M-cells: origin, morphology and role in mucosal immunity and microbial pathogenesis

Alterations in gut microbiota linked to provenance, sex, and chronic wasting disease in white-tailed deer (Odocoileus virginianus)

Chronic wasting disease (CWD) is a fatal, contagious, neurodegenerative prion disease affecting both free-ranging and captive cervid species. CWD is spread via direct or indirect contact or oral ingestion of prions. In the gastrointestinal tract, prions enter the body through microfold cells (M-cells), and the abundance of these cells can be influenced by the gut microbiota. To explore potential links between the gut microbiota and CWD, we collected fecal samples from farmed and free-ranging white-tailed deer (Odocoileus virginianus) around the Midwest, USA. Farmed deer originated from farms that were depopulated due to CWD. Free-ranging deer were sampled during annual deer harvests. All farmed deer were tested for CWD via ELISA and IHC, and we used 16S rRNA gene sequencing to characterize the gut microbiota. We report significant differences in gut microbiota by provenance (Farm 1, Farm 2, Free-ranging), sex, and CWD status. CWD-positive deer from Farm 1 and 2 had increased abundances of Akkermansia, Lachnospireacea UCG-010, and RF39 taxa. Overall, differences by provenance and sex appear to be driven by diet, while differences by CWD status may be linked to CWD pathogenesis.

The absorption of glycosaminoglycans of different molecular weight obtained from Apostichopus japonicus: an in vitro and in situ study

The purpose of this study was to investigate the absorption and transport of glycosaminoglycan from Apostichopus japonicus (AHG) and its depolymerized derivatives (DAHG-1, DAHG-2, DAHG-3). The AHG and depolymerized AHGs (DAHGs) were characterized by high-performance gel permeation chromatography (HPGPC), Raman spectroscopy and atomic force microscopy (AFM). The results showed that there was no significant difference of an AHG primary structure and functional groups during the depolymerization. Meanwhile, AFM observation showed that AHG and DAHGs possessed linear structures. In this study, a rapid and sensitive liquid chromatographic post-column derivatization method was used to investigate the absorption of AHG and DAHGs with the Caco-2 cell model, the M cell model and the intestinal recirculating perfusion. It was found that AHG and DAHGs can be absorbed in the intestine, and their transport involved endocytosis.

Oral Biologic Delivery: Advances Toward Oral Subunit, DNA, and mRNA Vaccines and the Potential for Mass Vaccination During Pandemics

Oral vaccination enables pain-free and self-administrable vaccine delivery for rapid mass vaccination during pandemic outbreaks. Furthermore, it elicits systemic and mucosal immune responses. This protects against infection at mucosal surfaces, which may further enhance protection and minimize the spread of disease. The gastrointestinal (GI) tract presents a number of prospective mucosal inductive sites for vaccine targeting, including the oral cavity, stomach, and small intestine. However, currently available oral vaccines are effectively limited to live-attenuated and inactivated vaccines against enteric diseases. The GI tract poses a number of challenges,including degradative processes that digest biologics and mucosal barriers that limit their absorption. This review summarizes the approaches currently under development and future opportunities for oral vaccine delivery to established (intestinal) and relatively new (oral cavity, stomach) mucosal targets. Special consideration is given to recent advances in oral biologic delivery that offer promise as future platforms for the administration of oral vaccines.

Mucin-Like Domain of Mucosal Addressin Cell Adhesion Molecule-1 Facilitates Integrin α4β7-Mediated Cell Adhesion Through Electrostatic Repulsion

The homing of lymphocytes from blood to gut-associated lymphoid tissue is regulated by interaction between integrin α4β7 with mucosal vascular addressin cell adhesion molecule 1 (MAdCAM-1) expressed on the endothelium of high endothelial venules (HEVs). However, the molecular basis of mucin-like domain, a specific structure of MAdCAM-1 regulating integrin α4β7-mediated cell adhesion remains obscure. In this study, we used heparan sulfate (HS), which is a highly acidic linear polysaccharide with a highly variable structure, to mimic the negative charges of the extracellular microenvironment and detected the adhesive behaviors of integrin α4β7 expressing 293T cells to immobilized MAdCAM-1 in vitro. The results showed that HS on the surface significantly promoted integrin α4β7-mediated cell adhesion, decreased the percentage of cells firmly bound and increased the rolling velocities at high wall shear stresses, which was dependent on the mucin-like domain of MAdCAM-1. Moreover, breaking the negative charges of the extracellular microenvironment of CHO-K1 cells expressing MAdCAM-1 with sialidase inhibited cell adhesion and rolling velocity of 293T cells. Mechanistically, electrostatic repulsion between mucin-like domain and negative charges of the extracellular microenvironment led to a more upright conformation of MAdCAM-1, which facilitates integrin α4β7-mediated cell adhesion. Our findings elucidated the important role of the mucin-like domain in regulating integrin α4β7-mediated cell adhesion, which could be applied to modulate lymphocyte homing to lymphoid tissues or inflammatory sites.

Farm Animal-derived Models of the Intestinal Epithelium: Recent Advances and Future Applications of Intestinal Organoids

Farm animals play an important role in translational research as large animal models of the gastrointestinal (GI) tract. The mechanistic investigation of zoonotic diseases of the GI tract, in which animals can act as asymptomatic carriers, could provide important information for therapeutic approaches. In veterinary medicine, farm animals are no less relevant, as they can serve as models for the development of diagnostic and therapeutic approaches of GI diseases in the target species. However, farm animal-derived cell lines of the intestinal epithelium are rarely available from standardised cell banks and, in addition, are not usually specific for certain sections of the intestine. Immortalised porcine or bovine enterocytic cell lines are more widely available, compared to goat or sheep-derived cell lines; no continuous cell lines are available from the chicken. Other epithelial cell types with intestinal section-specific distribution and function, such as goblet cells, enteroendocrine cells, Paneth cells and intestinal stem cells, are not represented in those cell line-based models. Therefore, intestinal organoid models of farm animal species, which are already widely used for mice and humans, are gaining importance. Crypt-derived or pluripotent stem cell-derived intestinal organoid models offer the possibility to investigate the mechanisms of inter-cell or host-pathogen interactions and to answer species-specific questions. This review is intended to give an overview of cell culture models of the intestinal epithelium of farm animals, discussing species-specific differences, culture techniques and some possible applications for intestinal organoid models. It also highlights the need for species-specific pluripotent stem cell-derived or crypt-derived intestinal organoid models for promotion of the Three Rs principles (replacement, reduction and refinement).

