Lactic acid bacterial colonization and human rotavirus infection influence distribution and frequencies of monocytes/macrophages and dendritic cells in neonatal gnotobiotic pigs

Yeast culture supplement during nursing and transport affects immunity and intestinal microbial ecology of weanling pigs

The objectives of this study were to determine the influence of a Saccharomyces cerevisiae fermentation product on innate immunity and intestinal microbial ecology after weaning and transport stress. In a randomized complete block design, before weaning and in a split-plot analysis of a 2 × 2 factorial arrangement of yeast culture (YY) and transport (TT) after weaning, 3-d-old pigs (n = 108) were randomly assigned within litter (block) to either a control (NY, milk only) or yeast culture diet (YY; delivered in milk to provide 0.1 g of yeast culture product/kg of BW) from d 4 to 21. At weaning (d 21), randomly, one-half of the NY and YY pigs were assigned to a 6-h transport (NY-TT and YY-TT) before being moved to nursery housing, and the other one-half were moved directly to nursery housing (NY-NT and YY-NT, where NT is no transport). The yeast treatment was a 0.2% S. cerevisiae fermentation product and the control treatment was a 0.2% grain blank in feed for 2 wk. On d 1 before transport and on d 1, 4, 7, and 14 after transport, blood was collected for leukocyte assays, and mesenteric lymph node, jejunal, and ileal tissue, and jejunal, ileal, and cecal contents were collected for Toll-like receptor expression (TLR); enumeration of Escherichia coli, total coliforms, and lactobacilli; detection of Salmonella; and microbial analysis. After weaning, a yeast × transport interaction for ADG was seen (P = 0.05). Transport affected (P = 0.09) ADFI after weaning. Yeast treatment decreased hematocrit (P = 0.04). A yeast × transport interaction was found for counts of white blood cells (P = 0.01) and neutrophils (P = 0.02) and for the neutrophil-to-lymphocyte ratio (P = 0.02). Monocyte counts revealed a transport (P = 0.01) effect. Interactions of yeast × transport (P = 0.001) and yeast × transport × day (P = 0.09) for TLR2 and yeast × transport (P = 0.08) for TLR4 expression in the mesenteric lymph node were detected. Day affected lactobacilli, total coliform, and E. coli counts. More pigs were positive for Salmonella on d 7 and 14 than on d 4, and more YY-TT pigs were positive (P = 0.07) on d 4. The number of bands for microbial amplicons in the ileum was greater for pigs in the control treatment than in the yeast treatment on d 0, and this number tended to decrease (P = 0.066) between d 1 and 14 for all pigs. Similarity coefficients for jejunal contents were greater (P = 0.03) for pigs fed NY than for those fed YY, but pigs fed YY had greater similarity coefficients for ileal (P = 0.001) and cecal (P = 0.058) contents. The number of yeast × transport × day interactions demonstrates the complexity of the stress and dietary relationship.

Development of γδ T cell subset responses in gnotobiotic pigs infected with human rotaviruses and colonized with probiotic lactobacilli

