Mast cells aggravate sepsis by inhibiting peritoneal macrophage phagocytosis

Controlling the overwhelming inflammatory reaction associated with polymicrobial sepsis remains a prevalent clinical challenge with few treatment options. In septic peritonitis, blood neutrophils and monocytes are rapidly recruited into the peritoneal cavity to control infection, but the role of resident sentinel cells during the early phase of infection is less clear. In particular, the influence of mast cells on other tissue-resident cells remains poorly understood. Here, we developed a mouse model that allows both visualization and conditional ablation of mast cells and basophils to investigate the role of mast cells in severe septic peritonitis. Specific depletion of mast cells led to increased survival rates in mice with acute sepsis. Furthermore, we determined that mast cells impair the phagocytic action of resident macrophages, thereby allowing local and systemic bacterial proliferation. Mast cells did not influence local recruitment of neutrophils and monocytes or the release of inflammatory cytokines. Phagocytosis inhibition by mast cells involved their ability to release prestored IL-4 within 15 minutes after bacterial encounter, and treatment with an IL-4–neutralizing antibody prevented this inhibitory effect and improved survival of septic mice. Our study uncovers a local crosstalk between mast cells and macrophages during the early phase of sepsis development that aggravates the outcome of severe bacterial infection.     

CD4-expressing cells are early mediators of the innate immune system during sepsis

It is well established that the immune response to sepsis is mediated by leukocytes associated with the innate immune system. However, there is an emerging view that T lymphocytes can also mediate this response. Here, we observed a significant depletion of both CD4 and CD8 T cells in human patients after blunt trauma. To determine what effect the loss of these cells may have during a subsequent infection, we obtained CD4- and CD8-deficient mice and subjected them to cecal ligation and puncture (CLP). We observed that CD4 knockout (KO) mice showed increased CLP-induced mortality compared with CD8-deficient and wild-type (WT) mice especially within the first 30 h of injury. CD4 KO mice also exhibited significantly increased IL-6 concentrations after the CLP. The CD4 KO mice had an increased concentration of bacteremia as compared with WT mice. Antibiotic treatment decreased mortality in the CD4 KO mice as compared with no changes in the wild mice after CLP. Neutrophils isolated from septic CD4 KO mice showed decreased spontaneous oxidative burst compared with neutrophils taken from septic controls. We examined the role of IFN-gamma by using mice deficient in this cytokine and found these mice to have significantly higher mortality as compared with WT mice. Finally, we detected a 2-fold increase in CD11b+ cells that exhibited intracellular IFN-gamma staining in the peritoneum of WT mice after CLP. The data suggest that CD4+ cells may facilitate the early clearance of bacteria by regulating neutrophils function possibly through an IFN-gamma-dependent mechanism.     

Protection from lethal septic peritonitis by neutralizing the biological function of interleukin 27

The immune response to bacterial infections must be tightly controlled to guarantee pathogen elimination while preventing tissue damage by uncontrolled inflammation. Here, we demonstrate a key role of interleukin (IL)-27 in regulating this critical balance. IL-27 was rapidly induced during murine experimental peritonitis induced by cecal ligation and puncture (CLP). Furthermore, mice deficient for the EBI3 subunit of IL-27 were resistant to CLP-induced septic peritonitis as compared with wild-type controls, and this effect could be suppressed by injection of recombinant single-chain IL-27. EBI3-/- mice displayed significantly enhanced neutrophil migration and oxidative burst capacity during CLP, resulting in enhanced bacterial clearance and local control of infection. Subsequent studies demonstrated that IL-27 directly suppresses endotoxin-induced production of reactive oxygen intermediates by isolated primary granulocytes and macrophages. Finally, in vivo blockade of IL-27 function using a newly designed soluble IL-27 receptor fusion protein led to significantly increased survival after CLP as compared with control-treated mice. Collectively, these data identify IL-27 as a key negative regulator of innate immune cell function in septic peritonitis. Furthermore, in vivo blockade of IL-27 is a novel potential therapeutic target for treatment of sepsis.     

