Splenectomy attenuates superoxide anion release into the hepatic sinusoids after lipopolysaccharide challenge

Neural control of the spleen as an effector of immune responses to inflammation: mechanisms and treatments

Immune system responses are a vital defense mechanism against pathogens. Inflammatory mediators finely regulate complex inflammatory responses from initiation to resolution. However, in certain conditions, the inflammation is initiated and amplified, but not resolved. Understanding the biological mechanisms underlying the regulation of the immune response is critical for developing therapeutic alternatives, including pharmaceuticals and bioelectronic tools. The spleen is an important immune effector organ since it orchestrates innate and adaptive immune responses such as pathogen clearance, cytokine production, and differentiation of cells, therefore playing a modulatory role that balances pro- and anti-inflammatory responses. However, modulation of splenic immune activity is a largely unexplored potential therapeutic tool that could be used for the treatment of inflammatory and life-threatening conditions. This review discusses some of the mechanisms controlling neuroimmune communication and the brain-spleen axis.

Enhanced Bacteremia in Dextran Sulfate-Induced Colitis in Splenectomy Mice Correlates with Gut Dysbiosis and LPS Tolerance

Because both endotoxemia and gut dysbiosis post-splenectomy might be associated with systemic infection, the susceptibility against infection was tested by dextran sulfate solution (DSS)-induced colitis and lipopolysaccharide (LPS) injection models in splenectomy mice with macrophage experiments. Here, splenectomy induced a gut barrier defect (FITC-dextran assay, endotoxemia, bacteria in mesenteric lymph nodes, and the loss of enterocyte tight junction) and gut dysbiosis (increased Proteobacteria by fecal microbiome analysis) without systemic inflammation (serum IL-6). In parallel, DSS induced more severe mucositis in splenectomy mice than sham-DSS mice, as indicated by mortality, stool consistency, gut barrier defect, serum cytokines, and blood bacterial burdens. The presence of green fluorescent-producing (GFP) E. coli in the spleen of sham-DSS mice after an oral gavage supported a crucial role of the spleen in the control of bacteria from gut translocation. Additionally, LPS administration in splenectomy mice induced lower serum cytokines (TNF-α and IL-6) than LPS-administered sham mice, perhaps due to LPS tolerance from pre-existing post-splenectomy endotoxemia. In macrophages, LPS tolerance (sequential LPS stimulation) demonstrated lower cell activities than the single LPS stimulation, as indicated by the reduction in supernatant cytokines, pro-inflammatory genes (iNOS and IL-1β), cell energy status (extracellular flux analysis), and enzymes of the glycolysis pathway (proteomic analysis). In conclusion, a gut barrier defect after splenectomy was vulnerable to enterocyte injury (such as DSS), which caused severe bacteremia due to defects in microbial control (asplenia) and endotoxemia-induced LPS tolerance. Hence, gut dysbiosis and gut bacterial translocation in patients with a splenectomy might be associated with systemic infection, and gut-barrier monitoring or intestinal tight-junction strengthening may be useful.

A leukotriene-dependent spleen-liver axis drives TNF production in systemic inflammation

Production of the proinflammatory cytokine tumor necrosis factor (TNF) must be precisely regulated for effective host immunity without the induction of collateral tissue damage. Here, we showed that TNF production was driven by a spleen-liver axis in a rat model of systemic inflammation induced by bacterial lipopolysaccharide (LPS). Analysis of cytokine expression and secretion in combination with splenectomy and hepatectomy revealed that the spleen generated not only TNF but also factors that enhanced TNF production by the liver, the latter of which accounted for nearly half of the TNF secreted into the circulation. Using mass spectrometry-based lipidomics, we identified leukotriene B₄ (LTB₄) as a candidate blood-borne messenger in this spleen-liver axis. LTB₄ was essential for spleen-liver communication in vivo, as well as for humoral signaling between splenic macrophages and Kupffer cells in vitro. LPS stimulated the splenic macrophages to secrete LTB₄, which primed Kupffer cells to secrete more TNF in response to LPS in a manner dependent on LTB₄ receptors. These findings provide a framework to understand how systemic inflammation can be regulated at the level of interorgan communication.

