Impairment of mucosal immunity by total parenteral nutrition: requirement for IgA in murine nasotracheal anti-influenza immunity

The gut microbiome and intestinal failure-associated liver disease

Intestinal failure-associated liver disease (IFALD) is a common hepatobiliary complication resulting from long-term parenteral nutrition (PN) in patients with intestinal failure. The spectrum of IFALD ranges from cholestasis, steatosis, portal fibrosis, to cirrhosis. Development of IFALD is a multifactorial process, in which gut dysbiosis plays a critical role in its initiation and progression in conjunction with increased intestinal permeability, activation of hepatic immune responses, and administration of lipid emulsion. Gut microbiota manipulation including pre/probiotics, fecal microbiota transplantation, and antibiotics has been studied in IFALD with varying success. In this review, we summarize current knowledge on the taxonomic and functional changes of gut microbiota in preclinical and clinical studies of IFALD. We also review the function of microbial metabolites and associated signalings in the context of IFALD. By providing microbiota-targeted interventions aiming to optimize PN-induced liver injury, our review provides perspectives for future basic and translational investigations in the field.

Secretory IgA in Mucosa of Pharynx and Larynx Plays an Important Role against Influenza A Virus Infection in Kidney Yang Deficiency Syndrome Model

Objective

Influenza virus poses a major threat to human health and has serious morbidity and mortality which commonly occurs in high-risk populations. Pharynx and larynx of the upper respiratory tract mucosa is the first defense line against influenza virus infection. However, the ability of the pharynx and larynx organ to eliminate the influenza pathogen is still not clear under different host conditions.

Methods

In this study, a mouse model of kidney yang deficiency syndrome (KYDS) was used to mimic high-risk peoples. Two different methods of influenza A (H1N1) virus infection by nasal dropping or tracheal intubation were applied to these mice, which were divided into four groups: normal intubation (NI) group, normal nasal dropping (ND) group, model intubation (MI) group, and model nasal dropping (MD) group. The normal control (NC) group was used as a negative control. Body weight, rectal temperature, and survival rate were observed every day. Histopathologic changes, visceral index, gene expressions of H1N1, cytokine expressions, secretory IgA (SIgA) antibodies of tracheal lavage fluids in the upper respiratory tract, and bronchoalveolar lavage fluids were analyzed by ELISA.

Results

The MD group had an earlier serious morbidity and mortality than the others. MI and NI groups became severe only in the 6^th to 7^th day after infection. The index of the lung increased significantly in NI, MI, and MD groups. Conversely, indices of the thymus and spleen increased significantly in NC and ND groups. H&E staining showed severe tissue lesions in MD, MI, and NI groups. H1N1 gene expressions were higher in the MD group compared with the MI group on the 3^rd day; however, the MD group decreased significantly on the 7^th day. IL-6 levels increased remarkably, and SIgA expressions decreased significantly in the MD group compared with the NC group.

Conclusions

SIgA secretions are influenced directly by different conditions of the host in the pharynx and larynx in the upper respiratory tract mucosa. In the KYDS virus disease mode, SIgA expressions could be inhibited severely, which leads to serious morbidity and mortality after influenza A virus infection. The SIgA expressions of the pharynx and larynx would be an important target in high-risk populations against the influenza A virus for vaccine or antiviral drugs research.

Protein Microarray Analysis of the Specificity and Cross-Reactivity of Influenza Virus Hemagglutinin-Specific Antibodies

Current seasonal influenza virus vaccines engender antibody-mediated protection that is hemagglutinin (HA) subtype specific and relatively short-lived. Coverage for other subtypes or even variants within a subtype could be improved from a better understanding of the factors that promote HA-specific antibody cross-reactivity. Current assays to evaluate cross-reactivity, such as the ELISA, require a separate test for each antigen and are neither high-throughput nor sample-sparing. To address this need, we produced an array of 283 purified HA proteins from influenza A virus subtypes H1 to H16 and H18 and influenza B virus. To evaluate performance, arrays were probed with sera from individuals before and after a booster dose of inactivated heterologous H5N1 vaccine and naturally infected cases at presentation and follow-up during the 2010 to 2011 influenza season, when H3N2 was prevalent. The response to the H5 vaccine boost was IgG only and confined to H5 variants. The response to natural H3N2 infection consisted of IgG and IgA and was reactive with all H3 variants displayed, as well as against other group 2 HA subtypes. In both groups, responses to HA1 proteins were subtype specific. In contrast, baseline signals were higher, and responses broader, against full-length HA proteins (HA1+HA2) compared to HA1 alone. We propose that these elevated baseline signals and breadth come from the recognition of conserved epitopes in the stalk domain by cross-reactive antibodies accumulated from previous exposure(s) to seasonal influenza virus. This array is a valuable high-throughput alternative to the ELISA for monitoring specificity and cross-reactivity of HA antibodies and has many applications in vaccine development.IMPORTANCE Seasonal influenza is a serious public health problem because the viral infection spreads easily from person to person and because of antigenic drift in neutralizing epitopes. Influenza vaccination is the most effective way to prevent the disease, although challenging because of the constant evolution of influenza virus subtypes. Our high-throughput protein microarrays allow for interrogation of subunit-specific IgG and IgA responses to 283 different HA proteins comprised of HA1 and HA2 domains as well as full-length HA proteins. This provides a tool that allows for novel insights into the response to exposure to influenza virus antigens. Data generated with our technology will enhance our understanding of the factors that improve the strength, breadth, and durability of vaccine-mediated immune responses and develop more effective vaccines.

