Urokinase-type plasminogen activator is required for the generation of a type 1 immune response to pulmonary Cryptococcus neoformans infection

Immunomodulatory responses of differentially polarized macrophages to fungal infections

Macrophages, the first line of defense against invasive fungi in the innate immune system, are widely distributed in the blood and tissues of the body. In response to various internal and external stimulators, macrophages can polarize into classically activated macrophages (M1) and alternatively activated macrophages (M2). These two types of polarized macrophages play different roles in antifungal activity and in maintaining the steady-state balance between inflammation and tissue repair. However, the antifungal mechanisms of M1- and M2-type macrophages have not been fully described. In this review, the immune regulatory mechanisms against pathogenic fungi of these two classical types of macrophages in various tissues are summarized. The effects of antifungal factors on macrophage differentiation are also highlighted. The description of these data, on the one hand provides valuable insight for future investigations and also highlights new strategies for the treatment of pathogenic fungal infections.

Preoperative Levels of the Soluble Urokinase-Type Plasminogen Activator Receptor as Predictor for New Episodes of Atrial Fibrillation After Vascular Surgery

INTRODUCTION

The soluble urokinase-type plasminogen activator receptor (suPAR) in uPAR soluble form is produced when the uPAR is cleaved from the cell membrane during the inflammatory process. Postoperative atrial fibrillation (AF) is the most common perioperative cardiac arrhythmia. It is speculated that elevated suPAR has a role in the development of AF. The aim of our study was to investigate the predictive role of preoperative suPAR in the occurrence of AF during the first 6 months after major vascular surgery.

METHODS

We included 119 male and 63 female patients with an average age of 67.19 ± 6.02 years, without permanent/persistent AF. Basic predictive model (BASIC) included traditional risk factors for AF: age, gender, body mass index-BMI, smoking status, presence of arterial hypertension, diabetes mellitus and dyslipidemia.

RESULTS

Over the 6-month period, 19 (10.4%) patients had one new episode of atrial fibrillation and 2 patients (1.1%) had 2 episodes of paroxysmal atrial fibrillation. Paroxysms of AF were significantly more frequent in patients who had a resection of an abdominal aneurysm than in patients with other types of major vascular surgery. BASIC had good discriminatory ability in the prediction of AF paroxysms during the first 6 months after surgery (AUC = 0.715, 95%CI 0.590-0.840). Adding suPAR to the basic model significantly improved the discriminative ability of the predictive model for AF episodes (ΔAUC = 0.238, p < 0.001). The predictive performance of the model BASIC+CRP+suPAR, measured using AUC, NRI and IDI statistics, was very similar to the model BASIC+suPAR.

CONCLUSION

AF is a common complication in surgical patients with high mortality and morbidity. suPAR could improve the ability of traditional risk factors to predict its occurrence up to 6 months after major vascular surgery.

Gingival Crevicular Fluid Zinc- and Aspartyl-Binding Protease Profile of Individuals with Moderate/Severe Atopic Dermatitis

Atopic dermatitis (AD) is a protease-modulated chronic disorder with heterogenous clinical manifestations which may lead to an imprecise diagnosis. To date, there are no diagnostic protease tests for AD. We explored the gingival crevicular fluid (GCF) protease profile of individuals with moderate/severe AD compared to healthy controls. An exploratory case-control study was conducted. AD patients (n = 23) and controls (n = 21) were enrolled at the International Center for Clinical Studies, Santiago, Chile. Complete dermatological and periodontal evaluations (involving the collection of GCF samples) were made. The levels of 35 proteases were analyzed using a human protease antibody array in matching AD patients (n = 6) and controls (n = 6) with healthy periodontium. The GCF levels of zinc-binding ADAM8, ADAM9, MMP8, Neprilysin/CD10, aspartyl-binding Cathepsin E, serin-binding Protein convertase9, and uPA/Urokinase proteases were lower in moderate/severe AD patients compared to controls (p < 0.05). No inter-group differences in the levels of the other 28 proteases were found. MMP8, Cathepsin E, and ADAM9 were the biomarkers with the highest sensitivity and specificity regarding the detection of AD (p < 0.05). The area under receiver operating characteristic (ROC) curve for MMP8 was 0.83 and MMP8 + ADAMP9 was 0.90, with no significant differences (p = 0.132). A combined model of MMP8, Cathepsin E, and ADAM9 was not considered since it did not converge. Then, levels of MMP8 in GCF were determined using a multiplex bead immunoassay in 23 subjects with AD and 21 healthy subjects. Lower levels of MMP8 in the GCF from the AD group versus healthy group (p = 0.029) were found. This difference remained significant after adjustment by periodontitis (p = 0.042). MMP8 revealed the diagnostic potential to identify AD patients versus healthy controls, (ROC area = 0.672, p < 0.05). In conclusion, differences in the protease profile between AD and control patients were associated with MMP8, Cathepsin E, and ADAM9. Based on the multiplex assay results, MMP8 was lower in AD patients than controls, suggesting that MMP8 may be a diagnostic biomarker candidate.

Multifaceted Role of the Urokinase-Type Plasminogen Activator (uPA) and Its Receptor (uPAR): Diagnostic, Prognostic, and Therapeutic Applications

The plasminogen activator (PA) system is an extracellular proteolytic enzyme system associated with various physiological and pathophysiological processes. A large body of evidence support that among the various components of the PA system, urokinase-type plasminogen activator (uPA), its receptor (uPAR), and plasminogen activator inhibitor-1 and -2 (PAI-1 and PAI-2) play a major role in tumor progression and metastasis. The binding of uPA with uPAR is instrumental for the activation of plasminogen to plasmin, which in turn initiates a series of proteolytic cascade to degrade the components of the extracellular matrix, and thereby, cause tumor cell migration from the primary site of origin to a distant secondary organ. The components of the PA system show altered expression patterns in several common malignancies, which have identified them as ideal diagnostic, prognostic, and therapeutic targets to reduce cancer-associated morbidity and mortality. This review summarizes the various components of the PA system and focuses on the role of uPA-uPAR in different biological processes especially in the context of malignancy. We also discuss the current state of knowledge of uPA-uPAR-targeted diagnostic and therapeutic strategies for various malignancies.

The urokinase-type plasminogen activator system and its role in tumor progression

In the multistage process of carcinogenesis, the key link in the growth and progression of the tumor is the invasion of malignant cells into normal tissue and their distribution and the degree of destruction of tissues. The most important role in the development of these processes is played by the system of urokinase-type plasminogen activator (uPA system), which consists of several components: serine proteinase – uPA, its receptor – uPAR and its two endogenous inhibitors – PAI-1 and PAI-2. The components of the uPA system are expressed by cancer cells to a greater extent than normal tissue cells. uPA converts plasminogen into broad spectrum, polyfunctional protease plasmin, which, in addition to the regulation of fibrinolysis, can hydrolyze a number of components of the connective tissue matrix (СTM), as well as activate the zymogens of secreted matrix metalloproteinases (MMР) – pro-MMР. MMРs together can hydrolyze all the main components of the СTM, and thus play a key role in the development of invasive processes, as well as to perform regulatory functions by activating and releasing from STM a number of biologically active molecules that are involved in the regulation of the main processes of carcinogenesis. The uPA system promotes tumor progression not only through the proteolytic cascade, but also through uPAR, PAI-1 and PAI-2, which are involved in both the regulation of uPA/uPAR activity and are involved in proliferation, apoptosis, chemotaxis, adhesion, migration and activation of epithelial-mesenchymal transition pathways. All of the above processes are aimed at regulating invasion, metastasis and angiogenesis. The components of the uPA system are used as prognostic and diagnostic markers of many cancers, as well as serve as targets for anticancer therapy.

