Detrimental role for CD4+ T lymphocytes in murine diffuse peritonitis due to inhibition of local bacterial elimination

Immune Polarization Potential of the S. aureus Virulence Factors SplB and GlpQ and Modulation by Adjuvants

Protection against Staphylococcus aureus is determined by the polarization of the anti-bacterial immune effector mechanisms. Virulence factors of S. aureus can modulate these and induce differently polarized immune responses in a single individual. We proposed that this may be due to intrinsic properties of the bacterial proteins. To test this idea, we selected two virulence factors, the serine protease-like protein B (SplB) and the glycerophosphoryl diester phosphodiesterase (GlpQ). In humans naturally exposed to S. aureus, SplB induces a type 2-biased adaptive immune response, whereas GlpQ elicits type 1/type 3 immunity. We injected the recombinant bacterial antigens into the peritoneum of S. aureus-naïve C57BL/6N mice and analyzed the immune response. This was skewed by SplB toward a Th2 profile including specific IgE, whereas GlpQ was weakly immunogenic. To elucidate the influence of adjuvants on the proteins’ polarization potential, we studied Montanide ISA 71 VG and Imject™Alum, which promote a Th1 and Th2 response, respectively. Alum strongly increased antibody production to the Th2-polarizing protein SplB, but did not affect the response to GlpQ. Montanide enhanced the antibody production to both S. aureus virulence factors. Montanide also augmented the inflammation in general, whereas Alum had little effect on the cellular immune response. The adjuvants did not override the polarization potential of the S. aureus proteins on the adaptive immune response.

Experimental pancreatitis is characterized by rapid T cell activation, Th2 differentiation that parallels disease severity, and improvement after CD4+ T cell depletion

BACKGROUND

Acute pancreatitis is a gastrointestinal disorder of high incidence resulting in life threatening complications in up to 20% of patients. Its severe form is characterized by an extensive and systemic immune response. We investigated the role of the adaptive immune response in two experimental models of pancreatitis.

METHODS

In C57BI/6-mice mild pancreatitis was induced by 8-hourly injections of caerulein and severe pancreatitis by additional, partial pancreatic duct ligation. T-cell-activation was determined by flow-cytometry of CD25/CD69, T-cell-differentiation by nuclear staining of the transcription-factors Tbet, Gata3 and Foxp3. In vivo CD4⁺ T-cells were depleted using anti-CD4 antibody. Disease severity was determined by histology, serum amylase and lipase activities, lung MPO and serum cytokine levels (IL-6, TNFα, IL-10).

RESULTS

In both models T-cells were activated. Th1-differentiation (Tbet) was absent during pancreatitis but we detected a pronounced Th2/Treg (Gata3/Foxp3) response which paralleled disease severity in both models. The complete depletion of CD4⁺ T-cells via anti-CD4 antibody, surprisingly, reduced disease severity significantly, as well as granulocyte infiltration and pro- and anti-inflammatory cytokine levels. Co-incubation of acini and T-cells did not lead to T-cell-activation by acinar cells but to acinar damage by T-cells. During pancreatitis no significant T-cell-infiltration into the pancreas was observed.

CONCLUSION

T cells orchestrate the early local as well as the systemic immune responses in pancreatitis and are directly involved in organ damage. The Th2 response appears to increase disease severity, rather than conferring an immunological protection.

Oxidation-Specific Epitopes (OSEs) Dominate the B Cell Response in Murine Polymicrobial Sepsis

In murine abdominal sepsis by colon ascendens stent peritonitis (CASP), a strong increase in serum IgM and IgG antibodies was observed, which reached maximum values 14 days following sepsis induction. The specificity of this antibody response was studied in serum and at the single cell level using a broad panel of bacterial, sepsis-unrelated as well as self-antigens. Whereas an antibacterial IgM/IgG response was rarely observed, studies at the single-cell level revealed that IgM antibodies, in particular, were largely polyreactive. Interestingly, at least 16% of the IgM mAbs and 20% of the IgG mAbs derived from post-septic mice showed specificity for oxidation-specific epitopes (OSEs), which are known targets of the innate/adaptive immune response. This identifies those self-antigens as the main target of B cell responses in sepsis.

