Endogenous tumor necrosis factor (TNF) production and modification of pathological lesions in experimental Escherichia coli endotoxemia of piglets

In vivo porcine lipopolysaccharide inflammation models to study immunomodulation of drugs

Lipopolysaccharide (LPS), a structural part of the outer membrane of Gram-negative bacteria, is one of the most effective stimulators of the immune system and has been widely applied in pigs as an experimental model for bacterial infection. For this purpose, a variety of Escherichia coli serotypes, LPS doses, routes and duration of administration have been used. LPS administration induces the acute phase response (APR) and is associated with dramatic hemodynamic, clinical and behavioral changes in pigs. Pro-inflammatory cytokines, including tumor necrosis factor α (TNF-α), interleukin (IL)-1 and IL-6 are involved in the induction of the eicosanoid pathway and the hepatic production of acute phase proteins, including C-reactive protein (CRP), haptoglobin (Hp) and pig major acute phase protein (pig-MAP). Prostaglandin E2 (PGE2) and thromboxane A2 (TXA2) play a major role in the development of fever and pulmonary hypertension in LPS-challenged pigs, respectively. The LPS-induced APR can be modulated by drugs. Steroidal and nonsteroidal anti-inflammatory drugs ((N)SAIDs) possess anti-inflammatory, antipyretic and analgesic properties through (non)-selective central and peripheral cyclooxygenase (COX) inhibition. Antimicrobial drugs, especially macrolide antibiotics, which are commonly used in veterinary medicine for the treatment of bacterial respiratory diseases, have been recurrently reported to exert clinically important immunomodulatory effects in human and murine research. To investigate the influence of these drugs on the clinical response, production of pro-inflammatory cytokines, acute phase proteins (APP) and the course of the febrile response in pigs, in vivo LPS inflammation models can be applied. Yet, to date, in vivo research on the immunomodulatory properties of antimicrobial drugs in these models in pigs is largely lacking. This review provides acritical overview of the use of in vivo porcine E. coli LPS inflammation models for the study of the APR, as well as the potential immunomodulatory properties of anti-inflammatory and antimicrobial drugs in pigs.

Immune response and pathophysiological features of Klebsiella pneumoniae liver abscesses in an animal model

Capsular serotypes K1 and K2, the rmpA gene (a regulator of the mucoid phenotype) and aerobactin from Klebsiella pneumoniae have been identified as the major virulence factors for pyogenic liver abscesses with high morbidity, mortality and severe complications. The pathological mechanisms remain unclear. In this study, we compared liver immune responses and pathological changes in response to different serotypes of K. pneumoniae infections. A mouse model was used to investigate cytokine and chemokine production, histopathology findings, phagocytic uptake and mortality induced by serotypes K1 (magA(+), rmpA(+), aerobactin(+)), K2 (magA(-), rmpA(+), aerobactin(+)), K62 (magA(-), rmpA(-), aerobactin(-)) and an acapsulated isogenic K1 mutant (ΔK1, magA(+), rmpA(+), aerobactin(+)). K. pneumoniae serotypes K1 and K2 showed lower 50% lethal dose values and more phagocytic resistance to neutrophils than K62 and the ΔK1 mutant. In sequential liver samples, viable bacteria counts increased 3 h to 3 days after low-dose inoculation (<10(1) colony-forming unit (cfu)) with K1 and K2, while K62 and ΔK1 cleared rapidly and became undetectable even with high-dose inoculation (∼2.9 × 10(5) cfu). Time-dependent increases in cytokines and chemokines, including tumor necrosis factor-α, interleukin (IL)-1β, IL-6, IL-10, keratinocyte-derived chemokines and macrophage inflammatory protein-2, were observed in the serum and liver tissue of K1- and K2-infected mice, and severe disease progression manifesting as microabscesses was also identified. K62 and ΔK1 inoculation did not result in similar immune responses and histological changes. These findings illustrate the critical role of phagocytic resistance against innate immunological defense mechanisms as well as its contribution to the development of liver abscesses.

