Subverting bradykinin-evoked inflammation by co-opting the contact system: lessons from survival strategies of Trypanosoma cruzi.

PURPOSE OF REVIEW: During Chagas disease, Trypanosoma cruzi alternates between intracellular and extracellular developmental forms. After presenting an overview about the roles of the contact system in immunity, I will review experimental studies showing that activation of the kallikrein-kinin system (KKS) translates into mutual benefits to the host/parasite relationship. RECENT FINDINGS: T. cruzi trypomastigotes initiate inflammation by activating tissue-resident innate sentinel cells via the TLR2/CXCR2 pathway. Following neutrophil-evoked microvascular leakage, the parasite's major cysteine protease (cruzipain) cleaves plasma-borne kininogens and complement C5. Tightly regulated by angiotensin-converting enzyme (ACE), kinins and C5a in turn further propagate inflammation via iterative cycles of mast cell degranulation, contact system activation, bradykinin release and activation of endothelial bradykinin B2 receptors (B2R). Recently, studies in the intracardiac model of infection revealed a dichotomic role for bradykinin and endothelin-1: generated upon contact activation (mast cell/KKS pathway), these pro-oedematogenic peptides reciprocally stimulate trypomastigote invasion of heart cells that naturally overexpress B2R and endothelin receptors (ETaR/ETbR). SUMMARY: Studies focusing on the immunopathogenesis of Chagas disease revealed that the contact system plays a dual role in host/parasite balance: T. cruzi co-opts bradykinin-induced plasma leakage as a strategy to increment heart parasitism and increase immune resistance by upregulating type-1 effector T-cell production in secondary lymphoid tissues.

Kinin receptors: Key regulators of autoimmunity.

The central function of the immune system is to protect the host from environmental agents such as microbes or chemicals, thereby preserving the integrity of the body, and preventing the onset of illness and infection. Moreover, the immune system is constantly challenged to discriminate self vs. non-self and mediate the correct response, a phenomenon called self-tolerance. The failure of mechanisms responsible for self-tolerance and induction of an immune response against components of the self, induces autoimmunity and culminates however, in several autoimmune diseases. The precise etiology of autoimmune diseases is not known, although the classic sign of an autoimmune disease is inflammation. In this context, kinins are a family of peptides involved in different physiological and pathological states, comprising inflammatory, vascular and pain processes, and are highly relevant as well as to a variety of diseases including hypertension, kidney diseases, Alzheimer's disease, cancer, obesity, epilepsy and traumatic injuries. These kinin effects are mediated by two related G-protein-coupled receptors named the bradykinin receptors (BKRs), B1 and B2. The kallikrein-kinin system (KKS) and their receptors appear to be involved in both the development and progression of autoimmune diseases, suggesting that modulators of BKRs, administered in monotherapy or in combination with existing therapies, may represent a potential new venue for an effective autoimmune disease treatment. This review article highlights historical and recent progress in understanding the role of BKRs as potential therapeutics for a number of autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, type I diabetes mellitus, inflammatory bowel diseases, and others.

Ischemia/reperfusion injury: effect of simultaneous inhibition of plasma cascade systems versus specific complement inhibition.

Ischemia/reperfusion injury (IRI) may occur from ischemia due to thrombotic occlusion, trauma or surgical interventions, including transplantation, with subsequent reestablishment of circulation. Time-dependent molecular and structural changes result from the deprivation of blood and oxygen in the affected tissue during ischemia. Upon restoration of blood flow a multifaceted network of plasma cascades is activated, including the complement-, coagulation-, kinin-, and fibrinolytic system, which plays a major role in the reperfusion-triggered inflammatory process. The plasma cascade systems are therefore promising therapeutic targets for attenuation of IRI. Earlier studies showed beneficial effects through inhibition of the complement system using specific complement inhibitors. However, pivotal roles in IRI are also attributed to other cascades. This raises the question, whether drugs, such as C1 esterase inhibitor, which regulate more than one cascade at a time, have a higher therapeutic potential. The present review discusses different therapeutic approaches ranging from specific complement inhibition to simultaneous inhibition of plasma cascade systems for reduction of IRI, gives an overview of the plasma cascade systems in IRI as well as highlights recent findings in this field.

