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© 2004 The American Society for Nutritional Sciences J. Nutr. 134:641-647, March 2004

Nutritional Immunology

Weaning Is Associated with an Upregulation of Expression of Inflammatory Cytokines in the Intestine of Piglets1,2

S. Pié, J. P. Lallès*, F. Blazy, J. Laffitte, B. Sève* and I. P. Oswald3

Unité de Pharmacologie-Toxicologie, Institut National de la Recherche Agronomique, 31931 Toulouse Cedex 9, France, and * Unité mixte de Recherches sur le Veau et le Porc, Institut National de la Recherche Agronomique, 35590 Saint Gilles, France

3To whom correspondence should be addressed. E-mail: ioswald{at}toulouse.inra.fr.


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 
Cytokines play a central role in immune cell response, but they also participate in the maintenance of tissue integrity. Changes in the cytokine network of the pig gut may be expected at weaning, because abrupt changes in dietary and environmental factors lead to important morphological and functional adaptations in the gut. This study measured the gene expression of 6 inflammatory cytokines along the small intestine (SI) and the proximal colon in 28-d-old piglets (n = 45) at different time points (0, 1, 2, 5 and 8 d) postweaning, using RT-PCR. Villus-crypt architecture and enzymatic activities of lactase and sucrase in the SI were also examined. The results confirmed that weaning is associated with morphological and enzymatic changes in the SI. In addition, the data indicated that cytokine response in the gut could be divided into two periods: an early acute response (0 to 2 d postweaning) and a late long-lasting response (2 to 8 d postweaning). Between d 0 and d 2, the levels of IL-1ß, IL-6, and TNF-{alpha} messenger RNA (mRNA) increased. Marked upregulation of IL-1ß mRNA occurred in most parts of the intestine, whereas IL-6 and TNF-{alpha} mRNA markedly increased only at specific sites in the intestine. Between d 2 and d 8, the levels of IL-1ß, IL-6, and TNF-{alpha} mRNA rapidly returned to preweaning values, except that the level of TNF-{alpha} mRNA remained high in the distal SI. Levels of IL-12 subunit p40 (IL-12p40) and IL-18 mRNA also decreased, compared to those on d 0. Taken together, these results demonstrate that weaning in piglets is associated with an early and transient response in gene expression of inflammatory cytokines in the gut.

KEY WORDS: • cytokines • intestine • piglets • weaning

Cytokines are small peptide molecules that are important mediators in the regulation of the immune and inflammatory responses. Although they are mostly derived from lymphocytes and macrophages, it is now clear that cytokines are also produced by cells not traditionally considered to be part of the immune system. These include epithelial cells, endothelial cells, and fibroblasts, which are effective sources and targets of cytokines.

The intestine forms a physical barrier that prevents toxic compounds and pathogens from entering the intestinal mucosa and systemic circulation. In the past decade, the concept has emerged that, in addition to its barrier properties, the intestinal epithelium plays an active role in organ integrity and body defense locally (1,2). Intestinal epithelial cells act as "watchdogs" for the immune system (1). They can signal the onset of the host innate and acquired immune response through the production of cytokines and chemokines that are crucial for the recruitment and activation of neutrophils, macrophages, T and B cells, and dendritic cells. Several cytokines, including transforming growth factor ß (TGF-ß),4 IL-1{alpha}, and IL-6 are constitutively expressed by the intestinal epithelium and may play a role in the basal influx of immune cells into the mucosa, in epithelial cell growth, and in homeostasis (3). Other cytokines, such as IL-8, IL-1ß, and TNF-{alpha} are also expressed by normal epithelial cells but are markedly upregulated in response to microbial infection (4).

Many studies report the changes in the expression of inflammatory cytokines in the intestine of humans and animals during enteric infection and intestinal inflammatory diseases (5–7). Both in vitro and in vivo investigations show that uncontrolled synthesis of proinflammatory cytokines can have a strong influence on gut integrity and epithelial functions, including permeability to macromolecules and transport of nutrients and ions (8). By contrast, only a few studies have investigated the gene expression of inflammatory cytokines during physiological processes such as weaning.

Weaning-associated intestinal inflammation occurs in various animal species. For example, an increase of both CD4+ (cluster of differentiation) and CD8+ T lymphocyte subsets occurs as soon as 2 d postweaning in piglets (9). In mice, weaning is characterized by an increased number of both Th1- (T helper) and Th2-secreting lymphocytes (10), also with changes in the distribution of lymphocyte subsets in the small intestine (SI) (11). Weaning is also associated with increased blood plasma IL-1 concentration in piglets and with gene expression in the intestine in rats (12,13). Finally, increased plasma concentrations of fibrinogen, an acute-phase protein of inflammation, and increased concentrations of the protease stromelysin in intestinal tissues are reported (9,12).

