Route and type of nutrition influence mucosal immunity to bacterial pneumonia

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.

Nutrition support in severe acute pancreatitis

Nutritional support can improve the outcome from severe acute pancreatitis in two ways: first by providing the building blocks for tissue repair and recovery, and second, by modulating the inflammatory response and preventing organ failure, both of which are responsible for most of the morbidity and mortality associated with the disease. This review discusses the evidence on which these statements are based.

LACK OF ENTERAL NUTRITION BLUNTS EXTRACELLULAR-REGULATED KINASE PHOSPHORYLATION IN GUT-ASSOCIATED LYMPHOID TISSUE

The mitogen-activated protein kinase (MAPK) family (extracellular-regulated kinase [ERK], p38, etc.) of signal transduction proteins includes important intracellular mediators of inflammation, playing critical roles in host defense. Phosphorylations of ERK and p38 are responsible for cell proliferation, cell differentiation, and cell death. We hypothesized that impaired gut-associated lymphoid tissue (GALT) function in the absence of enteral nutrition is associated with reduced MAPK phosphorylation in GALT cells. Fifty-three male Institute of Cancer Research mice were randomized into 3 groups; ad libitum chow, intragastric (i.g.)-TPN, and intravenous (i.v.)-TPN. TPN groups were administered a standard TPN solution. After 5 days of feeding, lymphocytes from Peyer patches (PPs), the lamina propria (LP) cells, and intraepithelial (IE) spaces in the small intestine were isolated. GALT lymphocyte numbers were determined. The lymphocytes were incubated with or without 50 ng/mL of phorbol myristate acetate (PMA) for 15 min, and phosphorylated ERK (p-ERK) and p38 (p-p38) levels were determined using laser scanning cytometry. In PP (GALT inductive site) lymphocytes, p-ERK was increased after PMA in all three groups. However, ERK phosphorylation in GALT effector sites (IE and LP) was enhanced only in the enteral groups. p38 phosphorylation was not increased in any GALT sites, in any of the three groups, in response to PMA. In another set of mice (n = 33), in vitro LP lymphocyte proliferation was assessed with BrdU with or without PMA. Cell proliferation was increased or maintained at high level with PMA in the i.g.-TPN and chow group, but remained low in the i.v.-TPN group. In conclusion, lack of enteral feeding blunts ERK activation and cell proliferation in response to PMA stimulation in GALT effector sites, which may be an important mechanism underlying reduced GALT function. The influence of nutrition on GALT p38 phosphorylation must be assessed with other types and dosages of stimulants.

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.

Total parenteral nutrition-related gastroenterological complications

Total parenteral nutrition is a life saving therapy for patients with chronic gastrointestinal failure, being an effective method for supplying energy and nutrients when oral or enteral feeding is impossible or contraindicated. Clinical epidemiological data indicate that total parenteral nutrition may be associated with a variety of problems. Herein we reviewed data on the gastroenterological tract regarding: (i) total parenteral nutrition-related hepatobiliary complications; and (ii) total parenteral nutrition-related intestinal complications. In the first group, complications may vary from mildly elevated liver enzyme values to steatosis, steatohepatitis, cholestasis, fibrosis and cirrhosis. In particular, total parenteral nutrition is considered to be an absolute risk factor for the development of biliary sludge and gallstones and is often associated with hepatic steatosis and intrahepatic cholestasis. In general, the incidence of total parenteral nutrition-related hepatobiliary complications has been reported to be very high, ranging from 20 to 75% in adults. All these hepatobiliary complications are more likely to occur after long-term total parenteral nutrition, but they seem to be less frequent, and/or less severe in patients who are also receiving oral feeding. In addition, end-stage liver disease has been described in approximately 15-20% of patients receiving prolonged total parenteral nutrition. Total parenteral nutrition-related intestinal complications have not yet been adequately defined and described. Epidemiological studies intended to define the incidence of these complications, are still ongoing. Recent papers confirm that in both animals and humans, total parenteral nutrition-related intestinal complications are induced by the lack of enteral stimulation and are characterised by changes in the structure and function of the gut. Preventive suggestions and therapies for both these gastroenterological complications are reviewed and reported in the present review.

Immunoglobulin a modulates inflammatory responses in an in vitro model of pneumonia

BACKGROUND

Preservation of mucosal immunity has been shown to affect the risk and outcome of pneumonia in severely injured patients. Secretory immunoglobulin A (SIgA) is the principle humoral defense of mucosal surfaces in the body and has several antiinflammatory properties. Polymorphonuclear neutrophils (PMN) function to kill invading microorganisms, but their exaggerated inflammatory responses may cause tissue injury to the host. The purpose of this study was to compare the ability of different immunoglobulin (Ig) isotypes to modulate PMN cytotoxic potential cocultured with respiratory epithelial cells challenged with bacteria.

METHODS

Calu-3 cell monolayers were established on membranes (0.1-microm pore) in a two-chamber culture system. Escherichia coli (EC) incubated with either polyclonal SIgA or IgG was inoculated into the apical chamber and PMNs (10/mL) added to the basal chamber. PMN cytotoxic potential was indexed by % CD11b expression, superoxide anion (O2) production, and elastase release. Dextran flux was used to index Calu-3 monolayer permeability.

RESULTS

Addition of EC to PMN-Calu-3 cell coculture increased % CD11b expression, O2 production, and elastase release. IgG had no effect on PMN activation after EC challenge. SIgA abrogated PMN activation and the increase in Calu-3 cell monolayer permeability noted with EC or EC + IgG treatment groups.

CONCLUSION

PMN cytotoxic potential was decreased by the presence of SIgA but not IgG in an in vitro model to simulate pneumonia in vivo. SIgA may not only function to protect against microbial invasion of mucosal surfaces, but may also protect against tissue injury from an exaggerated inflammatory response.