Effects of Pinus massoniana pollen polysaccharides on intestinal microenvironment and colitis in mice

The stability of the intestinal microenvironment is the basis for maintaining the normal physiological activities of the intestine. On the contrary, disordered dynamic processes lead to chronic inflammation and disease pathology. Pinus massoniana pollen polysaccharide (PPPS), isolated from Taishan Pinus massoniana pollen, has been reported with extensive biological activities, including immune regulation. However, the role of PPPS in the intestinal microenvironment and intestinal diseases is still unknown. In this work, we initiated our investigation by using 16S rRNA high-throughput sequencing technology to assess the effect of PPPS on gut microbiota in mice. The result showed that PPPS regulated the composition of gut microbiota in mice and increased the proportion of probiotics. Subsequently, we established immunosuppressive mice using cyclophosphamide (CTX) and found that PPPS regulated the immunosuppressive state of lymphocytes in Peyer's patches (PPs). Moreover, PPPS also regulated systemic immunity by acting on intestinal PPs. PPPS alleviated lipopolysaccharide (LPS) -induced Caco2 cell damage, indicating that PPPS has the ability to reduce the damage and effectively improve the barrier dysfunction in Caco2 cells. In addition, PPPS alleviated colonic injury and relieved colitis symptoms in dextran sodium sulfate (DSS)-induced colitis mice. Overall, our findings indicate that PPPS shows a practical regulatory effect in the intestinal microenvironment, which provides an essential theoretical basis for us to develop the potential application value of PPPS further.

The Application of Mucoadhesive Chitosan Nanoparticles in Nasal Drug Delivery

Mucosal delivery of antigens can induce both humoral and cellular immune responses. Particularly, the nasal cavity is a strongly inductive site for mucosal immunity among several administration routes, as it is generally the first point of contact for inhaled antigens. However, the delivery of antigens to the nasal cavity has some disadvantages such as rapid clearance and disposition of inhaled materials. For these reasons, remarkable efforts have been made to develop antigen delivery systems which suit the nasal route. The use of nanoparticles as delivery vehicles enables protection of the antigen from degradation and sustains the release of the loaded antigen, eventually resulting in improved vaccine and/or drug efficacy. Chitosan, which exhibits low toxicity, biodegradability, good cost performance, and strong mucoadhesive properties, is a useful material for nanoparticles. The present review provides an overview of the mucosal immune response induced by nanoparticles, recent advances in the use of nanoparticles, and nasal delivery systems with chitosan nanoparticles.

Human small intestinal organotypic culture model for drug permeation, inflammation, and toxicity assays

The gastrointestinal tract (GIT), in particular, the small intestine, plays a significant role in food digestion, fluid and electrolyte transport, drug absorption and metabolism, and nutrient uptake. As the longest portion of the GIT, the small intestine also plays a vital role in protecting the host against pathogenic or opportunistic microbial invasion. However, establishing polarized intestinal tissue models in vitro that reflect the architecture and physiology of the gut has been a challenge for decades and the lack of translational models that predict human responses has impeded research in the drug absorption, metabolism, and drug-induced gastrointestinal toxicity space. Often, animals fail to recapitulate human physiology and do not predict human outcomes. Also, certain human pathogens are species specific and do not infect other hosts. Concerns such as variability of results, a low throughput format, and ethical considerations further complicate the use of animals for predicting the safety and efficacy xenobiotics in humans. These limitations necessitate the development of in vitro 3D human intestinal tissue models that recapitulate in vivo–like microenvironment and provide more physiologically relevant cellular responses so that they can better predict the safety and efficacy of pharmaceuticals and toxicants. Over the past decade, much progress has been made in the development of in vitro intestinal models (organoids and 3D-organotypic tissues) using either inducible pluripotent or adult stem cells. Among the models, the MatTek’s intestinal tissue model (EpiIntestinal™ Ashland, MA) has been used extensively by the pharmaceutical industry to study drug permeation, metabolism, drug-induced GI toxicity, pathogen infections, inflammation, wound healing, and as a predictive model for a clinical adverse outcome (diarrhea) to pharmaceutical drugs. In this paper, our review will focus on the potential of in vitro small intestinal tissues as preclinical research tool and as alternative to the use of animals.

Pulmonary Innate Immune Response Determines the Outcome of Inflammation During Pneumonia and Sepsis-Associated Acute Lung Injury

The lung is a primary organ for gas exchange in mammals that represents the largest epithelial surface in direct contact with the external environment. It also serves as a crucial immune organ, which harbors both innate and adaptive immune cells to induce a potent immune response. Due to its direct contact with the outer environment, the lung serves as a primary target organ for many airborne pathogens, toxicants (aerosols), and allergens causing pneumonia, acute respiratory distress syndrome (ARDS), and acute lung injury or inflammation (ALI). The current review describes the immunological mechanisms responsible for bacterial pneumonia and sepsis-induced ALI. It highlights the immunological differences for the severity of bacterial sepsis-induced ALI as compared to the pneumonia-associated ALI. The immune-based differences between the Gram-positive and Gram-negative bacteria-induced pneumonia show different mechanisms to induce ALI. The role of pulmonary epithelial cells (PECs), alveolar macrophages (AMs), innate lymphoid cells (ILCs), and different pattern-recognition receptors (PRRs, including Toll-like receptors (TLRs) and inflammasome proteins) in neutrophil infiltration and ALI induction have been described during pneumonia and sepsis-induced ALI. Also, the resolution of inflammation is frequently observed during ALI associated with pneumonia, whereas sepsis-associated ALI lacks it. Hence, the review mainly describes the different immune mechanisms responsible for pneumonia and sepsis-induced ALI. The differences in immune response depending on the causal pathogen (Gram-positive or Gram-negative bacteria) associated pneumonia or sepsis-induced ALI should be taken in mind specific immune-based therapeutics.

Oral delivery of protein-based therapeutics: Gastroprotective strategies, physiological barriers and in vitro permeability prediction

The number of biological molecules emerging as therapeutics is growing exponentially due to their higher specificity and tolerability profiles compared to small molecules. Despite this, their traditionally parenteral delivery often results in poor patient compliance and incomplete treatment. Current research is focussed on developing effective oral delivery strategies to facilitate administration of these biomolecules, however no universal method exists to simultaneously provide gastric protection as well as enhance transport across the gastrointestinal epithelium. Furthermore, for efficient formulation development it is imperative that we can reliably analyse permeability of biomolecules through the gastrointestinal tract, highlighting the importance of the continual development and ongoing evaluation of in vitro predictive permeability tools. Here, we review the physiological obstacles associated with peptide and protein delivery throughout the gastrointestinal tract. Furthermore, we highlight methods utilised to circumvent these barriers and promote improved intestinal permeability. Lastly, we explore in vitro models employed to predict epithelial transport. Key findings highlight the need to carefully understand gastrointestinal physiology, allowing specific engineering of oral delivery systems for biomolecules. Significant importance is placed upon understanding enzymatic degradation susceptibility as well as uptake mechanisms for particulate and protein-based therapeutics for the development of successful oral protein delivery platforms.

Regulating the balance of Th17/Treg cells in gut-lung axis contributed to the therapeutic effect of Houttuynia cordata polysaccharides on H1N1-induced acute lung injury

Our previous study had demonstrated that oral administration of Houttuynia cordata polysaccharides (HCP) without in vitro antiviral activity ameliorated gut and lung injuries induced by influenza A virus (IAV) in mice. However, as macromolecules, HCP was hard to be absorbed in gastrointestinal tract and had no effect on lung injury when administrated intravenously. The action mechanism of HCP was thus proposed as regulating the gut mucosal-associated lymphoid tissue (GALT). Actually, HCP treatment restored the balance of Th17/Treg cells firstly in GALT and finally in the lung. HCP reduced the expression of chemokine CCL20 in the lung and regulated the balance of Th17/Treg carrying CCR6+ (the CCL20 receptor), which was associated with specific migration of Th17/Treg cells from GALT to lung. In vitro, HCP inhibited Th17 cell differentiation through the downregulation of phospho-STAT3, whereas it promoted Treg cell differentiation by upregulating phospho-STAT5. Furthermore, its therapeutic effect was abolished in RORγt-/- or Foxp3-/- mice. These findings indicated that oral administration of macromolecular polysaccharides like HCP might ameliorate lung injury in IAV infected mice via directly regulating the balance of Th17/Treg cells in gut-lung axis. Our results provided a potential mechanism underlying the therapeutic effect of polysaccharides on pulmonary infection.