From the nutritional perspective, controlling early intestinal inflammation is certainly a challenge in managing postweaning gut disorders in piglets. Recent evidence shows that nutrition can modulate the intestinal cytokine level. For example, a marked decrease in the levels of IL-10 and IL-4 occurs in mice lacking enteral feeding (14). Similarly, many prebiotic and probiotic substances alter the local production of cytokines (15).

The present study analyzed the pattern of proinflammatory cytokine gene expression in the intestine of piglets throughout weaning. The mRNA for IL-1ß, IL-6, TNF-{alpha}, and IL-8, which represent early nonspecific mediators of inflammation, and for IL-12 subunit p40 (IL-12p40) and IL-18, two cytokines involved in the development of inflammatory Th1 responses, were analyzed using semiquantitative RT-PCR.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 LITERATURE CITED
 
    Animals and diet. All experimental procedures were carried out in accordance with the guidelines of the U.S. National Institutes of Health and the French Institut National de la Recherche Agronomique (INRA) for the care and use of laboratory animals. The present experiment was conducted over 8 days postweaning with 45 Large White x Landrace crossbred piglets from 5 litters (8 to 10 piglets per litter). Piglets were weaned at the age of 28 d. One or two piglets in each litter were allocated to one of the 5 experimental groups killed at 0, 1, 2, 5, and 8 d postweaning according to their sex and body weight at weaning (6.19 ± 0.20 kg; mean ± SEM). All the piglets were transferred from the farrowing unit to the postweaning unit and kept in groups of littermates. The weaned piglets had free access to a solid starter diet from the time of weaning onward. The starter diet was designed by INRA according to energy and amino acid requirements for piglets (Table 1) and was prepared by a commercial plant (Cooperl-Hunaudaye).


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  		TABLE 1 Weaning starter feed composition

 
    Sequential killing and intestinal tissue sampling. The piglets were killed at 0, 1, 2, 5, and 8 d postweaning. The piglets were electrically stunned, then immediately killed by exsanguination, and the entire gastrointestinal tract was removed. The mesentery was cut using scissors, and the small and large intestine were aligned on a table and measured without applying any specific tension. The SI was divided into three parts of equal length, and 20-cm tissue segments were collected from the middle of each part (that is, at 17, 50, and 83% of the SI length). A 10-cm segment of proximal colon was collected 30 cm distal to the ileocecal valvula. Digesta were removed from these short segments by flushing through with cold saline. Subsamples (1 cm) of the SI segments were prepared for villus-crypt morphometry and cytokine mRNA extraction. The rest was kept on ice for the extraction of the mucosa by scraping with a microscope slide before assessing digestive enzyme activity. A subsample of the proximal colon was also kept for mRNA extraction.

    Small intestine morphology and enzyme activity. The SI segments for morphometry were fixed in buffered formalin (10%) for 24 h at 4°C, then washed and stored in ethanol:water (75:25, v:v). These samples were microdissected for villi and crypts and measured according to the technique of Goodlad et al. (16). Mucosal scrapings were prepared and snap-frozen in liquid nitrogen, then stored at -80°C until enzyme activity determination. The specific activities of lactase-phlorizine hydrolase (EC 3.2.1.23) and sucrase (EC 2.1.48–10) were determined according to the methods of Dalqvist et al. (17), using lactose and sucrose as the substrates, respectively. The protein content of tissue homogenates was measured using the Bio-Rad protein assay reagent (Bio-Rad). Enzyme activity was expressed as µmol hydrolyzed substrate · min-1 · g tissue protein-1.

    Extraction of RNA. At necropsy, samples from each intestinal segment were placed in 1 mL of Extract-all (Eurobio), frozen in liquid nitrogen, and stored at -80°C until mRNA analysis. Intestinal samples were homogenized using a Cat homogenizer (Labomoderne). Total RNA was extracted following the manufacturer’s recommendations. The RNA was resuspended in 50 µL of ultrapure water containing 0.20 g/L of diethyl pyrocarbonate (Sigma). Total RNA was quantified using a spectrophotometer at an optical density of 260 nm (OD260), and the purity was assessed by determining the OD260:OD280 ratio. This ratio ranged from 1.7 to 1.9 for all samples.