Antibody Production in Murine Polymicrobial Sepsis-Kinetics and Key Players

Although antigen-specific priming of antibody responses is impaired during sepsis, there is nevertheless a strong increase in IgM and IgG serum concentrations. Using colon ascendens stent peritonitis (CASP), a mouse model of polymicrobial abdominal sepsis, we observed substantial increases in IgM as well as IgG of all subclasses, starting at day 3 and peaking 2 weeks after sepsis induction. The dominant source of antibody-secreting cells was by far the spleen, with a minor contribution of the mesenteric lymph nodes. Remarkably, sepsis induction in splenectomized mice did not change the dynamics of the serum IgM/IgG reaction, indicating that the marginal zone B cells, which almost exclusively reside in the spleen, are dispensable in such a setting. Hence, in systemic bacterial infection, the function of the spleen as dominant niche of antibody-producing cells can be compensated by extra-splenic B cell populations as well as other lymphoid organs. Depletion of CD4+ T cells did not affect the IgM response, while it impaired IgG generation of all subclasses with the exception of IgG3. Taken together, our data demonstrate that the robust class-switched antibody response in sepsis encompasses both T cell-dependent and -independent components.

Behavioral and immunotoxic effects of Prograf® (tacrolimus) in the male Siamese fighting fish

Siamese fighting fish (Betta splendens) has been extensively exploited in the behavioral and physiological toxicology studies of drugs. Tacrolimus is an immunosuppressant drug largely used in liver and renal transplantations. Here we found that a 7-day exposure of male B. splendens to concentrations of 0.05 and 0.1 µg/mL Prograf® (tacrolimus) caused alterations in aggression and immunity indexes. Tacrolimus exposed fish presented lower opercular display in a mirror test which is indicative of reduced aggression. In addition, serum levels of lysozyme, IgM, alternative complement, and bactericidal activity of subjects exposed to 0.1 µg/mL tacrolimus were lower than those from the control treatment. These results showed the behavioral impairment and immunotoxic impacts of tacrolimus in a model of aquatic toxicology. The results suggest fishes provide a possible model for better understanding of the drug action in vertebrates, and possible consequences for the environment via its effects on non-target organisms in an ecotoxicology context.

Polymicrobial sepsis and non-specific immunization induce adaptive immunosuppression to a similar degree

Sepsis is frequently complicated by a state of profound immunosuppression, in its extreme form known as immunoparalysis. We have studied the role of the adaptive immune system in the murine acute peritonitis model. To read out adaptive immunosuppression, we primed post-septic and control animals by immunization with the model antigen TNP-ovalbumin in alum, and measured the specific antibody-responses via ELISA and ELISpot assay as well as T-cell responses in a proliferation assay after restimulation. Specific antibody titers, antibody affinity and plasma cell counts in the bone marrow were reduced in post-septic animals. The antigen-induced splenic proliferation was also impaired. The adaptive immunosuppression was positively correlated with an overwhelming general antibody response to the septic insult. Remarkably, antigen “overload” by non-specific immunization induced a similar degree of adaptive immunosuppression in the absence of sepsis. In both settings, depletion of regulatory T cells before priming reversed some parameters of the immunosuppression. In conclusion, our data show that adaptive immunosuppression occurs independent of profound systemic inflammation and life-threatening illness.