EXOGENOUS INTERLEUKIN 7 AFFECTS GUT-ASSOCIATED LYMPHOID TISSUE IN MICE RECEIVING TOTAL PARENTERAL NUTRITION

In the absence of enteral nutrient delivery, gut-associated lymphoid tissue (GALT) mass and function are reduced. The purpose of this study was to examine whether exogenous interleukin (IL)-7 treatment reverses intravenous (IV)-total parenteral nutrition (TPN)-induced changes in GALT, immunoglobulin (Ig) A levels, and gut barrier function. Eighty-nine mice were randomized to chow, TPN, or TPN + IL-7 (1 microg/kg, administered IV twice a day) and treated for 5 days. The entire small intestine was harvested and lymphocytes were isolated from Peyer's patches (PPs), intraepithelial (IE) spaces, and the lamina propria (LP). Small intestinal and bronchoalveolar IgA levels were measured. Proximal and distal small intestinal levels of IgA-stimulating (IL-10) and IgA-inhibiting (IFNgamma) cytokines were determined with enzyme-linked immunoabsorbant assay. Moreover, 1 x 10 live Pseudomonas aeruginosa were delivered by gavage and survival was observed. TPN decreased total cell yields from PPs, IE spaces, and the LP compared with the chow group. IL-7 treatment restored cell numbers. PP CD4+, PP CD8+, IE gammadeltaTCR+, and LP CD4+ cell numbers were higher in the TPN + IL-7 group than in the TPN group. Secretory IgA levels were lower in the TPN and TPN + IL-7 than in the chow group. In the distal small intestine, IFNgamma levels were similar in the three groups, whereas IL-10 levels were reduced in the TPN and TPN + IL-7 groups relative to the chow group. Survival times were reduced in the TPN compared with the chow group, but IL-7 treatment significantly improved survival. Thus, exogenous IL-7 does not improve secretory IgA levels, nor are there any remarkable effects on levels of gut IgA-mediating cytokines. However, IL-7 treatment during TPN reverses TPN-induced GALT atrophy and improves survival in a gut-derived sepsis model.

Internal biliary drainage improves decreased number of gut mucosal T lymphocytes and MAdCAM-1 expression in jaundiced rats

BACKGROUND

Although the effect of preoperative biliary drainage in patients with obstructive jaundice is controversial, bacterial or endotoxin translocation is one of the main postoperative problem in jaundiced patients. Failure in gut barrier functions causes bacterial translocation; homing and distribution of T lymphocytes in the intestinal lamina propria are important for gut mucosal immune defense. This study was performed to examine whether bile regulates the numbers of T lymphocyte subsets or the expression of mucosal addressin cell adhesion molecule-1 (MAdCAM-1) in experimental jaundice in rats with and without external and internal biliary drainage.

METHODS

Four groups of Wistar rats were used: those that received a sham operation (SHAM), common bile duct ligation (CBDL), CBDL followed by external drainage (ED), and CBDL followed by internal drainage (ID). Numbers of CD4(+) and CD8(+) T lymphocytes and MAdCAM-1-positive cells in the lamina propria were counted immunohistochemically in the specimens of jejunum and ileum of each group. Bacterial translocation was examined by culturing from the mesenteric lymph node complex isolated from rats in each group.

RESULTS

A significant decrease in numbers of CD4(+) and CD8(+) T lymphocytes and MAdCAM-1-positive cells in the lamina propria was seen in obstructive jaundice, although numbers of peripheral blood lymphocytes increased in comparison with the sham-operated control. The numbers of CD4(+) and CD8(+) T lymphocytes and MAdCAM-1 expression in the lamina propria did not recover to a normal level after external drainage, but did so after internal drainage. Frequencies of bacterial translocation were high in the CBDL and ED group. In contrast, bacterial translocation was not present in any animals in the SHAM group and was at a low percentage in the ID group.

CONCLUSIONS

Changes in the number of T lymphocytes and MAdCAM-1 expression are associated with the presence of bile in the gastrointestinal tract and are inversely correlated with the frequency of bacterial translocation induced by CBD ligation. MAdCAM-1 expression maintained by the presence of bile may regulate T-lymphocyte homing to the lamina propria in obstructive jaundice.

Effects of combined nutritional therapy on acute necrotizing pancreatitis in rats in the early phase of the disease

The aim of this study was to investigate the influence of a small amount of enteral nutrition along with parenteral nutrition on acute necrotizing pancreatitis (ANP) induced by glycodeoxycholic acid in rats in the early phase of disease. The induction of ANP resulted in a significant increase in mortality rate, intestinal permeability, bacterial infection in the pancreas and extrapancreatic organs, pancreatic necrosis and serum activity of urea and amylase, and a significant decrease in concentrations of calcium, protein and albumin. But no difference was observed between the pancreatitis groups. Significant hyperglycemia and increased liver transaminase activity were observed in rats treated with combined nutritional therapy (CNT). CNT did not improve the course of acute pancreatitis, intestinal permeability, bacterial translocation, or reduce the extent of acinar cell injury in ANP and is therefore unlikely to be of benefit in patients with pancreatitis in the early period.

A two institution experience with 226 endoscopically placed jejunal feeding tubes in critically ill surgical patients

BACKGROUND

Early jejunal feeding after surgery or trauma reduces infectious complications. Although not ideal gastric and postpyloric feedings are often used, however, because of difficulty in placing feeding tubes distal to the ligament of Treitz (LOT). Our hypothesis was that feeding tube placement distal to the LOT can be accomplished using a bedside transendoscopic technique.

METHODS

Transendoscopic jejunal (TEJ) tube placement and TEJ tubes inserted simultaneously through percutaneous gastrostomy (PEG) tubes (PEG/TEJ) were attempted to be placed distal to the LOT.