Membrane-anchored stalk domain of influenza HA enhanced immune responses in mice

Current strategies for influenza virus vaccines primarily aim to elicit immune responses towards the globular head domain of the hemagglutinin (HA) protein so that binding of the virus to membrane receptors on the host cells is inhibited. In the present study, we show a novel strategy to generate immunity against the highly conserved region of the influenza virus. The globular head domain was replaced by different linkers to generate a headless HA (stalk domain) and then coexpressed with influenza M1 proteinin Tni insect cells. The expression was validated by western blot analysis, and stalk domain with peptides (GGGGS)4 linkers was identified to anchor in a stable way to the cell membrane. An immunoelectron microscope showed that stalk domain with (GGGGS)4 linkers were steadily incorporated to the surface of influenza virus-like particles (VLPs). Mice immunized with these VLPs exhibited enhanced systemic antibody responses with increased binding avidity and study found high titers of ADCC antibodies to the influenza virus, these VLPs also induced mucosal immune responses and produced antigen-specific IgG and IgA in nasal and lung washes. In addition, antigen-specific IgG antibody-secreting cells (ASCs) increased significantly in the spleen and lymph node. The results of this study suggest that the headless HA is a useful target in developing a universal vaccine against influenza virus.

Respiratory Syncytial Virus: Infection, Detection, and New Options for Prevention and Treatment

Respiratory syncytial virus (RSV) infection is a significant cause of hospitalization of children in North America and one of the leading causes of death of infants less than 1 year of age worldwide, second only to malaria. Despite its global impact on human health, there are relatively few therapeutic options available to prevent or treat RSV infection. Paradoxically, there is a very large volume of information that is constantly being refined on RSV replication, the mechanisms of RSV-induced pathology, and community transmission. Compounding the burden of acute RSV infections is the exacerbation of preexisting chronic airway diseases and the chronic sequelae of RSV infection. A mechanistic link is even starting to emerge between asthma and those who suffer severe RSV infection early in childhood. In this article, we discuss developments in the understanding of RSV replication, pathogenesis, diagnostics, and therapeutics. We attempt to reconcile the large body of information on RSV and why after many clinical trials there is still no efficacious RSV vaccine and few therapeutics.

Vitamin A Deficiency Impairs Mucin Expression and Suppresses the Mucosal Immune Function of the Respiratory Tract in Chicks

The chicken immune system is immature at the time of hatching. The development of the respiratory immune system after hatching is vital to young chicks. The aim of this study was to investigate the effect of dietary vitamin A supplement levels on respiratory mucin and IgA production in chicks. In this study, 120 one-day-old broiler chicks were randomly divided into 4 groups consisting of three replicates of 10 broilers and subjected to dietary vitamin A supplement levels of 0, 1,500, 6,000, or 12,000 IU/kg for seven days. Compared with control birds, vitamin A supplementation significantly increased the mucin and IgA levels in the bronchoalveolar lavage fluid (BALF) as well as the IgA level in serum. In the lungs, vitamin A supplementation downregulated TNF-α and EGFR mRNA expression. The TGF-β and MUC5AC mRNA expression levels were upregulated by vitamin A supplementation at a dose of 6,000 IU/kg, and the IL-13 mRNA expression level was increased at the 12,000 IU/kg supplement level. Vitamin A deficiency (control) significantly decreased the mRNA expression levels of MUC2, IgA, EGFR, IL-13 and TGF-β in trachea tissue. Histological section analysis revealed that the number of goblet cells in the tracheal epithelium was less in the 0 and 12,000 IU/kg vitamin A supplement groups than in the other groups. In conclusion, vitamin A deficiency suppressed the immunity of the airway by decreasing the IgA and mucin concentrations in neonatal chicks. This study suggested that a suitable level of vitamin A is essential for the secretion of IgA and mucin in the respiratory tract by regulating the gene expression of cytokines and epithelial growth factors.

The enteric nervous system neuropeptide, bombesin, reverses innate immune impairments during parenteral nutrition

BACKGROUND

Lack of enteral stimulation during parenteral nutrition (PN) impairs mucosal immunity. Bombesin (BBS), a gastrin-releasing peptide analogue, reverses PN-induced defects in acquired immunity. Paneth cells produce antimicrobial peptides (AMPs) of innate immunity for release after cholinergic stimulation.

OBJECTIVE

Determine if BBS restores AMPs and bactericidal function during PN.

METHODS

Intravenously cannulated male ICR mice were randomized to Chow, PN, or PN+BBS (15 μg 3 times daily, n = 7 per group) for 5 days. Ileum was analyzed for AMPs (Protein: sPLA2 by fluorescence, lysozyme and RegIII-γ by western andcryptdin-4 by ELISA; mRNA: all by RT-PCR). Cholinergic stimulated (100 μM bethanechol) ileal specimens assessed Pseudomonas bactericidal activity. Ileum (Chow: n = 7; PN: n = 9; PN+BBS: n = 8) was assessed for Escherichia coli invasion in ex-vivo culture.

RESULTS

PN significantly decreased most AMPs versus Chow while BBS maintained Chow levels (sPLA2: Chow: 107 + 14*, PN: 44.6 + 7.2, PN+BBS: 78.7 + 13.4* Fl/min/μL/total protein; Lysozyme: Chow: 63.9 + 11.9*, PN: 26.8 + 6.2; PN+BBS: 64.9 + 13.8* lysozyme/total protein; RegIII-γ: Chow: 51.5 + 10.0*, PN: 20.4 + 4.3, PN+BBS: 31.0 + 8.4 RegIII-γ/total protein; Cryptdin-4: Chow: 18.4 + 1.5*, PN: 12.7 + 1.6, PN+BBS: 26.1 + 2.4*† pg/mg [all *P < 0.05 vs PN and †P < 0.05 vs Chow]). Functionally, BBS prevented PN loss of bactericidal activity after cholinergic stimulation (Chow: 25.3 + 3.6*, PN: 13.0 + 3.2; PN+BBS: 27.0 + 4.7* percent bacterial killing, *P < 0.05 vs PN). BBS reduced bacterial invasion in unstimulated tissue barely missing significance (P = 0.06).