Dual cytoprotective effects of splenectomy for small-for-size liver transplantation in rats

The problems associated with small-for-size liver grafts (ie, high mortality rates, postoperative complications, and acute rejection) remain critical issues in partial orthotopic liver transplantation (OLT). In association with partial OLT, splenectomy (SP) is a procedure used to reduce the portal pressure. However, the precise effects of SP on partial OLT have been unclear. In this study, using small-for-size liver grafts in rats, we examined the cytoprotective effects of SP on OLT. Liver grafts were assigned to 2 groups: a control group (OLT alone) and an SP group (OLT after SP). SP significantly increased animal survival and decreased liver damage. SP exerted the following cytoprotective effects: (1) it improved hepatic microcirculation and prevented increases in the portal pressure after OLT, (2) it suppressed the hepatic infiltration of neutrophils and macrophages through the direct elimination of splenic inflammatory cells before OLT, (3) it decreased the hepatic expression of tumor necrosis factor α and interleukin-6, (4) it attenuated sinusoidal endothelial injury, (5) it decreased plasma endothelin 1 levels and increased hepatic heme oxygenase 1 expression, (6) it suppressed hepatocellular apoptosis through the down-regulation of hepatic caspase-3 and caspase-8 activity, and (7) it increased hepatic regeneration. In conclusion, SP for small-for-size grafts exerts dual cytoprotective effects by preventing excessive portal vein hepatic inflow and eliminating splenic inflammatory cell recruitment into the liver; this in turn inhibits hepatocellular apoptosis and improves liver regeneration.

Role of the spleen in the development of steatohepatitis in high-fat-diet-induced obese rats

Obesity is considered a systemic low-grade inflammatory state. Although the spleen is the main immune organ with a close anatomical relationship with the liver, its role in the progression of fatty liver disease remains uncertain. Therefore, we sought to clarify the functional role of the spleen in the development of steatohepatitis in high-fat (HF)-diet-induced obese rats. Male Sprague-Dawley rats were fed HF food and divided into two groups, a splenectomy (SPX) group and a sham-operation (Sham) group. The liver and abdominal white adipose tissue (WAT) were removed one and six months after surgery, and we evaluated the effects of SPX on WAT and HF-induced fatty liver. SPX rats exhibited worse dyslipidemia and inflammatory changes in WAT one month after surgery. Hepatic steatosis and inflammation were accelerated by SPX, based on the time after surgery. At one month after surgery, the tissue triglyceride content increased in SPX rats, compared with Sham controls (P < 0.05). The liver histology also showed a worsening of steatosis in those rats. At six months after SPX, dramatic inflammatory and fibrotic changes were observed in liver tissue sections. Hepatic carnitine palmitoyltransferase-1 was suppressed at one and six months after SPX (P < 0.05 for each). WAT and liver tissue levels of inflammatory markers such as tumor necrosis factor-α, and the expression of Kupffer cells were all increased at six months in SPX rats, compared with Sham controls (P < 0.05 for each). Our results indicate that the preservation of the spleen contributes to the prevention of the progression of hepatic steatosis to steatohepatitis in obese rats.

Induction of shock after intravenous injection of adenovirus vectors: a critical role for platelet-activating factor

Innate immune responses are a major barrier to safe systemic gene therapy with adenovirus (Ad) vectors. We show that intravenous (IV) injection of rats with Ad5 vectors causes a novel rapid shock reaction that involves hypotension, hemoconcentration, tissue edema, and vasocongestion, with notable pathology in the pancreas and the gastrointestinal system. We show for the first time that this reaction is dependent on platelet-activating factor (PAF), a lipid signaling molecule that is a known shock inducer. Ad upregulated PAF within 5 minutes in vivo, and antagonists of the PAF receptor were able to prevent Ad-induced shock. Ad upregulated PAF via the reticuloendothelial system (RES), because splenectomy or depletion of phagocytes blocked the ability of Ad to induce both PAF and shock. Rats were considerably more sensitive to Ad-induced shock than were mice, but PAF mediated shock in both species. Other Ad-induced innate immune responses such as cytokine induction and thrombocytopenia were not mediated by PAF. In summary, systemic IV injection of Ad stimulates the RES to upregulate PAF within a matter of minutes, which results in shock. The identification of this novel pathway suggests strategies to improve the safety of systemic gene therapy with Ad vectors.