RESULTS

In all, 226 feeding tubes (185 TEJ, 41 PEG/TEJ) were placed in 179 trauma and 47 nontrauma patients over 3 years (August 20, 1998 to July 15, 2001). Tube location was jejunal in 93.8% of trauma patients, 76.6% of nontrauma patients, and 90.3% of all patients. (Confidence intervals were 89.3% to 96.5%, 62.8% to 86.4%, and 85.7% to 93.5%). Days of total parenteral nutrition were reduced 71.3% in trauma patients, 22.8% in nontrauma patients, and 45% overall at one institution.

CONCLUSIONS

Bedside TEJ and PEG/TEJ placement is safe and successful in placing feeding tubes distal to the LOT in more than 90% of critically ill surgical patients.

Enterocyte apoptosis and barrier function are modulated by SIgA after exposure to bacteria and hypoxia/reoxygenation

BACKGROUND

Secretory immunoglobulin A (SIgA) is the principal immune defense against luminal pathogens at gut mucosal surfaces. It also has anti-inflammatory activities that may be important for the maintenance of mucosal surface integrity. Enterocyte apoptosis (Apo) is increased after challenge with invasive bacteria and ischemia-reperfusion insults. Increased Apo also has been associated with impaired intestinal barrier function. However, the impact of SIgA on enterocyte apoptosis and mucosal barrier integrity after challenge with commensal bacteria and ischemia-reperfusion is unknown.

METHODS

Caco2 intestinal epithelial cell monolayers were subjected to 21% O(2) (control) or 95% N(2)/15% CO(2) (hypoxic) conditions for 90 minutes, followed by 21% O(2). Escherichia coli and SIgA were added in subsets. Caco2 cell Apo was identified by flow cytometry and barrier function indexed by permeability to dextran-fluorescein isothiocyanate.

RESULTS

There were no differences in the percentage of Apo Caco2 cells after exposure to either bacteria or hypoxic-reoxygenation versus control. There was a significant increase in Apo after the combined bacteria/hypoxia-reoxygenation challenge. SIgA abrogated the Apo response and preserved barrier function after this combined challenge.

CONCLUSION

Modulation of enterocyte Apo by SIgA may serve to maintain intestinal barrier function and thereby decrease the systemic inflammatory response after clinical conditions associated with gut ischemia-reperfusion insults.

Enteral feeding preserves mucosal immunity despite in vivo MAdCAM-1 blockade of lymphocyte homing

OBJECTIVE

To determine the influence of route of nutrition on gut mucosal addressin cellular adhesion molecule-1 (MAdCAM-1) expression and the effect of MAdCAM-1 blockade on gut-associated lymphoid tissue (GALT) lymphocyte populations and established respiratory antibacterial immunity.

SUMMARY BACKGROUND DATA

Lymphocytes, sensitized to antigens in Peyer's patches, migrate via mesenteric lymph nodes and home to intestinal lamina propria. MAdCAM-1 located on endothelial cells regulates this trafficking. Experimentally, parenteral nutrition (PN) decreases GALT cell mass and mucosal immunity when compared with enteral feeding.

METHODS

In experiment 1, MAdCAM-1 expression was quantified in 32 mice after 4 days of feeding chow, a complex diet, intragastric (IG)-PN, or PN. In experiment 2, MAdCAM-1 was measured in 102 mice 0, 4, 8, 12, 24, 48, or 72 hours after starting PN and at 0, 4, 8, 12, 24, or 48 hours after reinstituting chow following 5 days of PN. In experiment 3, 56 mice received chow, PN, chow + MECA-367 (anti-MAdCAM-1 mAb), or chow + Isotype control Ab (IsoAb) for 5 days, followed by Peyer's patches, lamina propria, and intraepithelial lymphocyte yield with respiratory and intestinal IgA levels. In experiment 4, 10 days after Pseudomonas immunization, mice received chow + MECA-367 or chow + IsoAb for 4 days followed by 1.2 x 108 Pseudomonas intratracheally.

RESULTS

Diet and route affect MAdCAM-1 expression (chow > complex diet > IG-PN > PN). Decreased MAdCAM-1 expression occurred within hours of starting PN in Peyer's patches, but not mesenteric lymph nodes or the intestine, and recovered quickly with enteral refeeding. MAdCAM-1 blockade reduced all GALT populations. Blockade had little effect on IgA levels and partially impaired the late response of established respiratory immunity.

CONCLUSIONS

Enteral feeding affects MAdCAM-1 expression. Complete MAdCAM-1 blockade reduces GALT lymphocytes to PN levels, but the chow feeding stimulus preserves IgA and early antibacterial resistance, implying the existence of non-MAdCAM-1 mechanisms to preserve mucosal immunity.

Enteral feeding preserves mucosal immunity despite in vivo MAdCAM-1 blockade of lymphocyte homing

OBJECTIVE

To determine the influence of route of nutrition on gut mucosal addressin cellular adhesion molecule-1 (MAdCAM-1) expression and the effect of MAdCAM-1 blockade on gut-associated lymphoid tissue (GALT) lymphocyte populations and established respiratory antibacterial immunity.

SUMMARY BACKGROUND DATA

Lymphocytes, sensitized to antigens in Peyer's patches, migrate via mesenteric lymph nodes and home to intestinal lamina propria. MAdCAM-1 located on endothelial cells regulates this trafficking. Experimentally, parenteral nutrition (PN) decreases GALT cell mass and mucosal immunity when compared with enteral feeding.