[Pathophysiology of peritonitis]

Despite intensive research efforts peritonitis leading to subsequent sepsis remains associated with a high mortality. The initial effector cells are the locally residing cells of the peritoneum, such as mesothelial cells, mast cells, macrophages and lymphocytes. Through the secretion of chemokines, an influx of neutrophils initially takes place followed by monocytes. The latter can differentiate into inflammatory macrophages. The non-directed activity of neutrophilic granulocytes is limited by the induction of apoptotic programs. Through the breaching of cytokines, bacteria and microbial products into the circulation, a systemic reaction in the sense of systemic inflammatory response syndrome (SIRS) or sepsis arises. This is viewed as a concomitant derailing of inflammatory as well as anti-inflammatory responses, which leads to extensive apoptosis of lymphocytes. The presentation of apoptotic cells leads to a strong immunosuppression. Due to the coexistence of hyperinflammation and immunosuppression, exact knowledge of the current immune status of the patient is a prerequisite in the development of immunotherapies for the treatment of sepsis.

Adenosine and the adenosine A2A receptor agonist, CGS21680, upregulate CD39 and CD73 expression through E2F-1 and CREB in regulatory T cells isolated from septic mice

The number of regulatory T cells (Treg cells) and the expression of ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1; also known as CD39) and 5'-ectonucleotidase (NT5E; also known as CD73) on the Treg cell surface are increased during sepsis. In this study, to determine the factors leading to the high expression of CD39 and CD73, and the regulation of the CD39/CD73/adenosine pathway in Treg cells under septic conditions, we constructed a mouse model of sepsis and separated the Treg cells using a flow cytometer. The Treg cells isolated from the peritoneal lavage and splenocytes of the mice were treated with adenosine or the specific adenosine A2A receptor agonist, CGS21680, and were transfected with specific siRNA targeting E2F transcription factor 1 (E2F-1) or cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB), which are predicted transcription regulatory factors of CD39 or CD73. The regulatory relationships among these factors were then determined by western blot analysis and dual-luciferase reporter assay. In addition, changes in adenosine metabolism were measured in the treated cells. The results revealed that adenosine and CGS21680 significantly upregulated CD39 and CD73 expression (P<0.01). E2F-1 and CREB induced CD39 and CD73 expression, and were upregulated by adenosine and CGS21680. Adenosine triphosphate (ATP) hydrolysis and adenosine generation were inhibited by the knockdown of E2F-1 or CREB, and were accelerated in the presence of CGS21680. Based on these results, it can be inferred that adenosine, the adenosine A2A receptor agonist, E2F-1 and CREB are the possible factors contributing to the high expression of CD39 and CD73 on the Treg cell surface during sepsis. Adenosine and its A2A receptor agonist served as the signal transducer factors of the CD39/CD73/adenosine pathway, accelerating adenosine generation. Our study may benefit further research on adenosine metabolism for the treatment of sepsis.

TNF-related apoptosis-inducing ligand deficiency enhances survival in murine colon ascendens stent peritonitis

Background

Apart from inducing apoptosis in tumor cells, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) influences inflammatory reactions. Murine colon ascendens stent peritonitis (CASP) represents a model of diffuse peritonitis. Recently, it has been demonstrated that administration of exogenous TRAIL not only induces apoptosis in neutrophils but also enhances survival in this model. The aim of this study was to examine the impact of genetic TRAIL deficiency on the course of CASP.

Methods

Peritonitis was induced in 6- to 8-week-old female TRAIL^−/− mice as well as in wild-type mice. The sepsis severity score and survival of mice were monitored. Bacterial loads in blood as well as in the lymphoid organs were examined. Additionally, the number of apoptotic cells within the lymphoid organs was determined.

Results

As early as 8 hours postinduction of CASP, TRAIL^−/− mice were significantly more affected by sepsis than wild-type mice, as measured by the sepsis severity score. However, during the further course of sepsis, TRAIL deficiency led to significantly decreased sepsis severity scores, resulting in an enhanced overall survival in TRAIL^−/− mice. The better survival of TRAIL^−/− mice was accompanied by a decreased bacterial load within the blood. In marked contrast, the number of apoptotic cells within the lymphoid organs was highly increased in TRAIL^−/− mice 20 hours after induction of CASP.

Conclusion

Hence, exogenous and endogenous TRAIL is protective during the early phase of sepsis, while endogenous TRAIL appears to be detrimental in the later course of this disease.