Splenectomy ameliorates acute multiple organ damage induced by liver warm ischemia reperfusion in rats

BACKGROUND

Liver ischemia/reperfusion (I/R) results in the release of destructive proinflammatory cytokines and oxygen-derived radicals, which in turn cause injury to liver and other organs such as kidney, lung, and intestine. Splenectomy protects organs from intestinal I/R injury. Therefore, the present study aims to investigate whether splenectomy could also ameliorate multiple organ damage caused by liver I/R.

METHODS

Wistar rats randomly assigned into 4 groups underwent sham-operation, splenectomy, hepatic I/R induced by occlusion of hepatic artery and portal vein, and splenectomy plus hepatic I/R, respectively. Blood samples were collected for assessing aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activity, and tumor necrosis factor-alpha (TNF-alpha) levels. The activity of myeloperoxidase (MPO) in liver tissues was assessed. Livers, kidneys, lungs, and small intestines underwent histopathologic examination for scoring injury severity and TUNEL assay for cell apoptosis. The expression of caspase-3 was evaluated with Western blot analysis.

RESULTS

Liver I/R resulted in liver injury as evidenced by morphologic abnormalities, increased serum activities of AST and ALT, and increased percentage of apoptotic cells. The activity of MPO in liver tissues and the serum levels of TNF-alpha were increased after I/R. Splenectomy significantly decreased the histologic severity score, apoptotic index, MPO activity, and serum levels of AST, ALT, and TNF-alpha. Hepatic I/R also caused damage to kidneys, lungs, and small intestines, as evaluated by histologic alterations and increased apoptotic cells; these changes were ameliorated by splenectomy. The expression of caspase-3 was upregulated in the 4 organs by hepatic I/R and inhibited by splenectomy.

CONCLUSIONS

Splenectomy protects the liver as well as the kidney, lung, and intestine from injury by hepatic I/R. Although the mechanism needs further investigation, this study demonstrated that splenectomy inhibited leukocyte infiltration in livers, release of TNF-alpha, cell apoptosis, and expression of caspase-3.

Effects of 17beta-estradiol and flutamide on splenic macrophages and splenocytes after trauma-hemorrhage

Since splenic immune functions are depressed in metestrus females following trauma-hemorrhage, we hypothesized that administration of the androgen receptor antagonist flutamide at the onset of resuscitation will maintain the immune function of the spleen following trauma-hemorrhage. Female C57BL6/J mice (metestrus state, 8-12 weeks old), underwent laparotomy and hemorrhagic shock (35.0+/-5.0 mm Hg for 90 min) and received 17beta-estradiol (50 microg/25 g), flutamide (625 microg/25 g) or 17beta-estradiol+flutamide. Four hours after resuscitation, the in vitro productive capacity of different cytokines (TNF-alpha, IL-6, IL-10, and IFN-gamma) by splenic MPhi and splenocytes were determined by flow cytometry. A significantly decreased cytokine production by both splenocytes and splenic MPhi was observed following trauma-hemorrhage compared to shams. Administration of 17beta-estradiol, flutamide and 17beta-estradiol+flutamide following trauma-hemorrhage resulted in a significant increase in the in vitro IL-6 release by splenic MPhi. The TNF-alpha productive capacity, however, was only restored by 17beta-estradiol and 17beta-estradiol+flutamide administration following trauma-hemorrhage. No significant effect of either treatment was observed with regard to the suppressed splenic MPhi IL-10 release. Anti-CD3 stimulation, administration of 17beta-estradiol and 17beta-estradiol+flutamide, but not the administration of flutamide alone resulted in a significant increased release of TNF-alpha, IL-6 and IFN-gamma compared to vehicle-treated animals. No significant effect of either treatment was found on IL-10 productive capacity. These results collectively suggest that flutamide administration following trauma-hemorrhage in females has beneficial effects on splenic immune function. However, flutamide administration in combination with estrogen does not provide any significant, additional effects over 17beta-estradiol administration alone.