    Detection of cytokine mRNA expression by RT-PCR and quantification of PCR products. Semiquantitative analysis of TNF-{alpha}, IL-1ß, IL-6, IL-8, IL-12p40, IL-18, and cyclophilin was carried out using RT-PCR as previously described (18), with minor modifications. In a first step, 1µg of total RNA was reverse transcribed using murine Moloney leukemia virus reverse transcriptase (Point Mutant; Promega), then resuspended in water to a total volume of 100 µL. Then 5 µL of cDNA for cyclophilin and 10 µL for the other tested cytokines was amplified by PCR, using deoxynucleoside triphosphates (2 mmol/L each; Eurobio), 0.2 pmol/L of 5' and 3' primers, 2 mmol/L of MgCl2, and 2.5 U of DNA Taq polymerase enzyme (Invitrogen) in a final volume of 50 µL (Table 2). In all cases, the denaturation was done at 94°C for 45 s and the extension at 72°C for 45 s. The initial denaturation was carried out for 5 min and the final extension for 10 min.


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  		TABLE 2 Oligonucleotide sequences and DNA probes designed for the detection of different porcine cytokines

 
In a second step, semiquantitative analysis of all PCR products was carried out by hybridization of 33P-labeled specific oligonucleotide probes (Table 2) to PCR products immobilized on nitrocellulose membranes by dot blotting, as previously described (19,20). The relative amounts of each product were determined by measuring radioactivity with a PhosphorImager (Molecular Dynamics). For each cytokine, the amount of the RT-PCR product was normalized to the value obtained with cyclophilin, used as a standard for each sample.

    Statistical analysis. All the data were analyzed using the General Linear Model procedure of the Statistical Analysis System (SAS Institute). The effect of the number of days postweaning was tested using the residual variation between piglets (main plot) as the error. This error was calculated by removing the treatment (day) and litter effects from the total variation between piglets. Each individual intestinal site was considered as a subplot within the piglet. Differences between sites and the day x site interactions were tested using the residual variation within piglets as the error. This error was calculated by removing the site and day x site interaction effects from the total variation within piglets. Day, site, and day x site interaction effects were considered significant at P < 0.05 (Fisher-Snedecor F-test). This was a condition for testing differences between two least-square means at P < 0.05 (protected t-test). Values presented are means ± SEM.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 LITERATURE CITED
 
    Influence of weaning on food intake, SI morphology, and enzyme activity. During the first 24 h postweaning, the piglets consumed 11 ± 3 g of the diet. This increased to 214 ± 15 and 384 ± 82 g on d 2 and d 8 postweaning, respectively. The mean total food intake over the experimental period was 2.1 ± 0.3 kg per piglet. No piglets developed diarrhea during the experiment.

Small intestine morphology and enzyme activities were also analyzed (Table 3). The villus perimeter in the proximal SI decreased by 29% (P < 0.05) over the first 24 h postweaning and did not change thereafter. This decrease was transient, between d 1 and d 2 postweaning, in the mid- and distal SI (both -16%, P < 0.05). By contrast, the SI crypt perimeter did not change at any site.


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  		TABLE 3 Intestinal architecture and enzyme activity in the small intestine of piglets at 0, 1, 2, 5, and 8 d postweaning1

 
The specific activity of lactase decreased by 74% (P < 0.05) in the proximal SI over the first 48 h postweaning and did not change thereafter. A substantial decrease (-56%, P < 0.05) occurred between d 0 and d 5 postweaning in the mid SI, with no change thereafter. By contrast, lactase activity in the distal SI did not change over time (P = 0.591).

The specific activity of sucrase also decreased in the proximal (-85%, P < 0.05) and distal (-30%, P < 0.05) SI between d 0 and d 1 and d 1 and d 2 postweaning, respectively, with no change thereafter. In contrast, the decrease in sucrase activity in the mid SI was only transient; the activity at d 8 did not differ from the preweaning value.

    Influence of weaning on the expression of proinflammatory cytokine mRNA. We next investigated the effect of weaning on the expression of proinflammatory cytokines. A significant increase in IL-1ß (74%, P < 0.01), IL-6 (134%, P < 0.01), and TNF-{alpha} (55%, P < 0.01) mRNA levels occurred in the mid SI on d 1 postweaning, compared with levels on d 0 (Fig. 1). Then, mRNA levels of these cytokines declined rapidly and returned to levels similar to those recorded on d 0. Decreases in IL-8 mRNA levels in the mid SI at d 8 (-26% compared with d 0, P < 0.05) and in IL-18 mRNA levels at d 2, 5, and 8 postweaning (-38%, P < 0.01; -27%, P < 0.01; and -21%, P < 0.05 compared with d 0, respectively) also occurred. By contrast, IL-12p40 mRNA expression did not change postweaning.