Adaptive Immunity to Cryptococcus neoformans Infections

The Cryptococcus neoformans/Cryptococcus gattii species complex is a group of fungal pathogens with different phenotypic and genotypic diversity that cause disease in immunocompromised patients as well as in healthy individuals. The immune response resulting from the interaction between Cryptococcus and the host immune system is a key determinant of the disease outcome. The species C. neoformans causes the majority of human infections, and therefore almost all immunological studies focused on C. neoformans infections. Thus, this review presents current understanding on the role of adaptive immunity during C. neoformans infections both in humans and in animal models of disease.

Urokinase plasminogen activator and receptor promote collagen-induced arthritis through expression in hematopoietic cells

The plasminogen activation (PA) system has been implicated in driving inflammatory arthritis, but the precise contribution of PA system components to arthritis pathogenesis remains poorly defined. Here, the role of urokinase plasminogen activator (uPA) and its cognate receptor (uPAR) in the development and severity of inflammatory joint disease was determined using uPA- and uPAR-deficient mice inbred to the strain DBA/1J, a genetic background highly susceptible to collagen-induced arthritis (CIA). Mice deficient in uPA displayed a near-complete amelioration of macroscopic and histological inflammatory joint disease following CIA challenge. Similarly, CIA-challenged uPAR-deficient mice exhibited significant amelioration of arthritis incidence and severity. Reduced disease development in uPA-deficient and uPAR-deficient mice was not due to an altered adaptive immune response to the CIA challenge. Reciprocal bone marrow transplant studies indicated that uPAR-driven CIA was due to expression by hematopoietic-derived cells, as mice with uPAR-deficient bone marrow challenged with CIA developed significantly reduced macroscopic and histological joint disease as compared with mice with uPAR expression limited to non-hematopoietic-derived cells. These findings indicate a fundamental role for uPAR-expressing hematopoietic cells in driving arthritis incidence and progression. Thus, uPA/uPAR-mediated cell surface proteolysis and/or uPAR-mediated signaling events promote inflammatory joint disease, indicating that disruption of this key proteolytic/signaling system may provide a novel therapeutic strategy to limit clinical arthritis.

Serum Soluble Urokinase-Type Plasminogen Activator Receptor Is Associated with Low Left Ventricular Ejection Fraction and Elevated Plasma Brain-Type Natriuretic Peptide Level

BACKGROUND

Recent studies have suggested that soluble urokinase plasminogen activator receptor (suPAR), a biomarker of subclinical levels of inflammation, is significantly correlated with cardiovascular events.

PURPOSE

We investigated the association between suPAR and left ventricular ejection fraction (LVEF), left ventricular mass index (LVMI), and plasma B-type natriuretic peptide (BNP) among cardiac inpatients.

METHODS AND RESULTS

In total, 242 patients (mean age 71.3 ± 9.8 years; 70 women) admitted to the cardiology department were enrolled in the study. suPAR was significantly correlated with LVEF (R = -0.24, P<0.001), LVMI (R = 0.16, P = 0.014) and BNP (R = 0.46, P<0.001). In logistic regression analysis, the highest suPAR tertile (> 3236 pg/mL) was associated with low LVEF (< 50%) and elevated BNP (> 300 pg/mL) with an odds ratio of 3.84 (95% confidence interval [CI], 1.22-12.1) and 5.36 (95% CI, 1.32-21.8), respectively, after adjusting for age, sex, log-transformed estimated glomerular filtration rate (log(eGFR)), C-reactive protein, and diuretic use. The association between suPAR and LVMI was not statistically significant. In multivariate receiver operating characteristic analysis, addition of log(suPAR) to the combination of age, sex, log(eGFR) and CRP incrementally improved the prediction of low LVEF (area under the curve [AUC], 0.827 to 0.852, P = 0.046) and BNP ≥ 300 pg/mL (AUC, 0.869 to 0.906; P = 0.029).

CONCLUSIONS

suPAR was associated with low LVEF and elevated BNP, but not with left ventricular hypertrophy, independent of CRP, renal function, and diuretic use among cardiac inpatients who were not undergoing chronic hemodialysis.

Regulation of epithelial sodium channels in urokinase plasminogen activator deficiency

Epithelial sodium channels (ENaC) govern transepithelial salt and fluid homeostasis. ENaC contributes to polarization, apoptosis, epithelial-mesenchymal transformation, etc. Fibrinolytic proteases play a crucial role in virtually all of these processes and are elaborated by the airway epithelium. We hypothesized that urokinase-like plasminogen activator (uPA) regulates ENaC function in airway epithelial cells and tested that possibility in primary murine tracheal epithelial cells (MTE). Both basal and cAMP-activated Na(+) flow through ENaC were significantly reduced in monolayers of uPA-deficient cells. The reduction in ENaC activity was further confirmed in basolateral membrane-permeabilized cells. A decrease in the Na(+)-K(+)-ATPase activity in the basolateral membrane could contribute to the attenuation of ENaC function in intact monolayer cells. Dysfunctional fluid resolution was seen in uPA-disrupted cells. Administration of uPA and plasmin partially restores ENaC activity and fluid reabsorption by MTEs. ERK1/2, but not Akt, phosphorylation was observed in the cells and lungs of uPA-deficient mice. On the other hand, cleavage of γ ENaC is significantly depressed in the lungs of uPA knockout mice vs. those of wild-type controls. Expression of caspase 8, however, did not differ between wild-type and uPA(-/-) mice. In addition, uPA deficiency did not alter transepithelial resistance. Taken together, the mechanisms for the regulation of ENaC by uPA in MTEs include augmentation of Na(+)-K(+)-ATPase, proteolysis, and restriction of ERK1/2 phosphorylation. We demonstrate for the first time that ENaC may serve as a downstream signaling target by which uPA controls the biophysical profiles of airway fluid and epithelial function.

SerpinB2 mediated regulation of macrophage function during enteric infection

Host defense is an orchestrated response involving changes in the expression of receptors and release of mediators from both immune and structural cells. There is a growing recognition of the important role of proteolytic pathways for the protective immune response to enteric pathogens. Enteric nematode infection induces a type 2 immune response with polarization of macrophages toward the alternatively activated phenotype (M2). The Th2 cytokines, IL-4, and IL-13, induce a STAT6-dependent upregulation of the expression of the protease inhibitor, serpinB2, which protects macrophages from apoptosis. M2 are critical to worm clearance and a novel role for serpinB2 is its regulation of the chemokine, CCL2, which is necessary for monocyte and/or macrophage influx into small intestine during infection. There is a growing list of factors including immune (LPS, Th2 cytokines) as well as hormonal (gastrin, 5-HT) that are linked to increased expression of serpinB2. Thus, serpinB2 represents an immune regulated factor that has multiple roles in the intestinal mucosa.