IL-10 Plasma Levels are Elevated After LPS Injection in Splenectomized A/J Mice1

BACKGROUND

Splenectomy is clinically indicated in certain cases of hypersplenism and splenic trauma. However, it is associated with serious complications, in particular, reduced clearance of encapsulated organisms and a high incidence of sepsis, which has been coined overwhelming post-splenectomy sepsis (OPSS). In addition to the role of the spleen in the clearance of microorganisms, this organ may be involved in regulation of the inflammatory response. We investigated the effect of splenectomy on the inflammatory process induced by LPS in a murine model that resembles, in part, the pathophysiological aspects of sepsis.

MATERIALS AND METHODS

Male mice (8-weeks-old) from different inbred strains were randomized into three groups: splenectomized (SPX), sham operated (SHAM), and non-operated controls (NoOp). After 9 days of recovery, mice were injected with LPS (15 mg/kg) and cytokine plasma levels were measured by ELISA at 1.5 or 6 h after injection. Peritoneal macrophages (PMphi) were isolated from the three groups, and cytokine production was evaluated after incubation with LPS in culture conditions.

RESULTS

IL-10 plasma levels were elevated in SPX A/J mice (6.7 +/- 0.4 mug/ml) after injection of LPS (15 mg/kg) compared to NoOp A/J mice (4.2 +/- 0.2 mug/ml, P < 0.05). Similar elevation in IL-10 plasma levels was detected in SPX DBA/2J mice as compared to NoOp DBA/2J mice, but not in C57BL/6J and BALB/cJ mice. In contrast, SPX AKR mice displayed lower IL-10 levels than NoOp mice. PMphis from SPX A/J mice produced elevated levels of IL-10 compared to PMphis from SHAM or NoOp A/J mice, mimicking the in vivo observations.

CONCLUSION

Our data suggest that the spleen plays an important role in modulating the inflammatory process induced by LPS, extending beyond passive clearance of encapsulated organisms. In addition, the contribution of the spleen to the inflammatory process may be influenced by the genetic background.

Avaliação do efeito da esplenectomia e auto-implante esplênico sobre algumas funções de monócitos em crianças com esquistossomose mansônica

Investigamos em portadores de esquistossomose hepatoesplênica após esplenectomia com ou sem auto-implante esplênico: índice de aderência, produção de superóxido (SP) e de TNF-alfa em monócitos, tratados ou não com tuftsina. Avaliamos três grupos: voluntários sadios CG (grupo controle) (n=12); esplenectomizados com auto-implante AG (n=18) e esplenectomizados sem auto-implante WAG (n=9). Índice de aderência e TNF-alfa não diferiram entre os grupos. SP foi semelhante em CG e AG na 1ª hora após estimulação celular. SP foi maior em todos intervalos de tempo nos grupos CG e AG, comparados ao WAG. O tratamento com tuftsina recuperou o padrão de normalidade de SP em AG, com aumento da 1ª para a 2ª hora nos níveis do CG. O tratamento com tuftsina não alterou SP em WAG, permanecendo reduzida em todos intervalos. O auto-implante esplênico parece recuperar e manter os parâmetros imunológicos avaliados, que têm participação importante na resposta do hospedeiro às infecções.

Aderência e atividade microbicida de monócitos em portadores de esquistossomose mansônica na forma hepatoesplênica cirúrgica

