Commensal microbial-host interaction is crucial for host metabolism, growth, development, and immunity. However, research on microbial-host immunity in large animal models has been limited. This study was conducted to investigate the effects of the commensal microbiota on immune function in two model groups: germ-free (GF) and specific-pathogen-free (SPF) piglets. The weight and organ index of the spleen of the GF piglet were larger than those in the SPF piglet (P < 0.05). The histological structure of the red pulp area and mean area of germinal centers were larger in the SPF piglet than in the GF piglet (P < 0.05), whereas the areas of staining of B cells and T cells in the spleen and mesenteric lymph nodes (MLNs) were lower in the GF piglet (P < 0.05). We identified immune-related genes in the spleen and MLNs using RNA sequencing, and used real-time quantitative PCR to analyze the expression of core genes identified in gene set enrichment analysis. The expression levels of genes in the transforming growth factor-β/SMAD3 signaling pathway, Toll-like receptor 2/MyD88/nuclear factor-κB signaling pathway, and pro-inflammatory factor genes IL-6 and TNF-α in the spleen and MLNs were higher in the SPF piglet and in splenic lymphocytes compared with those in the GF and control group, respectively, under treatment with acetic acid, propionic acid, butyric acid, lipopolysaccharide (LPS), or concanavalin A (ConA). The abundances of plasma cells, CD8++ T cells, follicular helper T cells, and resting natural killer cells in the spleen and MLNs were significantly greater in the SPF piglet than in the GF piglet (P < 0.05). In conclusion, the commensal microbiota influenced the immune tissue structure, abundances of immune cells, and expression of immune-related pathways, indicating the importance of the commensal microbiota for spleen and MLNs development and function. In our study, GF piglet was used as the research model, eliminating the interference of microbiota in the experiment, and providing a suitable and efficient large animal research model for exploring the mechanism of \"microbial-host\" interactions.

Salmonella Typhimurium is an enteric pathogen that causes acute and chronic infections in humans and animals. One-week-old germ-free piglets were orally colonized/infected with the Salmonella Typhimurium LT2 strain or its isogenic rough ΔrfaL, ΔrfaG or ΔrfaC mutants with exactly defined lipopolysaccharide (LPS) defects. After 24 h, the piglets were euthanized and the colonization of the small intestine, translocations into the mesenteric lymph nodes, liver, spleen, lungs, and bacteremia, along with changes in the ileum histology, and transcription levels of the tight junction proteins claudin-1, claudin-2, and occludin were all assessed. Additionally, transcription levels of IL-8, TNF-α, and IL-10 in the terminal ileum, and their local and systemic protein levels were evaluated. Wild-type Salmonella Typhimurium showed the highest translocation, histopathological changes, upregulation of claudins and downregulation of occludin, transcription of the cytokines, intestinal IL-8 and TNF-α levels, and systemic TNF-α and IL-10 levels. Depending on the extent of the incompleteness of the LPS, the levels of the respective elements decreased, or no changes were observed at all in the piglets colonized/infected with Δrfa mutants. Intestinal IL-10 and systemic IL-8 levels were not detected in any piglet groups. This study provided foundational data on the gnotobiotic piglet response to colonization/infection with the exactly defined rough Salmonella Typhimurium LT2 isogenic mutants.

To overcome shortages of human donor organs for organ failure patients, we made a commitment to develop gnotobiotic miniature swine as an alternative organ donor source for xenotransplantation. For this, we have constructed an absolute barrier-sustained gnotobiotic facility. Pregnant sows of gnotobiotic miniature swine, were procured and germfree piglets were obtained by hysterectomy. These were maintained in germfree isolators for about 4 weeks, deprived of colostrum and were fed sterilized soybean milk. They were associated with di-flora, anaerobic Lactobacillus sp. and Streptococcus sp. After confirmation of successful associations, gnotobiotic piglets were transferred into the facility aseptically. The piglets are maintained on high-efficiency particle air-filtered air in and out; maintaining constant room air pressure of 33 ± 3 mmAq, and sterile water and diet. In 10 sessions of hysterectomy, 18 male and 32 female piglets were obtained of which piglets (M six, F eight) died within 5 days. Among live piglets, piglets (M eight, F 12) were confirmed to be germfree by microbiological monitoring. For research of xenotransplantation, one consistent experimental result was essential. Therefore, major histocompatibility complex class II which related innate immunity, homozygotic gnotobiotic miniature swine was developed. As a result, genotyping revealed 14 individuals to be homozygous for major histocompatibility complex class II (DRB, DQB) as 0301, three individuals were homozygous as 0201 and each of two were homozygous for DQB as 0701 and DRB as 0404, respectively. Genetic modifications and immunological research for ideal alternative organ sources are in progress.