CONCLUSIONS

The enteric nervous system (ENS) controls AMP levels in Paneth cells during PN but mucosal protection by innate immunity requires both ENS and parasympathetic stimulation.

Innate Mucosal Immune System Response of BALB/c vs C57BL/6 Mice to Injury in the Setting of Enteral and Parenteral Feeding

BACKGROUND

Outbred mice exhibit increased airway and intestinal immunoglobulin A (IgA) following injury when fed normal chow, consistent with humans. Parenteral nutrition (PN) eliminates IgA increases at both sites. Inbred mice are needed for detailed immunological studies; however, specific strains have not been evaluated for this purpose. BALB/c and C57BL/6 are common inbred mouse strains but demonstrate divergent immune responses to analogous stress. This study addressed which inbred mouse strain best replicates the outbred mouse and human immune response to injury.

METHODS

Intravenously cannulated mice received chow or PN for 5 days and then underwent sacrifice at 0 or 8 hours following controlled surgical injury (BALB/c: n = 16-21/group; C57BL/6: n = 12-15/group). Bronchoalveolar lavage (BAL) was analyzed by enzyme-linked immunosorbent assay for IgA, tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6, while small intestinal wash fluid (SIWF) was analyzed for IgA.

RESULTS

No significant increase in BAL IgA occurred following injury in chow- or PN-fed BALB/c mice (chow: P = .1; PN: P = .7) despite significant increases in BAL TNF-α and SIWF IgA (chow: 264 ± 28 vs 548 ± 37, P < .0001; PN: 150 ± 12 vs 301 ± 17, P < .0001). Injury significantly increased mucosal IgA in chow-fed C57BL/6 mice (BAL: 149 ± 33 vs 342 ± 87, P = .01; SIWF: 236 ± 28 vs 335 ± 32, P = .006) and BAL cytokines. After injury, PN-fed C57BL/6 mice exhibited no difference in BAL IgA (P = .9), BAL cytokines, or SIWF IgA (P = .1).

CONCLUSIONS

C57BL/6 mice exhibit similar airway responses to injury as outbred mice and humans, providing an appropriate model for studying mucosal responses to injury. The BALB/c mucosal immune system responds differently to injury and does not replicate the human injury response.

IL-25 improves luminal innate immunity and barrier function during parenteral nutrition

BACKGROUND

Parenteral nutrition (PN) increases risks of infections in critically injured patients. Recently, PN was shown to reduce intestine luminal levels of the Paneth cell antimicrobial molecule secretory phospholipase A2 (sPLA2) and the goblet cell glycoprotein mucin2 (MUC2). These molecules are critical factors for innate mucosal immunity and provide barrier protection. Interleukin-4 (IL-4) and IL-13 regulate sPLA2 and MUC2 production through the IL-13 receptor. Because IL-25 stimulates IL-4 and IL-13 release and PN reduces luminal sPLA2 and MUC2, we hypothesized that adding IL-25 to PN would restore these innate immune factors and maintain barrier function.

METHODS

Two days after venous cannulation, male ICR (Institute of Cancer Research) mice were randomized to receive chow (n = 12), PN (n = 9), or PN + 0.7 μg of exogenous IL-25 (n = 11) daily for 5 days. Small-intestine wash fluid (SIWF) was collected for analysis of sPLA2 activity, MUC2 density, and luminal levels of IL-4 and IL-13. Small-intestinal tissue was harvested for analysis of tissue sPLA2 activity or immediate use in an ex-vivo intestinal segment culture (EVISC) to assess susceptibility of the tissue segments to enteroinvasive Escherichia coli.

RESULTS

PN reduced luminal sPLA2 (P < 0.0001) and MUC2 (P <0.002) compared with chow, whereas the addition of IL-25 to PN increased luminal sPLA2 (P < 0.0001) and MUC2 (P < 0.02) compared with PN. Tissue IL-4 and IL-13 decreased with PN compared with chow (IL-4: P < 0.0001, IL-13: P < 0.002), whereas IL-25 increased both cytokines compared with PN (IL-4: P < 0.03, IL-13: P < 0.02). Tissue levels of sPLA2 were significantly decreased with PN compared with chow, whereas IL-25 significantly increased tissue sPLA2 levels compared with PN alone. Functionally, more bacteria invaded the PN-treated tissue compared with chow (P < 0.01), and the addition of IL-25 to PN decreased enteroinvasion to chow levels (P < 0.01).

CONCLUSIONS

PN impairs innate mucosal immunity by suppressing luminal sPLA2 activity and MUC2 density compared with chow. PN also increases bacterial invasion in ex-vivo tissue. Administration of exogenous IL-25 reverses this dysfunction and increases luminal sPLA2 and MUC2. PN tissue treated with IL-25 was significantly more resistant to bacterial invasion than with PN alone, suggesting that IL-25-induced effects augment the barrier defense mechanisms.

Bombesin improves adaptive immunity of the salivary gland during parenteral nutrition

BACKGROUND

The parotid and submandibular salivary glands are gut-associated lymphoid tissues (GALTs) that secrete immune compounds into the oral cavity. Parenteral nutrition (PN) without enteral stimulation decreases GALT function, including intestinal lymphocyte counts and secretory immunoglobulin A (sIgA) levels. Since the neuropeptide bombesin (BBS), a gastrin-releasing peptide analogue, stimulates intestinal function and restores GALT parameters, we hypothesized that PN + BBS would stimulate parotid and salivary gland IgA levels, T lymphocytes, and IgA plasma cell counts compared with PN alone.