A cirurgia nas crianças portadoras de esquistossomose mansônica inclui esplenectomia, ligadura da veia gástrica esquerda e o auto-implante de tecido esplênico no omento maior. A eficácia desse procedimento pode ser responsável pelo desaparecimento da sepse fulminante pós-esplenectomia (SFPE) neste tipo de paciente. Esta condição é atribuída à diminuição de IgM, de linfócitos circulantes, de properdina e ausência de tuftsina, o que conduz a deficiência da atividade das células macrófágicas, que são responsáveis pela aderência à bactéria, fagocitose e destruição das mesmas. OBJETIVO: Analisar os aspectos funcionais dos monócitos destes pacientes, operados quando crianças, no Serviço de Cirurgia Geral da Criança do Hospital das Clínicas da UFPE, entre 1991 a 2000. MÉTODOS: Foram analisados os índices de aderência in vitro dos monócitos e a geração do ânion superóxido (O2-), em três grupos. O 1º, auto-implante (AI), constituído por 18 portadores de esquistossomose mansônica na forma hepatoesplênica, submetidos a esplenectomia, ligadura da veia gástrica esquerda e auto-implante de tecido esplênico no omento maior; o 2º, (ESP), formado por nove pacientes similares, submetidos a esplenectomia e desconexão ázigo-portal, e o 3º,(CT), constituído por 12 adolescentes sadios, oriundos da mesma condição sócio-econômica-geográfica. RESULTADOS: Não houve diferença no índice de aderência entre os três grupos. Os monócitos dos pacientes do grupo AI tiveram a geração de O2- semelhante à dos indivíduos do grupo CT, e significantemente maior do que os pacientes do grupo ESP. CONCLUSÕES: Os monócitos dos portadores de esquistossomose hepatoesplênica submetidos a esplenectomia, ligadura da veia gástrica esquerda e auto-implante de tecido esplênico no omento maior se mostram funcionalmente similares aos de indivíduos normais da mesma condição sócio-econômica-geográfica.

Splenectomy ameliorates hepatic ischemia and reperfusion injury mediated by heme oxygenase-1 induction in the rat

BACKGROUND/AIMS

Ischemia/reperfusion (I/R) induces severe organic injury. I/R injury seems to be mainly caused by oxidative stress. The aim of this study was to determine the role of the spleen in experimental hepatic I/R injury in the rat. Stress protein heme oxygenase (HO)-1 plays a protective role against the oxidative injury. In normal state, HO-1 is highly expressed in the spleen.

METHODS

Liver HO-1 expression was assessed by Western blot before and after splenects. Liver injury was assessed by measurement of ALT and AST and by histopathology.

RESULTS

Although HO-1 was not detected in normal liver, levels of HO-1 protein gradually increased and peaked on 3 days after splenectomy. When splenectomy was performed 3 days prior to the hepatic (45-min) ischemia followed by (2-h) reperfusion, the levels of serum aspartate transaminase (AST) and alanine transaminase (ALT), as markers for hepatic injury, were improved compared to the rats with I/R alone. In addition, prior administration of zinc-protoporphyrin IX, a specific inhibitor of HO, suppressed the protective effect of the splenectomy on the subsequent hepatic I/R injury. Histopathological examination also confirmed these results.

CONCLUSIONS

Our findings suggest that the elevated HO-1 levels by splenectomy play a protective role against hepatic I/R injury.

Splenectomy ablates endotoxin-induced IFNgamma response in rats

The mechanism of liver injury in endotoxemia is unclear. Previous studies have shown that splenectomy protects the liver from endotoxin-induced injury. The purpose of this study was to determine the relationship of TNFalpha and IFNgamma release and endotoxin-induced liver injury in splenectomized and nonsplenectomized rats. Splenectomized and nonsplenectomized (Sham) rats with chronic catheters in the aorta and inferior vena cava (IVC) were parenterally infused with 10 to 5000 microg/kg endotoxin. TNFalpha, IFNgamma, and alanine aminotransferase (ALT), a marker of hepatocellular damage, were measured in aortic blood. Compared to sham controls, splenectomized animals demonstrated significantly reduced endotoxin-induced ALT concentrations at endotoxin doses >10 microg/kg. Peak endotoxin-induced TNFalpha concentrations were not significantly different between the splenectomized and sham groups. In contrast, peak endotoxin-induced IFNgamma concentrations were significantly decreased in the splenectomized group. These data suggest a relationship between endotoxin-induced IFNgamma and liver injury. We speculate that the spleen contributes to the endotoxin-induced liver injury by modulating release of IFNgamma.