METHODS

In experiment 1, MAdCAM-1 expression was quantified in 32 mice after 4 days of feeding chow, a complex diet, intragastric (IG)-PN, or PN. In experiment 2, MAdCAM-1 was measured in 102 mice 0, 4, 8, 12, 24, 48, or 72 hours after starting PN and at 0, 4, 8, 12, 24, or 48 hours after reinstituting chow following 5 days of PN. In experiment 3, 56 mice received chow, PN, chow + MECA-367 (anti-MAdCAM-1 mAb), or chow + Isotype control Ab (IsoAb) for 5 days, followed by Peyer's patches, lamina propria, and intraepithelial lymphocyte yield with respiratory and intestinal IgA levels. In experiment 4, 10 days after Pseudomonas immunization, mice received chow + MECA-367 or chow + IsoAb for 4 days followed by 1.2 x 108 Pseudomonas intratracheally.

RESULTS

Diet and route affect MAdCAM-1 expression (chow > complex diet > IG-PN > PN). Decreased MAdCAM-1 expression occurred within hours of starting PN in Peyer's patches, but not mesenteric lymph nodes or the intestine, and recovered quickly with enteral refeeding. MAdCAM-1 blockade reduced all GALT populations. Blockade had little effect on IgA levels and partially impaired the late response of established respiratory immunity.

CONCLUSIONS

Enteral feeding affects MAdCAM-1 expression. Complete MAdCAM-1 blockade reduces GALT lymphocytes to PN levels, but the chow feeding stimulus preserves IgA and early antibacterial resistance, implying the existence of non-MAdCAM-1 mechanisms to preserve mucosal immunity.

Route of nutrition influences generation of antibody-forming cells and initial defense to an active viral infection in the upper respiratory tract

OBJECTIVE

To assess whether lack of enteral feeding significantly impairs generation of specific immune responses to an acute viral infection.

SUMMARY BACKGROUND DATA

Parenteral feeding provides adequate nutrients to meet metabolic needs, but lack of enteral stimulation creates a defect in mucosal immunity characterized by loss of IgA-mediated defenses in the respiratory tract.

METHODS

The enzyme-linked Immunospot (ELISPOT) assay was used to determine accumulation of immunologic cells in the nasal passages after diet manipulation. Viral shedding and nasal IgA levels were measured in additional groups of mice.

RESULTS

After determining the time course of antibody-forming cells (AFCs) via ELISPOT to an active infection with the A/PR8 influenza virus, a significant reduction was found in total AFCs, IgA-producing AFCs, and IgG-producing AFCs over the course of a 13-day experiment with significant depression in viral-specific respiratory IgA levels. Eight days following an active infection, seven of nine total parenteral nutrition-fed animals continued to have viral shedding in the nasal passages compared to one of nine chow-fed mice and one of six animals fed a complex enteral diet.

CONCLUSIONS

Lack of enteral stimulation significantly impairs the generation of IgA-mediated mucosal immunity.

Glutamine improves impaired cellular exudation and polymorphonuclear neutrophil phagocytosis induced by total parenteral nutrition after glycogen-induced murine peritonitis

Clinical and laboratory evidence shows that enteral feeding significantly reduces pneumonia and intra-abdominal abscess formation after celiotomy for severe trauma. Supplementation of total parenteral nutrition (TPN) with glutamine (GLN) supports impaired immunity induced by TPN in several animal and human studies. This work investigates the peritoneal cellular response and polymorphonuclear neutrophil (PMN) bactericidal function after mouse chemical peritonitis after TPN with and without GLN. Thirty-three mice received chow, TPN, or 2% GLN-supplemented TPN (GLN-TPN) for 5 days. All mice then received 2 mL of a 1% glycogen solution intraperitoneally to induce cell exudation, and peritoneal exudative cells (PECs) were recovered 4 h later. Total and differential PEC numbers, as well as PMN phagocytosis, reactive oxygen intermediate production (ROI), CD11b (integrin aM chain) expression, and CD16/32 (Fcgamma II/III receptor) expression were measured. PMN, macrophage, and lymphocyte cell numbers were significantly lower with TPN than with chow or GLN-TPN groups, with no differences between chow and GLN-TPN. TPN significantly lowered peritoneal PMN phagocytosis compared with chow (P < 0.05) and approached significance with GLN-TPN (P = 0.06). There were no significant differences in ROI production or CD11b and CD16/32 expression on peritoneal PMN. GLN supplementation improved the reduction in cell exudation and PMN phagocytosis induced by TPN after chemical peritonitis.

Effect of route and type of nutrition on intestine-derived inflammatory responses

BACKGROUND

Immunological links between the gastrointestinal (GI) tract and respiratory tract has been postulated in the development and maintenance of mucosal immunity. Route and type of nutrition affects mucosal immunity by reducing cell populations within the Peyer's patches of the small intestine and lamina propria as well as altering cytokine profiles within these sites. In addition to the mucosal affects, these alternations in cytokines (decreases in interleukin-4 and interleukin-10) also appear to influence the vascular endothelium of the GI tract.

DATA SOURCES

This review examines the laboratory data regarding cytokine profile within the gut, endothelial adhesion molecule expression within the intestinal and extraintestinal organs, and the effect of these alterations on neutrophil accumulation and organ responses to gut ischemia/reperfusion. It also describes the effect of a specific nutrient, glutamine, on the starved gut.

CONCLUSIONS

Changes induced by failure to feed the GI tract affects GI vascularity increasing expression of proinflammatory adhesion molecules. These adhesion molecules attract neutrophils and prime them for subsequent ischemic events. Lack of feeding the gastrointestinal tract acts as a "first hit" and increases the inflammatory response to a secondary insult in the lungs, liver, and GI tract. The addition of the specific nutrient, glutamine, reverses many of these defects and favorably influences the proinflammatory effects of gut starvation.

Nutrition support of the trauma patient

Hypercatabolism after trauma may lead to acute protein malnutrition, ultimately resulting in multiple organ failure. Nutrition support may prevent this sequence. This review addresses the need for early nutrition support, the preferred route of substrate delivery, and the potential advantages of "immune-enhancing" diets.