MAPK/NF-κB-dependent upregulation of kinin receptors mediates airway hyperreactivity: a new perspective for the treatment.

Airway hyperreactivity (AHR) is a major feature of asthmatic and inflammatory airways. Cigarette smoke exposure, and bacterial and viral infections are well-known environmental risk factors for AHR, but knowledge about the underlying molecular mechanisms on how these risk factors lead to the development of AHR is limited. Activation of intracellular mitogen-activated protein kinase (MAPK)/nuclear factor-kappa B (NF-κB) and their related signal pathways including protein kinase C (PKC), phosphoinositide 3-kinase (PI3K) and protein kinase A (PKA) signaling pathways may result in airway kinin receptor upregulation, which is suggested to play an important role in the development of AHR. Environmental risk factors trigger the production of pro-inflammatory mediators such as tumor necrosis factor-α (TNF-α) and interleukins (ILs) that activate intracellular MAPK- and NF-κB-dependent inflammatory pathways, which subsequently lead to AHR via kinin receptor upregulation. Blockage of intracellular MAPK/NF-κB signaling prevents kinin B1 and B2 receptor expression in the airways, resulting in a decrease in the response to bradykinin (kinin B2 receptor agonist) and des-Arg9-bradykinin (kinin B1 receptor agonist). This suggests that MAPK- and NF-κB-dependent kinin receptor upregulation can provide a novel option for treatment of AHR in asthmatic as well as in other inflammatory airway diseases.

The procoagulant and proinflammatory plasma contact system.

The contact system is a plasma protease cascade that is initiated by coagulation factor XII activation on cardiovascular cells. The system starts procoagulant and proinflammatory reactions, via the intrinsic pathway of coagulation or the kallikrein-kinin system, respectively. The biochemistry of the contact system in vitro is well understood, however, its in vivo functions are just beginning to emerge. Data obtained in genetically engineered mice have revealed an essential function of the contact system for thrombus formation. Severe deficiency in contact system proteases impairs thrombus formation but does not reduce the hemostatic capacity of affected individuals. The system is activated by an inorganic polymer, polyphosphate that is released from activated platelets. Excessive inherited activation of the contact system causes a life-threatening swelling disorder, hereditary angioedema. Activation of the contact system by pathogens contributes to leakage in bacterial infections. Mast-cell-derived heparin triggers contact-system-mediated edema formation with implications for allergic disease states. Here we present an overview about the plasma contact system in occlusive and inflammatory disease and its contribution to health and pathology.

Kinins, airway obstruction, and anaphylaxis.

Anaphylaxis is a term that implies symptoms that are present in many organs, some of which are potentially fatal. The pathogenic process can either be IgE-dependent or non-IgE-dependent; the latter circumstance may be referred to as anaphylactoid. Bradykinin is frequently responsible for the manifestations of IgE-independent reactions. Blood levels may increase because of overproduction; diseases such as the various forms of C1 inhibitor deficiency (hereditary or acquired) or hereditary angioedema with normal C1 inhibitor are examples in this category. Blood levels may also increase because of an abnormality in bradykinin metabolism; the angioedema due to ACE inhibitors is a commonly encountered example. Angioedema due to bradykinin has the potential to cause airway obstruction and asphyxia as well as severe gastrointestinal symptoms simulating an acute abdomen. Formation of bradykinin in plasma is a result of a complex interaction among proteins such as factor XII, prekallikrein, and high molecular weight kininogen (HK) resulting in HK cleavage and liberation of bradykinin. These proteins also assemble along the surface of endothelial cells via zinc-dependent interactions with gC1qR, cytokeratin 1, and u-PAR. Endothelial cell expression (or secretion) of heat-shock protein 90 or prolylcarboxypeptidase can activate the prekallikrein-HK complex to generate bradykinin in the absence of factor XII, however factor XII is then secondarily activated by the kallikrein that results. Bradykinin is destroyed by carboxypeptidase N and angiotensin-converting enzyme. The hypotension associated with IgE-dependent anaphylaxis maybe mediated, in part, by massive proteolytic digestion of HK by kallikreins (tissue or plasma-derived) or other cell-derived kininogenases.