Role of coagulation FVIII in septic peritonitis assessed in hemophilic mice

BACKGROUND: Inhibition of blood coagulation appears to be an important therapeutic strategy to improve the outcome in sepsis. However, the beneficial effect of anticoagulant treatment in sepsis is solely based on experimental data using inhibitors of the extrinsic coagulant pathway. The role of the intrinsic pathway of coagulation in the pathogenesis of sepsis has not been explored yet. OBJECTIVE: In the current study, we contribute to determine the role of factor (F)VIII, the key player of the intrinsic coagulant pathway, on host defense against peritonitis. METHOD: Hemizygous FVIII-deficient mice and their wild-type littermates were challenged with 1 x 10(4) bacteria in a septic peritonitis model. RESULTS: The intraperitoneal injection of Escherichia coli led to growth and dissemination of bacteria and provoked an inflammatory response as evident from elevated cytokine levels, increased cell influx into tissues, liver necrosis, and endothelialitis resulting in mortality. The FVIII-deficient genotype slightly reduced bacterial outgrowth but had no effect on markers of inflammation and/or survival. In addition, FVIII-deficient mice showed profound activation of coagulation, thereby improving the hemophilic phenotype of FVIII-deficient mice. CONCLUSION: FVIII deficiency slightly modifies host defense in septic peritonitis in mice, but does not influence the final outcome of peritonitis. Therefore, we question the importance of the intrinsic coagulant pathway during sepsis.     

Divergent roles of IL-23 and IL-12 in host defense against Klebsiella pneumoniae

Interleukin (IL)-23 is a heterodimeric cytokine that shares the identical p40 subunit as IL-12 but exhibits a unique p19 subunit similar to IL-12 p35. IL-12/23 p40, interferon gamma (IFN-gamma), and IL-17 are critical for host defense against Klebsiella pneumoniae. In vitro, K. pneumoniae-pulsed dendritic cell culture supernatants elicit T cell IL-17 production in a IL-23-dependent manner. However, the importance of IL-23 during in vivo pulmonary challenge is unknown. We show that IL-12/23 p40-deficient mice are exquisitely sensitive to intrapulmonary K. pneumoniae inoculation and that IL-23 p19-/-, IL-17R-/-, and IL-12 p35-/- mice also show increased susceptibility to infection. p40-/- mice fail to generate pulmonary IFN-gamma, IL-17, or IL-17F responses to infection, whereas p35-/- mice show normal IL-17 and IL-17F induction but reduced IFN-gamma. Lung IL-17 and IL-17F production in p19-/- mice was dramatically reduced, and this strain showed substantial mortality from a sublethal dose of bacteria (10(3) CFU), despite normal IFN-gamma induction. Administration of IL-17 restored bacterial control in p19-/- mice and to a lesser degree in p40-/- mice, suggesting an additional host defense requirement for IFN-gamma in this strain. Together, these data demonstrate independent requirements for IL-12 and IL-23 in pulmonary host defense against K. pneumoniae, the former of which is required for IFN-gamma expression and the latter of which is required for IL-17 production.     

Reduced peroxisome proliferator-activated receptor α expression is associated with decreased survival and increased tissue bacterial load in sepsis

The peroxisome proliferator-activated receptor α (PPAR-α) is a member of the nuclear receptor family with many important physiologic roles related to metabolism and inflammation. Previous research in pediatric patients with septic shock revealed that genes corresponding to the PPAR-α signaling pathway are significantly downregulated in a subgroup of children with more severe disease. In this study, PPAR-α expression analysis using whole-blood derived RNA revealed that PPAR-α expression was decreased in patients with septic shock and that the magnitude of that decrement correlated with the severity of disease. In a mouse model of sepsis, induced by cecal ligation and puncture, knockout mice lacking PPAR-α had decreased survival compared with wild-type animals. Plasma cytokine analysis demonstrated decreased levels of interleukin 1β (IL-1β), IL-6, IL-17, keratinocyte-derived cytokine, macrophage chemoattractant protein 1, macrophage inflammatory protein 2, and tumor necrosis factor α at 24 h in PPAR-α knockout animals. Cell surface markers of activation on splenic dendritic cells, macrophages, and CD8 T cells were reduced in PPAR-α null animals, and the bacterial load in lung and splenic tissues was increased. These data indicate that reduced or absent PPAR-α expression confers a survival disadvantage in sepsis and that PPAR-α plays a role in maintaining appropriate immune functions during the sepsis response.     

Inactivation of LRG-47 and IRG-47 reveals a family of interferon gamma-inducible genes with essential, pathogen-specific roles in resistance to infection.