Induction of apoptotic lesions in liver and lymphoid tissues and modulation of cytokine mRNA expression by acute exposure to deoxynivalenol in piglets

Six 1-month-old piglets were intravenously injected with deoxynivalenol (DON) at the concentration of 1 mg/kg body weight, with three pigs each necropsied at 6 and 24 h post-injection (PI) for investigation of hepatotoxicity and immunotoxicity with special attention to apoptotic changes and cytokine mRNA expression. Histopathological examination of the DON-injected pigs revealed systemic apoptosis of lymphocytes in lymphoid tissues and hepatocytes. Apoptosis of lymphocytes and hepatocytes was confirmed by the TdT-mediated dUTP-biotin nick end-labeling (TUNEL) method and immunohistochemical staining against single-stranded DNA and cleaved caspase-3. The number of TUNEL-positive cells in the thymus and Peyer's patches of the ileum was increased at 24 h PI compared to 6 h PI, but the peak was at 6 h PI in the liver. The mRNA expression of interleukin (IL)-1β, IL-6, IL-18, and tumor necrosis factor (TNF)-α in the spleen, thymus and mesenteric lymph nodes were determined by semi-quantitative RT-PCR, and elevated expression of IL-1β mRNA at 6 h PI and a decrease of IL-18 mRNA at 24 h PI were observed in the spleen. IL-1β and IL-6 mRNA expressions increased significantly at 6 h PI in the thymus, but TNF-α decreased at 6 h PI in the mesenteric lymph nodes. These results show the apoptosis of hepatocytes suggesting the hepatotoxic potential of DON, in addition to an immunotoxic effect on the modulation of proinflammatory cytokine genes in lymphoid organs with extensive apoptosis of lymphocytes induced by acute exposure to DON in pigs.

In vitro down regulation of proinflammatory cytokines induced by LPS tolerance in pig CD14+ cells

LPS tolerance is characterized by a reduced sensitivity to subsequent challenge of LPS. In human and mouse models LPS tolerance is closely associated with marked unbalanced production of leukocyte-derived inflammatory mediators which, when overexpressed, led to septic syndrome and shock. Here we characterized the in vitro induction of LPS tolerance in porcine CD14+ spleen cells in order to give insights into LPS tolerance in pigs. Following LPS stimulation, TNF-alpha and, to a minor extent, IL-8 production showed a significant reduction in CD14+ spleen monocytes that were pretreated with LPS in comparison to naïve cells, while IL-1beta production was slightly influenced by LPS stimulation and it was not affected by subsequent LPS challenge. Our findings showed that porcine CD14+ cells undergo a process, which resembles LPS tolerance, providing evidence that swine represent a valuable and useful model to perform experiments to study LPS tolerance and its biological significance.

Inflammatory Cytokines, Pleuropneumonia Infection and the Effect of Dexamethasone

OBJECTIVES

Actinobacillus pleuropneumoniae causes an often fatal infection of swine due to pleuropneumonia. To determine if inflammatory cytokines are associated with A. pleuropneumoniae-induced pneumonia, infected and noninfected animals were concomitantly administered saline or dexamethasone.

METHODS

Twenty-four swine were treated with saline, A. pleuropneumoniae, dexamethasone, or A. pleuropneumoniae and dexamethasone (n = 6). The plasma levels of TNF-alpha, IL-1beta, IL-6, IL-8, and IL-10 were examined through time of necropsy (72 h). Gross pathology and histopathology was performed on all animals.

RESULTS

Dexamethasone had no effect on A. pleuropneumoniae-induced increases in lung/body weight ratios. Gross pathology of the infected pigs included fibrinous pleuropneumonia with necrosis and hemorrhage in a focal to a multifocal pattern. Histopathology of infected pig lungs revealed necrotizing extensive, fibrinopurulent pneumonia with edema and fibrinopurulent pleuritis. Plasma IL-6 levels were elevated in A. pleuropneumoniae-infected animals beginning 6 h after infection. Dexamethasone treatment did not alter A. pleuropneumoniae-induced plasma IL-6 levels. A. pleuropneumoniae infection did not elicit plasma levels of TNF-alpha, IL-1beta, IL-8, or IL-10.

CONCLUSION

These results suggest that the pneumonia caused by A. pleuropneumoniae infection is not due to the release of systemic inflammatory cytokines.