The plasminogen activator system: involvement in central nervous system inflammation and a potential site for therapeutic intervention

Background

Extracellular proteases such as plasminogen activators (PAs) and matrix metalloproteinases modulate cell-cell and cell-matrix interactions. Components of the PA/plasmin system have been shown to be increased in areas of inflammation, and have been suggested to play a role in inflammatory neurologic disorders such as epilepsy, stroke, brain trauma, Alzheimer's' disease and multiple sclerosis (MS). In the present study, we evaluated the involvement of the PA system in the animal model of MS, experimental autoimmune encephalomyelitis (EAE).

Methods

EAE was induced by myelin oligodendrocyte glycoprotein (MOG) in mice deficient for the urokinase PA (uPA^−/−), or the urokinase PA receptor (uPAR^−/−). Mice were evaluated for EAE clinical signs and histopathologic parameters, and compared with wild-type (WT) EAE mice. Lymphocytes from the knockout (KO) and WT mice were analyzed for ex vivo restimulation, cytokine secretion, and antigen presentation. Finally, WT EAE mice were treated with PAI-1dp, an 18 amino acid peptide derived from the PA inhibitor protein (PAI-1).

Results

EAE was aggravated in uPA^−/− and uPAR^−/− mice, and this was accompanied by more severe histopathologic features and microglial activation. By contrast, specific T- cell reactivity towards the encephalitogenic antigen MOG was markedly reduced in the KO animals, as shown by a marked reduction in proliferation and pro-inflammatory cytokine secretion in these mice. Antigen presentation was also reduced in all the KO animals, raising an immunologic paradox. When the mice were treated with PAI-1, a peptide derived from the PA system, a marked and significant improvement in EAE was seen. The clinical improvement was linked to reduced T-cell reactivity, further emphasizing the importance of the PA system in immunomodulation during neuroinflammation.

Conclusions

Cumulatively, our results suggest a role for uPA and uPAR in EAE pathogenesis, as exacerbation of disease was seen in their absence. Furthermore, the successful amelioration of EAE by PAI-1 treatment suggests that the PA system can be considered a potential site for therapeutic intervention in the treatment of neuroimmune diseases.

Urokinase plasminogen activator induces pro-fibrotic/m2 phenotype in murine cardiac macrophages

Objective

Inflammation and fibrosis are intertwined in multiple disease processes. We have previously found that over-expression of urokinase plasminogen activator in macrophages induces spontaneous macrophage accumulation and fibrosis specific to the heart in mice. Understanding the relationship between inflammation and fibrosis in the heart is critical to developing therapies for diverse myocardial diseases. Therefore, we sought to determine if uPA induces changes in macrophage function that promote cardiac collagen accumulation.

Methods and Results

We analyzed the effect of the uPA transgene on expression of pro-inflammatory (M1) and pro-fibrotic (M2) genes and proteins in hearts and isolated macrophages of uPA overexpressing mice. We found that although there was elevation of the pro-inflammatory cytokine IL-6 in hearts of transgenic mice, IL-6 is not a major effector of uPA induced cardiac fibrosis. However, uPA expressing bone marrow-derived macrophages are polarized to express M2 genes in response to IL-4 stimulation, and these M2 genes are upregulated in uPA expressing macrophages following migration to the heart. In addition, while uPA expressing macrophages express a transcriptional profile that is seen in tumor–associated macrophages, these macrophages promote collagen expression in cardiac but not embryonic fibroblasts.

Conclusions

Urokinase plasminogen activator induces an M2/profibrotic phenotype in macrophages that is fully expressed after migration of macrophages into the heart. Understanding the mechanisms by which uPA modulates macrophage function may reveal insights into diverse pathologic processes.

Levels of components of the urokinase-type plasminogen activator system are related to chronic obstructive pulmonary disease parenchymal destruction and airway remodelling

OBJECTIVE

Retrospective study to investigate levels of components of the urokinase-type plasminogen activator (uPA) system in patients with chronic obstructive pulmonary disease (COPD).

METHODS

Peripheral lung tissue was obtained from patients who underwent surgical resection for benign lung diseases: 16 patients with COPD, 10 controls without lung function impairment who were smokers, and 10 controls without lung function impairment who were nonsmokers. Immunohistochemical staining for uPA, uPA receptor (uPAR) and plasminogen activator inhibitor-1 (PAI-1) was quantified. Airway remodelling (collagen; detected by Sirius red staining), lung function (determined by spirometry) and emphysema (alveolar destruction; percentage of low attenuation areas on computed tomography scan) were evaluated.

RESULTS

uPA, uPAR and PAI-1 were significantly different in structural lung cells and pulmonary macrophages from patients with COPD compared with controls. There were significant positive correlations between collagen levels and uPA and PAI-1, and between uPA and degree of emphysema. There were significant inverse correlations between lung function and uPA, uPAR and PAI-1.

CONCLUSION

Correlations between components of the uPA system and lung function, small airway fibrosis and emphysema indicate a role for the uPA system in COPD.

Induction of brain microvascular endothelial cell urokinase expression by Cryptococcus neoformans facilitates blood-brain barrier invasion

The invasive ability of the blood-borne fungal pathogen Cryptococcus neoformans can be enhanced through interactions with host plasma components, such as plasminogen. Previously we showed by in vitro studies that plasminogen coats the surface of C. neoformans and is converted to the active serine protease, plasmin, by host plasminogen activators. Viable, but not formaldehyde- or sodium azide-killed, cryptococcal strains undergo brain microvascular endothelial cell-dependent plasminogen-to-plasmin activation, which results in enhanced, plasmin-dependent cryptococcal invasion of primary bovine brain microvascular endothelial cells and fungal ability to degrade plasmin substrates. In the present work, brain microvascular endothelial cells cultured with viable, but not killed, cryptococcal strains led to significant increases in both urokinase mRNA transcription and cell-associated urokinase protein expression. Soluble urokinase was also detected in conditioned medium from brain microvascular endothelial cells cultured with viable, but not killed, C. neoformans. Exposure of plasminogen pre-coated viable C. neoformans to conditioned medium from strain-matched brain microvascular endothelial cell-fungal co-cultures resulted in plasminogen-to-plasmin activation and plasmin-dependent cryptococcal invasion. siRNA-mediated silencing of urokinase gene expression or the use of specific inhibitors of urokinase activity abrogated both plasminogen-to-plasmin activation on C. neoformans and cryptococcal-brain microvascular endothelial cell invasion. Our results suggest that pathogen exploitation of the host urokinase-plasmin(ogen) system may contribute to C. neoformans virulence during invasive cryptococcosis.