The cytokine interferon (IFN)-gamma regulates immune clearance of parasitic, bacterial, and viral infections; however, the underlying mechanisms are poorly understood. Recently, a family of IFN-gamma-induced genes has been identified that encode 48-kD GTP-binding proteins that localize to the endoplasmic reticulum of cells. The prototype of this family, IGTP, has been shown to be required for host defense against acute infections with the protozoan parasite Toxoplasma gondii, but not for normal clearance of the bacterium Listeria monocytogenes and murine cytomegalovirus (MCMV). To determine whether other members of the gene family also play important roles in immune defense, we generated mice that lacked expression of the genes LRG-47 and IRG-47, and examined their responses to representative pathogens. After infection with T. gondii, LRG-47-deficient mice succumbed uniformly and rapidly during the acute phase of the infection; in contrast, IRG-47-deficient mice displayed only partially decreased resistance that was not manifested until the chronic phase. After infection with L. monocytogenes, LRG-47-deficient mice exhibited a profound loss of resistance, whereas IRG-47-deficient mice exhibited completely normal resistance. In addition, both strains displayed normal clearance of MCMV. Thus, LRG-47 and IRG-47 have vital, but distinct roles in immune defense against protozoan and bacterial infections.     

B cells enhance early innate immune responses during bacterial sepsis

Microbes activate pattern recognition receptors to initiate adaptive immunity. T cells affect early innate inflammatory responses to viral infection, but both activation and suppression have been demonstrated. We identify a novel role for B cells in the early innate immune response during bacterial sepsis. We demonstrate that Rag1(-/-) mice display deficient early inflammatory responses and reduced survival during sepsis. Interestingly, B cell-deficient or anti-CD20 B cell-depleted mice, but not α/β T cell-deficient mice, display decreased inflammatory cytokine and chemokine production and reduced survival after sepsis. Both treatment of B cell-deficient mice with serum from wild-type (WT) mice and repletion of Rag1(-/-) mice with B cells improves sepsis survival, suggesting antibody-independent and antibody-dependent roles for B cells in the outcome to sepsis. During sepsis, marginal zone and follicular B cells are activated through type I interferon (IFN-I) receptor (IFN-α/β receptor [IFNAR]), and repleting Rag1(-/-) mice with WT, but not IFNAR(-/-), B cells improves IFN-I-dependent and -independent early cytokine responses. Repleting B cell-deficient mice with the IFN-I-dependent chemokine, CXCL10 was also sufficient to improve sepsis survival. This study identifies a novel role for IFN-I-activated B cells in protective early innate immune responses during bacterial sepsis.     

Response to influenza infection in mice with a targeted disruption in the interferon gamma gene

Interferon gamma (IFN-gamma) is a pleiotropic cytokine secreted by T lymphocytes and natural killer (NK) cells and has been noted to be a first line of host defense in the control of viral infections. To examine further the role of this cytokine in the control of viral infections, mice with a targeted mutation in the IFN-gamma gene were infected with influenza virus, and the in vivo antibody and cell- mediated immune response to viral infection were examined. In addition, cell lines and clones were derived from the immunized animals and the in vitro cytokine production and cytotoxic T lymphocyte (CTL) response were analyzed. The absence of IFN-gamma led to increased production of influenza-specific IgG1, IL-4, and IL-5 as compared to wild-type littermate control animals. In contrast, there was no difference noted in the development of an effective CTL response between IFN-gamma- deficient and wild-type animals. In this model of experimental influenza infection, IFN-gamma is not necessary for the development of an effective humoral or cellular immune response to challenge with this respiratory virus.     

Bacterial clearance and mortality are not improved by a combination of IL-10 neutralization and IFN-gamma administration in a murine model of post-CLP immunosuppression