METHODS

Male (Institute of Cancer Research) ICR mice received intravenous catheters and were randomized to chow with saline, PN, or PN + BBS (15 µg/tid/mouse) for 5 days (8/group), 2 days after cannulation. Salivary glands were weighed and either frozen for IgA and amylase analysis or fixed for histological analysis of acinar cells, IgA+ plasma cells, and T lymphocytes. Small intestinal wash fluid was collected for IgA regression analysis with salivary glands.

RESULTS

PN reduced organ weight, acinar cell size, and amylase activity compared with chow; BBS had no significant effects on these parameters. Compared with chow, PN significantly reduced salivary gland IgA levels, IgA+ plasma cells, and T lymphocytes. PN + BBS significantly elevated IgA and restored cellularity compared with PN. Salivary gland tissue homogenate IgA levels significantly correlated with intestinal fluid IgA levels.

CONCLUSIONS

Compared with chow, PN results in atrophy of the salivary glands characterized by reduced amylase, IgA, and immune cellularity. BBS has no effect on acinar cells or amylase activity compared with PN but maintains tissue IgA and plasma cells and T-lymphocyte numbers compared with chow.

Nanoclusters self-assembled from conformation-stabilized influenza M2e as broadly cross-protective influenza vaccines

Influenza vaccines with broad cross-protection are urgently needed. The highly conserved ectodomain of the influenza matrix protein 2 (M2e) can be a promising candidate if its low immunogenicity was overcome. In this study, we generated protein nanoclusters self-assembled from conformation-stabilized M2e tetramers (tM2e) to improve its immunogenicity. The resulting nanoclusters showed an average hydrodynamic diameter of 227 nm. Vaccination with the nanoclusters by an intranasal route elicited high levels of serum antigen-specific IgG in mice (approximately 100-fold higher than that obtained with soluble tM2e), as well as antigen-specific T cell and mucosal antibody responses. The immunity conferred complete protection against lethal challenge with homo- as well as heterosubtypic viruses. These results demonstrate that nanoclusters assembled from conformation-stabilized M2e are promising as a potential universal influenza A vaccine. Self-assembly into nanoclusters represents a novel approach for increasing the immunogenicity of vaccine antigens.

FROM THE CLINICAL EDITOR

In order to develop more effective influenza vaccination, the highly conserved ectodomain of M2e could be a promising candidate. Unfortunately, it is a weak antigen for vaccination purposes. In this study, self-assembled protein nanoclusters of tM2e were generated and tested. The nanoclusters demonstrated superior vaccination properties, with complete protection against lethal challenge in the studied rodent model, raising hope for the introduction of similar vaccines to challenge human influenza outbreaks.

Virus-like particles containing the tetrameric ectodomain of influenza matrix protein 2 and flagellin induce heterosubtypic protection in mice

The ectodomain of matrix protein 2 (M2e) is highly conserved among influenza A viruses and can be a promising candidate antigen for a broadly cross-protective vaccine. In this study, a tetrameric M2e (tM2e) and a truncated form of flagellin (tFliC) were coincorporated into virus-like particles (VLPs) to enhance its immunogenicity. Our data showed that the majority of M2e in VLPs was presented as tetramers by introducing a foreign tetramerization motif GCN4. Intranasal immunization with tM2e VLPs significantly enhanced the levels of serum IgG and IgG subclasses compared to soluble M2e (sM2e) in mice. tM2e VLPs also induced higher M2e-specific T-cell and mucosal antibody responses, conferring complete protection against homologous influenza virus infection. The immunogenicity of tM2e VLPs was further enhanced by coincorporation of the membrane-anchored tFliC (tM2e chimeric VLPs) or coadministration with tFliC VLPs as a mixture, but not the soluble flagellin, inducing strong humoral and cellular immune responses conferring cross-protection against lethal challenge with heterotypic influenza viruses. These results support the development of tM2e chimeric VLPs as universal vaccines and warrant further investigation.

Enteral nutrition discontinuation and outcomes in general critically ill patients

OBJECTIVE

To determine the relationship between enteral nutrition discontinuation and outcome in general critically ill patients.

MATERIALS AND METHODS

All patients admitted to a mixed intensive care unit in a tertiary care hospital from May-August 2009 were screened for an indication for enteral nutrition. Patients were followed up until leaving the intensive care unit or a maximum of 28 days. The gastrointestinal failure score was calculated daily by adding values of 0 if the enteral nutrition received was identical to the nutrition prescribed, 1 if the enteral nutrition received was at least 75% of that prescribed, 2 if the enteral nutrition received was between 50-75% of that prescribed, 3 if the enteral nutrition received was between 50-25% of that prescribed, and 4 if the enteral nutrition received was less than 25% of that prescribed.

RESULTS

The mean, worst, and categorical gastrointestinal failure scores were associated with lower survival in these patients. Age, categorical gastrointestinal failure score, type of admission, need for mechanical ventilation, sequential organ failure assessment, and Acute Physiologic and Chronic Health Evaluation II scores were selected for analysis with binary regression. In both models, the categorical gastrointestinal failure score was related to mortality.

CONCLUSION

The determination of the difference between prescribed and received enteral nutrition seemed to be a useful prognostic marker and is feasible to be incorporated into a gastrointestinal failure score.

