Role of mesenteric lymph nodes and aging in secretory IgA production in mice

The intestinal immune system and gut barrier function in obesity and ageing

Obesity and ageing predispose to numerous, yet overlapping chronic diseases. For example, metabolic abnormalities, including insulin resistance (IR) and type 2 diabetes (T2D) are important causes of morbidity and mortality. Low-grade chronic inflammation of tissues, such as the liver, visceral adipose tissue and neurological tissues, is considered a significant contributor to these chronic diseases. Thus, it is becoming increasingly important to understand what drives this inflammation in affected tissues. Recent evidence, especially in the context of obesity, suggests that the intestine plays an important role as the gatekeeper of inflammatory stimuli that ultimately fuels low-grade chronic tissue inflammation. In addition to metabolic diseases, abnormalities in the intestinal mucosal barrier have been linked to a range of other chronic inflammatory conditions, such as neurodegeneration and ageing. The flow of inflammatory stimuli from the gut is in part controlled by local immunological inputs impacting the intestinal barrier. Here, we will review the impact of obesity and ageing on the intestinal immune system and its downstream consequences on gut barrier function, which is strongly implicated in the pathogenesis of obesity and age-related diseases. In particular, we will discuss the effects of age-related intestinal dysfunction on neurodegenerative diseases.

Evaluation of the Relationships between Intestinal Regional Lymph Nodes and Immune Responses in Viral Infections in Children

Viral infections increase the risk of developing allergies in childhood, and disruption of mucosal homeostasis is presumed to be involved. However, no study has reported a role for viral infections in such disruption. In this study, we clarified the mechanism of immunoglobulin A (IgA) overproduction in viral infections. Autopsies were performed on 33 pediatric cases, IgA and interferon (IFN)β levels were measured, and histopathological and immunohistochemical examinations were conducted. Furthermore, we cultured human cells and measured IFNβ and IgA levels to examine the effect of viral infections on IgA production. Blood IgA levels in viral infections were higher than in bacterial infections. Moreover, IFNβ levels in most viral cases were below the detection limit. Cell culture revealed increased IgA in gastrointestinal lymph nodes, especially in Peyer’s patches, due to enhanced IFNβ after viral stimulation. Conversely, respiratory regional lymph nodes showed enhanced IgA with no marked change in IFNβ. Overproduction of IgA, identified as an aberration of the immune system and resulting from excessive viral infection-induced IFNβ was observed in the intestinal regional lymph nodes, particularly in Peyer’s patches. Further, increased IgA without elevated IFNβ in the respiratory system suggested the possibility of a different mechanism from the gastrointestinal system.

12α-Hydroxylated bile acid enhances accumulation of adiponectin and immunoglobulin A in the rat ileum

We previously reported that dietary supplementation with cholic acid (CA), the primary 12α-hydroxylated (12αOH) bile acid (BA), reduces plasma adiponectin concentration in rats. The aim of this study was to examine the distribution of adiponectin in the body of CA-fed rats and its influence on mucosal immunoglobulin A concentration in the intestine. Rats were fed a diet supplemented with or without CA (0.5 g CA/kg diet) for 13 weeks. A reduction in plasma adiponectin level was observed from week 3. At the end of the experiment, the CA diet reduced plasma adiponectin concentration both in the portal and aortic plasma. Accumulation of adiponectin was accompanied by an increase in cadherin-13 mRNA expression in the ileal mucosa of CA-fed rats. No increase was observed in adiponectin mRNA expression in the ileal and adipose tissues of the CA-fed rats. Immunoglobulin A concentration in the ileal mucosa was elevated in the CA-fed rats and was correlated with the ileal adiponectin concentration. 12αOH BAs may modulate mucosal immune response that are involved in the accumulation of adiponectin in the ileum.