Full activation of CD4+ T cells early during sepsis requires specific antigen

Supplemental digital content is available in the text.

During sepsis, CD4⁺ T cells express activation markers within the first 24 h. In the present study, the mechanisms of T-cell activation and its consequences were addressed in an acute peritonitis model in mice. The response of CD4⁺ T cells to sepsis induction was compared between OTII mice, characterized by ovalbumin-specific T-cell receptor–transgenic T cells, and C57BL/6 controls (wild type [WT] mice). Because ovalbumin was absent during peritonitis, the OTII CD4⁺ T cells could not be activated by canonical antigen recognition. In both OTII and WT control mice, CD4⁺ T effector cells and CD4⁺ Foxp3⁺ regulatory T cells (Tregs) expressed the activation marker CD69 early after sepsis onset. However, full activation with upregulation of CD25 and proliferation took place only in the presence of the antigen. Besides this, the fraction of Tregs was lower in OTII than that in WT mice. Sepsis mortality was increased in OTII mice. Our data show that, in sepsis, partial activation of CD4⁺ T cells is induced by a T-cell receptor–independent pathway, whereas full stimulation and proliferation require a specific antigen. Antigen-dependent T-cell effector functions as well as Treg activity may contribute to sepsis survival.

Members of the novel UBASH3/STS/TULA family of cellular regulators suppress T-cell-driven inflammatory responses in vivo

The UBASH3/STS/TULA family consists of two members sharing substantial homology and a similar multi-domain architecture, which includes a C-terminal histidine phosphatase domain capable of dephosphorylating phosphotyrosine-containing substrates. TULA-family proteins act as downregulators of receptor-induced activation in several cell types, including T cells and platelets. Deletion of both family members in mice has been shown to result in hyperresponsiveness of T cells to T-cell receptor (TCR)/CD3 complex engagement, but little is known about the biological consequences of double knockout (dKO) and especially of either single KO (sKO). We elucidated the biological consequences of the lack of TULA-family proteins in dKO and TULA and TULA-2 sKO animals. In order to do so, we examined immune responses in Trinitrobenzene sulfonic acid (TNBS)-induced colitis, a mouse model of human inflammatory bowel disease, which is characterized by the involvement of multiple cell types, of which T cells have a crucial role, in the development of a pathological inflammatory condition. Our data indicate that TNBS treatment upregulates T-cell responses in all KO mice studied to a significantly higher degree than in wild-type mice. Although the lack of either TULA-family member exacerbates inflammation and T-cell responses in a specific fashion, the lack of both TULA and TULA-2 in dKO exerts a higher effect than the lack of a single family member in TULA and TULA-2 sKO. Analysis of T-cell responses and TCR-mediated signaling argues that the proteins investigated affect T-cell signaling by regulating phosphorylation of Zap-70, a key protein tyrosine kinase.

Morphogenesis is not required for Candida albicans-Staphylococcus aureus intra-abdominal infection-mediated dissemination and lethal sepsis

Intra-abdominal polymicrobial infections cause significant morbidity and mortality. An established experimental mouse model of Staphylococcus aureus-Candida albicans intra-abdominal infection results in ∼60% mortality within 48 h postinoculation, concomitant with amplified local inflammatory responses, while monomicrobial infections are avirulent. The purpose of this study was to characterize early local and systemic innate responses during coinfection and determine the role of C. albicans morphogenesis in lethality, a trait involved in virulence and physical interaction with S. aureus. Local and systemic proinflammatory cytokines were significantly elevated during coinfection at early time points (4 to 12 h) compared to those in monoinfection. In contrast, microbial burdens in the organs and peritoneal lavage fluid were similar between mono- and coinfected animals through 24 h, as was peritoneal neutrophil infiltration. After optimizing the model for 100% mortality within 48 h, using 3.5 × 10(7) C. albicans (5× increase), coinfection with C. albicans yeast-locked or hypha-locked mutants showed similar mortality, dissemination, and local and systemic inflammation to the isogenic control. However, coinfection with the yeast-locked C. albicans mutant given intravenously (i.v.) and S. aureus given intraperitoneally (i.p.) failed to induce mortality. These results suggest a unique intra-abdominal interaction between the host and C. albicans-S. aureus that results in strong inflammatory responses, dissemination, and lethal sepsis, independent of C. albicans morphogenesis.