Gut–Brain Axis: Focus on Neurodegeneration and Mast Cells

Many studies highlighted that a bidirectional communication between the gut and the central nervous system (CNS) exists. A vigorous immune response to antigens must be avoided, and pathogenic organisms crossing the gut barrier must be detected and killed. For this reason, the immune system developed fine mechanisms able to maintain this delicate balance. The microbiota is beneficial to its host, providing protection against pathogenic bacteria. It is intimately involved in numerous aspects of host physiology, from nutritional status to behavior and stress response. In the last few years, the implication of the gut microbiota and its bioactive microbiota-derived molecules in the progression of multiple diseases, as well as in the development of neurodegenerative disorders, gained increasing attention. The purpose of this review is to provide an overview of the gut microbiota with particular attention toward neurological disorders and mast cells. Relevant roles are played by the mast cells in neuroimmune communication, such as sensors and effectors of cytokines and neurotransmitters. In this context, the intake of beneficial bacterial strains as probiotics could represent a valuable therapeutic approach to adopt in combination with classical therapies. Further studies need to be performed to understand if the gut bacteria are responsible for neurological disorders or if neurological disorders influence the bacterial profile.

Identification of scavenger receptor B1 as the airway microfold cell receptor for Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) can enter the body through multiple routes, including via specialized transcytotic cells called microfold cells (M cell). However, the mechanistic basis for M cell entry remains undefined. Here, we show that M cell transcytosis depends on the Mtb Type VII secretion machine and its major virulence factor EsxA. We identify scavenger receptor B1 (SR-B1) as an EsxA receptor on airway M cells. SR-B1 is required for Mtb binding to and translocation across M cells in mouse and human tissue. Together, our data demonstrate a previously undescribed role for Mtb EsxA in mucosal invasion and identify SR-B1 as the airway M cell receptor for Mtb.

Induction of Th2 response through TLR2-mediated MyD88-dependent pathway in human microfold cells stimulated with chitosan nanoparticles loaded with Brucella abortus Mdh

Drug delivery by the nasal or oral route is considered the preferred route of administration because it can induce systemic mucosal immunity. However, few studies have examined the immunogenicity and transport of antigen at the level of the microfold (M) cell, the epithelial cell that specializes in antigen sampling at mucosal surfaces. In our previous study, Brucella abortus malate dehydrogenase (Mdh) was loaded in chitosan nanoparticles (CNs), and it induced high production of proinflammatory cytokines in THP-1 cells and systemic IgA in BALB/C mice. In the present study, an in vitro M cell model was used in which Caco-2 cells and Raji B cells were co-cultured to investigate the impact of the uptake and immunogenicity of B. abortus Mdh on nanoparticle transport in human M cells. Our results showed that loaded CNs induced enhanced transport of Mdh in the M cell model. ELISAs showed significantly higher production of IL-1β and IL-6 in the CN-Mdh stimulation group than that seen in the Mdh stimulation group. The observed increase of gene expression of TLR2, MyD88, TRAF6, IRF4 and CD14 implied that MyD88-dependent TLR2 signaling was activated by stimulation with CNs-Mdh. These results suggest that Mdh and CNs may function synergistically to enhance Th2-related responses triggered by the MyD88-dependent TLR2 signaling pathway and could induce an inflammatory response in M cells as an M cell-targeted delivery system. This study will contribute to the development of not only effective antigens for intracellular bacteria, including B. abortus, but also vaccine delivery systems that target M cells.

Alterations of the Viable Ileal Microbiota of the Gut Mucosa-Lymph Node Axis in Pigs Fed Phytase and Lactic Acid-Treated Cereals

The gut-lymph node axis is a critical player in the symbiotic relationship between gut microbiota and the host. However, little is known about the impact of diet-related bacterial shifts in the gut lumen on bacterial translocation into lymph nodes. Here, we (i) characterized changes in the viable microbiota composition along the ileal digesta-mucosa-lymph node axis and (ii) examined the effect of dietary phytase supplementation and lactic acid (LA) soaking of cereals on the bacterial taxonomy along this axis, together with their effect on the mucosal expression of innate immune and barrier function genes in pigs (n = 8/diet). After 18 days on diets, ileal digesta, mucosa, and ileocecal lymph nodes (ICLNs) were collected for RNA isolation and 16S rRNA-based high-resolution community profiling. Bacterial communities were dominated by Lactobacillaceae and Clostridiaceae, with clearly distinguishable profiles at the three sampling sites. Specific bacterial subsampling was indicated by enrichment of the ICLNs with Lactobacillaceae, Lachnospiraceae, Veillonellaceae, and Methanobacteriaceae and less Clostridiaceae, Pasteurellaceae, Helicobacteraceae, and Enterobacteriaceae compared to that of the mucosa. LA treatment of cereals reduced proteolytic taxa in the lumen, including pathobionts like Helicobacteraceae, Campylobacteraceae, and Fusobacteriaceae When combined, phytase- and LA-treated cereals largely increased species richness, while the single treatments reduced Actinobacteria and Bacteroidetes in ICLNs and increased mucosal MUC2 expression. In contrast, phytase reduced mucosal CDH1 expression, indicating altered barrier function with potential effects on bacterial translocation. Overall, both treatments, although often differently, changed the viable microbiome along the digesta-mucosa-lymph node axis in the ileum, probably due to altered substrate availability and microbial-host interactions.IMPORTANCE A host's diet largely determines the gut microbial composition and therefore may influence bacterial translocation into ICLNs. Due to its importance for cell metabolism, the intestinal phosphorus availability, which was modified here by phytase and LA treatment of cereals, affects the intestinal microbiota. Previous studies mainly focused on bacteria in the lumen. The novelty of this work resides mainly in that we report diet-microbe effects along the digesta-mucosa-ICLN axis and linked those effects to mucosal expression of barrier function genes as crucial components for host health. Lymph nodes can serve as reservoir of pathobionts; therefore, present diet-microbiome-host interactions have implications for food safety.

Intestinal Organoids Generated from Human Pluripotent Stem Cells

The gastrointestinal system is one of the most complex organ systems in the human body, and consists of numerous cell types originating from three germ layers. To understand intestinal development and homeostasis and elucidate the pathogenesis of intestinal disorders, including unidentified diseases, several in vitro models have been developed. Human pluripotent stem cells (PSCs), including embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), have remarkable developmental plasticity and possess the potential for a wide variety of applications. Three-dimensional organs, termed organoids and produced in vitro by PSCs, contain not only epithelium but also mesenchymal tissue and partially recapitulate intestinal functions. Such intestinal organoids have begun to be applied in disease models and drug development and have contributed to a detailed analysis of molecular interactions and findings in the synergistic development of biomedicine for human digestive organs. In this review, we describe gastrointestinal organoid technology derived from PSCs and consider its potential applications.