Production and Function of Immunoglobulin A

Among antibodies, IgA is unique because it has evolved to be secreted onto mucosal surfaces. The structure of IgA and the associated secretory component allow IgA to survive the highly proteolytic environment of mucosal surfaces but also substantially limit IgA's ability to activate effector functions on immune cells. Despite these characteristics, IgA is critical for both preventing enteric infections and shaping the local microbiome. IgA's function is determined by a distinct antigen-binding repertoire, composed of antibodies with a variety of specificities, from permissive polyspecificity to cross-reactivity to exquisite specificity to a single epitope, which act together to regulate intestinal bacteria. Development of the unique function and specificities of IgA is shaped by local cues provided by the gut-associated lymphoid tissue, driven by the constantly changing environment of the intestine and microbiota.

Adjuvant Strategies for Lactic Acid Bacterial Mucosal Vaccines

Lactic acid bacteria (LAB) are Gram-positive, acid-tolerant bacteria that have long been used in food fermentation and are generally recognized as safe (GRAS). LAB are a part of a normal microbiome and act as probiotics, improving the gastrointestinal microbiome and health when consumed. An increasing body of research has shown the importance of the microbiome on both mucosal immune heath and immune response to pathogens and oral vaccines. Currently, there are few approved mucosal vaccines, and most are attenuated viruses or bacteria, which necessitates cold chain, carries the risk of reversion to virulence, and can have limited efficacy in individuals with poor mucosal health. On account of these limitations, new types of mucosal vaccine vectors are necessary. There has been increasing interest and success in developing recombinant LAB as next generation mucosal vaccine vectors due to their natural acid and bile resistance, stability at room temperature, endogenous activation of innate and adaptive immune responses, and the development of molecular techniques that allow for manipulation of their genomes. To enhance the immunogenicity of these LAB vaccines, numerous adjuvant strategies have been successfully employed. Here, we review these adjuvant strategies and their mechanisms of action which include: Toll-like receptor ligands, secretion of bacterial toxins, secretion of cytokines, direct delivery to antigen presenting cells, and enterocyte targeting. The ability to increase the immune response to LAB vaccines gives them the potential to be powerful mucosal vaccine vectors against mucosal pathogens.

Intestinal epithelial barrier functions in ageing

The intestinal epithelial barrier protects the mucosa of the gastrointestinal (GI)-tract and plays a key role in maintaining the host homeostasis. It encompasses several elements that include the intestinal epithelium and biochemical and immunological products, such as the mucus layer, antimicrobial peptides (AMPs) and secretory immunologlobulin A (sIgA). These components are interlinked with the large microbial community inhabiting the gut to form a highly sophisticated biological system that plays an important role on many aspects of human health both locally and systemically. Like any other organ and tissue, the intestinal epithelial barrier is affected by the ageing process. New insights have surfaced showing that critical functions, including intestinal stem cell regeneration and regulation of the intestinal crypt homeostasis, barrier integrity, production of regulatory cytokines, and epithelial innate immunity to pathogenic antigens change across life. Here we review the age-associated changes of the various components of the intestinal epithelial barrier and we highlight the necessity to elucidate further the mechanisms underlying these changes. Expanding our knowledge in this area is a goal of high medical relevance and it will help to define intervention strategies to ameliorate the quality of life of the ever-expanding elderly population.

Immunomodulatory Protein Hydrolysates and Their Application

Immunomodulatory protein hydrolysate consumption may delay or prevent western immune-related diseases. In order to purposively develop protein hydrolysates with an optimal and reproducible immunomodulatory effect, knowledge is needed on which components in protein hydrolysates are responsible for the immune effects. Important advances have been made on this aspect. Also, knowledge on mechanisms underlying the immune modulating effects is indispensable. In this review, we discuss the most promising application possibilities for immunomodulatory protein hydrolysates. In order to do so, an overview is provided on reported in vivo immune effects of protein hydrolysates in both local intestinal and systemic organs, and the current insights in the underlying mechanisms of these effects. Furthermore, we discuss current knowledge and physicochemical approaches to identify the immune active protein sequence(s). We conclude that multiple hydrolysate compositions show specific immune effects. This knowledge can improve the efficacy of existing hydrolysate-containing products such as sports nutrition, clinical nutrition, and infant formula. We also provide arguments for why immunomodulatory protein hydrolysates could be applied to manage the immune response in the increasing number of individuals with a higher risk of immune dysfunction due to, for example, increasing age or stress.