Angiotensin-converting enzyme limits inflammation elicited by Trypanosoma cruzi cysteine proteases: a peripheral mechanism regulating adaptive immunity via the innate kinin pathway.

Tissue injury by pathogens induces a stereotyped inflammatory response that alerts the innate immune system of the potential threat to host integrity. Here, we review knowledge emerging from investigations of the role of the kinin system in the mechanisms that link innate to the adaptive phase of immunity. Progress in this field started with results demonstrating that bradykinin is an endogenous danger signal that induces dendritic cell (DC) maturation via G protein-coupled bradykinin B2 receptors (B2R). The immunostimulatory role of kinins was recently confirmed in two different mouse models of Trypanosoma cruzi infection, a parasitic protozoan equipped with kinin-releasing cysteine proteases (cruzipain). Infection by the intraperitoneal route showed that DCs from B2R-/- mice (susceptible phenotype) failed to sense kinin 'danger' signals proteolytically released by parasites, explaining why these mutant mice display lower frequencies of interferon-gamma-producing effector T-cells. Studies of the dynamics of inflammation in the subcutaneous model of infection revealed that the balance between cruzipain and angiotensin-converting enzyme, respectively acting as kinin-generating and degrading enzymes, governs extent of DC maturation and TH1 development via the B2R-dependent innate pathway. Studies of the kinin role in immunity may shed light on the relationship between proteolytic networks and the cytokine circuits that guide T-cell development.

Bradykinin B2 Receptors of dendritic cells, acting as sensors of kinins proteolytically released by Trypanosoma cruzi, are critical for the development of protective type-1 responses.

Although the concept that dendritic cells (DCs) recognize pathogens through the engagement of Toll-like receptors is widely accepted, we recently suggested that immature DCs might sense kinin-releasing strains of Trypanosoma cruzi through the triggering of G-protein-coupled bradykinin B2 receptors (B2R). Here we report that C57BL/6.B2R-/- mice infected intraperitoneally with T. cruzi display higher parasitemia and mortality rates as compared to B2R+/+ mice. qRT-PCR revealed a 5-fold increase in T. cruzi DNA (14 d post-infection [p.i.]) in B2R-/- heart, while spleen parasitism was negligible in both mice strains. Analysis of recall responses (14 d p.i.) showed high and comparable frequencies of IFN-gamma-producing CD4+ and CD8+ T cells in the spleen of B2R-/- and wild-type mice. However, production of IFN-gamma by effector T cells isolated from B2R-/- heart was significantly reduced as compared with wild-type mice. As the infection continued, wild-type mice presented IFN-gamma-producing (CD4+CD44+ and CD8+CD44+) T cells both in the spleen and heart while B2R-/- mice showed negligible frequencies of such activated T cells. Furthermore, the collapse of type-1 immune responses in B2R-/- mice was linked to upregulated secretion of IL-17 and TNF-alpha by antigen-responsive CD4+ T cells. In vitro analysis of tissue culture trypomastigote interaction with splenic CD11c+ DCs indicated that DC maturation (IL-12, CD40, and CD86) is controlled by the kinin/B2R pathway. Further, systemic injection of trypomastigotes induced IL-12 production by CD11c+ DCs isolated from B2R+/+ spleen, but not by DCs from B2R-/- mice. Notably, adoptive transfer of B2R+/+ CD11c+ DCs (intravenously) into B2R-/- mice rendered them resistant to acute challenge, rescued development of type-1 immunity, and repressed TH17 responses. Collectively, our results demonstrate that activation of B2R, a DC sensor of endogenous maturation signals, is critically required for development of acquired resistance to T. cruzi infection.