Infants born to mothers with IBD present with altered gut microbiome that transfers abnormalities of the adaptive immune system to germ-free mice

BACKGROUND AND AIMS

Prenatal and early life bacterial colonisation is thought to play a major role in shaping the immune system. Furthermore, accumulating evidence links early life exposures to the risk of developing IBD later in life. We aimed to assess the effect of maternal IBD on the composition of the microbiome during pregnancy and on the offspring's microbiome.

METHODS

We prospectively examined the diversity and taxonomy of the microbiome of pregnant women with and without IBD and their babies at multiple time points. We evaluated the role of maternal IBD diagnosis, the mode of delivery, antibiotic use and feeding behaviour on the microbiome composition during early life. To assess the effects of IBD-associated maternal and infant microbiota on the enteric immune system, we inoculated germ-free mice (GFM) with the respective stool and profiled adaptive and innate immune cell populations in the murine intestines.

RESULTS

Pregnant women with IBD and their offspring presented with lower bacterial diversity and altered bacterial composition compared with control women and their babies. Maternal IBD was the main predictor of the microbiota diversity in the infant gut at 7, 14, 30, 60 and 90 days of life. Babies born to mothers with IBD demonstrated enrichment in Gammaproteobacteria and depletion in Bifidobacteria. Finally, GFM inoculated with third trimester IBD mother and 90-day infant stools showed significantly reduced microbial diversity and fewer class-switched memory B cells and regulatory T cells in the colon.

CONCLUSION

Aberrant gut microbiota composition persists during pregnancy with IBD and alters the bacterial diversity and abundance in the infant stool. The dysbiotic microbiota triggered abnormal imprinting of the intestinal immune system in GFM.

MUCOSAL anti-infections vaccines: Beyond conventional vaccines

An urgent search is currently underway for alternatives to antibiotics to prevent infections, due to the accelerated evolution and increase in antibiotic resistance. This problem is more serious for patients with recurrent infections, since they have to use many cycles of antibiotics per year, so the risk for antibiotic resistance is higher and can be life-threatening. In recent years, the use of prophylactic vaccines via the mucosal route for these patients with recurrent infections has been demonstrated as a potentially beneficial and safe alternative to prevent infections. The new knowledge about mucosal immunity and trained immunity, a form of innate immunity memory that can enhance the response to different infectious threads, has made it easier to extend its use. The application of the new concepts of trained immunity may explain the simultaneous pro-tolerogenic and boosting effect or effects of these drugs on diverse immune cells for different infections. In this review, we describe the immunomodulatory mechanisms of mucosal polybacterial vaccines and their connection with trained immunity and its utility in the prevention of recurrent infections in immunosuppressed patients.

Nanoparticles for mucosal vaccine delivery

Mucosal surfaces represent important routes of entry into the human body for the majority of pathogens, and they constitute unique sites for targeted vaccine delivery. Nanoparticle-based drug delivery systems are emerging technologies for delivering and improving the efficacy of mucosal vaccines. Recent studies have provided new insights into formulation and delivery aspects of importance for the design of safe and efficacious mucosal subunit vaccines based on nanoparticles. These include novel nanomaterials, their physicochemical properties and formulation approaches, nanoparticle interaction with immune cells in the mucosa, and mucosal immunization and delivery strategies. Here, we present recent progress in the application of nanoparticle-based approaches for mucosal vaccine delivery and discuss future research challenges and opportunities in the field.

Recent Approaches for Solid Dose Vaccine Delivery

Recent studies on vaccine delivery systems are exploring the possibility of replacing liquid vaccines with solid dose vaccines due to the many advantages that solid dose vaccines can offer. These include the prospect of a needle-free vaccine delivery system leading to better patient compliance, cold chain storage, less-trained vaccinators and fewer chances for needle stick injury hazards. Some studies also indicate that vaccines in a solid dosage form can result in a higher level of immunogenicity compared to the liquid form, thus providing a dose-sparing effect. This review outlines the different approaches in solid vaccine delivery using various routes of administration including, oral, pulmonary, intranasal, buccal, sublingual, and transdermal routes. The various techniques and their current advancements will provide a knowledge base for future work to be carried out in this arena.

Expression, Purification, and in vivo Evaluation of GFP-Fused M Cell Targeting Receptor Binding Domain of Protein FimH

Background:

The number of oral vaccines is still limited due to many difficulties suffered in the intestinal environment, such as mucosal clearance, vast area, harsh conditions, deteriorative enzymes, impermeability, tolerance, etc. Numerous strategies have focused on directing antigen to the receptors of M cells, which is the main gateway to acquire and initiate specific responses to antigens in intestine. FimHrb is a receptor binding domain of type 1 of fimbriae from E. coli and Salmonella that can bind to GP2 receptor expressed exclusively on M cells.

Objective:

In this study, we evaluated the potential of FimHrb for oral vaccine development via its ability to adhere M cells.

Methods:

The coding gene of FimHrb fused Green Fluorescent Protein (GFP) was cloned and expressed intracellularly in E. coli host strain. The recombinant protein FimHrb-GFP was then purified by IMAC method through 6x His tag designed downstream of GFP. Finally, the purified protein was monitored its binding on murine M cells in Payer Patch region.

Results:

Following the methods mentioned above, the coding gene FimHrb-GFP was successfully cloned into vector pET22b and intracellularly expressed in soluble form at low temperature induction. The purity and the recovered yield of this protein were 90% and 20%, respectively. After that, the adhesion of FimHrb-GFP was monitored in murine small intestine, which showed that the protein bound to Peyer Patch region and did not restrict on M cells.

Conclusion:

With the present data, we revealed a candidate protein FimHrb targeted receptor on M cells for oral vaccine development and other factors in E. coli would supplement FimH to provide the specific invasion of these bacteria via M cells.

Using 3D gastrointestinal tract in vitro models with microfold cells and mucus secreting ability to assess the hazard of copper oxide nanomaterials

BACKGROUND

Copper oxide nanomaterials (CuO NMs) are exploited in many products including inks, cosmetics, textiles, wood preservatives and food contact materials. Their incorporation into these products may enhance oral exposure in consumer, environmental and occupational settings. Undifferentiated and differentiated monocultures of Caco-2 cells are commonly used to assess NM toxicity to the intestine in vitro. However, the integration of other cell types into Caco-2 in vitro models increases their physiological relevance. Therefore, the aim of this study is to evaluate the toxicity of CuO NMs and copper sulphate (CuSO4) to intestinal microfold (M) cell (Caco-2/Raji B) and mucus secreting (Caco-2/HT29-MTX) co-culture in vitro models via assessment of their impact on barrier integrity, viability and interleukin (IL)-8 secretion. The translocation of CuO NMs and CuSO4 across the intestinal barrier was also investigated in vitro.