Efficient induction of comprehensive immune responses to control pathogenic E. coli by clay nano-adjuvant with the moderate size and surface charge

In recent decades, diseases caused by pathogenic Escherichia coli (E. coli), enterohaemorrhagic E. coli (EHEC) O26 have been increasingly reported worldwide, which are as severe as those caused by EHEC strain O157:H7 and require effective intervention strategies. Herein, we report the application of clay nanoparticles, i.e. hectorites as effective nano-adjuvants for vaccination against EHEC O26 colonization. We show that medium size HEC (hectorite, around 73~77 nm diameter) is able to induce efficient humoral and cellular immune responses against EHEC antigen - intimin β (IB), which are significantly higher than those triggered by commercially used adjuvants - QuilA and Alum. We also demonstrate that mice immunized with IB adjuvanted with HEC nanoparticles elicit sufficient secretion of mucosal IgA, capable of providing effective protection against EHEC O26 binding to ruminant and human cells. In addition, we demonstrate for the first time that hectorites are able to initiate maturation of RAW 264.7 macrophages, inducing expression of co-stimulatory cytokines at a low nanoparticle concentration (10 μg/mL). Together these data strongly suggest that hectorite with optimized size is a highly efficient vaccine nano-adjuvant.

Intermittent fasting favored the resolution of Salmonella typhimurium infection in middle-aged BALB/c mice

Intermittent fasting (IF) reportedly increases resistance and intestinal IgA response to Salmonella typhimurium infection in mature mice. The aim of this study was to explore the effect of aging on the aforementioned improved immune response found with IF. Middle-aged male BALB/c mice were submitted to IF or ad libitum (AL) feeding for 40 weeks and then orally infected with S. typhimurium. Thereafter, infected animals were all fed AL (to maximize their viability) until sacrifice on day 7 or 14 post-infection. We evaluated body weight, bacterial load (in feces, Peyer's patches, spleen and liver), total and specific intestinal IgA, lamina propria IgA+ plasma cells, plasma corticosterone, and messenger RNA (mRNA) expression of α-chain, J-chain, and the polymeric immunoglobulin receptor (pIgR) in liver and intestinal mucosa. In comparison with the infected AL counterpart, the infected IF group (long-term IF followed by post-infection AL feeding) generally had lower intestinal and systemic bacterial loads as well as higher total IgA on both post-infection days. Both infected groups showed no differences in corticosterone levels, body weight, or food and caloric intake. The increase in intestinal IgA was associated with enhanced pIgR mRNA expression in the intestine (day 7) and liver. Thus, to maintain body weight and caloric intake, IF elicited metabolic signals that possibly induced the increased hepatic and intestinal pIgR mRNA expression found. The increase in IgA probably resulted from intestinal IgA transcytosis via pIgR. This IgA response along with phagocyte-induced killing of bacteria in systemic organs (not measured) may explain the resolution of the S. typhimurium infection.

Enhancement of intestinal IgA production by Ajoene in mice

We investigated the effects of ajoene on intestinal IgA production. Ajoene (1.35, 4.5, and 13.5 µg/kg/d) was administered to mice for 4 weeks. The fecal IgA level in the 13.5 µg/kg/d group increased after 3 weeks. The intestinal IgA level also increased in a dose-dependent manner upon ajoene administration. An oil-macerated garlic extract, with 1500 µg/g of ajoene, enhanced the intestinal IgA production.

Aging correlates with reduction in regulatory-type cytokines and T cells in the gut mucosa

Aging is reported to be associated with decline in oral tolerance induction, which is initiated at the intestinal mucosal surface. Herein, we examined the effect of aging in T cells and cytokines at the intestinal mucosa that might be involved in oral tolerance induction. Frequencies of regulatory-type IEL subsets such as TCRγδ(+) and TCRαβ(+)CD8αα(+) were lower in aged mice. Mucosal CD4(+)CD25(+)Foxp3(+) and CD4(+)LAP(+) T cells increased with aging but activated CD44(+)CD4(+) mucosal T cells also augmented. Production of TGF-β and IL-10 in the small intestine of old mice was reduced. Moreover, the ability of mucosal dendritic cells of aged mice to stimulate TGF-β secretion and differentiation of CD4(+)LAP(+) T cells in co-culture studies also declined with aging. Reduction in these regulatory-type cytokines and T cells may help to explain the decline in susceptibility to oral induction during aging. However, not all mucosal regulatory elements were altered by aging and CD4(+)CD25(+)Foxp3(+) T cells were especially resistant to changes. Persistence of some mechanisms of regulation may play a critical role in maintaining mucosal homeostasis during aging.