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  		FIGURE 1 Changes in expression of proinflammatory cytokine mRNA levels in the mid-SI of piglets on the day of weaning (d 0) and on d 1, 2, 5, and 8 postweaning. Results are expressed in arbitrary units (AU) as the ratio between the cytokine-specific and the cyclophilin RT-PCR values. Values are means ± SEM, n = 8–10. Means without a common letter differ (P < 0.05).

 
Modifications in the transcript levels of these proinflammatory cytokines upon weaning also occurred in the other intestinal segments (Figs. 2and 3; Table 4). Some cytokines, such as IL-1ß, presented a similar profile of mRNA expression over time throughout the intestine (Fig. 2). Indeed, as already described for the mid-SI, there was an early and transient upregulation of IL-1ß mRNA in the distal SI (79%, P < 0.05) and in the proximal colon (39%, P < 0.05). There was a slight increase in IL-1ß mRNA expression (25%, P < 0.10) in the proximal SI. Other cytokines, such as TNF-{alpha}. displayed a specific pattern of mRNA expression according to the intestinal site (Fig. 3). Increased TNF-{alpha} mRNA expression on d 1 postweaning was followed by decreases in the proximal SI and in the mid-SI. In the distal SI, TNF-{alpha} mRNA expression was higher on d 2, 5, and 8 postweaning (65%, P < 0.01; 51%, P < 0.05; and 60%, P < 0.01, respectively) than on d 0 or d 1. Finally, TNF-{alpha} mRNA expression in the proximal colon did not change.



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  		FIGURE 2 Pattern of IL-1ß mRNA expression in the proximal, mid-, and distal SI and in the proximal colon of the intestine of piglets on the day of weaning (d 0) and on d 1, 2, 5, and 8 postweaning. Results are expressed in arbitrary units (AU) as the ratio between the cytokine-specific and the cyclophilin RT-PCR values. Values are means ± SEM, n = 8–10. Means without a common letter differ (P < 0.05).

 


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  		FIGURE 3 Pattern of TNF-{alpha} mRNA expression in the proximal, mid-, and distal SI and in the proximal colon of the intestine of piglets on the day of weaning (d 0) and on d 1, 2, 5, and 8 postweaning. Results are expressed in arbitrary units (AU) as the ratio between the cytokine-specific and the cyclophilin RT-PCR values. Values are means ± SEM, n = 8–10). Means without a common letter differ (P < 0.05).

 

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  		TABLE 4 Cytokine mRNA levels in the small intestine and proximal colon of piglets at 0, 1, 2, 5, and 8 d postweaning1

 
The level of expression of mRNA encoding for the 4 other cytokines (IL-6, IL-8, IL-18, and the heavy chain of IL-12) in the different parts of the intestine was also measured (Table 4). The proinflammatory cytokine response in the gut can be divided into two periods: an early acute response (0 to 2 d postweaning) and a late long-lasting response (2 to 8 d postweaning). The former phase was characterized by a transient increase of mRNA expression of the inflammatory cytokines IL-1ß, IL-6, and TNF-{alpha} throughout the intestine. By contrast, during the second phase, the level of mRNA encoding for most of the investigated cytokines remained stable (IL-1ß, IL-6) or decreased (IL-12p40, IL-18), with the exception of the TNF-{alpha} mRNA level, which increased in the distal intestine (Fig. 4).



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  		FIGURE 4 Overview of proinflammatory cytokine expression in the intestine of piglets after weaning. (*) Significant (P < 0.05) postweaning upregulation (601) or downregulation ({searrow}) of cytokine mRNA levels as compared to preweaning values.

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
LITERATURE CITED
 
The present study demonstrated that weaning in piglets is associated with a transient inflammation of the gut. Indeed, an intestinal upregulation of IL-1ß, IL-6, and TNF-{alpha} mRNA occurred during the first 2 d postweaning. After 2 d postweaning, the mRNA level of these cytokines returned to preweaning levels, with the exception of the TNF-{alpha} mRNA level in the distal intestine, which remained high. Changes in morphology and enzyme activity of the SI also occurred, as consistently shown in other studies (21). For example, the enzyme activity values we recorded were in the same range as those previously published for piglets weaned at 21 d of age (22).