Immunocompromise after a major injury is presumed to be a predisposing factor for sepsis. Mice subjected to sublethal cecal ligation and puncture (CLP) and challenged 5 days later with Pseudomonas aeruginosa had more bacterial growth in lung tissue, lower serum interferon gamma (IFN-gamma) and interleukin (IL) 12,and higher serum IL-10 when compared with sham CLP mice challenged with Pseudomonas. To test the functional significance of these alterations in cytokine production in the immune response to bacteria, we administered IFN-gamma and anti-IL-10 to post-CLP mice before the Pseudomonas challenge. Administration of IFN-gamma and anti-IL-10 did not improve bacterial clearance or mortality in post-CLP mice. In further studies, we administered IFN-gamma to IL-10 knockout mice before a challenge with P. aeruginosa. Our results showed no significant differences in bacterial clearance or mortality in IL-10 knockout mice with or without IFN-gamma treatment compared with wild-type controls. Finally, because most mortality occurred within 2 to 3 days of the Pseudomonas challenge in the aforementioned studies and was likely associated with a marked proinflammatory response, we investigated the effect of IFN-gamma and anti-IL-10 on clearance of Pseudomonas in C3H/HeJ mice, which do not mount an exaggerated proinflammatory response to endotoxin or Gram-negative bacteria. Neither clearance of the Pseudomonas bacteria nor mortality was improved in C3H/HeJ mice receiving anti-IL-10 and IFN-gamma. These results suggest that the suppressed IFN-gamma and IL-12 responses, in combination with an exaggerated IL-10 response to P. aeruginosa challenge after injury, do not correlate with bacterial clearance or survival.     

Neutralization of IL-10 restores the downregulation of IL-18 receptor on natural killer cells and interferon-γ production in septic mice, thus leading to an improved survival

The objective of the study was to investigate the mechanisms of insufficient interferon-γ (IFN-γ) response to interleukin 18 (IL-18) and the treatment for the insufficient response in septic mice. Interleukin 18 stimulation does not restore IFN-γ production by blood mononuclear cells in septic patients but does restore its production in postoperative patients. Although sepsis impairs the IFN-γ response to IL-18, little is known about why the IL-18/IFN-γ-mediated immune response is ineffective in patients with sepsis. A cecal ligation and puncture was made in C57BL/6 mice following a sublethal lipopolysaccharide challenge to examine their IFN-γ response to IL-18, focusing on natural killer (NK) cells and cytokines. We next examined the effect of neutralization of IL-10 on the NK cell and survival in septic mice. Interleukin 18 injection did not restore IFN-γ production in septic (cecal ligation and puncture) mice. Despite an increase in the numbers of liver NK cells, the IL-18 receptor (IL-18R) expression was decreased in the septic mice compared with sham mice. Serum IL-10 levels were positively correlated with the percentage of liver NK cells, but negatively with their IL-18R expression. Neutralization of IL-10 restored the IL-18R expression on liver NK cells and restored the IFN-γ response in the septic mice, improving their survival. Sepsis might impair IL-18R expression on liver and spleen NK cells and impair the IL-18-mediated IFN-γ response. Neutralization of IL-10 may restore this response in septic hosts, thereby improving survival.     

The contribution of CD4+ CD25+ T-regulatory-cells to immune suppression in sepsis

Studies have indicated that there is a development of generalized immune dysfunction after septic insult. However, the mechanisms responsible for these changes remain unclear. Recently, accumulating evidence shows that several lymphocyte subpopulations such as NKT-, CD4(+)-Th2-T-, CD8(+)-T-, gammadelta-T-, and CD4+ CD25+ T regulatory cells are capable of actively contributing to the induction of septic immune suppression. Thus, our aim was to investigate the contribution of CD4+ CD25+ cells to the immune dysfunction seen in sepsis. To study this, C57BL/6J, C57BL/6-Il6(tm1Kopf) (interleukin [IL] 6 -/-), and C57BL/6-Il10(tm1Cgn) (IL-10 -/-) mice were subjected to cecal ligation and puncture (CLP) or sham operations. Twenty-four hours later, blood was collected, and splenocytes were isolated. Phenotypic expression of CD4/CD25 (by fluorescence-activated cell sorter), cell proliferation (presented as proliferation index = [with anti-CD3]/[without anti-CD3]), and immune suppressive capacity (by in vitro add-back experiments) were assessed. The results indicate a marked elevation in CD4+ CD25+ cell levels and their proliferation index after sepsis in background mice. CD4+ CD25- cells from sham and CLP mice proliferated equally. However, coculture of CD4+ CD25- with CD4+ CD25+ cells suppressed their proliferation in both sham and CLP mice. Depletion of CD25+ cells in vivo before CLP markedly restored CD4+ CD25- proliferative capacity and Th1 cytokine release while not altering plasma proinflammatory cytokine levels. Subsequently, IL-6 -/- and IL-10 -/- mice were used to elucidate the possible mediator(s) regulating the changes seen after sepsis. Although CD4+ CD25+ cells increased after septic insult in both C57BL/6J and IL-6 -/- mice, this was not observed in IL-10 -/- mice. Similarly, in vitro proliferation studies showed that proliferation index increased in CD4+ CD25+ cells from septic C57BL/6J and IL6 -/- mice, but it remained the same in IL-10 -/- mice. Surprisingly, depletion of CD25+ cells before inducing sepsis did not alter septic mortality. Together, these findings suggest that although CD4+ CD25+ T regulatory cells induced by IL-10 seem to contribute to aspects of sepsis-induced lymphoid immune suppression, the oblation of CD25+ cells does not provide a survival advantage or disadvantage.     

