, IL-6, IL-8 and TNF-α, and anti-inflammatory factors IL-10 and TGF-β, using RT-PCR. Differences were considered significant at (*) 0.01 < p < 0.05, (**) p < 0.01

Fig. 6

Analysis of total bacteria, Lactobacillus, and Enterobacteriaceae. Quantitative PCR analysis of gene copy numbers for Lactobacillus, Enterobacteriaceae, and total bacteria. a Bacterial from jejunal mucosal scrapings. b Bacteria in feces. Differences were considered significant at (*) 0.01 < p < 0.05, (**) p < 0.01