The pulmonary physician in critical care - part 9: non-ventilatory strategies in ARDS

Pharmacological approaches to the treatment of ARDS are reviewed. Future treatments should be targeted at elements of the pathological process that produce specific clinical problems.

Early enteral nutrition in the cardiothoracic intensive care unit

BACKGROUND AND AIMS

Early enteral nutrition (EN) improves intestinal integrity, motility and immunocompetence. However, technical problems such as diarrhoea and gastric residual volumes are said to be associated with the method and have prevented its implementation. We have prospectively assessed clinical problems connected to early EN.

PATIENTS AND METHODS

Seventy-three consecutive patients eligible for EN were assessed and observed until discharge from the intensive care unit (ICU) or until they resumed oral nutrition. They had surgery for coronary artery bypass grafting and/or valvular disease, thoracic or thoracoabdominal aortic aneurysms or other combined procedures. Two cardiac patients were not subjected to surgery.

RESULTS

In 59/73 patients, EN was started within 3 days. EN was discontinued in half of the patients when they were able to feed themselves. Twelve patients vomited, one of them severely. Dislocation of the nasogastric tube occurred in 28 patients. The 15 patients with diarrhoea were treated with 2-6 broad-spectrum antibiotics during their ICU-stay. Out of 73, 40 patients did not show any gastric residual volume (GRV). GRV decreased during EN in 50% of the patients with fairly large or large residual volumes. The incidence of aspiration pneumonia was 10%.

CONCLUSION

In the cardiothoracic ICU, individually adjusted early EN is feasible with few problems.

Nutritional support

Despite the increasing obesity of the American population, many chronically ill patients are malnourished. When this malnutrition is combined with the hypermetabolic response and protein catabolism of an acute event, such as an operation, nutritional support becomes an important facet for optimal critical care. This chapter reviews the basic tenants of nutritional support with special emphasis on patients with pulmonary compromise. Important aspects of caloric and protein support are discussed and enteral nutrition is emphasized because of its numerous advantages and documented improvement in outcome.

Current aspects of mucosal immunology and its influence by nutrition

BACKGROUND

A significant body of clinical literature demonstrates that enteral feeding significantly reduces the incidence of pneumonia compared to patients fed parenterally. An immunologic link between the gastrointestinal tract and respiratory tract is postulated via the common mucosal immune hypothesis. This hypothesis states that cells are sensitized within the Peyer's patches of the small intestine and are subsequently distributed to submucosal locations in both intestinal and extra intestinal sites. This system is exquisitely sensitive to route and type of nutrition.

DATA SOURCE

This review examines the laboratory data regarding cell numbers, cell phenotypes, cytokine profile, and immunologic function in both intestinal and extra intestinal sites in animals that have been administered either parenteral feeding or various types of enteral feeding. It also establishes links between a specific nutrient, glutamine, the enteric nervous system, by way of neuropeptides, and mucosal immunity.

CONCLUSION

Progress in understanding relationships between nutrient availability, enteric nervous system stimulation, and nutrient delivery on mucosal immunity offers opportunities to explore immune systems previously not appreciated by clinicians and basic scientists. These opportunities offer new challenges to the physician scientist, basic scientist, and clinician to understand, manipulate, and apply these concepts to the critically ill patient population by favorably influencing immunologic barriers and the inflammatory response.

The neuropeptide bombesin improves IgA-mediated mucosal immunity with preservation of gut interleukin-4 in total parenteral nutrition-fed mice

BACKGROUND

The Th2 cytokines, interleukin-4 (IL-4) and interleukin-10 (IL-10), stimulate IgA production. Total parenteral nutrition (TPN) reduces IL-4 and IL-10 messenger RNA in gut lamina propria lymphocytes, total IL-4 and IL-10 in gut homogenates, and IgA-mediated mucosal immunity. Bombesin (BBS) can maintain mucosal immunity in TPN-fed mice, but the effects of BBS on gut IL-4 and IL-10 levels and their mRNA expression in the lamina propria are unknown.

METHODS

In experiment 1, mice that were fed chow, TPN, or TPN + BBS (15 microg/kg intravenously-three times a day) for 5 days were killed, and respiratory tract IgA and intestinal IgA, IL-4, and IL-10 levels were measured. In experiment 2, IL-4 and IL-10 mRNA were measured in isolated lamina propria lymphocytes from chow-, TPN-, and TPN+BBS-fed mice by reverse transcriptase-polymerase chain reaction. Intestines were harvested 1 hour after injection of 100 7 microg of lipopolysaccharide intraperitoneally. Samples were standardized to beta-actin.

RESULTS

TPN-fed mice had significantly lower respiratory tract IgA levels than chow- or TPN + BBS-fed mice. TPN+BBS did not increase intestinal IL-10 or IL-10 lamina propria mRNA levels but maintained intestinal IL-4 levels and lamina propria IL-4 mRNA expression equal to those of chow-fed mice.

CONCLUSIONS

BBS reverses the effects of TPN on intestinal and respiratory tract IgA levels and most effects on gut cytokines. Lamina propria cytokine mRNA levels reflect total gut cytokine concentration.

Most infectious complications in parenterally fed trauma patients are not due to elevated blood glucose levels

OBJECTIVE

To determine the relationship between hyperglycemia and infectious complications in nutritional studies of trauma patients.

METHODS

Retrospective review of serum glucose values in two published randomized, prospective studies of patients receiving either enteral or parenteral feeding (trial 1) or isonitrogenous, isocaloric enteral diets (trial 2). Trial 2 also included patients prospectively followed who received little or no enteral feeding.

