B cells and the intestinal microbiome in time, space and place

The gut immune system is shaped by the continuous interaction with the microbiota. Here we dissect temporal, spatial and contextual layers of gut B cell responses. The microbiota impacts on the selection of the developing pool of pre-immune B cells that serves as substrate for B cell activation, expansion and differentiation. However, various aspects of the gut B cell response display unique features. In particular, occurrence of somatically mutated B cells, chronic gut germinal centers in T cell-deficient settings and polyreactive binding of gut IgA to the microbiota questioned the nature and microbiota-specificity of gut germinal centers. We propose a model to reconcile these observations incorporating recent work demonstrating microbiota-specificity of gut germinal centers. We speculate that adjuvant effects of the microbiota might modify permissiveness for B cell to enter and exit gut germinal centers. We propose that separating aspects of time, space and place facilitate the occasionally puzzling discussion of gut B cell responses to the microbiota.

Intestinal endothelial cells increase HIV infection and latency in resting and activated CD4 + T cells, particularly affecting CCR6 + CD4 + T cells

BACKGROUND

With suppressive antiretroviral therapy, HIV infection is well-managed in most patients. However, eradication and cure are still beyond reach due to latent viral reservoirs in CD4 + T cells, particularly in lymphoid tissue environments including the gut associated lymphatic tissues. In HIV patients, there is extensive depletion of T helper cells, particularly T helper 17 cells from the intestinal mucosal area, and the gut is one of the largest viral reservoir sites. Endothelial cells line lymphatic and blood vessels and were found to promote HIV infection and latency in previous studies. In this study, we examined endothelial cells specific to the gut mucosal area-intestinal endothelial cells-for their impact on HIV infection and latency in T helper cells.

RESULTS

We found that intestinal endothelial cells dramatically increased productive and latent HIV infection in resting CD4 + T helper cells. In activated CD4 + T cells, endothelial cells enabled the formation of latent infection in addition to the increase of productive infection. Endothelial-cell-mediated HIV infection was more prominent in memory T cells than naïve T cells, and it involved the cytokine IL-6 but did not involve the co-stimulatory molecule CD2. The CCR6 + T helper 17 subpopulation was particularly susceptible to such endothelial-cell-promoted infection.

CONCLUSION

Endothelial cells, which are widely present in lymphoid tissues including the intestinal mucosal area and interact regularly with T cells physiologically, significantly increase HIV infection and latent reservoir formation in CD4 + T cells, particularly in CCR6 + T helper 17 cells. Our study highlighted the importance of endothelial cells and the lymphoid tissue environment in HIV pathology and persistence.

In-vivo analysis of Protec™ and β-glucan supplementation on innate immune performance and intestinal health of rainbow trout

Functional diets are often given to fish during key stages to improve health through the interaction of the feed components with the host intestine. The additional factors added in these diets are known to modulate the immune response and as such may also offer protection against pathogenic challenges. The present study was undertaken to evaluate whether β-glucan supplementation for 6 weeks can alter the magnitude of immune response to immunological challenges and subsequently offer an improved innate immune response to bacterial challenge in rainbow trout. Two experimental diets were used to study these effects: a basic commercial diet supplemented with β-glucan and a commercially available functional diet (Protec™) that has β-glucan as a functional component in addition to other components were compared to a basic commercial control diet. No significant differences were observed in biometric data. Histological analysis revealed a significantly greater number of goblet cells in the fish fed Protec™ and β-glucan diets compared to those fed a control diet. Cell marker gene expression of distal intestine leucocytes indicated higher expression of T- and B-cells marker genes to both the β-glucan containing diets in comparison to control. The Protec™ diet demonstrated modulation of innate immune markers after 6 weeks of feeding with key antimicrobial genes (SAA, HAMP, IL-1β and TNFα) showing significant increases compared to the other diets. After stimulation with both PAMPs and an immune challenge with A. salmonicida fish fed the β-glucan diet and the Protec™ exhibited modulation of the innate immune response. An immune challenge with A. salmonicida was carried out to identify if dietary composition led to differences in the innate immune response of rainbow trout. Modulation of the magnitude of response in some immune genes (SAA, IL-1β and HAMP) was observed in both the distal intestine and head kidney in the Protec™ and β-glucan fed fish compared to those fed the control diet.

Maternal 18:3n-3 favors piglet intestinal passage of LPS and promotes intestinal anti-inflammatory response to this bacterial ligand

We recently observed that maternal 18:3n-3 increases piglet jejunal permeability. We hypothesized that this would favor intestinal lipopolysaccharide (LPS) passage and alter gut immune system education toward this bacterial ligand. Sows were fed 18:3n-3 or 18:2n-6 diets throughout gestation and lactation. In each litter, two piglets were given oral Gram-negative spectrum antibiotic from post-natal day (PND) 14 to 28. All piglets were weaned on a regular diet at PND28. 18:3n-3 piglets exhibited greater jejunal permeability to FITC-LPS at PND28. Levels of 18:3n-3 but neither 20:5n-3 nor 20:4n-6 were greater in mesenteric lymph nodes (MLN) of 18:3n-3 piglets. Jejunal explant or MLN cell cytokine responses to LPS were not influenced by the maternal diet. Antibiotic increased jejunal permeability to FITC-LPS and lowered the level of 20:5n-3 in MLN, irrespective of the maternal diet. At PND52, no long-lasting effect of the maternal diet or antibiotic treatment on jejunal permeability was noticed. 18:3n-3 and 20:4n-6 levels were greater and lower, respectively, in MLN of 18:3n-3 compared to 18:2n-6 piglets. IL-10 production by MLN cells in response to LPS was greater in the 18:3n-3 group, irrespective of the neonatal antibiotic treatment. IL-8 secretion by jejunal explants in response to LPS was lower in antibiotic-treated 18:3n-3 compared to 18:2n-6 piglets. Finally, proportion of MHC class II(+) antigen-presenting cells was greater in 18:3n-3 than 18:2n-6 MLN cells. In conclusion, maternal 18:3n-3 directs the intestinal immune response to LPS toward an anti-inflammatory profile beyond the breastfeeding period; microbiota involvement seems dependent of the immune cells considered.