A novel interpretation of immune redundancy and duality in reperfusion injury with important implications for intervention in ischaemic disease.

The majority of ischaemia related injury occurs upon tissue reperfusion. Knock-out mouse models have recently shed light on the underlying molecular mechanisms, and suggest that this may be the result of an innate autoimmune response. Based on these new findings we present a novel model of immune redundancy and duality in reperfusion injury. Natural antibody, mannan-binding lectin and toll-like receptor 4 are three pre-formed innate immune receptors that recognise pathogenic molecular patterns. Removing either significantly ameliorates reperfusion injury. We propose that these three receptors serve as key parallel recognition elements that respond to the same or similar ischaemic neo-antigens, of which at least one may have a lipopolysaccharide-like motif. This would fit both with the ligand preference of the three receptors, and the observation that giving monoclonal antibody to lipopolysaccharide reduces reperfusion injury. The consequent injury caused by receptor activation appears to be mainly related to the complement anaphylatoxins, and less to phagocytes, oxidative radicals, and the membrane attack complex. C5a levels in particular are predictive of overall injury, and we suggest this anaphylatoxin causes most of reperfusion injury via both direct toxic effects and a generalised immune activation. The former is illustrated by the recent observation that excess C5a alone can cause cardiac dysfunction. As for the latter, there is evidence that adaptive immunity (especially CD4+ cells) and other serum cascades (coagulation and kallikrein) are involved, and may have been recruited by complement. Furthermore, excess C5a can cause innate immune overactivation that paralyses neutrophils, reduces complement lytic function, and leads to systemic inflammation. This is analogous to what happens in sepsis, and would explain the passive role in IRI of normal immune effectors. Finally, there is a duality complement's function in reperfusion, as some elements are conductive of damage, whilst others may help inflammatory resolution. Most important among the latter are the opsonins, like C3b and apparently C1q, which help macrophages clear apoptosing cells before they undergo secondary necrosis. This model has important implications for clinical interventions. Firstly, redundancy means that inhibiting multiple receptors may achieve a larger mortality reduction than the small and inconsistent one seen in the published monotherapy trials. Secondly, duality means that a non-specific inhibition of complement would reduce both injury and resolution. Therefore, a specific inhibition of the lectin pathway and/or an inhibition of the downstream effectors upon which the receptors converge (e.g. C5a) seem to be a better interceptive strategy.

Review article: Acute serious and fatal reactions to contrast media: our current understanding.

Serious or fatal reactions to a contrast medium (CM) are unpredictable but fortunately rare. History of serious reaction to CM, bronchial asthma or multiple allergies increases the incidence of serious reactions by a factor of 5. Serious or fatal reaction to CM could be due to direct effect on basophils and mast cells or IgE mediated (type 1 hypersensitivity reaction). Activation of the kinin system leading to the formation of bradykinin could also be involved. Complement activation is unlikely to be a primary factor in initiating a serious reaction to CM. Avoiding CM administration in patients at high risk of serious reaction is advisable, but if the administration is deemed essential all precautions should be implemented and measures to treat serious reactions should be readily available. Oxygen supplementation, intravenous administration of physiological fluids and intramuscular injection of 0.5 ml adrenalin (1:1000) should be considered in the first line management of acute anaphylaxis. The ability to assess and treat serious CM reaction effectively is an essential skill that the radiologist should have and maintain.

Kinins are involved in the development of allergic nasal hyperresponsiveness in guinea pigs.