RESULTS

Patients randomized to enteral or parenteral feeding in trial 1 exhibited no significant differences in the highest recorded serum glucose (SG) until the fourth or fifth day after protocol entry. SG tended to be higher in infected than non-infected patients in the first 4 hospital days, but SG was far below values considered to increase the risk for infection (SG > 220 mg/dL). In trial 2, glucose levels tended to be slightly higher in infected than in noninfected patients within the first 5 days reaching statistical significance by day 5. Unfed control patients had similar SG values but significantly more major infectious complications.

CONCLUSIONS

Patients developing infections had slightly higher SG levels than noninfected patients early in admission, but these SG values were far below levels considered a risk for infective complications. Significant hyperglycemia does not explain differences in infectious complications in critically ill trauma patients randomized to various routes and types of nutrition.

Enteral nutrition prevents remote organ injury and death after a gut ischemic insult

OBJECTIVE

To determine whether parenteral feeding (IV-TPN) influences the local and systemic response to an intestinal insult.

SUMMARY BACKGROUND DATA

Parenteral feeding increases ICAM-1 expression and attracts neutrophils (PMNs) to the intestine compared with enterally fed animals. Because the gut is a priming bed for PMNs, the authors hypothesized that IV-TPN may affect organ injury after gut ischemia-reperfusion (I/R).

METHODS

Mice were randomized to chow, IV-TPN, intragastric TPN, or complex enteral diet for 5 days' feeding. In experiment 1, 162 mice underwent 15 or 30 minutes of gut I/R, and death was recorded at 72 hours. In experiment 2, 43 mice underwent 15 minutes of gut ischemia and permeability was measured by 125I-labeled albumin at 3 hours after reperfusion. Lung PMN accumulation was measured by myeloperoxidase assay. In experiment 3, albumin leak was tested in the complex enteral diet group (n = 5) and the intragastric TPN group (n = 5) after 30 minutes of gut ischemia and 1 hour of reperfusion.

RESULTS

In experiment 1, enteral feeding significantly reduced the death rate compared with IV-TPN after 15 minutes of I/R. After 30 minutes of gut ischemia, the IV-TPN and intragastric TPN groups showed a higher death rate than the chow and enteral diet groups. In experiment 2, IV-TPN significantly increased pulmonary and hepatic 125I albumin leak compared with enteral feeding without increasing pulmonary myeloperoxidase levels. In experiment 3, there were no differences in 125I albumin leak between the complex enteral diet and intragastric TPN groups.

CONCLUSION

Enteral feeding reduced the death rate and organ permeability after 15 minutes of ischemia. However, prolonged ischemia (30 minutes) eliminated any benefits of intragastric TPN on survival.

Lack of enteral feeding increases expression of E-selectin after LPS challenge

BACKGROUND

Total parenteral nutrition (IV-TPN) increases neutrophil accumulation in the small intestine, expression of intestinal ICAM-1 and P-selectin, and upregulates E-selectin expression in the lung. Endothelial activation induced by lack of enteral nutrition may change the response to injury or infection. This study investigated whether nutrition influenced the expression of the adhesion molecule, E-selectin and ICAM-1, following endotoxin challenge.

MATERIALS AND METHODS

Forty-three mice were injected with saline, 2, 20, 200, 2000, or 10000 microg/kg lipopolysaccharide (LPS) intraperitoneally. E-selectin expression in the lung, small intestine, and heart was quantified at 3 h after challenge, while ICAM-1 was measured at 5 h, using the dual-radiolabeled monoclonal antibody technique. Next, 80 mice were fed chow, intragastric (IG)-TPN, or IV-TPN for 5 days, and then received intraperitoneal 2 or 200 microg/kg LPS. E-selectin and ICAM-1 expression in organs was measured at 3 and 5 h after endotoxin, respectively.

RESULTS

E-selectin expression in organs increased LPS dose dependently. ICAM-1 levels reached early peaks in the lung and in the intestine. Also, IV-TPN significantly increased E-selectin expression in the small intestine and tended to increase pulmonary E-selectin, when compared to chow or IG-TPN animals. There were no significant differences in E-selectin expression among three diet groups after 200 microg/kg LPS challenge. No differences in ICAM-1 expression were observed in any organ among the three groups after 2 or 200 microg/kg LPS injection.

CONCLUSIONS

E-selectin rather than ICAM-1, because of the expression pattern after various dosages of LPS challenge, may be a determining factor for the degree of LPS-induced inflammation at the early phase. Lack of enteral nutrition may increase inflammatory response through enhanced gut E-selectin levels after a small dose of LPS.

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

Secretory IgA (SIgA) is the primary mucosal Ig and has been shown to mediate nasotracheal (NT) mucosal immunity in normal immune BALB/c mice. This finding has been challenged by a report of NT immunity without IgA in knockout mice, suggesting that IgA may not be necessary for the protection of mucosal surfaces. Although other protective mechanisms may become active in the congenital absence of SIgA, these mechanisms are not the primary means of protection in normal mice. In this paper we show that feeding chemically defined total parenteral nutrition (TPN) to genetically normal, immune ICR mice by the i.v. route results in loss of nasal anti-influenza immunity and a significant drop in influenza-specific SIgA in the upper respiratory tract compared with chow-fed mice (p < 0.005), while the serum influenza-specific IgG titer is unaffected. Loss of upper respiratory tract mucosal immunity is not related to serum Ab, because 10 of 13 TPN-fed mice shed virus into their nasal secretions despite adequate serum anti-influenza IgG titers. The number of IgG Ab-secreting cells in the nasal passages and spleens of TPN-fed mice was unaffected, while both the number and the percentage of splenic IgA-secreting cells were decreased relative to those in chow-fed animals. The loss of immunity is due to the route of nutrition, not the composition of the diet, because TPN solution fed orally via gastrostomy instead of i.v. maintains NT anti-influenza mucosal immunity. We hypothesize that delivery of nutrition via the gut triggers the release of gastrointestinal neuropeptides necessary for maintenance of the mucosal immune system.