Inflammatory mediator production in swine following endotoxin challenge with or without co-administration of dexamethasone

The inflammatory response in swine challenged with lipopolysaccharide (LPS) has only been partially characterized. As swine are increasingly used in biomedical research, it is important to determine if they respond to endotoxin challenge in a manner similar to other model systems. Accordingly, 24 Poland China x Landrace barrows were treated with saline, LPS, dexamethasone, or LPS and dexamethasone, with six animals in each treatment group. The kinetics of TNFalpha, IL-1beta, IL-6, IL-8, IL-10, nitric oxide (nitrate/nitrite), and neopterin production in swine plasma were examined at 1, 3, 6, 9, and 24 h after acute LPS challenge. Lipopolysaccharide increased plasma TNFalpha levels, which peaked 1 h post-challenge. Dexamethasone decreased LPS-induced TNFalpha by approximately 60%. Plasma IL-6 levels peaked 3 h post-LPS challenge, returning to basal levels by 9 h. Swine given both LPS and dexamethasone had minimal IL-6 levels. Control and dexamethasone-only treated animals never exhibited systemic TNFalpha or IL-6 levels. Lipopolysaccharide increased plasma IL-10 1 h after challenge. Dexamethasone did not alter plasma IL-10 levels in LPS-challenged swine. Interleukin-1beta was constitutively present in plasma and was not altered by any combination of treatments. Plasma IL-8 was not observed in any treatment group. Plasma nitrate/nitrite levels were maximal 24 h post-challenge. Dexamethasone treatment prevented increases in plasma nitrate/nitrite levels in LPS-treated animals. Lipopolysaccharide induced levels of neopterin; dexamethasone served to further increase plasma neopterin levels in LPS-challenged animals. The discordant regulation of inflammatory mediators suggests that the immunological responses by swine to LPS are distinct from the responses seen in rodent and human studies.

Long-term recombinant porcine somatotropin (PST) treatment mitigates the responses to subchronic lipopolysaccharide in swine

The effect of multiple lipopolysaccharide (LPS) challenges in swine undergoing long-term treatment with porcine somatotropin (PST) was determined. Changes in aspartate serine transaminase (AST) occurred only at 24h following the first LPS challenge dose (P<0.05), while PST treatment moderated any change from occurring. Nonesterified free fatty acid (NEFA) levels were elevated in PST treated animals for the first 3 days following daily LPS treatment (P<0.05), while LPS treatment alone had no effect on plasma NEFA levels. Plasma urea nitrogen (PUN) levels were unchanged by LPS following the initial LPS challenge, but were decreased following the second challenge dose (P=0.014). These changes were long lasting, with a return to normal PUN levels not evident until Day 6. The PST treatment mitigated changes in PUN (P<0.05) when LPS was administered. Haptoglobin plasma levels, along with lipid peroxide production were not affected by LPS challenge or PST administration. LPS challenge reduced the levels of immunoreactive heat shock protein 70 (HSP70) throughout the entire challenge period (P<0.001). PST-LPS animals had normal levels of this protein. The results of the present study demonstrate that long-term PST treatment mitigates the adverse effects of subchronic LPS administration.

The effect of endotoxin and dexamethasone on enrofloxacin pharmacokinetic parameters in swine

The impact of Escherichia coli-derived lipopolysaccharide (LPS) on the pharmacokinetic parameters of enrofloxacin in swine was assessed to determine whether this model would substitute for a pleuropneumonia infection model for pharmacokinetic evaluation of drugs. All animals received a single i.v. dose of enrofloxacin (5 mg/kg). Half the animals also received dexamethasone (0.5 mg/kg) to determine the impact of inflammation on any changes in enrofloxacin pharmacokinetics, as most of the effects of LPS are due to elaboration of inflammatory mediators. Administration of LPS alone (2.0 microg/kg) was associated with a decrease in clearance of enrofloxacin. Volume of distribution at steady state was increased in the dexamethasone-treated animals. The terminal elimination half-life of enrofloxacin was significantly increased in the LPS group. Dexamethasone administration, either alone or in combination with LPS challenge, increased the volume of distribution both at steady state and during the elimination phase. Lipopolysaccharide challenge did not affect the volume of distribution. Lipopolysaccharide challenge did not affect urinary excretion of enrofloxacin but did increase the urinary excretion of its principal metabolite, ciprofloxacin. However, the increased excretion did not begin until 24 h after administration of enrofloxacin. Because these pharamcokinetic results are different from those obtained with the pleuropneumonia model using the bacteria Actinobacillus pleuropneumoniae, the results of this study demonstrate that LPS is not a generic substitute for infection for the pharmacokinetic evaluation of drugs.