Mucosal immunity and nasal influenza vaccination

Influenza remains a threat to public health, with immunization being a suitable method of infection prevention and control. Our understanding of the immunological regulations at the mucosa, antigen processing and presentation, and B-cell activation has improved, enabling research and targeted induction of immune responses at the site of antigen delivery. Nasal influenza immunization has distinct features compared with intramuscular vaccines, providing protection at the pathogen's entry site, higher levels of mucosal antibodies, cross-protection and needle-free application. This review summarizes our knowledge about mucosal immunity and the experience from clinical trials on the impact and safety of nasal influenza vaccination.

Nutrition and gut immunity

The human intestine contains huge amounts of nonpathologic bacteria surviving in an environment that is beneficial to both the host and the bacterial populations. When short pauses in oral intake occur with minimal alterations in the mucosa-microbial interface, critical illness, with its attendant acidosis, prolonged gastrointestinal tract starvation, exogenous antibiotics, and breakdown in mucosal defenses, renders the host vulnerable to bacterial challenge and also threatens the survival of the bacteria. This review examines the altered innate and adaptive immunologic host defenses that occur as a result of altered oral or enteral intake and/or injury.

Enteral versus parenteral nutrition: effect on intestinal barrier function

Total parenteral nutrition (TPN), or the complete absence of enteral nutrients, is commonly used in a clinical setting. However, a major consequence of TPN administration is the development of mucosal atrophy and a loss of epithelial barrier function (EBF); and this loss may lead to an increase in clinical infections and septicemia. Our laboratory has investigated the mechanism of this TPN-associated loss of EBF using a mouse model. We have demonstrated that the mucosal lymphoid population significantly changes with TPN, and leads to a rise in interferon gamma (IFN-gamma) and decline in interleukin-10 (IL-10) expression-both of which contribute to the loss of EBF. Associated with these cytokine changes is a dramatic decline in the expression of tight junction and adherens junction proteins. This article discusses the potential mechanisms responsible for these changes, and potential strategies to alleviate this loss in EBF.

Food fight! Parenteral nutrition, enteral stimulation and gut-derived mucosal immunity

INTRODUCTION

Nutrition support is an integral component of modern patient care. Type and route of nutritional support impacts clinical infectious outcomes in critically injured patients.

DISCUSSION

This article reviews the relationships between type and route of nutrition and gut-derived mucosal immunity in both the clinical and laboratory settings.

Decreased enteral stimulation alters mucosal immune chemokines

BACKGROUND

Migration of lymphocytes into and through the mucosal immune system depends upon adhesion molecules to attract circulating cells and chemokines to stimulate diapedesis into tissues. Decreased enteral stimulation significantly reduces mucosal addressin cellular adhesion molecule-1 (MAdCAM-1) levels, an adhesion molecule critical for homing of T and B cells to Peyer's patches (PP), which reduces PP and intestinal T and B cells. We studied the effect of type and route of nutrition on tissue specific chemokines in PP (CXCL-12, -13 and CCL-19, -20 and -21), small intestine (SI; CCL-20, -25 and -28) and lung (CXCL-12, CCL-28).

METHODS

Intravenously cannulated male Institute of Cancer Research (ICR) mice were randomized to chow or parenteral nutrition (PN) for 5 days. PP, SI, and lung chemokine mRNA levels were measured using real-time qRT-polymerase chain reaction, and analyzed semiquantitatively by the DeltaDeltaCt method. Protein levels were quantified using enzyme-linked immunosorbent assay (ELISA) techniques, and groups compared using Student's t-test.

RESULTS

PP CXCL13 protein significantly decreased, whereas CCL21 protein increased significantly in the parenterally fed group. Parenteral feeding significantly decreased SI CCL20 and CCL 25 protein levels. CCL28 decreased significantly in the SI and lung of intravenously fed animals. mRNA levels changed in the opposite direction (compared with protein) for all chemokines except CCL28.

CONCLUSIONS

Decreased enteral stimulation significantly alters key mucosal immune chemokine protein levels at multiple sites. In general, PN (and concomitant lack of enteral stimulation) results in decreased levels of chemokines that control lymphocyte migration within the mucosal immune system.

Induction of secretory immunity and memory at mucosal surfaces

Mucosal epithelia comprise an extensive vulnerable barrier which is reinforced by numerous innate defence mechanisms cooperating intimately with adaptive immunity. Local generation of secretory IgA (SIgA) constitutes the largest humoral immune system of the body. Secretory antibodies function both by performing antigen exclusion at mucosal surfaces and by virus and endotoxin neutralization within epithelial cells without causing tissue damage. SIgA is thus persistently containing commensal bacteria outside the epithelial barrier but can also target invasion of pathogens and penetration of harmful antigens. Resistance to toxin-producing bacteria such as Vibrio cholerae and enterotoxigenic Escherichia coli appears to depend largely on SIgA, and so does herd protection against horizontal faecal-oral spread of enteric pathogens under naïve or immunized conditions--with a substantial innate impact both on cross-reactivity and memory. Like natural infections, live mucosal vaccines or adequate combinations of non-replicating vaccines and mucosal adjuvants, give rise not only to SIgA antibodies but also to longstanding serum IgG and IgA responses. However, there is considerably disparity with regard to migration of memory/effector cells from mucosal inductive sites to secretory effector sites and systemic immune organs. Also, although immunological memory is generated after mucosal priming, this may be masked by a self-limiting response protecting the inductive lymphoid tissue in the gut. The intranasal route of vaccine application targeting nasopharynx-associated lymphoid tissue may be more advantageous for certain infections, but only if successful stimulation is achieved without the use of toxic adjuvants that might reach the central nervous system. The degree of protection obtained after mucosal vaccination ranges from reduction of symptoms to complete inhibition of re-infection. In this scenario, it is often difficult to determine the relative importance of SIgA versus serum antibodies, but infection models in knockout mice strongly support the notion that SIgA exerts a decisive role in protection and cross-protection against a variety of infectious agents. Nevertheless, relatively few mucosal vaccines have been approved for human use, and more basic work is needed in vaccine and adjuvant design, including particulate or live-vectored combinations.