Impairment of mucosal immunity by parenteral nutrition: depressed nasotracheal influenza-specific secretory IgA levels and transport in parenterally fed mice

OBJECTIVE

To examine the effects on mucosal selective transport of polymeric IgA (pIgA) and the ability of exogenous pIgA to provide protection despite altered mucosal transport.

SUMMARY BACKGROUND DATA

Parenteral nutrition significantly impairs established antipseudomonal immunity and IgA-mediated antiviral immunity in association with gut-associated lymphoid tissue mass atrophy. Lack of enteral feeding also induces mucosal effects.

METHODS

After immunization, nasotracheal levels of influenza-specific IgA were measured in cannulated mice randomized to chow feeding or parenteral nutrition. Nonimmune animals were randomized to chow or total parenteral nutrition, and after 5 days of diet were given a mixture of two antiinfluenza monoclonal antibodies, pIgA and IgG. Four hours after injection, nasal washes were collected and influenza-specific antibody levels were determined by enzyme-linked immunosorbent assay to calculate the selective transport index of IgA relative to IgG. In the final experiment, immunized animals were randomized to chow or parenteral feeding, and after 5 days, parenterally fed animals received either normal mouse serum or antiviral pIgA before viral challenge. Viral shedding was measured at 42 hours after challenge.

RESULTS

Parenteral nutrition significantly reduced virus-specific IgA in nasotracheal washes. Parenteral nutrition depressed the selective transport index, demonstrating impaired mucosal transport of pIgA. Parenterally fed animals given specific antiviral pIgA but not normal mouse serum eliminated virus from the airway and regained mucosal protection, demonstrating adequate residual transport for immunity if adequate pIgA is present.

CONCLUSION

Although both decreased IgA production due to gut-associated lymphoid tissue atrophy and impaired mucosal transport occur when enteral feeding is not provided, residual transport can provide antiviral protection if exogenous antiviral pIgA is available. Production, rather than transport, may be the most important factor in maintaining established respiratory tract IgA-mediated immunity.

Infection control issues of enteral feeding systems

Enteral feeding systems provide a mechanism for nutritional support for patients who may be unable to tolerate oral dietary sustenance. This review takes into account recent infection control issues relating to enteral feeding systems. The review is organized into the following areas of emphasis: infections associated with enteral tube feeding, the stability and contamination of enteral tube feeding, the risk:benefit analysis of enteral tube feeding, and the protective effects of enteral tube feeding.

Individual neuropeptides regulate gut-associated lymphoid tissue integrity, intestinal immunoglobulin A levels, and respiratory antibacterial immunity

BACKGROUND

Total parenteral nutrition (TPN) leads to atrophy of the gut-associated lymphoid tissue (GALT) and a significant decrease in intestinal immunoglobulin A (IgA) levels, a major constituent of mucosal immunity. Bombesin (BBS) prevents TPN-induced GALT atrophy and maintains intestinal IgA levels. BBS, a neuropeptide analogous to gastrin-releasing peptide in humans, stimulates the release of other gut neuropeptides including cholecystokinin (CCK), gastrin, and neurotensin (NT). This study investigates the ability of CCK, gastrin, or NT to individually prevent TPN-induced GALT atrophy and preserve respiratory immunity.

METHODS

Experiment 1: Male mice were randomly assigned to receive chow, TPN, TPN plus CCK, TPN plus gastrin, or TPN plus NT. After 5 days of feeding, Peyer's patches (PP) from the proximal and distal small bowel were harvested and analyzed for cell yields. PP cells were also analyzed for GALT cell type. Small bowel IgA levels were measured by enzyme-linked immunosorbent assay (ELISA). Experiment 2: Mice were randomly assigned to receive either liposomes containing Pseudomonas antigen or liposomes without antigen. After 10 days, mice were randomly assigned to the same five treatment groups, fed for 5 days, and then given intratracheal Pseudomonas. Mortality was assessed after 48 hours.

RESULTS

Experiment 1: GALT cell reductions due to IV-TPN were greater in the distal than proximal small bowel. All three neuropeptides prevented most TPN-induced GALT atrophy due mainly to the maintenance of the B-cell and T-cell populations in the PP of the distal bowel. Intestinal IgA levels were significantly higher in the animals treated with neuropeptides than animals treated with TPN only; however, these IgA levels were not maintained at levels observed in chow-fed animals. Experiment 2: Immunization resulted in significantly lower mortality in animals fed chow, TPN plus CCK, and TPN plus gastrin. TPN alone and TPN plus NT resulted in loss of immunity and mortality rate at comparable levels to unimmunized animals.

CONCLUSIONS

Supplementation of IV-TPN with CCK, gastrin, and NT prevents GALT atrophy, primarily in the distal bowel. Intestinal IgA levels improve but not to normal levels. CCK and gastrin reversed IV-TPN-induced effects on antibacterial pneumonia in immunized animals while NT did not.

Glutamine-enriched total parenteral nutrition maintains intestinal interleukin-4 and mucosal immunoglobulin A levels

BACKGROUND

Total parenteral nutrition (TPN) prevents progressive malnutrition but fails to maintain intestinal gut-associated lymphoid tissue (GALT) or established respiratory antiviral or antibacterial mucosal immunity. Our previous work demonstrated that decreases in intestinal immunoglobulin A (IgA) were associated with decreases in Th2-type IgA-stimulating cytokines, interleukin (IL)-4 and IL-10. Because glutamine supplementation of TPN partially preserves respiratory defenses and normalizes GALT, we investigated the ability of parenteral glutamine to normalize respiratory and intestinal IgA levels and measured Th2 cytokines in intestinal homogenates.