Weaning of piglets. Effects of an exposure to a pathogenic strain of Escherichia coli

The influence of weaning on day 32 and a simultaneous challenge with a pathogenic strain of Escherichia coli was studied in eight piglets. Another nine weaned but non-infected piglets were used as controls. The distribution of peripheral blood mononuclear cells (PBMC) into subpopulations, as well as their response when stimulated in vitro by pokeweed mitogen, changed in a similar manner during post-weaning in both groups. In contrast, superior responses were recorded for PBMC collected from the challenged pigs when stimulated in vitro with concanavalin A and with a heat-inactivated extract of the E. coli strain used for infection, respectively. Despite a successful colonization of the challenge strain, no clinical signs of disease were recorded. Nor did the daily weight gain or the number of E. coli, enterococci, or Clostridium perfringens excreted per gram of faeces differ between the groups. However, the weaning induced a marked decrease in the diversity of coliforms in individual piglets, which announced a reduced colonization resistance of that flora. Also, a decreased homogeneity between coliform floras of different piglets was observed following weaning. The decreased homogeneity indicated that different strains of E. coli were predominant in different animals, which may in turn facilitate the spread of pathogenic strains. The enteric changes were more pronounced and lasted longer in infected animals. Still, the influence of a sole pathogenic strain of E. coli was not enough to induce post-weaning diarrhoea.

Involvement of apoptosis in the endotoxemic lesions of the liver and kidneys of piglets

The involvement of apoptosis was evaluated in lesions of endotoxemic piglets. A single injection with E. coli O111:B4 lipopolysaccharide (LPS) induced foci of coagulative necrosis in the liver and kidneys. No significant change was observed in these organs at 1.5 hr after LPS injection, but at 6 hr, epithelial cells with chromatin condensation or fragmentation and apoptotic bodies were visible. Foci of coagulative necrosis were formed within 24 hr after LPS inoculation. In and adjacent to the necrotic foci, dead hepatocytes with nuclear condensation or fragmentation were scattered. These dead cells were positively stained by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) methods. Electronmicroscopy revealed apoptotic cells with condensed or fragmented homogeneous nuclear chromatin, and necrotic cells with irregularly destroyed nuclei and cytoplasmic membranes. Apoptotic cell death were also observed in parietal cells of the stomach and lymphocytes in the lymphatic system. DNA ladders with approximately 200-bp multimers were observed in hepatic, renal and thymic samples prepared after 6 and 24 hr of LPS injection by agarose gel electrophoresis. These results suggest that apoptosis is involved in the pathology of swine endotoxemia.

Effects on endotoxin pathogenicity in pigs with acute septicemia of Haemophilus parasuis infection

Changes of endotoxin in plasma, and the response of the coagulation system and blood cells in septicemia of Haemophilus parasuis infection were examined by inoculation with H. parasuis in specific pathogen-free (SPF) pigs. Eight pigs were inoculated intratracheally with 10(5), 10(6) and 10(7) colony formation units (CFU) of the strain Nagasaki (serovar 5). All pigs died 28 to 42 hr after inoculation. Haematologically, severe leukopenia occurred 24 hr post inoculation (hpi) until death. Glucose concentration decreased from 24 hpi to death. In the coagulation system, decrease of platelet counts, prolongation of prothrombin time, activated partial thromboplastin time, and increase of fibrinogen-fibrin degradation products were observed in all inoculated pigs. Endotoxin was detected in the plasma of all the inoculated pigs from 16 hpi to death, and its concentration rose dramatically just before death. H. parasuis was re-isolated from the blood of all inoculated pigs from 16 hpi to death, and also from almost all organs and body fluids of the pigs. The pigs had microthrombi in the kidney, liver and lungs, and many also had pneumonia, meningitis and serositis. H. parasuis antigen was detected in the lesions by the immunoperoxidase technique. The results indicated that disseminated intravascular coagulation (DIC) and endotoxin shock involved aggravation of clinical signs and death on the pigs induced to septicemia of H. parasuis.