Foxp3+ regulatory T cells are required for recovery from severe sepsis

The role of regulatory T cells (Tregs) in bacterial sepsis remains controversial because antibody-mediated depletion experiments gave conflicting results. We employed DEREG mice (DEpletion of REGulatory T cells) and a caecal ligation and puncture model to elucidate the role of CD4⁺Foxp3⁺ Tregs in sepsis. In DEREG mice natural Tregs can be visualized easily and selectively depleted by diphtheria toxin because the animals express the diphtheria toxin receptor and enhanced green fluorescent protein as a fusion protein under the control of the foxp3 locus. We confirmed rapid Treg-activation and an increased ratio of Tregs to Teffs in sepsis. Nevertheless, 24 h after sepsis induction, Treg-depleted and control mice showed equally strong inflammation, immune cell immigration into the peritoneum and bacterial dissemination. During the first 36 h of disease survival was not influenced by Treg-depletion. Later, however, only Treg-competent animals recovered from the insult. We conclude that the suppressive capacity of Tregs is not sufficient to control overwhelming inflammation and early mortality, but is a prerequisite for the recovery from severe sepsis.

The impact of tacrolimus on the immunopathogenesis of staphylococcal enterotoxin-induced systemic inflammatory response syndrome and pneumonia

Staphylococcal superantigens (SAg) are a family of potent exotoxins produced by Staphylococcus aureus. They play an important role in the pathogenesis of staphylococcal shock and pneumonia by causing a robust activation of the immune system and eliciting a strong surge in systemic cytokine and chemokine levels. Given the biological functions of SAg, we evaluated the efficacy of tacrolimus, a potent immunosuppressive agent, in the prophylaxis and therapy of staphylococcal TSS and pneumonia using human leukocyte antigen (HLA)-DR3 transgenic mice. Tacrolimus significantly inhibited staphylococcal SAg induced T cell activation in vitro. In vivo, tacrolimus significantly suppressed the SAg-induced elevation in serum cytokine and chemokine levels when given prophylactically, when administered immediately or even 2 h following systemic SAg challenge. Paradoxically, neither the prophylactic nor post-exposure treatment with tacrolimus protected mice from lethal SAg-induced TSS. A closer examination revealed that tacrolimus failed to suppress SAg-induced T cell proliferation and systemic pathology, including gut dysfunction. Tacrolimus also failed to protect from lethal pneumonia induced by a SAg-producing S. aureus strain. Thus, our study showed that even though T cell activation by SAg plays a major role in the immunopathogenesis of TSS and pneumonia, tacrolimus alone has no beneficial effect.

B cells enhance early innate immune responses during bacterial sepsis

Type I interferon–responsive B cells provide early protection against 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.

Colon ascendens stent peritonitis (CASP)--a standardized model for polymicrobial abdominal sepsis

Sepsis remains a persistent problem on intensive care units all over the world. Understanding the complex mechanisms of sepsis is the precondition for establishing new therapeutic approaches in this field. Therefore, animal models are required that are able to closely mimic the human disease and also sufficiently deal with scientific questions. The Colon Ascendens Stent Peritonitis (CASP) is a highly standardized model for polymicrobial abdominal sepsis in rodents. In this model, a small stent is surgically inserted into the ascending colon of mice or rats leading to a continuous leakage of intestinal bacteria into the peritoneal cavity. The procedure results in peritonitis, systemic bacteraemia, organ infection by gut bacteria, and systemic but also local release of several pro- and anti-inflammatory cytokines. The lethality of CASP can be controlled by the diameter of the inserted stent. A variant of this model, the so-called CASP with intervention (CASPI), raises opportunity to remove the septic focus by a second operation according to common procedures in clinical practice. CASP is an easily learnable and highly reproducible model that closely mimics the clinical course of abdominal sepsis. It leads way to study on questions in several scientific fields e.g. immunology, infectiology, or surgery.