Local expression of IL-1, IL-6, and TNF-{alpha} mRNA has been largely documented after bacterial or viral infection in pigs (5,23) and in humans during gut inflammatory diseases such as Crohn’s disease and ulcerative colitis (24,25). However, in contrast to the chronic production of cytokines observed in these diseases, in the present study the mRNA expression of IL-1, IL-6, and TNF-{alpha} was rapidly downregulated after d 2 postweaning. Given that excessive inflammatory response can lead to a large amount of tissue damage, this downregulation demonstrates a rapid adaptation at the time of weaning, at least in terms of expression of proinflammatory cytokines.

To our knowledge, there are no other reports on the early and transient cytokine gene expression we observed in the gut of weaned piglets. Only a few studies provide evidence of cytokine regulation by weaning. There are reports of increased production of both Th1 (IL-2 and IFN-{gamma}) and Th2 (IL-5 and IL-6) cytokines by intestinal lymphocytes in the gut at 7 d postweaning in mice (10,26). There are descriptions of the changes in the gut levels of IL-1ß, TNF-{alpha}, and TGF-ß mRNA in rats, comparing unweaned and adult animals (13,27). In accordance with our results, McCracken et al. (12) also found a transient increase in plasma IL-1 concentrations over the first 2 d postweaning period in piglets. However, these authors did not show any changes in plasma TNF-{alpha} and IL-6 concentrations.

Analysis of the different parts of the gut demonstrated that mRNA expression of inflammatory cytokines varied according to the site analyzed. Except for IL-1ß, which displayed the same kinetic pattern in nearly all parts of the gut during weaning, the inflammatory cytokines were regulated in only some compartments of the gut after weaning. Differential expression of inflammatory cytokines in the intestinal tract of piglets also occurs in response to other gut disturbances such as infections (7,28). These differential inflammatory responses may reflect, at least in part, functional and anatomical differences between the different sections of the gut (29).

In the present study, we observed a transient increase in mRNA encoding for inflammatory cytokines in the intestine of 28-d-old weaned piglets. In another recent experiment carried out in another country, using piglets of different breeds and a slightly different protocol, we also observed an increased expression of IL-1, IL-6, and TNF-{alpha} in the intestine of 28-d-old weaned piglets (S. Pié, B. A. Williams, and I. P. Oswald, unpublished observations). Although these experiments have not been repeated with younger animals, McCraken et al. (12) report an increased concentration of IL-1 in the plasma of 21-d-old weaned piglets. Anatomical changes that occur at weaning can be observed irrespective of the age of weaning, but their amplitude may vary (30–32). Thus, we can anticipate that a transient increase of inflammatory cytokines also occurs in piglets weaned earlier than 4 wk, as is the common practice in the United States. However, additional experiments are needed to determine the magnitude of this inflammatory response.

The cytokine IL-1ß can be upregulated in response to a wide range of specific and nonspecific stimuli. In the present study, IL-1ß expression increased in all intestinal segments investigated. This result suggests that the intestinal upregulation of IL-1ß mRNA is probably more related to the general stress associated with weaning than to a specific stimulation. Although the role of this cytokine at weaning is largely unknown, studies suggest that increased expression of IL-1ß in rats could be involved in the differentiation and/or activation of epithelial cells at weaning (13,27).

Analysis of TNF-{alpha} and IL-6 mRNA expression showed that the changes in gene expression of these cytokines are site specific. The site-specific effect might be linked to particular lymphoid structures in the SI, the Peyer’s patches, which are the predominant structures where antigens are taken up from the gut lumen (33,34). It is noteworthy that the expression of TNF-{alpha}, downregulated 2 d postweaning in the mid-SI, remained elevated in the distal SI at 8 d postweaning. This persistent stimulation of TNF-{alpha} expression in this segment, which contains a large proportion of bacteria, might be the result of an active immune stimulation by microbial products and/or by the local translocation of bacteria. In accordance with this hypothesis, several authors found that oral infection of germ-free piglets with Escherichia coli or Salmonella typhimurium increased TNF-{alpha} expression in the ileum (28,35,36).

Whereas IL-1ß, IL-6, and TNF-{alpha} mRNA increased rapidly in the gut of weaned piglets, a late downregulation of IL-12p40 mRNA and IL-18 mRNA occurred. Both cytokines promote inflammatory responses by enhancing the type 1 lymphocyte and natural killer cell responses (37). The late postweaning decrease of IL-12p40 and IL-18 mRNA may reflect an adaptative immune response to the weaning transition. Alternatively, the downregulation of these cytokines may be the consequence of the maturation of the intestinal immune system.