The Expression of Fibrinolytic Components in Chronic Paranasal Sinus Disease

Background

Fibrinolytic components, their receptors, and inhibitors are considered to play an important role in inflammation and tissue remodeling including chronic rhinosinusitis (CRS). To clarify the relationship between these components and the pathology of CRS, we analyzed fibrinolytic components in sinonasal mucosa of CRS.

Methods

Sinonasal mucosa samples from 12 patients with CRS without nasal polyp (CRSsNP), 14 patients with CRS with nasal polyp (CRSwNP), and 12 control patients were prepared. By immunohistochemistry and ELISA, samples were studied with respect to urokinase-type plasminogen activator (uPA), uPA receptor (uPAR), plasminogen activator inhibitor-1 (PAI-1) and key mediators in sinus disease, TGF-beta1 and eosinophil cationic protein (ECP).

Results

uPA- or uPAR-positive inflammatory cells were increased in CRSwNP compared to controls and CRSsNP, whereas PAI-1-positive cells were increased in CRSsNP compared to CRSwNP and controls. ELISA measurements revealed that uPAR concentrations were increased in both CRSsNP (16.1 ng/mL; 10.4–22.9; p < 0.05) and CRSwNP (20.8 ng/mL; 9.62–25.9; p < 0.01) compared to controls (8.7 ng/mL; 7.9–12.9), and PAI-1 concentrations were increased in CRSsNP (198.8 ng/mL; 147.4–234.1) compared to controls (107.3 ng/mL; 92.6–175.3; p < 0.01) and CRSwNP (113.5 ng/mL; 105.1–193.5; p < 0.05). Moreover, the concentrations of TGF-beta1 correlated with PAI-1 in CRSsNP, and ECP correlated with uPAR protein in CRSwNP.

Conclusion

Fibrinolytic components were highly expressed in CRSwNP compared to normal controls, whereas the inhibiting protein was up-regulated in CRSsNP. Furthermore, correlations between the expressions of fibrinolytic components and key mediators in CRS were found.

Urokinase-type plasminogen activator system and human cationic antimicrobial protein 18 in serum and induced sputum of patients with chronic obstructive pulmonary disease

BACKGROUND AND OBJECTIVE

There is increasing evidence that the innate immune system plays an important role in the pathogenesis of COPD. The objective of this study was to quantify several innate immune biomarkers in serum and induced sputum of COPD patients, and healthy non-smokers and smokers.

METHODS

Serum and induced sputum levels of urokinase-type plasminogen activator (uPA), urokinase-type plasminogen activator receptor (uPAR), urokinase-type plasminogen activator inhibitor (PAI-1) and human cationic antimicrobial protein 18 (CAP18) were measured by ELISA, in 13 patients with stage I or stage II COPD (COPD I + II), 15 patients with stage III or stage IV COPD (COPD III + IV), 18 healthy non-smokers and 14 healthy smokers. In addition, membrane-bound uPAR in peripheral blood and induced sputum was assessed by flow cytometry.

RESULTS

Levels of uPAR, PAI-1 and CAP18 were elevated in induced sputum of COPD I + II and COPD III + IV patients, compared with healthy non-smokers (P < 0.05) and healthy smokers (P < 0.05). uPAR, PAI-1 and CAP18 levels were significantly higher in COPD III + IV patients compared with COPD I + II patients (P < 0.05). The expression of uPAR on induced sputum neutrophils and macrophages was significantly higher in COPD patients compared with healthy non-smokers (P < 0.05) and healthy smokers (P < 0.05). Sputum uPAR and CAP18 levels showed significant inverse correlations with FEV(1)% and 6MWD, and significant positive correlations with St. George's Respiratory Questionnaire scores.

CONCLUSIONS

In COPD patients, increased induced sputum levels of uPAR, PAI-1 and CAP18 were associated with airflow limitation, health status and exercise tolerance, suggesting that these biomarkers may be implicated in the pathogenesis of COPD.

Plasminogen activator inhibitor-1 and asthma: role in the pathogenesis and molecular regulation

Plasminogen activator inhibitor (PAI)-1 is a major inhibitor of the fibrinolytic system. PAI-1 levels are markedly increased in asthmatic airways, and mast cells (MCs), a pivotal cell type in the pathogenesis of asthma, are one of the main sources of PAI-1 production. Recent studies suggest that PAI-1 may promote the development of asthma by regulating airway remodelling, airway hyperresponsiveness (AHR), and allergic inflammation. The single guanosine nucleotide deletion/insertion polymorphism (4G/5G) at -675 bp of the PAI-1 gene is the major genetic determinant of PAI-1 expression. Plasma PAI-1 level is higher in people with the 4G/4G genotype than in those with the 5G/5G genotype. A strong association between the 4G/5G polymorphism and the risk and the severity of asthma has been suggested. Levels of plasma IgE and PAI-1 and severity of AHR are greater in asthmatic patients with the 4G/4G genotype than in those with the 5G/5G genotype. The PAI-1 promoter with the 4G allele renders higher transcription activity than the PAI-1 promoter with the 5G allele in stimulated MCs. The molecular mechanism for the 4G allele-mediated higher PAI-1 expression is associated with greater binding of upstream stimulatory factor-1 to the E-box adjacent to the 4G site (E-4G) than to the E-5G. In summary, PAI-1 may play an important role in the pathogenesis of asthma. Further studies evaluating the mechanisms of PAI-1 action and regulation may lead to the development of a novel prognostic factor and therapeutic target for the treatment and prevention of asthma and other PAI-1-associated diseases.

Enhanced levels of urokinase plasminogen activator and its soluble receptor in common variable immunodeficiency

Common variable immunodeficiency (CVID) is a heterogeneous syndrome characterized by defective immunoglobulin production and high frequency of bacterial infections, autoimmunity and manifestations of chronic inflammation. The urokinase plasminogen activator (uPA), its cell bound and soluble receptor (uPAR, suPAR) have complex biological functions involving innate immune defense mechanisms and regulation of inflammation. Based on this dual role, we hypothesized that the uPA system could be affected in CVID, and examined expression of components of the uPA system in subgroups of CVID. All CVID-patients had increased plasma levels of suPAR with particularly high levels in those with splenomegaly and thrombocytopenia. Plasma uPA levels were also raised in these patients, and both suPAR and uPA levels correlated with the monocyte activation marker neopterin. Monocytes from CVID patients had increased expression of uPAR. We show an increased activation of the uPA system possibly contributing to the inflammatory phenotype seen in subgroups of CVID patients.

Hyperexpression of NOD2 in intestinal mast cells of Crohn's disease patients: preferential expression of inflammatory cell-recruiting molecules via NOD2 in mast cells

NOD2, an intracellular sensor of bacteria-derived muramyl dipeptide (MDP) has been implicated as a key player in intestinal immune health and disease. Mast cells (MCs) have been reported to be increased in the gut of patients with inflammatory bowel disease. However, NOD2 expression and its role in human primary MCs are unknown. The number of NOD2(+) intestinal MCs was significantly increased in the Crohn's disease (CD) specimens compared to Ulcerative colitis (UC) specimens and controls. IFN-gamma upregulated NOD2 expression in MCs. CXCL10 and urokinase-type plasminogen activator (uPA) upregulation was specific to MCs activated by MDP compared to MCs activated by LPS and IgE/anti-IgE. MDP-induced upregulation of ICAM-1, VCAM-1, and uPA was specific to MCs compared to mononuclear cells. The number of CXCL10(+)NOD2(+) intestinal MCs was significantly increased in the CD patients. Our results suggest that NOD2(+) MCs have specific pathogenic roles that involve the recruitment of inflammatory cells in CD.