Glucan phosphate potentiates endotoxin-induced interferon-gamma expression in immunocompetent mice, but attenuates induction of endotoxin tolerance.

Glucan phosphate has been shown to enhance antimicrobial immunity in a variety of experimental models. However, the mechanisms by which glucans enhance resistance to infection remain largely unknown. Interferon-gamma (IFN-gamma) is a key regulator of both innate and acquired immunity. Suppression of IFN-gamma production is a prominent feature of the altered immune response that follows major trauma or sepsis. The present studies were designed to determine the effect of glucan phosphate on IFN-gamma expression in normal mice and endotoxin [lipopolysaccharide (LPS)]-tolerant mice. The model of LPS tolerance was used because it results in patterns of cytokine expression similar to those commonly observed following severe trauma or sepsis. Glucan treatment potentiated LPS-induced IFN-gamma expression in control mice. The induction of LPS tolerance resulted in marked suppression of LPS-induced IFN-gamma production. However, co-administration of glucan with LPS, during the tolerance induction phase, attenuated the LPS-tolerant response. Interleukin-12 (IL-12) and IL-18 are important mediators of LPS-induced IFN-gamma production. LPS-induced IL-12 p40 mRNA expression was increased in the spleens of glucan-treated mice compared with controls. Induction of LPS tolerance caused marked suppression of IL-12 production, a response that was attenuated by glucan treatment. IL-18 was constitutively expressed in both control and LPS-tolerant mice, and LPS-induced serum levels of IL-18 were increased in mice treated with glucan. T cells isolated from glucan-treated mice exhibited increased IFN-gamma expression in response to IL-12 and IL-18, as well as increased expression of the IL-12 and IL-18 receptors. The ability of glucan to potentiate IFN-gamma expression in control mice provides a potential mechanism by which glucan enhances antimicrobial immunity. The ability of glucan to attenuate suppressed IFN-gamma expression in LPS-tolerant mice denotes its potential benefit for the treatment of trauma and sepsis-induced immunosuppression.     

Efficacy of gamma interferon and specific antibody for treatment of microsporidiosis caused by Encephalitozoon cuniculi in SCID mice

Microsporidia are eukaryotic, obligate, intracellular protists that are emerging pathogens in immunocompromised hosts, including AIDS patients and organ transplant recipients. The efficacy of gamma interferon (IFN-gamma) for the treatment of microsporidiosis caused by Encephalitozoon cuniculi was studied by means of adoptive transfer and IFN-gamma administration in SCID mice. While the adoptive transfer of CD4(+) T cells from immunocompetent mice prolonged survival of SCID mice infected perorally with E. cuniculi, survival was not improved by adoptive transfer of CD4(+) T lymphocytes from IFN-gamma-deficient mice. The protective effect of IFN-gamma was confirmed in cytokine therapy experiments in which SCID mice receiving IFN-gamma survived significantly longer than mice receiving mock injections. The administration of serum containing specific antibodies against E. cuniculi was found to prolong the survival of concurrently IFN-gamma-treated SCID mice. The data presented in this study suggest that IFN-gamma is potentially useful as a cytokine therapy for microsporidiosis, especially in CD4(+) T-cell-deficient patients.     

Persistent inflammation and T cell exhaustion in severe sepsis in the elderly

Introduction

Sepsis is known as a complex immunological response with hyperinflammation in the acute phase followed by immunosuppression. Although aging is crucial in sepsis, the impact of aging on inflammation and immunosuppression is still unclear. The purpose of this study was to investigate the relationship between inflammation and immunosuppression in aged patients and mice after sepsis.