Is there evidence that the gut contributes to mucosal immunity in humans?

BACKGROUND

Our understanding of the common mucosal immune system derives from animal studies. Antigen-sensitized lymphocytes in the gut-associated lymphoid tissue (GALT) migrate via the blood to mucosal tissues to generate the mucosal-associated lymphoid tissue (MALT). In these sites, B cells differentiate into plasma cells and produce antigen-specific secretory IgA, the principal specific immune antiviral and antibacterial defense of moist mucosal surfaces. Responses to oral intake seem necessary to actively maintain this system in health. Experimentally, lack of enteral stimulation with parenteral feeding alters GALT and MALT size and function. These alterations disturb intestinal and extraintestinal mucosal immunity.

METHODS

This review is an overview of current and classical studies demonstrating the human mucosal immune system and interactions with nutrition.

RESULTS

Human evidence of the mucosal immune system exists, although most data are indirect. Gut stimulation after oral intake induces a generalized immune response in the human MALT through a mucosal-immune network. Examples include neonatal development of GALT influenced by enteral feeding, the presence of antigen-specific IgA and antigen-specific IgA-secreting plasma cells in distant mucosal effector sites such as the breast after gut luminal antigen exposure, and isolation of IgA-producing cells from circulating blood.

CONCLUSIONS

It is unlikely that clinical studies will ever completely define the effect of route of feeding in all patient populations. This may be possible, however, if investigators understand, define and characterize nutrition-dependent immunologic mechanisms, allowing clinicians to examine clinical responses to nutrition in specific patient populations. This might allow generation of new approaches to protect mucosal immunity.

Parenteral nutrition and fasting reduces mucosal addressin cellular adhesion molecule-1 (MAdCAM-1) mRNA in Peyer's patches of mice

BACKGROUND

Mucosal addressin cellular adhesion molecule-1 (MAdCAM-1) in Peyer's patches (PP) is the gateway molecule for cellular migration into the mucosal immune system. Lack of enteral feeding during parenteral nutrition (PN) rapidly decreases PP MAdCAM-1, leading to drops in mucosal T and B cells and intestinal and respiratory IgA. We determined the molecular events associated with MAdCAM-1 mRNA and protein during PN (short and long term) and fasting (1 and 2 days).

METHODS

Experiment 1: Cannulated mice received PN for 8 hours (short-term PN, n = 6) or chow + saline (chow, n = 6). Experiment 2: Cannulated mice received PN (long-term PN, n = 4) or chow (n = 3) for 5 days. Experiment 3: Noncannulated chow mice were fasted for 1 and 2 days (n = 2/time). Total cellular RNA from the PP was quantified for MAdCAM-1 mRNA by real-time polymerase chain reaction (PCR). MAdCAM-1 protein was measured by Western blot.

RESULTS

PN rapidly down-regulated MAdCAM-1 gene expression. After 8 hours of PN with lack of enteral feeding, MAdCAM-1 mRNA levels dropped 20% (0.8-fold vs chow, p > .05); 5 days of PN reduced MAd-CAM-1 levels 64% (0.34-fold vs chow, p < .05). PN reduced MAdCAM-1 protein levels by 30% (chow: 329 +/- 14 vs PN: 230 +/- 35, p < .05) after 5 days. Fasting of uncannulated mice decreased MAdCAM-1 mRNA levels by 16% (0.84-fold, p < .05) at day 1 and 30% (0.7-fold, p < .05) by day 2 compared with chow.

CONCLUSIONS

Both PN with lack of enteral feeding and fasting down-regulate MAdCAM-1 mRNA and protein levels in PP. The MAdCAM-1 changes are due to lack of enteral stimulation rather than toxic effects of PN.

Parenteral nutrition impairs gut-associated lymphoid tissue and mucosal immunity by reducing lymphotoxin Beta receptor expression

OBJECTIVE

To determine the effects of parenteral nutrition (PN) on LTbetaR in gut-associated lymphoid tissue (GALT), particularly the intestine and Peyer's patches (PP).

SUMMARY BACKGROUND DATA

Lack of enteral stimulation with PN impairs mucosal immunity and reduces IgA levels through depression of GALT cytokines (IL-4 and IL-10) and GALT specific adhesion molecules. We have shown that each is critical to intact mucosal immunity through effects on lymphocyte homing, IgA production, and resistance to antibacterial and antiviral immunity. IgA is the principal specific immunologic mucosal defense. LTbetaR stimulation controls production of IL-4, the adhesion molecule MAdCAM-1, and other key components of GALT, all of which are important in increasing IgA levels and maintaining mucosal defenses.

METHODS

Experiment 1: LTbetaR expression in intestine and PP was analyzed by Western blot after 5 days of chow, a complex enteral diet (CED), or PN. Diets were isocaloric and isonitrogenous except for chow. Experiment 2: After completing pilot experiments to determine the appropriate dose of the LTbetaR agonistic antibody, mice received chow, PN + 5 mug of anti-LTbetaR mAb (2 times/d, i.v.) or PN + isotype control antibody. PP lymphocytes and intestinal IgA levels were measured after 2 days.

RESULTS

Lack of enteral stimulation with PN significantly decreased LTbetaR expression in intestine and PP compared with chow and CED. LTbetaR stimulation with an agonistic anti-LTbetaR mAb significantly increased PP lymphocyte counts and intestinal IgA in PN fed-mice.