Role of Fibrinolysis in the Nasal System

In this chapter, we show the presence of tissue-type plasminogen activator (t-PA), urokinase-type plasminogen activator (u-PA), and plasminogen activator inhibitor-1 (PAI-1) in nasal mucosa. It is suggested that t-PA synthesized in mucous cells is promptly secreted and modifies the watery nasal discharge in allergic rhinitis and that u-PA activity may help with the passage of large amounts of rhinorrhea by reducing its viscosity. Furthermore, we clarify the relation between fibrinolytic components and the pathology of allergy, particularly during the development of nasal allergy and nasal tissue changes. Wild-type (WT) mice can develop nasal allergy for ovalbumin (OVA) sensitization, but PAI-1-deficient mice (PAI-1^-/-) cannot. The production of specific immunoglobulins IgG1 and IgE in the serum and production of interleukins IL-4 and IL-5 in splenocyte culture supernatant increased significantly in WT-OVA mice. In PAI-1^-/- mice, these reactions were absent, and specific IgG2a in serum and interferon-γ in splenocyte culture medium increased significantly. Histopathologically, there was marked goblet cell hyperplasia and eosinophil infiltration into the nasal mucosa in WT-OVA mice, but these were absent in PAI-1^-/- mice. These results indicate that the immune response in WT-OVA mice can be classified as a dominant Th2 response, which would promote collagen deposition. In contrast, the Th2 response in PAI-1^-/- mice was down-regulated and the immune response shifted from Th2-dominant reaction to a Th1-dominant one. Taken together, these findings suggest that PAI-1 plays an important role not only in thrombolysis but also in the immune response.

Tobacco smoke induces urokinase-type plasminogen activator and cell invasiveness: evidence for an epidermal growth factor receptor dependent mechanism

Multiple tobacco smoke-related premalignant and malignant lesions develop synchronously or metachronously in various organ sites, including the oral cavity. Both field cancerization and clonal migration seem to contribute to the occurrence of multiple tumors. Although the importance of endogenous factors (e.g., oncogenes) in regulating clonal migration is well established, little is known about the role of exogenous factors. Hence, the main objective of this study was to elucidate the mechanism by which tobacco smoke stimulated the migration of cells through extracellular matrix (ECM). Treatment of MSK-Leuk1 cells with a saline extract of tobacco smoke induced the migration of cells through ECM. Tobacco smoke induced the expression of urokinase-type plasminogen activator (uPA), resulting in plasmin-dependent degradation of ECM and increased cell migration. AG1478, a small-molecule inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase, a neutralizing antibody to EGFR, or an antibody to amphiregulin, an EGFR ligand, also blocked tobacco smoke-mediated induction of uPA and cell migration through ECM. PD98059, an inhibitor of mitogen-activated protein kinase (MAPK) kinase activity, caused similar inhibitory effects. Taken together, these results suggest that tobacco smoke activated the EGFR-->extracellular signal-regulated kinase 1/2 MAPK pathway, causing induction of uPA. This led, in turn, to increased plasmin-dependent degradation of matrix proteins and enhanced cell migration through ECM. These data strongly suggest that chemicals in tobacco smoke can mimic the effects of oncogenes in regulating uPA-dependent cell invasion through ECM. These findings also strengthen the rationale for determining whether inhibitors of EGFR tyrosine kinase reduce the risk of tobacco smoke-related second primary tumors.

uPA deficiency exacerbates muscular dystrophy in MDX mice

Duchenne muscular dystrophy (DMD) is a fatal and incurable muscle degenerative disorder. We identify a function of the protease urokinase plasminogen activator (uPA) in mdx mice, a mouse model of DMD. The expression of uPA is induced in mdx dystrophic muscle, and the genetic loss of uPA in mdx mice exacerbated muscle dystrophy and reduced muscular function. Bone marrow (BM) transplantation experiments revealed a critical function for BM-derived uPA in mdx muscle repair via three mechanisms: (1) by promoting the infiltration of BM-derived inflammatory cells; (2) by preventing the excessive deposition of fibrin; and (3) by promoting myoblast migration. Interestingly, genetic loss of the uPA receptor in mdx mice did not exacerbate muscular dystrophy in mdx mice, suggesting that uPA exerts its effects independently of its receptor. These findings underscore the importance of uPA in muscular dystrophy.

4G/5G plasminogen activator inhibitor-1 polymorphisms and haplotypes are associated with pneumonia

RATIONALE

Plasminogen activator inhibitor (PAI)-1 inhibits urokinase and tissue plasminogen activator, required for host response to infection. Whether variation within the PAI-1 gene is associated with increased susceptibility to infection is unknown.

OBJECTIVES

To ascertain the role of the 4G/5G polymorphism and other genetic variants within the PAI-1 gene. We hypothesized that variants associated with increased PAI-1 expression would be associated with an increased occurrence of community-acquired pneumonia (CAP).

METHODS

Longitudinal analysis (>12 yr) of the Health, Aging, and Body Composition cohort, aged 65-74 years at start of analysis.

MEASUREMENTS AND MAIN RESULTS

We genotyped the 4G/5G PAI-1 polymorphism and six additional single nucleotide polymorphisms. Of the 3,075 subjects, 272 (8.8%) had at least one hospitalization for CAP. Among whites, variants at the PAI4G,5G, PAI2846, and PAI7343 sites had higher risk of CAP (P = 0.018, 0.021, and 0.021, respectively). At these sites, variants associated with higher PAI-1 expression were associated with increased CAP susceptibility. Compared with the 5G/5G genotypes at PAI4G,5G site, the 4G/4G and 4G/5G genotypes were associated with a 1.98-fold increased risk of CAP (95% confidence interval, 1.2-3.2; P = 0.006). In whole blood stimulation assay, subjects with a 4G allele had 3.3- and 1.9-fold increased PAI-1 expression (P = 0.043 and 0.034, respectively). In haplotype analysis, the 4G/G/C/A haplotype at the PAI4G,5G, PAI2846, PAI4588, and PAI7343 single nucleotide polymorphisms was associated with higher CAP susceptibility, whereas the 5G/G/C/A haplotype was associated with lower CAP susceptibility. No associations were seen among blacks.

CONCLUSIONS

Genotypes associated with increased expression of PAI-1 were associated with increased susceptibility to CAP in elderly whites.