γδ T cell responses are induced by various viral and bacterial infections. Different γδ T cells contribute to activation and regulation of the inflammatory response and to epithelial repair. How γδ T cells respond to rotavirus infection and how the colonization of probiotics influences the γδ T cell response were unknown. In this study, we evaluated by multicolor flow cytometry the frequencies and distribution of total γδ T cells and three major subsets (CD2-CD8-, CD2+CD8- and CD2+CD8+) in ileum, spleen and blood of gnotobiotic (Gn) pigs at early (3-5 days) and late phases (28 days) after rotavirus infection. The Gn pigs were inoculated with the virulent human rotavirus Wa strain and colonized with a mixture of two strains of probiotics Lactobacillus acidophilus and Lactobacillus reuteri. In naïve pigs, the highest frequency of total γδ T cells was found in blood, followed by spleen and ileum at the early age (8-10 days old) whereas in older pigs (32 days of age) the highest frequency of total γδ T cells was found in ileum and spleen followed by blood. Rotavirus infection significantly increased frequencies of intestinal total γδ T cells and the putatively regulatory CD2+CD8+ γδ T cell subset and decreased frequencies of the putatively proinflammatory CD8- subsets in ileum, spleen and blood at post-infection days (PID) 3 or 5. The three γδ T cell subsets distributed and responded differently after rotavirus infection and/or lactobacilli colonization. The CD2+CD8+ subset contributed the most to the expansion of total γδ T cells after rotavirus infection in ileum because more than 77% of the total γδ T cells there were CD2+CD8+ cells. There was an additive effect between lactobacilli and rotavirus in inducing total γδ T cell expansion in ileum at PID 5. The overall effect of lactobacilli colonization versus rotavirus infection on frequencies of the CD2+CD8+ γδ T cell subset in ileum was similar; however, rotavirus-infected pigs maintained significantly higher frequencies of CD8- subsets in ileum than lactobacilli-colonized pigs. The dynamic γδ T cell responses suggest that γδ T cell subsets may play important roles in different stages of immune responses after rotavirus infection and probiotic colonization. The knowledge on the kinetics and distribution patterns of γδ T cell subsets in naïve pigs and after rotavirus infection or lactobacilli colonization provides the foundation for further mechanistic studies of their functions.

Rearing environment affects development of the immune system in neonates

Early-life exposure to appropriate microbial flora drives expansion and development of an efficient immune system. Aberrant development results in increased likelihood of allergic disease or increased susceptibility to infection. Thus, factors affecting microbial colonization may also affect the direction of immune responses in later life. There is a need for a manipulable animal model of environmental influences on the development of microbiota and the immune system during early life. We assessed the effects of rearing under low- (farm, sow) and high-hygiene (isolator, milk formula) conditions on intestinal microbiota and immune development in neonatal piglets, because they can be removed from the mother in the first 24 h for rearing under controlled conditions and, due to placental structure, neither antibody nor antigen is transferred in utero. Microbiota in both groups was similar between 2 and 5 days. However, by 12-28 days, piglets reared on the mother had more diverse flora than siblings reared in isolators. Dendritic cells accumulated in the intestinal mucosa in both groups, but more rapidly in isolator piglets. Importantly, the minority of 2-5-day-old farm piglets whose microbiota resembled that of an older (12-28-day-old) pig also accumulated dendritic cells earlier than the other farm-reared piglets. Consistent with dendritic cell control of T cell function, the effects on T cells occurred at later time-points, and mucosal T cells from high-hygiene, isolator pigs made less interleukin (IL)-4 while systemic T cells made more IL-2. Neonatal piglets may be a valuable model for studies of the effects of interaction between microbiota and immune development on allergy.

Effect of probiotic supplementation in the first 6 months of life on specific antibody responses to infant Hepatitis B vaccination

Probiotics have been shown to enhance specific immune responses to vaccines. We aim to assess the effect of probiotic supplementation on specific IgG antibody responses to Hepatitis B (HepB) vaccination in infants. Compared to controls, probiotic supplementation improved HepB surface antibody responses in subjects receiving monovalent doses of HepB vaccine at 0, 1 month and a DTPa-HepB combination vaccine at 6 months [placebo (n=28): 187.97 (180.70-195.24), probiotic (n=29): 345.70 (339.41-351.99)mIU/ml] (p=0.069), but not those who received 3 monovalent doses [placebo (n=68): 302.34 (296.31-308.37), probiotic (n=77): 302.06 (296.31-307.81)mIU/ml] (p=0.996). Probiotics may enhance specific antibody responses in infants receiving certain Hepatitis B vaccine schedules.

Intestinal bacteria and the regulation of immune cell homeostasis

The human intestine is colonized by an estimated 100 trillion bacteria. Some of these bacteria are essential for normal physiology, whereas others have been implicated in the pathogenesis of multiple inflammatory diseases including IBD and asthma. This review examines the influence of signals from intestinal bacteria on the homeostasis of the mammalian immune system in the context of health and disease. We review the bacterial composition of the mammalian intestine, known bacterial-derived immunoregulatory molecules, and the mammalian innate immune receptors that recognize them. We discuss the influence of bacterial-derived signals on immune cell function and the mechanisms by which these signals modulate the development and progression of inflammatory disease. We conclude with an examination of successes and future challenges in using bacterial communities or their products in the prevention or treatment of human disease.