RESULTS

CuO NMs and CuSO4 impaired the function of the intestinal barrier in the co-culture models [as indicated by a reduction in transepithelial electrical resistance (TEER) and Zonular occludens (ZO-1) staining intensity]. Cu translocation was observed in both models but was greatest in the Caco-2/Raji B co-culture. CuO NMs and CuSO4 stimulated an increase in IL-8 secretion, which was greatest in the Caco-2/HT29-MTX co-culture model. CuO NMs and CuSO4 did not stimulate a loss of cell viability, when assessed using light microscopy, nuclei counts and scanning electron microscopy. CuO NMs demonstrated a relatively similar level of toxicity to CuO4 in both Caco-2/Raji B and Caco-2/HT29-MTX co- culture models.

CONCLUSIONS

The Caco-2/Raji B co-culture model was more sensitive to CuO NM and CuSO4 toxicity than the Caco-2/HT29-MTX co-culture model. However, both co-culture models were less sensitive to CuO NM and CuSO4 toxicity than simple monocultures of undifferentiated and differentiated Caco-2 cells, which are more routinely used to investigate NM toxicity to the intestine. Obtained data can therefore feed into the design of future studies which assess the toxicity of substances (e.g. NMs) and pathogens to the intestine (e.g. by informing model and endpoint selection). However, more testing with a wider panel of NMs would be beneficial in order to help select which in vitro models and endpoints to prioritise when screening the safety of ingested NMs. Comparisons with in vivo findings will also be essential to identify the most suitable in vitro model to screen the safety of ingested NMs.

Evaluating Shigella flexneri Pathogenesis in the Human Enteroid Model

The enteric pathogen Shigella is one of the leading causes of moderate-to-severe diarrhea and death in young children in developing countries. Transformed cell lines and animal models have been widely used to study Shigella pathogenesis.

The enteric pathogen Shigella is one of the leading causes of moderate-to-severe diarrhea and death in young children in developing countries. Transformed cell lines and animal models have been widely used to study Shigella pathogenesis. In addition to altered physiology, transformed cell lines are composed of a single cell type that does not sufficiently represent the complex multicellular environment of the human colon. Most available animal models do not accurately mimic human disease. The human intestinal enteroid model, derived from LGR5⁺ stem cell-containing intestinal crypts from healthy subjects, represents a technological leap in human gastrointestinal system modeling and provides a more physiologically relevant system that includes multiple cell types and features of the human intestine. We established the utility of this model for studying basic aspects of Shigella pathogenesis and host responses. In this study, we show that Shigellaflexneri is capable of infecting and replicating intracellularly in human enteroids derived from different segments of the intestine. Apical invasion by S. flexneri is very limited but increases ∼10-fold when enteroids are differentiated to include M cells. Invasion via the basolateral surface was at least 2-log₁₀ units more efficient than apical infection. Increased secretion of interleukin-8 and higher expression levels of the mucin glycoprotein Muc2 were observed in the enteroids following S. flexneri infection. The human enteroid model promises to bridge some of the gaps between traditional cell culture, animal models, and human infection.

Mucosa: Key Interactions Determining Sexual Transmission of the HIV Infection

In the context of HIV sexual transmission at the genital mucosa, initial interactions between the virus and the mucosal immunity determine the outcome of the exposure. Hence, these interactions have been deeply explored in attempts to undercover potential targets for developing preventative strategies. The knowledge gained has led to propose a hypothetical model for mucosal HIV transmission. Subsequent research studies on this topic further revealed new mechanisms and identified new host-HIV interactions. This review aims at integrating these findings to inform better and update the current model of HIV transmission. At the earliest stage of virus exposure, the epithelial integrity and the presence of antiviral factors are critical in preventing viral entry to the submucosa. However, the virus has been shown to enter to the submucosa in the presence of physical abrasion or via epithelial transmigration using paracellular passage or transcytosis mechanisms. The efficiency of these processes is greater with cell-associated viral inoculums and can be influenced by the presence of viral and immune factors, and by the structure of the exposed epithelium. Once the virus reaches the submucosa, dendritic cells and fibroblasts, as recently described, have been shown in vitro of being capable of facilitating the transfer of viral particles to susceptible cells, leading to viral dissemination, most likely in a trans-infection manner. The presence of activated CD4⁺ T cells in submucosa increases the probability of infection, where the predominant microbiota could be implicated through the modulation of an inflammatory microenvironment. Other factors such as genital fluids and hormones could also play an essential role in HIV transmission. Here, we review the most recent evidence described for mucosal HIV-transmission contributing with the understanding of this phenomenon.

The vermiform appendix: an immunological organ sustaining a microbiome inoculum

The hominoid vermiform appendix has been characterized as a diverticulum of the caecum and describes an entity at the juxtaposition of the colon in the confluence of tanias. The independent development of the lymphoid follicle centres of the appendix is progressed at birth in the presence of the intestinal commensal microbiome, an obligatory prompt for the diversification of intestinal and extra-intestinal mucosal immunological tissue. In the vermiform appendix, this activity is centred on further developing the inventory of primary antibodies and the maturation of T- and B-lymphocyte cells in the follicles within the lymphoid tissue. Furthermore, the columnar epithelia, enterocytes and goblet cells comprise the complement of cells that occupy the lamina propria and muscularis mucosae of the vermiform appendix's mucosa, while macrophages and an abundance of immunoglobulin A and immunoglobulin G generating plasma cells seed the lamina propria Intraepithelial immune cells consisting predominantly of specific CD8⁺ T regulatory lymphocytes occupy sites in the appendix analogous to those present in the intestinal epithelia of the caecal colon. The complement of bacterial genera concealed in the vermiform appendix is posited extant as a biofilm inoculum of the intestinal commensal microbiome. This facilitates re-inoculation of the proximal colon and to a lesser degree the terminal ilium post an intestinal perturbation such as occurs with daily lifestyle stressors, dietary choices and the short-term administration of antibiotics rather than an infectious fulminant colitis. A plausible appreciation results of the importance of multiple immunological aspects of a healthy vermiform appendix and the provision of a commensal biofilm to the gut that repairs a dysbiotic microbiome contributing to balancing intestinal pro- and anti-inflammatory activity for maintaining homeostasis in the gut. Since the composition of the gut microbiome can vary over the short-term and long-term, it is plausible that the appendix inoculum may be instrumental in maintaining the intestinal microbiome.

Surface engineered polyanhydride-based oral Salmonella subunit nanovaccine for poultry

PURPOSE

Salmonellosis is a severe economic threat in poultry and a public health concern. Currently available vaccines are ineffective, and thus, developing effective oral Salmonella vaccine is warranted. Especially, a potent oral vaccine such as the mucoadhesive polyanhydride nanoparticle (PNP) protects the vaccine cargo and delivers to intestinal immune sites to elicit robust mucosal immunity and mitigate Salmonella colonization and shedding.

MATERIALS AND METHODS

We designed a Salmonella subunit vaccine using PNP containing immunogenic Salmonella outer membrane proteins (OMPs) and flagellar (F) protein-entrapped and surface F-protein-coated PNPs (OMPs-F-PNPs) using a solvent displacement method. Using high-throughput techniques, we characterized the OMPs-F-PNPs physicochemical properties and analyzed its efficacy in layer birds vaccinated orally.