Association of urokinase-type plasminogen activator with asthma and atopy

RATIONALE

Urokinase plasminogen activator (uPA) interacts with its receptor on inflammatory and migrating cells to regulate extracellular matrix degradation, cell adhesion, and inflammatory cell activation. It is necessary for the development of an appropriate immune response and is involved in tissue remodeling. The PLAU gene codes for this enzyme, and is located on 10q24. This region has demonstrated evidence for linkage in a genome scan for asthma in a sample from northeastern Quebec. Here, we hypothesized that uPA may function as a regulator of asthma susceptibility.

OBJECTIVES

To test for association between asthma and genetic variants of PLAU.

METHODS

We sequenced PLAU and tested for genetic association between identified variants and asthma-related traits in a French-Canadian familial collection (231 families, 1,139 subjects). Additional association studies were performed in two other family-based Canadian cohorts (Canadian Asthma Primary Prevention Study [CAPPS], 238 trios; and Study of Asthma Genes and the Environment [SAGE], 237 trios).

MEASUREMENTS AND MAIN RESULTS

In the original sample, under the dominant model, the common alleles, rs2227564C (P141) and rs2227566T, were associated with asthma (p = 0.011 and 0.045, respectively) and with airway hyperresponsiveness (AHR) (p = 0.026 and 0.038, respectively). Analysis of the linkage disequilibrium pattern also revealed association of the common haplotype for asthma, atopy, and AHR (p = 0.031, 0.043, and 0.006, respectively). Whereas no significant association was detected for PLAU single-nucleotide polymorphisms in the CAPPS cohort, association was observed in the SAGE cohort between the rs4065C allele and atopy under additive (p = 0.005) and dominant (p = 0.0001) genetic models.

CONCLUSIONS

This suggests a role for the uPA pathway in the pathogenesis of the disease.

Mactinin treatment promotes wound-healing-associated inflammation in urokinase knockout mice

Mactinin, a 31 kDa fragment from the amino-terminal end of alpha-actinin, is chemotactic for monocytes and can promote monocyte/macrophage maturation. Macrophages are essential for wound healing, in which they play key roles in debridement, angiogenesis, fibroblast proliferation, and collagen metabolism. We have previously determined that urokinase is necessary to form mactinin from extracellular alpha-actinin, which may be present at sites of inflammation as a result of cell movement. Thus, urokinase knockout mice are unable to form mactinin and therefore are an ideal model to study mactinin's effects on wound healing. Saline- and mactinin-treated wounds were analyzed in a subcutaneous sponge wound model in both wild-type and urokinase knockout mice. The wounded urokinase knockout mice had markedly decreased leukocyte infiltration compared with wounded wild-type mice. In addition, production of the proinflammatory cytokine, interleukin-12, and of collagen was also decreased in knockouts. Treatment of knockout mice with mactinin resulted in leukocyte infiltration numbers, interleukin-12 levels, and hydroxyproline measurements similar to those in wild-type mice. The results suggest that impaired wound healing in urokinase-deficient mice can be restored by administration of mactinin.

Urokinase-induced activation of the gp130/Tyk2/Stat3 pathway mediates a pro-inflammatory effect in human mesangial cells via expression of the anaphylatoxin C5a receptor

Glomerular mesangial cells (MCs) are central to the pathogenesis of progressive glomeruli-associated renal diseases. However, molecular mechanisms underlying changes in MC functions still remain poorly understood. Here, we show that in MCs, the urokinase-type plasminogen activator (uPA) induces, via its specific receptor (uPAR, CD87), upregulated expression of the complement anaphylatoxin C5a receptor (C5aR, CD88), and modulates C5a-dependent functional responses. This effect is mediated via the interaction of the uPA-specific receptor (uPAR, CD87) and gp130, a signal transducing subunit of the receptor complexes for the IL-6 cytokine family. The Janus kinase Tyk2 and the transcription factor Stat3 serve as downstream components in the signaling cascade resulting in upregulation of C5aR expression. In vivo, expression of C5aR and uPAR was increased in the mesangium of wild-type mice in a lipopolysaccharide (LPS)-induced model of inflammation, whereas in uPAR(-/-) animals C5aR expression remained unchanged. This is the first demonstration in vitro and in vivo that uPA acts in MCs as a modulator of immune responses via control of immune-competent receptors. The data suggest a novel role for uPA/uPAR in glomeruli-associated renal failure via a signaling cross-talk between the fibrinolytic and immune systems.

Sputum Cathelicidin, Urokinase Plasminogen Activation System Components, and Cytokines Discriminate Cystic Fibrosis, COPD, and Asthma Inflammation

BACKGROUND

Interest in airways inflammatory disease has increasingly focused on innate immunity. We investigated several components of innate immunity in induced sputum of patients with cystic fibrosis (CF), COPD, and asthma, and healthy control subjects.

METHODS

Twenty eight patients with mild CF lung disease (age > or = 12 years; FEV1, 74 +/- 3% predicted [mean +/- SE]), 74 adults with COPD (FEV1, 55 +/- 2% of predicted), 34 adults with persistent asthma (FEV1, 66 +/- 2% of predicted), and 44 adult control subjects (FEV1, 85 +/- 1% of predicted) were studied while in stable clinical condition. Levels of sputum interleukin (IL)-8, IL-10, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, human cationic antimicrobial protein 18 (CAP18), urokinase-type plasminogen activator (uPA), uPA receptor (uPAR), and plasminogen activator inhibitor (PAI)-1 were determined. Cell sources were investigated by flow cytometry and immunohistochemistry. Spirometry was performed prior to sputum induction.

RESULTS

CF patient sputum showed greatest increase in IL-8 compared to that of patients with COPD and asthma (which were also greater than control subjects), and elevated levels of TNF-alpha and IL-10 compared to other groups. There were no differences in IFN-gamma. CAP18 levels were elevated in CF and COPD patients compared to control subjects, while asthma patients had reduced CAP18 levels. uPA levels were similar but uPAR was elevated in CF and COPD patients more so than in asthma patients, while PAI-1 levels were elevated in all three disease groups. CAP18 localized to neutrophil secondary granules; neutrophils were also sources of IL-8 and PAI-1. CAP18 and PAI-1 negatively correlated with pulmonary function.

CONCLUSION

Induced-sputum innate immune factor levels discriminate inflammatory changes in CF, COPD, and asthma, suggesting potential roles in pathophysiology and as well as providing disease-specific biomarker patterns.