Methods

Fifty-five patients with severe sepsis and 30 healthy donors were prospectively enrolled, and 90-day survival was compared between elderly (≥65 years) and adult (18–64 years) septic patients with serial measurement of serum interleukin (IL)-6. Within 24 h after diagnosis of severe sepsis, peripheral blood mononuclear cells were stimulated ex vivo to measure expression of the activation maker CD25 in T cells, IL-2 levels in the supernatant, and proliferation. In the mouse study, young (6–8 weeks) and aged (20–22 months) C57/B6 mice were subjected to cecal ligation and puncture (CLP), and survival was compared after 7 days with serial measurement of serum IL-6. Expression of the negative co-stimulatory molecules, CD25, and IL-2 in CD4+ T cells was measured.

Results

The survival rate in elderly sepsis patients and aged septic mice was significantly lower than that in adult patients and young septic mice (60% vs. 93% in septic patients, 0% vs. 63% in septic mice, P < 0.05). Serum IL-6 levels in elderly sepsis patients and aged septic mice were persistently higher than those in adult patients and young septic mice. Expression of negative co-stimulatory molecules in CD4+ T cells in the spleen, lymph nodes, and peripheral blood was significantly higher in aged mice than in young mice (P < 0.01). Ex vivo stimulation decreased CD25 expression, IL-2 production, and proliferation to a greater extent in CD4+ T cells from elderly patients and aged septic mice than in those from adult patients and young septic mice. Elderly patients demonstrated increased detection of gram-negative bacteria at days 14–16 and 28–32 after sepsis (P < 0.05).

Conclusions

Persistent inflammation and T cell exhaustion may be associated with decreased survival in elderly patients and mice after sepsis.     

Requirement for natural killer cell-produced interferon gamma in defense against murine cytomegalovirus infection and enhancement of this defense pathway by interleukin 12 administration

The presence of natural killer (NK) cells contributes to early defense against murine cytomegalovirus (MCMV) infection. Although NK cells can mediate in vivo protection against MCMV, the mechanism by which they do so has not been defined. The studies presented here evaluate cytokine production by NK cells activated during MCMV infection and the role of NK cell-produced cytokines in early in vivo antiviral defenses. Experiments with normal C57BL/6, T cell-deficient C57BL/6 nude, and severe combined immunodeficient mice lacking T and B cells demonstrated that both interferon gamma (IFN-gamma) and tumor necrosis factor (TNF) production were induced at early times after infection with MCMV. Conditioned media samples prepared with cells from these mice, on day 2 after infection, produced 11-43 pg/million cells of IFN-gamma and 12-19 pg/million cells of TNF as evaluated by specific protein enzyme-linked immunosorbent assays. Studies in the NK- and T cell-deficient mouse line, E26, in mice that had been depleted in vivo of NK cells by treatment with antibodies eliminating NK cells, anti-asialo ganglio-N- tetraosylceramide or anti-NK1.1, and with populations of cells that had been depleted of NK cells by complement treatment with the anti-NK cell antibody, SW3A4, demonstrated that NK cells were solely responsible for the IFN-gamma but were not required for TNF production. The in vivo absence of NK cells was accompanied by increased viral hepatitis and viral replication in both immunocompetent and immunodeficient mice, as well as decreased survival time of immunodeficient mice. In vivo treatments with antibodies neutralizing IFN-gamma demonstrated that this factor contributed to the NK cell-mediated antiviral defense and reduced the measured parameters of viral defense to levels indistinguishable from those observed in NK cell-deficient mice. These effects appeared to be independent of cytolytic activity, as NK cells isolated from anti-IFN-gamma-treated mice mediated killing at levels comparable to those observed in control-treated mice. The consequences of interleukin 12 (IL-12) administration, a known potent inducer of IFN- gamma production by NK cells, were evaluated in MCMV-infected mice. Low IL-12 doses, i.e., 1 ng/d, increased NK cell cytotoxicity and IFN-gamma production up to twofold and resulted in improved antiviral status; virus-induced hepatitis was decreased as much as fivefold, and viral burdens were decreased to levels below detection.(ABSTRACT TRUNCATED AT 400 WORDS)     