RESULTS

The candidate vaccine was resistant in acidic microenvironment and had ideal physicochemical properties for oral delivery in terms of particle size, charge, morphology, biocompatibility, and pH stability. In vitro, in vivo, and ex vivo studies showed that F-protein surface-anchored nanoparticles were better targeted to chicken immune cells in peripheral blood and splenocytes and intestinal Peyer's patch sites. In layer chickens inoculated orally with OMPs-F-PNPs, substantially higher OMPs-specific IgG response and secretion of Th1 cytokine IFN-γ in the serum, enhanced CD8+/CD4+ cell ratio in spleen, and increased OMPs-specific lymphocyte proliferation were observed. OMPs-F-PNPs vaccination also upregulated the expression of toll-like receptor (TLR)-2 and -4, TGF-β, and IL-4 cytokines' genes in chicken cecal tonsils (lymphoid tissues). Importantly, OMPs-F-PNPs vaccine cleared Salmonella cecal colonization in 33% of vaccinated birds.

CONCLUSION

This pilot in vivo study demonstrated the targeted delivery of OMPs-F-PNPs to ileum mucosal immune sites of chickens and induced specific immune response to mitigate Salmonella colonization in intestines.

Immunological Tolerance and Function: Associations Between Intestinal Bacteria, Probiotics, Prebiotics, and Phages

Post-birth there is a bacterial assault on all mucosal surfaces. The intestinal microbiome is an important participant in health and disease. The pattern of composition and concentration of the intestinal microbiome varies greatly. Therefore, achieving immunological tolerance in the first 3-4 years of life is critical for maintaining health throughout a lifetime. Probiotic bacteria are organisms that afford beneficial health effects to the host and in certain instances may protect against the development of disease. The potential benefits of modifying the composition of the intestinal microbial cohort for therapeutic benefit is evident in the use in high risks groups such as premature infants, children receiving antibiotics, rotavirus infections in non-vaccinated children and traveler's diarrhea in adults. Probiotics and prebiotics are postulated to have immunomodulating capabilities by influencing the intestinal microbial cohort and dampening the activity of pathobiont intestinal microbes, such as Klebsiella pneumonia and Clostridia perfringens. Lactobacilli and Bifidobacteria are examples of probiotics found in the large intestine and so far, the benefits afforded to probiotics have varied in efficacy. Most likely the efficacy of probiotic bacteria has a multifactorial dependency, namely on a number of factors that include agents used, the dose, the pattern of dosing, and the characteristics of the host and the underlying luminal microbial environment and the activity of bacteriophages. Bacteriophages, are small viruses that infect and lyse intestinal bacteria. As such it can be posited that these viruses display an effective local protective control mechanism for the intestinal barrier against commensal pathobionts that indirectly may assist the host in controlling bacterial concentrations in the gut. A co-operative activity may be envisaged between the intestinal epithelia, mucosal immunity and the activity of bacteriophages to eliminate pathobiots, highlighting the potential role of bacteriophages in assisting with maintaining intestinal homeostasis. Hence bacteriophage local control of inflammation and immune responses may be an additional immunological defense mechanism that exploits bacteriophage-mucin glycoprotein interactions that controls bacterial diversity and abundance in the mucin layers of the gut. Moreover, and importantly the efficacy of probiotics may be dependent on the symbiotic incorporation of prebiotics, and the abundance and diversity of the intestinal microbiome encountered. The virome may be an important factor that determines the efficacy of some probiotic formulations.

Tailoring Formulations for Intranasal Nose-to-Brain Delivery: A Review on Architecture, Physico-Chemical Characteristics and Mucociliary Clearance of the Nasal Olfactory Mucosa

The blood-brain barrier and the blood-cerebrospinal fluid barrier are major obstacles in central nervous system (CNS) drug delivery, since they block most molecules from entering the brain. Alternative drug delivery routes like intraparenchymal or intrathecal are invasive methods with a remaining risk of infections. In contrast, nose-to-brain delivery is a minimally invasive drug administration pathway, which bypasses the blood-brain barrier as the drug is directed from the nasal cavity to the brain. In particular, the skull base located at the roof of the nasal cavity is in close vicinity to the CNS. This area is covered with olfactory mucosa. To design and tailor suitable formulations for nose-to-brain drug delivery, the architecture, structure and physico-chemical characteristics of the mucosa are important criteria. Hence, here we review the state-of-the-art knowledge about the characteristics of the nasal and, in particular, the olfactory mucosa needed for a rational design of intranasal formulations and dosage forms. Also, the information is suitable for the development of systemic or local intranasal drug delivery as well as for intranasal vaccinations.

Host-microbe interaction in the gastrointestinal tract

The gastrointestinal tract is a highly complex organ in which multiple dynamic physiological processes are tightly coordinated while interacting with a dense and extremely diverse microbial population. From establishment in early life, through to host-microbe symbiosis in adulthood, the gut microbiota plays a vital role in our development and health. The effect of the microbiota on gut development and physiology is highlighted by anatomical and functional changes in germ-free mice, affecting the gut epithelium, immune system and enteric nervous system. Microbial colonisation promotes competent innate and acquired mucosal immune systems, epithelial renewal, barrier integrity, and mucosal vascularisation and innervation. Interacting or shared signalling pathways across different physiological systems of the gut could explain how all these changes are coordinated during postnatal colonisation, or after the introduction of microbiota into germ-free models. The application of cell-based in-vitro experimental systems and mathematical modelling can shed light on the molecular and signalling pathways which regulate the development and maintenance of homeostasis in the gut and beyond.

Salmonella Typhi Colonization Provokes Extensive Transcriptional Changes Aimed at Evading Host Mucosal Immune Defense During Early Infection of Human Intestinal Tissue

Commensal microorganisms influence a variety of host functions in the gut, including immune response, glucose homeostasis, metabolic pathways and oxidative stress, among others. This study describes how Salmonella Typhi, the pathogen responsible for typhoid fever, uses similar strategies to escape immune defense responses and survive within its human host. To elucidate the early mechanisms of typhoid fever, we performed studies using healthy human intestinal tissue samples and "mini-guts," organoids grown from intestinal tissue taken from biopsy specimens. We analyzed gene expression changes in human intestinal specimens and bacterial cells both separately and after colonization. Our results showed mechanistic strategies that S. Typhi uses to rearrange the cellular machinery of the host cytoskeleton to successfully invade the intestinal epithelium, promote polarized cytokine release and evade immune system activation by downregulating genes involved in antigen sampling and presentation during infection. This work adds novel information regarding S. Typhi infection pathogenesis in humans, by replicating work shown in traditional cell models, and providing new data that can be applied to future vaccine development strategies.