The Urokinase/Urokinase Receptor System Mediates the IgG Immune Complex-Induced Inflammation in Lung

Immune complex (IC) deposition induces an acute inflammatory response with tissue injury. IC-induced inflammation is mediated by inflammatory cell infiltration, a process highly regulated by the cell surface-specific receptor (uPAR), a binding partner for the urokinase-type plasminogen activator (uPA). We assessed the role of the uPA/uPAR system in IC-induced inflammation using the pulmonary reverse passive Arthus reaction in mice lacking uPA and uPAR compared with their corresponding wild-type controls. Both uPA-deficient C57BL/6J (uPA(-/-)) and uPAR-deficient mice on a mixed C57BL/6J (75%) x 129 (25%) background (uPAR(-/-)) demonstrated a marked reduction of the inflammatory response due to decreased production of proinflammatory mediators TNF-alpha and Glu-Leu-Arg (ELR)-CXC chemokine MIP-2. In uPAR(-/-) animals, the reduction of inflammatory response was more pronounced because of decreased migratory capacity of polymorphonuclear leukocytes. We show that the uPA/uPAR system is activated in lung of wild-type mice, particularly in resident alveolar macrophages (AM), early in IC-induced alveolitis. This activation is necessary for an adequate C5a anaphylatoxin receptor signaling on AM that, in turn, modulates the functional balance of the activating/inhibitory IgG FcgammaRs responsible for proinflammatory mediator release. These data provide the first evidence that the uPA/uPAR plays an important immunoregulatory role in the initiation of the reverse passive Arthus reaction in the lung by setting the threshold for C5a anaphylatoxin receptor/FcgammaR activation on AM. The findings indicate an important link between the uPA/uPAR system and the two main components involved in the IC inflammation, namely, complement and FcgammaRs.

Protection of plasminogen activator inhibitor-1-deficient mice from nasal allergy

This study was performed to clarify the relationship between fibrinolytic components and the pathology of allergy, particularly that during the development of nasal allergy and nasal tissue changes. Intranasal OVA challenge after sensitization by i.p. administration of OVA induced a higher level of excess subepithelial collagen deposition in wild-type (WT) C57BL/6J mice than in plasminogen activator inhibitor (PAI)-1-deficient (PAI-1(-/-)) mice. The excess PAI-1 induction in the nasal mucosa and higher level of active PAI-1 in the nasal lavage fluid of WT-OVA mice compared with those in WT-control mice suggested that the decrease of proteolytic activity inhibits the removal of subepithelial collagen. The frequency of sneezing, nasal rubbing, nasal hyperresponsiveness, production of specific IgG1 and IgE in the serum, and production of IL-4 and IL-5 in splenocyte culture supernatant increased significantly in WT-OVA mice. In PAI-1(-/-) mice, these reactions were absent, and specific IgG2a in serum and IFN-gamma in splenocyte culture medium increased significantly. Histopathologically, there were marked goblet cell hyperplasia and eosinophil infiltration into the nasal mucosa in WT-OVA mice, but these were absent in PAI-1(-/-) mice. These results indicate that the immune response in WT-OVA mice can be classified as a dominant Th2 response, which would promote collagen deposition. In contrast, the Th2 response in PAI-1(-/-) mice was down-regulated, and the immune response shifted from Th2-dominant reaction to a Th1-dominant one. Taken together, these findings suggest that PAI-1 plays an important role not only in thrombolysis but also in immune response.

The role of urokinase in innate immunity against Staphylococcus aureus

Urokinase (uPA) is a serine protease that not only displays fibrinolytic function but also promotes host leukocytes to home to inflammatory sites. We have recently demonstrated that staphylokinase (SAK), which is a fibrinolytic protein secreted by Staphylococcus aureus, forms complexes with human neutrophil peptides (HNPs), which are members of the defensin family and have anti-microbial properties, thereby inhibiting the bactericidal effects of the HNPs. The aim of this study was to assess whether endogenous uPA, which has fibrinolytic properties similar to those of SAK, binds to HNPs and interferes with SAK/HNPs interaction. To this end, an ELISA was used to analyze the interactions between uPA and HNPs. HMW uPA had the ability to bind to both HNP types. The biological consequences of the formation of this complex were analyzed with respect to its bactericidal properties. HMW uPA killed S. aureus, albeit at relatively high doses (50-100 mug/ml). In contrast, the binding of HMW uPA to HNPs had no impact on the bactericidal functions of the HNPs. Importantly, the addition of HMW uPA to SAK eliminated the ability of SAK to neutralize HNPs. Our results demonstrate that endogenous HMW uPA inhibits S. aureus growth both directly, by cytolysis, and indirectly, by abrogation of the neutralizing effect of SAK on the bactericidal activities of HNPs. These findings indicate novel functions of HMW uPA in the host defense against staphylococcal infections.

The immune response to fungal infections

During the past two decades, invasive fungal infections have emerged as a major threat to immunocompromised hosts. Patients with neoplastic diseases are at significant risk for such infections as a result of their underlying illness and its therapy. Aspergillus, Candida, Cryptococcus and emerging pathogens, such as the zygomycetes, dark walled fungi, Trichosporon and Fusarium, are largely opportunists, causing infection when host defences are breached. The immune response varies with respect to the fungal species and morphotype encountered. The risk for particular infections differs, depending upon which aspect of immunity is impaired. This article reviews the current understanding of the role and relative importance of innate and adaptive immunity to common and emerging fungal pathogens. An understanding of the host response to these organisms is important in decisions regarding use of currently available antifungal therapies and in the design of new therapeutic modalities.

Urokinase-type plasminogen activator is a preferred substrate of the human epithelium serine protease tryptase epsilon/PRSS22

Tryptase epsilon is a member of the chromosome 16p13.3 family of human serine proteases that is preferentially expressed by epithelial cells. Recombinant pro-tryptase epsilon was generated to understand how the exocytosed zymogen might be activated outside of the epithelial cell, as well as to address its possible role in normal and diseased states. Using expression/site-directed mutagenesis approaches, we now show that Lys20, Cys90, and Asp92 in the protease's substrate-binding cleft regulate its enzymatic activity. We also show that Arg(-1) in the propeptide domain controls its ability to autoactivate. In vitro studies revealed that recombinant tryptase epsilon possesses a restricted substrate specificity. Once activated, tryptase epsilon cannot be inhibited effectively by the diverse array of protease inhibitors present in normal human plasma. Moreover, this epithelium protease is not highly susceptible to alpha1-antitrypsin or secretory leukocyte protease inhibitor, which are present in the lung. Recombinant tryptase epsilon could not cleave fibronectin, vitronectin, laminin, single-chain tissue-type plasminogen activator, plasminogen, or any prominent serum protein. Nevertheless, tryptase epsilon readily converted single-chain pro-urokinase-type plasminogen activator (pro-uPA/scuPA) into its mature, enzymatically active protease. Tryptase epsilon also was able to induce pro-uPA-expressing smooth muscle cells to increase their migration through a basement membrane-like extracellular matrix. The ability to activate uPA in the presence of varied protease inhibitors suggests that tryptase epsilon plays a prominent role in fibrinolysis and other uPA-dependent reactions in the lung.