Effect of early enteral immunonutrition on the secretion of TH1/TH2 cytokines in Peyer's patches of scalded rats

AIM: To investigate the changes in the secretion of TH1/TH2 cytokines in Peyer's patches of scalded rats after enteral nutrition supplementation.

METHODS: Sixty-four Sprague-Dawley rats were divided into EN group (n = 32) and EIN group (n = 32). Rats were subjected to a 30% TBSA III degree scald injury. The EN group was given standard enteral nutrition (Nutrison Multi Fibre), while the EIN group was given enteral immunonutrition. Peyer's patches were excised to isolate lymphocytes to determine the changes in the secretion of TH1/TH2 cytokines.

RESULTS: On day 1 after scalding, the concentrations of IL-2 and IFN-γ released from Peyer's patch lymphocytes were significantly higher in the two experimental groups compared with pre-scald values (19.7 ± 7.3 vs 92.6 ±21.3 and 97.6 ± 25.4; 63.7 ± 27.3 vs 279.4 ± 89.7 and 292.7 ± 97.4; all P < 0.01). On day 10, the concentrations of IL-2 and IFN-γ released from Peyer's patch lymphocytes were significantly lower in the EIN group than in the EN group (41.6 ± 16.5 vs 55.9 ± 14.4; 71.6 ± 26.9 vs 104.3 ± 31.7; both P < 0.01 or 0.05). The concentrations of IL-4 and IL-10 were significantly higher in the EIN group than in the EN group on days 4, 7 and 10.

CONCLUSION: The expression of Th1 cytokines is up-regulated in Peyer's patches of scalded rats. Enteral immunonutrition supplementation can promote the expression of Th2 cytokines, help correct TH2/TH1 imbalance, and improve mucosal barrier function.

Further Characterization of Activin A-induced IgA Response in Murine B Lymphocytes

We have recently shown that activin A, a member of TGF-β superfamily, stimulates mouse B cells to express IgA isotype but other isotypes. In the present study, we further characterized effects of activin A on B cell growth and IgA expression. We found that activin A did not have effect on LPS-stimulated cell viability. In parallel, CFSE staining analysis revealed that activin A did not alter cell division. An increase of IgA secretion by activin A was completely abrogated by anti-activin A Ab but not by anti-TGFβ1 Ab. In the same conditions, no other isotypes are significantly affected by each antibody treatment. Finally, activin A, as similar to TGF-β1, increased IgA secretion by mesenteric lymph node cells. These results suggest that activin A can specifically stimulate IgA response, independent of TGF-β in the gut.

Specific immune responses but not basal functions of B and T cells are impaired in aged mice

Senescence is characterized by several alterations in the immune system. Such modifications can be found in lymphoid organs as well as in the cellular components of the immune system. Several reports have suggested that immune dysfunction can affect both T and B cells, but T cells have been shown to be more susceptible to the effects of aging. B cell function may also be altered with reduction in germinal center formation, antibody response, and affinity maturation of antibodies. Herein we showed that although antigen-specific antibody response to a soluble antigen declines in 18-month old mice, total levels of serum antibodies as well as frequencies of spleen and bone marrow antibody-producing cells are increased in aged mice. In addition, proliferative response of non-stimulated spleen T cells from aged mice were augmented and insensitive to increasing doses of concanavalin A stimulation as compared to young mice that showed a typical dose-dependent response to mitogen stimulation in vitro. These data suggest that the higher activation mode of B and T cells in senescent mice is a result of an increased frequency of cells committed to previous antigenic experiences and with poor ability to respond to novel antigenic challenges.