Lipid-Based Particles: Versatile Delivery Systems for Mucosal Vaccination against Infection

Vaccination is the process of administering immunogenic formulations in order to induce or harness antigen (Ag)-specific antibody and T cell responses in order to protect against infections. Important successes have been obtained in protecting individuals against many deleterious pathological situations after parenteral vaccination. However, one of the major limitations of the current vaccination strategies is the administration route that may not be optimal for the induction of immunity at the site of pathogen entry, i.e., mucosal surfaces. It is now well documented that immune responses along the genital, respiratory, or gastrointestinal tracts have to be elicited locally to ensure efficient trafficking of effector and memory B and T cells to mucosal tissues. Moreover, needle-free mucosal delivery of vaccines is advantageous in terms of safety, compliance, and ease of administration. However, the quest for mucosal vaccines is challenging due to (1) the fact that Ag sampling has to be performed across the epithelium through a relatively limited number of portals of entry; (2) the deleterious acidic and proteolytic environment of the mucosae that affect the stability, integrity, and retention time of the applied Ags; and (3) the tolerogenic environment of mucosae, which requires the addition of adjuvants to elicit efficient effector immune responses. Until now, only few mucosally applicable vaccine formulations have been developed and successfully tested. In animal models and clinical trials, the use of lipidic structures such as liposomes, virosomes, immune stimulating complexes, gas-filled microbubbles and emulsions has proven efficient for the mucosal delivery of associated Ags and the induction of local and systemic immune reponses. Such particles are suitable for mucosal delivery because they protect the associated payload from degradation and deliver concentrated amounts of Ags via specialized sampling cells (microfold cells) within the mucosal epithelium to underlying antigen-presenting cells. The review aims at summarizing recent development in the field of mucosal vaccination using lipid-based particles. The modularity ensured by tailoring the lipidic design and content of particles, and their known safety as already established in humans, make the continuing appraisal of these vaccine candidates a promising development in the field of targeted mucosal vaccination.

Enhancement of oral bioavailability of magnolol by encapsulation in mixed micelles containing pluronic F127 and L61

OBJECTIVES

We aimed to prepare novel magnolol-loaded mixed micelles (MAG-M) by pluronic F127 and L61 to overcome the challenges of magnolol's poor solubility and then further improve its oral bioavailability.

METHODS

Magnolol-loaded mixed micelles containing pluronic F127 and L61 were prepared by an organic solvent evaporation method. Physicochemical, transport experiment across Caco-2 cell monolayers and pharmacokinetic studies were performed to characterize MAG-M and to determine the final improvement of the oral bioavailability.

KEY FINDINGS

The MAG-M solution was transparent and colourless with average size, polydispersity index and zeta potential of 228.0 ± 2.1 nm, 0.298 ± 0.012 and -0.89 ± 0.02 mV. The micelle solution has a higher EE% and DL% of 81.57 ± 1.49% and 27.58 ± 0.53%, respectively. TEM result showed that the morphology of MAG-M was homogeneous and spherical shape. The dilution stability of MAG-M was no significant change in particle size and entrapment efficiency. MAG was demonstrated a sustained-release behaviour after encapsulated in micelles. MAG permeability across a Caco-2 cell monolayer was enhanced, and the pharmacokinetics study of MAG-M showed a 2.83-fold increase in relative oral bioavailability compared with raw MAG.

CONCLUSIONS

The mixed micelles containing pluronic F127 and L61 as drug delivery system provided a well strategy for resolving the poor solubility and bioavailability problems of MAG.

Exploring Host-Commensal Interactions in the Respiratory Tract

Commensal microbes are currently in the limelight in biomedical research because they play an important role in health and disease. Humans harbor an enormous diversity of commensals in various parts of the body, including the gastrointestinal and respiratory tracts. Advancement in metagenomic and other omic approaches, and development of suitable animal models have provided an unprecedented appreciation into the diversity of commensals, and the intricacies of their intimate communication with the host immune system. Most studies have focused on the host–commensal interaction in the gut, while less is known on this relationship in other sites of the body, such as the respiratory tract. In this article, we review emerging data from human and animal studies on the host responses to respiratory commensals, immune cross-reactivity between commensals and pathogens, and use of commensals as a vaccine delivery system. A better understanding of the delicate interplay between commensals and host may aid in efforts to develop effective vaccines and therapeutics.

Nose, Larynx, and Trachea

Chapter 22 outlines the morphology of the nose, larynx, and trachea. The text includes descriptions of spontaneous and treatment-related lesions observed in the tissues in toxicity and carcinogenicity studies.

The text begins with a description of the normal upper respiratory tract through the stages of embryonic development. Anatomy and histology are discussed before delving into the various degenerative, regenerative, and adaptive lesions found in toxicology studies. Included in the text is information on inflammatory and vascular lesions, and how trauma and injury, as well as exposure to irritants, can elicit inflammatory responses.

Molecular pathology of the upper respiratory tract is investigated, as well as an examination of the molecular alterations within specific cell types, providing a better understanding of the mechanisms of tissue injury.

High-Altitude-Induced alterations in Gut-Immune Axis: A review

High-altitude sojourn above 8000 ft is increasing day by day either for pilgrimage, mountaineering, holidaying or for strategic reasons. In India, soldiers are deployed to these high mountains for their duty or pilgrims visit to the holy places, which are located at very high altitude. A large population also resides permanently in high altitude regions. Every year thousands of pilgrims visit Holy cave of Shri Amarnath ji, which is above 15 000 ft. The poor acclimatization to high altitude may cause alteration in immunity. The low oxygen partial pressure may cause alterations in gut microbiota, which may cause changes in gut immunity. Effect of high altitude on gut-associated mucosal system is new area of research. Many studies have been carried out to understand the physiology and immunology behind the high-altitude-induced gut problems. Few interventions have also been discovered to circumvent the problems caused due to high-altitude conditions. In this review, we have discussed the effects of high-altitude-induced changes in gut immunity particularly peyer's patches, NK cells and inflammatory cytokines, secretary immunoglobulins and gut microbiota. The published articles from PubMed and Google scholar from year 1975 to 2017 on high-altitude hypoxia and gut immunity are cited in this review.

Food contact materials and gut health: Implications for toxicity assessment and relevance of high molecular weight migrants

Gut health is determined by an intact epithelial barrier and balanced gut microbiota, both involved in the regulation of immune responses in the gut. Disruption of this system contributes to the etiology of various non-communicable diseases, including intestinal, metabolic, and autoimmune disorders. Studies suggest that some direct food additives, but also some food contaminants, such as pesticide residues and substances migrating from food contact materials (FCMs), may adversely affect the gut barrier or gut microbiota. Here, we focus on gut-related effects of FCM-relevant substances (e.g. surfactants, N-ring containing substances, nanoparticles, and antimicrobials) and show that gut health is an underappreciated target in the toxicity assessment of FCMs. Understanding FCMs' impact on gut health requires more attention to ensure safety and prevent gut-related chronic diseases. Our review further points to the existence of large population subgroups with an increased intestinal permeability; this may lead to higher uptake of compounds of not only low (<1000 Da) but also high (>1000 Da) molecular weight. We discuss the potential toxicological relevance of high molecular weight compounds in the gut and suggest that the scientific justification for the application of a molecular weight-based cut-off in risk assessment of FCMs should be reevaluated.