We evaluated roles of kinins in allergen-induced nasal blockage and sneezing, and development of nasal hyperresponsiveness to leukotriene D4 in a Japanese cedar pollen-induced allergic rhinitis model of guinea pigs. Sensitised guinea pigs were repeatedly challenged by pollen inhalation once every week. Neither a bradykinin B1 receptor antagonist, des-Arg9-[Leu8]bradykinin nor a bradykinin B2 receptor antagonist, icatibant suppressed allergen-induced sneezing and nasal blockage. However, development of nasal hyperresponsiveness to leukotriene D4 was significantly suppressed by them. The amount of bradykinin in nasal cavity lavage fluid was immediately increased after the challenge. In non-sensitised animals, hyperresponsiveness to leukotriene D4 was developed by a bradykinin B2 receptor agonist, bradykinin, but not by a bradykinin B1 receptor agonist, des-Arg10-kallidin, while in the sensitised-challenged animal, both agonists developed hyperresponsiveness. In conclusion, the nasal hyperresponsiveness appeared to be induced by kinins produced in response to the antigen challenge through activation of not only bradykinin B2 but also B1 receptors.

Kinins and kinin receptors: importance for the activation of leukocytes.

In this article, we analyzed the role of kinins and kinin receptors with respect to the activation of leukocytes. In these cells, the biological effects of kinin peptides are mediated by kinin receptor subtypes B1, B2, or both, depending on species and cell type. In contrast to the other leukocytes, neutrophils contain the complete system for the synthesis and release of bioactive kinins. Consequently, very high concentrations of these peptides can be reached in the close neighborhood of the kinin receptors, in particular at the site of inflammation. Kinins are responsible for many effects in leukocytes including the release of other inflammatory mediators, such as cytokines, prostaglandins, leukotrienes, and reactive oxygen species. Obviously, the potency of kinins to stimulate leukocytes is dependent on the differentiation and especially on the activation stage of these cells. An upregulation of kinin receptors on neutrophils and macrophages appears to be involved in increasing the sensitivity of these cells to kinins at the site of inflammation.

Salivary gland tissue kallikrein family and processing of growth factor precursors and proenzymes.

Four major enzymes of the tissue kallikrein family were purified from the mouse submandibular gland and characterized. The sequences indicated that they were mK1, mK9, mK13, and mK22. All four enzymes showed kinin-releasing activity, with mK1 exhibiting the highest activity. Like mK13, mK9 and mK22 also processed prorenin to give renin and/or arginyl renin, although their activities were less than that of mK13. The results suggest that tissue kallikrein family enzymes bearing higher kinin-releasing activity have lower prorenin-converting activity and vice versa. These enzymes may possibly have a physiological role in the tissue renin-angiotensin system.

Periapical inflammatory responses and their modulation.

Periapical inflammatory responses occur as a consequence of bacterial infection of the dental pulp, as a result of caries, trauma, or iatrogenic insult. Periapical inflammation stimulates the formation of granulomas and cysts, with the destruction of bone. These inflammatory responses are complex and consist of diverse elements. Immediate-type responses--including vasodilatation, increased vascular permeability, and leukocyte extravasation--are mediated by endogenous mediators, including prostanoids, kinins, and neuropeptides. Non-specific immune responses--including polymorphonuclear leukocyte and monocyte migration and activation, and cytokine production--are elicited in response to bacteria and their products. Interleukin-1 and prostaglandins in particular have been implicated as central mediators of periapical bone resorption. Chronic periapical inflammation further involves specific T- and B-cell-mediated anti-bacterial responses, and activates a network of regulatory cytokines which are produced by Th1- and Th2-type T-lymphocytes. Various naturally occurring and genetically engineered models of immunodeficiency are beginning to help elucidate those components of the immune system which protect the pulpal/periapical complex. Both specific and non-specific responses interface with and are regulated by the neural system. The modulation of these responses by immune response modifies, cytokine antagonists, and other novel therapeutic agents is discussed. As an experimental model, periapical inflammation has many advantages which permit it to be used in studies of microbial ecology and pathogenesis, host response, neuroimmunology, and bone resorption and regeneration.

Autoradiographic and immunological techniques to analyse kinin receptor distribution in rat and human tissues.