Resistance of CD7-deficient mice to lipopolysaccharide-induced shock syndromes

CD7 is an immunoglobulin superfamily molecule involved in T and natural killer (NK) cell activation and cytokine production. CD7-deficient animals develop normally but have antigen-specific defects in interferon (IFN)-gamma production and CD8(+) CTL generation. To determine the in vivo role of CD7 in systems dependent on IFN-gamma, the response of CD7-deficient mice to lipopolysaccharide (LPS)-induced shock syndromes was studied. In the high-dose LPS-induced shock model, 67% of CD7-deficient mice survived LPS injection, whereas 19% of control C57BL/6 mice survived LPS challenge (P < 0.001). CD7-deficient or C57BL/6 control mice were next injected with low-dose LPS (1 microgram plus 8 mg D-galactosamine [D-gal] per mouse) and monitored for survival. All CD7-deficient mice were alive 72 h after injection of LPS compared with 20% of C57BL/6 control mice (P < 0.001). After injection of LPS and D-gal, CD7-deficient mice had decreased serum IFN-gamma and tumor necrosis factor (TNF)-alpha levels compared with control C57BL/6 mice (P < 0.001). Steady-state mRNA levels for IFN-gamma and TNF-alpha in liver tissue were also significantly decreased in CD7-deficient mice compared with controls (P < 0.05). In contrast, CD7-deficient animals had normal liver interleukin (IL)-12, IL-18, and interleukin 1 converting enzyme (ICE) mRNA levels, and CD7-deficient splenocytes had normal IFN-gamma responses when stimulated with IL-12 and IL-18 in vitro. NK1.1(+)/ CD3(+) T cells are known to be key effector cells in the pathogenesis of toxic shock. Phenotypic analysis of liver mononuclear cells revealed that CD7-deficient mice had fewer numbers of liver NK1.1(+)/CD3(+) T cells (1.5 +/- 0.3 x 10(5)) versus C57BL/6 control mice (3.7 +/- 0.8 x 10(5); P < 0.05), whereas numbers of liver NK1.1(+)/CD3(-) NK cells were not different from controls. Thus, targeted disruption of CD7 leads to a selective deficiency of liver NK1.1(+)/ CD3(+) T cells, and is associated with resistance to LPS shock. These data suggest that CD7 is a key molecule in the inflammatory response leading to LPS-induced shock.     

T cells, but not B cells, are required for bowel inflammation in interleukin 2-deficient mice

Interleukin-2 (IL-2)-deficient (IL-2-/-) mice develop anemia and colonic inflammatory bowel disease. To elucidate the mechanism of this disease, we have bred IL-2-/- mice to two strains of immunodeficient mice, RAG-2-deficient (RAG-2-/-, lacking B and T cells) and JH- deficient mice (JH-/-, lacking B cells). IL-2-/-, RAG-2-/- double- mutant mice are disease free, while IL-2-/-, JH-/- double-mutant mice succumb to bowel disease at the same rate as IL-2-/- littermates. IL-2- /-, JH-/- mice do not, however, succumb to anemia. Thus, spontaneous intestinal inflammation in IL-2-/- mice requires mature T cells, not B cells, while anemia is dependent on B cells.     

Mast cell dipeptidyl peptidase I mediates survival from sepsis

Sepsis is a common, life-threatening disease for which there is little treatment. The cysteine protease dipeptidyl peptidase I (DPPI) activates granule-associated serine proteases, several of which play important roles in host responses to bacterial infection. To examine DPPI's role in sepsis, we compared DPPI(-/-) and DPPI(+/+) mice using the cecal ligation and puncture (CLP) model of septic peritonitis, finding that DPPI(-/-) mice are far more likely to survive sepsis. Outcomes of CLP in mice lacking mast cell DPPI reveal that the absence of DPPI in mast cells, rather than in other cell types, is responsible for the survival advantage. Among several cytokines surveyed in peritoneal fluid and serum, IL-6 is highly and differentially expressed in DPPI(-/-) mice compared with DPPI(+/+) mice. Remarkably, deleting IL-6 expression in DPPI(-/-) mice eliminates the survival advantage. The increase in IL-6 in septic DPPI(-/-) mice, which appears to protect these mice from death, may be related to reduced DPPI-mediated activation of mast cell tryptase and other peptidases, which we show cleave IL-6 in vitro. These results indicate that mast cell DPPI harms the septic host and that DPPI is a novel potential therapeutic target for treatment of sepsis.