Peritoneal damage: the inflammatory response and clinical implications of the neuro-immuno-humoral axis

BACKGROUND

The peritoneum is a bilayer serous membrane that lines the abdominal cavity. We present a review of peritoneal structure and physiology, with a focus on the peritoneal inflammatory response to surgical injury and its clinical implications.

METHODS

We conducted a nonsystematic clinical review. A search of the Ovid MEDLINE database from 1950 through January 2009 was performed using the following search terms: peritoneum, adhesions, cytokine, inflammation, and surgery.

RESULTS

The peritoneum is a metabolically active organ, responding to insult through a complex array of immunologic and inflammatory cascades. This response increases with the duration and extent of injury and is central to the concept of surgical stress, manifesting via a combination of systemic effects, and local neural pathways via the neuro-immuno-humoral axis. There may be a decreased systemic inflammatory response after minimally invasive surgery; however, it is unclear whether this is due to a reduced local peritoneal reaction.

CONCLUSIONS

Interventions that dampen the peritoneal response and/or block the neuro-immuno-humoral pathway should be further investigated as possible avenues of enhancing recovery after surgery, and reducing postoperative complications.

Lymphocytes modulate peritoneal leukocyte recruitment in peritonitis

OBJECTIVE AND DESIGN

To investigate the modulating role of lymphocytes in leukocyte recruitment in a murine model of peritonitis.

MATERIALS OR SUBJECTS

RAG-1 knockout (KO) mice, NUDE mice and microMT KO mice were compared to their wild-type controls.

TREATMENT

Mice were administered with 1 ml of Brewer's thioglycollate (BTG) and terminal peritoneal lavages were performed at 8, 24, 72 and 120 h after treatment.

METHODS

Leukocyte numbers recruited at the different time points following a BTG administration were determined. Chemokine and cytokine levels were assessed by either ELISAs or cytometric bead array.

RESULTS

RAG-1 KO mice (absent B and T cells) exhibited increased early neutrophil infiltration and blunted late monocyte/macrophage infiltration. NUDE mice (absent T cells) exhibited both increased neutrophil and monocyte/macrophage infiltration. In contrast, microMT KO mice (absent B cells) demonstrated reduced influx of both neutrophils and monocyte/macrophages. Chemokine analysis revealed various differences in important chemokines.

CONCLUSIONS

These data suggest that T cells act to suppress leukocyte recruitment while B cells promote leukocyte recruitment.

Detrimental role of CC chemokine receptor 4 in murine polymicrobial sepsis

CC chemokine receptor 4 (CCR4) and its two ligands, CCL17 and CCL22, are critically involved in different immune processes. In models of lipopolysaccharide-induced shock, CCR4-deficient (CCR4(-/-)) mice showed improved survival rates associated with attenuated proinflammatory cytokine release. Using CCR4(-/-) mice with a C57BL/6 background, this study describes for the first time the role of CCR4 in a murine model of polymicrobial abdominal sepsis, the colon ascendens stent peritonitis (CASP). CASP-induced sepsis led to a massive downregulation of CCR4 in lymphoid and nonlymphoid tissues, whereas the expression of CCL17 and CCL22 was independent of the presence of CCR4. After CASP, CCR4(-/-) animals showed a strongly enhanced bacterial clearance in several organs but not in the peritoneal lavage fluid and the blood. In addition, significantly reduced levels of proinflammatory cytokines/chemokines were measured in organ supernatants as well as in the sera of CCR4(-/-) mice. CCR4 deficiency consequently resulted in an attenuated severity of systemic sepsis and a strongly improved survival rate after CASP or CASP with intervention. Thus, our data provide clear evidence that CCR4 plays a strictly detrimental role in the course of polymicrobial sepsis.