Kinins are vasoactive peptides that have traditionally been associated with vascular tone regulation. Nevertheless, the availability of adequate probes directed to kinin receptors has resulted in the identification of these proteins in organs and cells outside the cardiovascular system. The sensitivity, specificity and simplicity of the techniques developed to visualize kinin receptors have allowed the identification of the specific cells that express these receptors under physiological conditions and the investigation of the possible modifications that they may undergo during the onset and development of experimentally induced or diseased-related pathological conditions.

Plasma kinins increase after angiotensin-converting enzyme inhibition in human subjects.

1. In patients treated with angiotensin-converting enzyme inhibitors, kinin-related effects have been postulated repeatedly, but information on changes in plasma kinin levels in these patients is sparse. Difficulties in the measurement of plasma kinins account for this, at least in part. 2. The main purpose of the present study was to investigate, in normal human subjects, the effect of the angiotensin-converting enzyme inhibitor quinapril on plasma kinins. 3. High-affinity antisera (Kd < 10(-11) mol/l) of C-terminal specificity were raised in rabbits for radioimmunoassay of immunoreactive kinins activating the bradykinin B2-receptor, and three different liquid- and solid-phase extraction methods for plasma kinins were evaluated. Ethanol and subsequent petroleum ether extraction of 5-40 fmol of bradykinin added to plasma yielded recoveries of 39 +/- 16% (mean +/- SD); normal kinin levels in human plasma were 18.6 +/- 3.3 pmol/l (mean +/- SEM). Solid-phase extraction on urea-equilibrated phenylsilylsilica produced recoveries of 89 +/- 5% and normal values of 36.4 +/- 18 pmol/l. Finally, with an assay based on ethanol extraction alone, recoveries of 100 +/- 16% and normal values of 16.8 +/- 5.8 pmol/l were obtained, with a detection limit of 1.5 fmol/ml of plasma. Blanks were below the detection limit. Serial dilution of plasma extracts (n = 4) provided linear kinin concentrations (r = 0.99). For two different plasma pools, coefficients of variation for within-assay precision were 16.7% and 21.7%, respectively. Between-assay coefficients of variation were 12.8% and 17.4%.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoclonal ligand binding site related anti-idiotypic antibodies elicited with a polyclonal kinin antibody.

Splenocytes from mice immunized with homogenous, polyclonal, rabbit kinin antibody (BK21) were fused using polyethylene glycol with the mouse myeloma cell line SP2/o. Eleven monoclonal antibodies, whose binding to BK21 could be inhibited by bradykinin, were obtained from 3 fusions. All of these anti-idiotypic antibodies were of the IgG1k isotype, except for one, which was an IgG2ak. An IgMk, auto-anti-idiotypic antibody, reactive with BK21 was obtained from a fusion of SP2/o cells and splenocytes from a mouse immunized with bradykinin conjugated with carbodiimide to keyhole limpet hemocyanin. Bradykinin could completely inhibit the binding of all of the anti-idiotypic antibodies to BK21 in an enzyme-linked immunosorbent assay. This result is consistent with the anti-idiotypic antibodies being reactive with the ligand binding sites of BK21. It was possible to separate the anti-idiotypic antibodies into 2 groups. The first group, 10 of the 12 antibodies tested, was more sensitive to inhibition by bradykinin than the second group and was not readily inhibited by des-Arg9-bradykinin. The second group was about 7 times more sensitive to inhibition by des-Arg9-bradykinin than by bradykinin. Further experiments will be needed to determine whether or not these monoclonal anti-idiotypic antibodies are "internal image" antibodies.

Allergic and inflammatory aspects of chronic rhinosinusitis.

The pathophysiology of rhinosinusitis is complex and poorly understood. Although it is recognized that obstruction of the sinus ostia which is surgically correctable contributes to recurrent bacterial sinusitis, allergic and nonallergic inflammation may contribute to or mimic infectious rhinosinusitis. Those aspects of rhinosinusitis which are not necessarily surgically correctable require consideration and may affect surgical prognosis. This article focuses on those considerations.