Rotavirus infection activates dendritic cells from Peyer's patches in adult mice

This study used an in vivo mouse model to analyze the response of dendritic cells (DCs) in Peyer's patches (PPs) within the first 48 h of infection with the wild-type murine rotavirus EDIM (EDIM(wt)). After the infection, the absolute number of DCs was increased by 2-fold in the PPs without a modification of their relative percentage of the total cell number. Also, the DCs from PPs of infected mice showed a time-dependent migration to the subepithelial dome (SED) and an increase of the surface activation markers CD40, CD80, and CD86. This response was more evident at 48 h postinfection (p.i.) and depended on viral replication, since DCs from PPs of mice inoculated with UV-treated virus did not show this phenotype. As a result of the activation, the DCs showed an increase in the expression of mRNA for the proinflammatory cytokines interleukin-12/23p40 (IL-12/23p40), tumor necrosis factor alpha (TNF-alpha), and beta interferon (IFN-beta), as well as for the regulatory cytokine IL-10. These results suggest that, a short time after rotavirus infection, the DCs from PPs play a critical role in controlling the infection and, at the same time, avoiding an excessive inflammatory immune response.

Primary porcine CD11R1+ antigen-presenting cells isolated from small intestinal mucosa mature but lose their T cell stimulatory function in response to cholera toxin treatment

Antigen-presenting cells (APCs) in the small intestinal mucosa perform dual functions of maintaining tissue homeostasis and of protecting against intestinal pathogens as key inducers of both innate and adaptive immune responses. Intestinal APCs are thus important regulators of intestinal immunity and also potential target cells for mucosal adjuvants such as cholera toxin (Ctx), which was used successfully in several oral vaccination studies in pigs. The aims of the present study were (1) to isolate porcine small intestinal APCs and evaluate the feasibility of using these cells for functional in vitro studies and (2) to determine the response of intestinal APCs to Ctx. Microscopic and flow cytometric analyses using antibodies to CD1, CD11R1, CD16, and SIRPalpha (SWC3) revealed the presence of multiple subsets of MHC-II(++) APCs in porcine small intestinal mucosa. The alpha-integrin subunit CD11R1 was most frequently expressed and therefore chosen as a selection marker. CD11R1(+) cells were enriched from total lamina propria cells to >90% purity by immunomagnetic separation. Within the CD11R1 cells, we identified two populations with distinct forward and side scatter characteristics: (1) APCs identified by their high expression of MHC-II and consisting of SIRPalpha(+) and SIRPalpha(-) subsets, and (2) contaminating eosinophils. In culture, intestinal APCs spontaneously matured, as shown by significant (>5-fold) increase in CD80/CD86 expression. The SIRPalpha(+) APCs quickly disappeared from the cultures, likely due to increased apoptotic cell death. However, the observed spontaneous changes in the isolated cell population did not mask the effects of stimulation with Ctx, which resulted in a 2.5-fold increase in the expression of maturation markers CD80/CD86, but significant loss of T cell stimulatory function, corroborating previous results obtained with MoDC.

The food contaminant fumonisin B(1) reduces the maturation of porcine CD11R1(+) intestinal antigen presenting cells and antigen-specific immune responses, leading to a prolonged intestinal ETEC infection

Consumption of food or feed contaminated with fumonisin B₁ (FB₁), a mycotoxin produced by Fusarium verticillioides, can lead to disease in humans and animals. The present study was conducted to examine the effect of FB₁ intake on the intestinal immune system. Piglets were used as a target and as a model species for humans since their gastro-intestinal tract is very similar. The animals were orally exposed to a low dose of FB₁ (1 mg/kg body weight FB₁) for 10 days which did not result in clinical signs. However, when compared to non-exposed animals, FB₁-exposed animals showed a longer shedding of F4⁺ enterotoxigenic Escherichia coli (ETEC) following infection and a lower induction of the antigen-specific immune response following oral immunization. Further analyses to elucidate the mechanisms behind these observations revealed a reduced intestinal expression of IL-12p40, an impaired function of intestinal antigen presenting cells (APC), with decreased upregulation of Major Histocompatibility Complex Class II molecule (MHC-II) and reduced T cell stimulatory capacity upon stimulation. Taken together, these results indicate an FB₁-mediated reduction of in vivo APC maturation.