Intestinal macrophages in Peyer's patches, sacculus rotundus and appendix of Angora rabbit

The largest pool of macrophages in the body is harboured by the intestinal mucosa. As the principal phagocytic component of the immune system, macrophages are essential for maintaining mucosal homeostasis as they prevent commensal bacteria from adhering to mucosal epithelial cells. This study provides a RAM11 immunohistochemical and electron microscopic investigation of the existence, localization and distribution of intestinal macrophages in organized gut-associated lymphoid tissue (GALT), including Peyer's patches (PPs), the sacculus rotundus (SR) and the appendix, in the Angora rabbit. Although rabbit intestinal macrophages did not express the tissue macrophage marker macrosialin (CD68), they expressed RAM11. RAM11-positive intestinal macrophages were mostly localized to the subepithelial dome region, interfollicular area and germinal centres (GCs) of the GALT and the lamina propria or submucosa of the ileum and jejunum devoid of PPs and were also observed in the follicle-associated epithelium of PPs, but not in that of the SR and appendix. RAM11-positive macrophages containing engulfed apoptotic bodies were present in the GCs of the lymphoid follicles in the GALT. Electron microscopy further revealed multiple macrophages containing apoptotic bodies within the GCs of the follicles in the GALT. Some macrophage aggregations were observed in the GC and between the GC and the corona region of the follicles in the SR and appendix. Rabbit intestinal macrophages thus undertake both potent phagocytic activity and the efficient scavenging of apoptotic cells. Immunohistochemical data suggest that RAM11 can be reliably used for the determination of intestinal macrophages in the GALT of rabbits.

Recent advances on biodegradable polymeric carrier-based mucosal immunization: an overview

Mucosal administration of vaccine is most prevalent way to induce desired immunity against various types of antigen and microbial in central and in addition, the peripheral blood in most external mucosal surface. Mucosal delivery of vaccine provides both humoral and cellular responses against mucosal infection. Mucosa, which are exposed to heavy loads of commensal and pathogenic microorganism, are one of the main region where infections are built up, also, thus have frontline status in immunity, making mucosa perfect site for vaccines application. The nasal route is favoured over parenteral route due to ease of administration, protection of antigen from degradation and induces sIgA which is not produced by systemic immunity. Natural and synthetic polymers are utilized to get nanoparticles carrier systems for development of nasal mucosal antibodies. The present review summarized the recent development in the field of vaccine delivery by means of mucoadhesive polymeric carriers. This review also describes the recent patent conceded for mucosal immunization utilizing these polymeric carriers.

Biosafety study and mechanism comparison on two types of silica with different nanostructures

Silica is frequently used in oral drug delivery; however, its biosafety, particularly concerned with its nanostructure, has not been comprehensively studied yet. Here, the in vitro and in vivo biosafety of two types of silica (A200, nano-sized or micron-sized agglomerates; S350, micro-sized particles with nanopores) were compared and the possible reasons for the differences were explored. The results indicated that both A200 and S350 could inhibit the growth of Caco-2 cells by inducing apoptosis and changing the cell cycle progression. A200 showed a stronger influence than S350 in most of the in vitro experiments. In the in vivo study in KM mice, both A200 and S350 could change the blood constituents under the tested conditions; A200 also increased the levels of inflammatory factors in plasma and the numbers of CD4+ lymphocyte subsets. No obvious organic damage was observed in either the A200-treated or S350-treated groups. The transport study showed that neither A200 nor S350 were readily transported across the intestinal epithelial barrier in vitro and in vivo, but A200 could transport across the lymphatic-associated epithelium and accumulate in the Peyer's Patches, which might explain the A200-induced immune response. The increased transport of A200 might relate to its particle size, dispersion state and specific surface area. In conclusion, these results demonstrated that A200 and S350 exhibited diverse biosafety aspects, which correlated with their different nanostructures. We believe this study will provide some scientific information about the biosafety of A200 and S350 for their applications in oral drug delivery systems.

Nasal vaccination with poly(β-amino ester)-poly(d,l-lactide-co-glycolide) hybrid nanoparticles

Mucosal vaccination stimulates both mucosal and systemic immunity. However, mucosal applications of vaccine antigens in their free form generally result in poor systemic immune responses and need adjuvantation. In this study, bovine serum albumin loaded, new hybridised poly(β-amino ester)-poly(d,l-lactide-co-glycolide) nanoparticles were prepared by double emulsion-solvent evaporation method, characterised and evaluated in vivo as nasal vaccine carriers. Cationic spherical particles with a mean size of 240nm, good physical stability and high encapsulation efficiency were obtained. Protein structure was not affected throughout preparation and minimal toxicity was shown in Calu-3 and A549 cells. Nasal vaccination with these nanoparticles revealed markedly higher humoral immune responses compared with free antigen following intranasal and subcutaneous immunisation. Mucosal immune response was also stimulated and cytokine titres indicated that Th1 and Th2 pathways were successfully activated. This study shows that the formulated hybrid nanoparticles can be a promising carrier for nasal immunisation of poor antigenic proteins.

Escherichia albertii, a novel human enteropathogen, colonizes rat enterocytes and translocates to extra-intestinal sites

Diarrhea is the second leading cause of death of children up to five years old in the developing countries. Among the etiological diarrheal agents are atypical enteropathogenic Escherichia coli (aEPEC), one of the diarrheagenic E. coli pathotypes that affects children and adults, even in developed countries. Currently, genotypic and biochemical approaches have helped to demonstrate that some strains classified as aEPEC are actually E. albertii, a recently recognized human enteropathogen. Studies on particular strains are necessary to explore their virulence potential in order to further understand the underlying mechanisms of E. albertii infections. Here we demonstrated for the first time that infection of fragments of rat intestinal mucosa is a useful tool to study the initial steps of E. albertii colonization. We also observed that an E. albertii strain can translocate from the intestinal lumen to Mesenteric Lymph Nodes and liver in a rat model. Based on our finding of bacterial translocation, we investigated how E. albertii might cross the intestinal epithelium by performing infections of M-like cells in vitro to identify the potential in vivo translocation route. Altogether, our approaches allowed us to draft a general E. albertii infection route from the colonization till the bacterial spreading in vivo.

Translocation of nanoparticles and Mycobacterium marinum across the intestinal epithelium in zebrafish and the role of the mucosal immune system

Nano- and microparticles are promising carrier systems for oral delivery of drugs or vaccines, particularly in fish aquaculture. However, the mechanisms of uptake, trans-epithelial transport and immune response to nano/micrometer sized particles, or microorganisms such as bacteria are poorly understood in fish. Here, adult zebrafish were used to study the uptake of different nano- and microparticles and the pathogenic bacteria Mycobacterium marinum in the intestine, and their interactions with epithelial cells and the mucosal immune system. Fluorescent particles or bacteria were delivered directly into the adult zebrafish intestine by oral intubation and their localization was imaged in intestine, liver and spleen sections. Zebrafish do not appear to have M-cells, but both nanoparticles and bacteria were rapidly taken up in the intestine and transported to the liver and spleen. In each tissue, both bacteria and particles largely localized to leukocytes, presumably macrophages.

Morphogenesis and maturation of the embryonic and postnatal intestine

The intestine is a vital organ responsible for nutrient absorption, bile and waste excretion, and a major site of host immunity. In order to keep up with daily demands, the intestine has evolved a mechanism to expand the absorptive surface area by undergoing a morphogenetic process to generate finger-like units called villi. These villi house specialized cell types critical for both absorbing nutrients from food, and for protecting the host from commensal and pathogenic microbes present in the adult gut. In this review, we will discuss mechanisms that coordinate intestinal development, growth, and maturation of the small intestine, starting from the formation of the early gut tube, through villus morphogenesis and into early postnatal life when the intestine must adapt to the acquisition of nutrients through food intake, and to interactions with microbes.