METHODS

Animals were cannulated and randomly assigned to receive chow (n = 17), TPN (n = 18), or an isonitrogenous, isocaloric TPN solution formulated by removing the appropriate amount of amino acids and replacing them with 2% glutamine (n = 18) for 5 days. Respiratory tract and intestinal washings were obtained for IgA and the intestine homogenized and analyzed for IL-4 and IL-10.

RESULTS

TPN decreased intestinal and respiratory IgA in association with decreases in intestinal IL-4 and IL-10 compared with chow-fed animals. Glutamine significantly improved respiratory and intestinal IgA levels, significantly improved IL-4 compared with TPN animals, and maintained IL-10 levels midway between chow-fed and TPN animals.

CONCLUSIONS

Glutamine-enriched TPN preserved both extraintestinal and intestinal IgA levels and had a normalizing effect on Th2-type IgA-stimulating cytokines.

Bombesin recovers gut-associated lymphoid tissue and preserves immunity to bacterial pneumonia in mice receiving total parenteral nutrition

OBJECTIVE

To study the ability of bombesin (BBS) to recover gut-associated lymphoid tissue (GALT) and preserve immunity in a lethal model of Pseudomonas aeruginosa (Ps) pneumonia in mice receiving total parenteral nutrition (TPN).

SUMMARY BACKGROUND DATA

TPN causes depression of mucosal immunity compared with enterally fed animals, which may explain the increased incidence of pneumonia in parenterally fed trauma patients. BBS prevents this TPN-induced GALT atrophy, depressed gastrointestinal and respiratory tract IgA levels, and impaired antiviral IgA-mediated mucosal immunity. The authors examined whether some supplement could be added to TPN to avoid this GALT atrophy and lower the incidence of infectious complications in the parenterally fed animal.

METHODS

Male mice were randomized to chow or intravenous (IV) TPN. After 5 days of IV TPN, mice received 0, 1, 2, or 3 days of BBS IV three times a day and then were killed to harvest Peyer's patch, intraepithelium, and lamina propria for cell yields. Gastrointestinal and respiratory tract IgA levels were analyzed by enzyme-linked immunosorbent assay. Next, mice underwent intranasal inoculation with liposomes alone (nonimmune) or liposome-containing Ps polysaccharide. Ps immune mice were catheterized and randomized to chow, IV TPN, or IV TPN + BBS. The liposome group received chow but no IV catheter. These mice were given an LD90 dose of intratracheal Ps, and death rates were recorded.

RESULTS

GALT and gastrointestinal and respiratory tract IgA levels improved to those in chow-fed mice after 3 days of BBS. Immunization reduced the death rate from 92% in chow-fed liposome-only animals to 20% in immunized animals. TPN-fed animals lost their mucosal immunity, with a death rate of 86% compared with 21% in the TPN + BBS group.

CONCLUSION

The results demonstrate that BBS reverses TPN-induced changes in GALT and preserves mucosal immunity. Ps immunization reduces the death rate in a gram-negative pneumonia model and maintains gastrointestinal and respiratory immunity in Ps immune mice receiving IV TPN.

The gut's role in metabolism, mucosal barrier function, and gut immunology

The gastrointestinal tract functions not only to absorb nutrients, it also plays an important immunologic role during health and critical illness. Under experimental and certain clinical conditions, stimulating the gut attentuates the stress response and avoids mucosal atrophy and increases permeability. Gut stimulation prevents atrophy of the gut-associated lymphoid tissue, the body's major defender of moist mucosal surfaces. A better understanding of gut function and improved nutrient delivery has clinical implications in the treatment of critically ill patients.

Route and type of nutrition influence IgA-mediating intestinal cytokines

OBJECTIVE

To examine the levels of a Th1 IgA-inhibiting cytokine (interferon gamma) and the Th2 IgA-stimulating cytokines (interleukin [IL]-4, IL-5, IL-6, and IL-10) within the intestine of animals manipulated with enteral or parenteral nutrition, and to correlate these cytokine alterations with intestinal IgA levels.

SUMMARY BACKGROUND DATA

Enteral feeding significantly reduces the incidence of pneumonia in critically injured patients compared with intravenous total parenteral nutrition (IV TPN) or no nutritional support. Experimentally, complex diets prevent impairments in mucosal immunity induced by IV TPN. These impairments include decreases in intestinal and respiratory tract IgA levels, impaired IgA-mediated antiviral defenses, and increases in the mortality rate against established immunity to Pseudomonas pneumonia. Intragastric (IG) TPN maintains antiviral defenses but only partially preserves protection against Pseudomonas pneumonia. Because IgA levels depend on interactions between Th1 IgA-inhibiting and Th2 IgA-stimulating cytokines, the authors postulated differences in gut cytokine balance in enterally and parenterally fed mice.

METHODS

Sixty-one mice were randomized to receive chow, IV TPN, IG TPN, or an isocaloric, complex enteral diet. After 5 days of feeding, animals were killed and supernatants from samples of intestine were harvested, homogenized, and assayed for Th1 and Th2 cytokines by enzyme-linked immunosorbent assay.

RESULTS

The Th2 cytokines, IL-5 and IL-6, and the Th1 cytokine, interferon gamma, remained unchanged by diet. IL-4 levels decreased significantly in both IV and IG TPN groups versus the chow or complex enteral diet groups, whereas IL-10 decreased only in IV TPN mice. Decreases in Th2 cytokines correlated with intestinal IgA levels.

CONCLUSION

Chow and complex enteral diets maintain a normal balance between IgA-stimulating and IgA-inhibiting cytokines while preserving normal antibacterial and antiviral immunity. The IgA-stimulating cytokine IL-4 drops significantly in mice receiving IG and IV TPN in association with reduced IgA levels, whereas IL-10 decreases significantly only in mice receiving IV TPN. These data are consistent with severely impaired mucosal immunity with IV TPN and partial impairment with IG TPN and provide a cytokine-mediated explanation for reduction in diet-induced mucosal immunity.