CONCLUSIONS

LTbetaR expression is critical for GALT control mechanisms and intact mucosal immunity. PN reduces LTbetaR expression, PP lymphocytes, and intestinal IgA production. Exogenous LTbetaR stimulation reverses PN-induced depression of gut mucosal immunity.

Role of IgA versus IgG in the Control of Influenza Viral Infection in the Murine Respiratory Tract

The roles of IgG and secretory IgA in the protection of the respiratory tract (RT) against influenza infection remain unclear. Passive immunization with Ab doses resulting in serum IgG anti-influenza virus Ab titers far in excess of those observed in immune mice has compounded the problem. We compared the effects of i.v. anti-influenza virus IgG and i.v. anti-influenza virus polymeric IgA (pIgA) mAb administered in amounts designed to replicate murine convalescent serum or nasal Ab titers, respectively. A serum anti-influenza virus IgG titer 2.5 times the normal convalescent serum anti-influenza virus IgG titer was required for detectible Ab transudation into nasal secretions, and a serum IgG titer 7 times normal was needed to lower nasal viral shedding by 98%. Anti-influenza virus pIgA at a nasal Ab titer comparable to that seen in convalescent mice eliminated nasal viral shedding. The RT of influenza-infected pIgA- or IgG-protected mice were studied by scanning electron microscopy. Only pIgA was found to prevent virally induced pathology in the upper RT, suggesting that IgG did not prevent viral infection of the nose, but neutralized newly replicated virus after infection had been initiated. In contrast, IgG, but not pIgA, was found to prevent viral pathology in the murine lung. Our results help to resolve the controversy of IgA- vs IgG-mediated protection of the RT; both Abs are important, with plasma IgG Ab serving as the back-up for secretory IgA-mediated protection in the nasal compartment, and IgG being the dominant Ab in protection of the lung.

Role of secretory antibodies in the defence against infections

Adaptive immunity mediated by secretory antibodies is important in the defence against mucosal infections. Specific secretory immunoglobulin A (SIgA) can inhibit initial pathogen colonization by performing immune exclusion both on the mucosal surface and within virus-infected secretory epithelial cells without causing tissue damage. Resistance against toxin-producing bacteria such as Vibrio cholerae appears to be particularly dependent on SIgA antibodies. Like natural infections, live topical vaccines or adequate combinations of inactivated vaccines and mucosal adjuvants give rise not only to SIgA antibodies, but also to long-standing serum IgG and IgA responses. The intranasal route of vaccine application could be particularly attractive to achieve this result, but only if successful stimulation is obtained without the use of toxic adjuvants. The degree of protection after vaccination may range from complete inhibition of reinfection to reduction of symptoms. In this scenario it is generally difficult to determine unequivocally the relative importance of SIgA versus serum antibodies. However, infection models in knockout mice strongly support the notion that SIgA exerts a decisive role in protection and cross-protection against a variety of infectious agents.

Semi-quantitative detection of viral RNA in influenza A virus-infected mice for evaluation of antiviral compounds

The aim of the study was to establish a murine model for sensitive screening of potential compounds with in vitro anti-influenza A virus activity. The evaluation in this in vivo model is based on semi-quantitative detection of viral RNA using one-step reverse transcriptase polymerase chain reaction (RT-PCR). After intranasal infection of fully-conscious mice with influenza A virus, the viral load of the respiratory tract tissues was investigated. Peaks were observed in the nasopharynx between Days 1 and 4, in the trachea on Day 4, and in the lungs between Days 4 and 7 post infection. The elimination of virus correlated with the appearance of specific serum antibodies. After 4 days of treatment with zanamivir, trachea and lungs revealed negative RT-PCR results, whereas viral load in the nasopharynx was significantly reduced. In conclusion, the virus spread in the described murine model is similar to upper respiratory tract infection with influenza virus in human. Viral load measurement by semi-quantitative detection of viral RNA allows rapid and sensitive screening of potential compounds with in vitro anti-influenza A virus activity.

Intravenous erythromycin facilitates bedside placement of postpyloric feeding tubes in critically ill adults: a double-blind, randomized, placebo-controlled study

OBJECTIVE To evaluate the efficacy of intravenous erythromycin as a method to facilitate feeding tube placement into the small intestine in critically ill patients. DESIGN Double blind, randomized, controlled trial. SETTING Medical and surgical intensive care units in an academic medical center. PATIENTS Prospective cohort of 36 consecutive adults requiring intensive care unit care and enteral tube feeding for nutritional support. INTERVENTION Infusion of a single dose of intravenous erythromycin (500 mg) or saline before placement of 10-Fr feeding tubes using a standardized active bedside protocol. MEASUREMENTS AND MAIN RESULTS We determined the success rate of feeding tube placement into or beyond the second portion of the duodenum and the time required for this procedure by experienced nurses. The feeding tube was considered to be postpyloric when the tip was in the second portion of the duodenum or beyond. The predictive value of a serial step-up in gastrointestinal aspirate pH from < or = 5.0 to > or = 6.0 was also determined. Use of intravenous erythromycin significantly improved the rate of feeding tube placement into the duodenum or jejunum (erythromycin group, 13 of 14 patients or 93% vs. the control group, 12 of 22 patients or 55%; p < .03). Erythromycin administration also significantly decreased the procedure time from 25 +/- 3 to 15 +/- 2 mins (p < .04). Feeding tube placement into either duodenum or jejunum was confirmed in all 18 patients with a pH step-up from < or = 5.0 to > or = 6.0.