In terms of intestinal function, studies with laboratory animals show that inflammatory cytokines play an important role in intestinal physiology (8) and can act on the intestinal barrier to increase epithelial nutrient and ion transport. For example, TNF-{alpha} and IL-1ß stimulate Cl- intestinal secretion, whereas IL-1{alpha} inhibits Na+ and Cl- absorption (8). There is a recent report that IL-1{alpha}, IL-6, and IL-8 increase glucose and proline absorption in the rabbit SI (38). For pigs, little information on the potential role of inflammatory cytokines in the intestine is available. One study on porcine intestinal ion transport shows that TNF-{alpha} may be involved in the stimulation of Cl- secretion in the ileum (39). These data suggest that the increased expression of TNF-{alpha}, which was observed in the present study, may be implicated in the development of postweaning diarrhea. Indeed, epidemiological studies show that the prevalence of diarrhea is maximal ~7 to 9 d postweaning (40), when TNF-{alpha} mRNA levels are high in the distal SI. We recently demonstrated an early but transient postweaning increase in glucose absorption and Cl- intestinal secretion by piglet jejunum in vitro (41). This fits with the contemporary increase in gene expression of inflammatory cytokines observed in the present study. Inflammatory cytokines also increase intestinal permeability (8), and an early postweaning increase in jejunal permeability in piglets was recently reported (42).

In addition to their role in epithelial ion transport, inflammatory cytokines can also regulate brush border enzymes (43). In particular, downregulation of sucrase-isomaltase by IL-6 has been demonstrated in the Caco2 human colonic intestinal epithelial cell line (44). In the present study, decreased sucrase activity in the proximal and mid-SI of piglets correlated with a significant upregulation of IL-6 mRNA, suggesting that IL-6 may also regulate sucrase-isomaltase activity at weaning. Proinflammatory cytokines also participate in tissue integrity (45). For example, TNF-{alpha} affects epithelial permeability through its effect on the structure of epithelial cell tight junctions (8). At weaning, upregulation of TNF-{alpha} mRNA may influence the barrier integrity of the epithelium, favoring the trans-epithelial passage of microorganisms and leading to bacterial infections and diarrhea. Studies also describe a mitogenic action of TNF-{alpha} and IL-8 on intestinal mucosa (46) as well as a potent role of IL-1ß in epithelial cell turnover (47,48). These cytokines may thus play a role in the cell renewal and the morphological changes observed in the intestinal epithelium in piglets at weaning.

In conclusion, our results demonstrate that weaning is associated with an early inflammatory response that may contribute to both anatomical and functional intestinal disorders in piglets. Weaning involves multiple changes. In addition to the change from a liquid to a solid diet, weaning is a time of stress for the weanling: first, as it is taken away from its mother; second as it is moved to a new building; and, third, as it is exposed to numerous piglets other than its siblings and to their potential aggressive behavior. Further studies are needed to delineate the respective influence of diet and stress on the proinflammatory cytokine patterns at weaning.


   ACKNOWLEDGMENTS
 
The authors thank H. Demay and P. Touanel for the care of the animals, N. Beaumanoir for skillful technical assistance in intestinal morphology and enzyme activity measurements, and N. Ledger for helpful comments regarding the manuscript.


   FOOTNOTES
 
1 Presented in part at the 9th International Symposium on Digestive Physiology in Pigs, May 14–17, 2003, Banff, AB, Canada [Pié, S., Lallès, J. P. & Oswald, I. P. (2003) Influence of weaning on intestinal pro-inflammatory patterns in piglets (Ball, R. O., ed.), vol. 2, pp. 99–101. University of Alberta]. Back

2 Supported by a grant from the European Union (EU project QLK5-CT-2000–00522). The authors are solely responsible for the work described in this article, and their opinions are not necessarily those of the European Union. Back

4 Abbreviations used: IL-12p40, IL-12 subunit p40; CD, cluster of differentiation; INRA, Institut National de la Recherche Agronomique; OD260, optical density of 260 nm; SI, small intestine; TGF-ß, transforming growth factor ß; Th, T helper. Back

Manuscript received 30 July 2003. Initial review completed 11 September 2003. Revision accepted 28 October 2003.


   LITERATURE CITED
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 LITERATURE CITED
 

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