The porcine dendritic cell family

Considering the pivotal roles played by dendritic cells (DCs) in both innate and adaptive immune responses, advances in the field of porcine immunology DC biology have recently progressed rapidly. As with the more extensively studied murine and human DCs, porcine DC can be generated from bone marrow haematopoietic cells or monocytes, and have been analysed in various immunological and non-immunological tissues. Both conventional DC (cDC) and plasmacytoid DC (pDC) have been characterized. The function of porcine monocyte-derived DC has not only been characterized in terms of antigen presentation and lymphocyte activation, but also their response to various ligands of pattern recognition receptors. These have been characterized in terms of the induction of DC maturation and pro-inflammatory, Th1-like or Th2-like cytokines secretion. Porcine pDC most effectively sense virus infections and are characterized by their capacity to produce large quantities of IFN-alpha and the pro-inflammatory cytokines TNF-alpha, IL-6 and IL-12. As such, the DC family as a whole is a powerful ally in the host battle against pathogen attack. Nevertheless, DC in particular tissue environments or under particular stimuli can down-regulate immune response development. This is not only important for preventing over-activation of the immune system and also for ensuring tolerance against self or "friendly" substances including food components, but may also be used as a mechanism of pathogens to evade immune responses.

Toll-like receptor and innate cytokine responses induced by lactobacilli colonization and human rotavirus infection in gnotobiotic pigs

Toll-like receptors (TLR) play an important role in the recognition of microbes by host sentinel cells that leads to the subsequent innate and adaptive immune responses. In this study, we evaluated the patterns of TLR2-, TLR3- and TLR9-expressing antigen presenting cells (APCs) in spleen and blood of gnotobiotic (Gn) pigs after colonization with a mixture of two strains of lactic acid bacteria (LAB), Lactobacillus acidophilus and Lactobacillus reuteri or infection with the virulent human rotavirus (HRV) Wa strain. We also assessed the influence of LAB on TLR and serum innate cytokine responses induced by HRV. Distributions of subpopulations of APCs [CD14+/-SWC3+CD11R1- monocytes/macrophages and CD14+/-SWC3+CD11R1+ conventional dendritic cells (cDCs)] were described in our previous report (Zhang, W., Wen, K., Azevedo, M.S., Gonzalez, A.M., Saif, L.J., Li, G., Yousef, A.E., Yuan, L., 2008. Lactic acid bacterial colonization and human rotavirus infection influence distribution and frequencies of monocytes/macrophages and dendritic cells in neonatal gnotobiotic pigs. Vet. Immunol. Immunopathol. 121, pp. 222-231). We demonstrated that LAB induced strong TLR2-expressing APC responses in blood and spleen, HRV induced a TLR3 response in spleen, and TLR9 responses were induced by either HRV (in spleen) or LAB (in blood). LAB and HRV have an additive effect on TLR2- and TLR9-expressing APC responses, consistent with the adjuvant effect of LAB. Overall, the frequencies of TLR-expressing CD14+ APCs were higher than CD14- APCs. LAB enhanced the IFN-gamma and IL-4 responses in serum, but it had a suppressive effect on the TLR3- and TLR9-expressing CD14- APC responses in spleen and the serum IFN-alpha response induced by HRV. These results elucidated the systemic TLR2-, TLR3-, and TLR9-expressing monocyte/macrophage and cDC responses after HRV infection, LAB colonization, and the two combined. Our findings facilitate the understanding of the mechanism of LAB's adjuvant effect on rotavirus vaccines and the diverse innate and adaptive immune responses induced by commensal LAB colonization versus rotavirus infection and the interactions between them.