CONCLUSION

A single bolus dose of intravenous erythromycin facilitates active bedside placement of postpyloric feeding tubes in critically ill adult patients.

Intranasal immunization with recombinant antigens associated with new cationic particles induces strong mucosal as well as systemic antibody and CTL responses

New cationic nanoparticles (SMBV) were evaluated for use as a nasal vaccine delivery system for two recombinant proteins: HBsAg and beta-galactosidase. Each protein was formulated with SMBV and intranasally administrated to non-anesthetized mice. In each model, the formulated protein induced high levels of specific serum IgG antibodies and cytotoxic T lymphocyte (CTL) responses. Moreover, specific IgA antibodies were found in nasal as well as in vaginal washes of intranasally immunized mice with the protein associated with SMBV. In contrast, no IgG or IgA antibodies and no CTL were detected in mice immunized with free protein. The detection of a CTL response and an increase in both IgG1 and IgG2a antibodies in serum suggest that SMBV amplifies both Th1 and Th2 responses without modifying the Th1/Th2 profile of the immune response induced by the natural protein. These data demonstrate the high potential of SMBV for use as a nasal delivery system for sub-unit vaccines.

Current understanding of gastrointestinal immunoregulation and its relation to food allergy

Tolerance to food antigens induced via the gut ("oral tolerance") appears to be a rather robust adaptive immune mechanism. However, the neonatal period is particularly critical in terms of mucosal defense, with regard to infections and priming for allergic disease. This is so because the intestinal barrier function provided by secretory antibodies, as well as the immunoregulatory network, is poorly developed for a variable period after birth. Notably, the postnatal development of mucosal immune homeostasis depends on the establishment of a normal commensal microbial flora and also on adequate timing and dose of dietary antigens when first introduced. In this context, breastfeeding appears to exert both shielding and positive regulatory effects. Altogether, the intestinal immune system normally seems rather fit for tolerance induction against innocuous antigens because most children with food allergy "outgrow" their problems, whereas airway allergy tends to persist.

Protection against influenza virus infection in polymeric Ig receptor knockout mice immunized intranasally with adjuvant-combined vaccines

The role of secretory IgA in conferring cross-protective immunity was examined in polymeric (p)IgR knockout (KO) mice immunized intranasally with different inactivated vaccines prepared from A/PR/8/34 (H1N1), A/Yamagata/120/86 (H1N1), A/Beijing/262/95 (H1N1), and B/Ibaraki/2/85 viruses and infected with the A/PR/8/34 virus in the upper respiratory tract (RT)-restricting volume. In wild-type mice, immunization with A/PR/8/34 or its variant (A/Yamagata/120/86 and A/Beijing/262/95) vaccines conferred complete protection or partial cross-protection against infection, while the B-type virus vaccine failed to provide protection. The protection or cross-protection was accompanied by an increase in the nasal A/PR/8/34 hemagglutinin-reactive IgA concentration, which was estimated to be >30 times the serum IgA concentration and much higher than the nasal IgG concentration. In contrast, the blockade of transepithelial transport of dimeric IgA in pIgR-KO mice reduced the degree of protection or cross-protection, in parallel with the marked increase in serum IgA concentration and the decrease in nasal IgA concentration (about 20 and 0.3 times those in wild-type mice, respectively). The degree of the reduction of protection or cross-protection was moderately reversed by the low but non-negligible level of nasal IgA, transudates from the accumulated serum IgA. These results, together with the absence of the IgA-dependent cross-protection in the lower RT and the unaltered level of nasal or serum IgG in wild-type and pIgR-KO mice, confirm that the actively secreted IgA plays an important role in cross-protection against variant virus infection in the upper RT, which cannot be substituted by serum IgG.

Intranasal vaccination with pneumococcal surface protein A and interleukin-12 augments antibody-mediated opsonization and protective immunity against Streptococcus pneumoniae infection

Streptococcus pneumoniae is a major pathogen in humans that enters the host primarily through the respiratory tract. Targeting mucosal surfaces directly may therefore be an optimal approach for vaccination to prevent bacterial colonization and invasive disease. We have previously demonstrated the effectiveness of interleukin-12 (IL-12) delivered intransally (i.n.) as an antiviral respiratory adjuvant. In this study, we examined the effects of i.n. IL-12 treatment on induction of protective humoral immunity against S. pneumoniae. Immunization i.n. with pneumococcal surface protein A (PspA) and IL-12 resulted in enhanced lung IL-10 mRNA expression and marked augmentation of respiratory and systemic immunoglobulin G1 (IgG1), IgG2a, and IgA antibody levels compared to those in animals receiving PspA alone. In addition, i.n. vaccination with PspA and IL-12 provided increased protection against nasopharyngeal carriage. Flow cytometric analysis revealed a threefold increase in antibody-mediated, complement-independent opsonic activity in the sera of PspA- and IL-12-treated animals, which was mainly contributed by IgG2a and, to a lesser extent, IgA. Passive transfer of these immune sera conferred complete protection from death upon systemic pneumococcal challenge. These findings demonstrate the effectiveness of combining PspA and IL-12 at mucosal sites to achieve optimal antibody-mediated opsonization and killing of S. pneumoniae.

IgA and the IgA Fc receptor

IgA has traditionally been regarded a non-inflammatory antibody. This might indeed be true for secretory IgA (SIgA), which exerts its function at mucosal surfaces where commensal microorganisms and dietary antigens prevail. Serum IgA, however, potently triggers (pro)-inflammatory activity upon binding to the myeloid IgA receptor, FcalphaRI. Here, new insights in the roles of IgA and FcalphaRI are addressed and a model integrating the various functions of IgA in immunity is discussed.