Regulation of the single-chain urokinase-urokinase receptor complex activity by plasminogen and fibrin: novel mechanism of fibrin specificity

Activation of plasminogen by urokinase plasminogen activator (uPA) plays important roles in several physiologic and pathologic conditions. Cells secrete uPA as a single-chain molecule (scuPA). scuPA can be activated by proteolytic cleavage to a 2-chain enzyme (tcuPA). scuPA is also activated when it binds to its receptor (uPAR). The mechanism by which the enzymatic activity of the scuPA/suPAR complex is regulated is only partially understood. We now report that the plasminogen activator activity of the scuPA/suPAR complex is inhibited by Glu- and Lys-plasminogen, but not by mini-plasminogen. In contrast, neither Glunor Lys-plasminogen inhibits the activation of plasminogen by 2-chain uPA. Inhibition of scuPA/suPAR activity was evident at a Glu-plasminogen concentration of approximately 100 nM, and at physiologic plasma concentrations inhibition was nearly complete. A plasminogen fragment containing kringles 1-3 inhibited the enzymatic activity of scuPA/suPAR with an inhibition constant (Ki) equal to 1.9 microM, increased the Michaelis constant (Km) of scuPA/suPAR from 18 nM to 49 nM, and decreased the catalytic constant (Kcat) approximately 3-fold from 0.035 sec(-1) to 0.011 sec(-1). Inhibition of scuPA/suPAR by plasminogen was completely abolished in the presence of fibrin clots. These studies provide insight into the regulation of uPA-mediated plasminogen activation and identify a novel mechanism for its fibrin specificity.

Urease expression by Cryptococcus neoformans promotes microvascular sequestration, thereby enhancing central nervous system invasion

Our objective was to determine the role of the cryptococcal virulence factor urease in pulmonary-to-central nervous system, dissemination, invasion, and growth. C. neoformans H99, the urease knockout strain (ure1) derived from H99, and the urease restored strain ure1+URE1-1 were used for the studies. The absence of cryptococcal urease (ure1infection) resulted in significant protection from the high mortality observed in H99-infected mice. All H99-infected mice had extremely high cryptococcal loads in their brains at the time of death, whereas only two of six animals that died of ure1 infection had detectable C. neoformans in the brain. Histological analysis of the blood-to-brain invasion by C. neoformans H99 demonstrated wedging of the yeasts in small capillaries, altered structure of microvessel walls, formation of mucoid cysts initiated in the proximity of damaged microcapillaries, and the absence of an inflammatory response. Direct inoculation of H99, ure1, and ure1+URE1-1 into the brain demonstrated that urease was not required to grow in the brain. However, the dissemination patterns in the brain, spleen, and other organs after intravenous inoculation indicated that cryptococcal urease contributes to the central nervous system invasion by enhancing yeast sequestration within microcapillary beds (such as within the brain) during hematogenous spread, thereby facilitating blood-to-brain invasion by C. neoformans.

Urokinase-deficient mice fail to generate a type 2 immune response following schistosomal antigen challenge

Activated lymphocytes express urokinase-type plasminogen activator (uPA). Previous work suggests that uPA modulates T-lymphocyte responses. Mice deficient in uPA (uPA(-/-)) fail to generate type 1 (T1) immune responses during infection with Cryptococcus neoformans. Failure to generate either a T1 or a T2 immune response is not predictive of defects in the alternative response. Conversely, down-regulation of one type of immune response may result in inappropriate overactivation of the other. It is not known whether the immune defect in uPA(-/-) mice affects only T1 responses or whether T2 responses are also impaired. Impairment of both T1 and T2 responses would suggest a global T-cell defect in the absence of uPA. To determine the role of uPA in T2 immune responses, wild-type (WT) and uPA(-/-) mice were primed and challenged with schistosomal egg antigen (SEA). This elicits strong polarization to T2 immune responses in immunocompetent mice. The challenged WT mice developed delayed-type hypersensitivity (DTH) to SEA; high levels of serum immunoglobulin E (IgE); a strong T2 cytokine phenotype with markedly elevated levels of interleukin-4 (IL-4), IL-5, and IL-13; and eosinophil-rich pulmonary granulomas. uPA(-/-) mice failed to develop DTH to SEA; did not polarize Ig production to IgE; did not produce high levels of IL-4, IL-5, or IL-13; and had markedly reduced numbers of granuloma-associated eosinophils. uPA(-/-) mice fail to generate polarized T2 immune responses to a T2-inducing pathogen. These findings, in conjunction with our previous work, demonstrate that mice deficient in uPA have profoundly impaired immunity involving both T1 and T2 polarization and are largely immunologically unresponsive.

The fibrinolytic system in dissemination and matrix protein deposition during a mycobacterium infection

The fibrinolytic system is known to play an important role in the inflammatory response to bacterial infections. In the present study, relationships between protein components of the fibrinolytic system and infectivity by Mycobacterium avium were analyzed. Infections were initiated through noninvasive intratracheal administration of M. avium 724 in mice individually deficient for plasminogen, tissue-type plasminogen activator, urokinase-type plasminogen activator, and urokinase-type plasminogen activator receptor, along with wild-type control mice. There were no differences in lung colony counts among all mouse genotypes throughout a 10-week infection. However, in tissue-type plasminogen activator and plasminogen-deficient mice an earlier dissemination of M. avium to other organs was observed. Nevertheless, the M. avium growth rates in the liver, spleen, and lung did not differ between the various mouse populations throughout a 10-week infection. Histochemical and immunohistochemical analyses at 5 and 10 weeks after infection demonstrated that plasminogen-deficient mice, compared to wild-type mice, had enhanced fibrin and fibronectin deposition, as well as increased neutrophil infiltration within liver granulomas. These results suggest that plasmin(ogen) plays a role in the turnover of extracellular matrix proteins within granulomas and has a limited effect in the early dissemination of M. avium from lungs. Thus, plasmin(ogen) functions in limiting progressive fibrosis in the granuloma during a chronic mycobacterial infection.

Urokinase-type plasminogen activator potentiates lipopolysaccharide-induced neutrophil activation

Urokinase plasminogen activator (uPA) is a serine protease that catalyzes the conversion of plasminogen to plasmin. Although increased circulating levels of uPA are present in endotoxemia and sepsis, conditions in which activated neutrophils contribute to the development of acute organ dysfunction, the ability of uPA to participate directly in LPS-induced neutrophil activation has not been examined. In the present experiments, we show that uPA can enhance activation of neutrophils exposed to submaximal stimulatory doses of LPS. In particular, uPA increased LPS-induced activation of intracellular signaling pathways, including Akt and c-Jun N-terminal kinase, nuclear translocation of the transcriptional regulatory factor NF-kappa B, and expression of proinflammatory cytokines, including IL-1 beta, macrophage-inflammatory protein-2, and TNF-alpha. There was no effect of uPA on LPS-induced activation of p38 mitogen-activated protein kinase in neutrophils. Transgenic mice unable to produce uPA (uPA(-/-)) were protected from endotoxemia-induced lung injury, as determined by development of lung edema, pulmonary neutrophil accumulation, lung IL-1 beta, macrophage-inflammatory protein-2, and TNF-alpha cytokine levels. These results demonstrate that uPA can potentiate LPS-induced neutrophil responses and also suggest that such effects are sufficiently important in vivo to play a major contributory role in neutrophil-mediated inflammatory responses, such as the development of acute lung injury.

Epidermal growth factor receptor-dependent and -independent cell-signaling pathways originating from the urokinase receptor

Urokinase-type plasminogen activator (uPA) and vitronectin activate cell-signaling pathways by binding to the uPA receptor (uPAR). Because uPAR is glycosylphosphatidylinositol-anchored, the signaling receptor is most likely a uPAR-containing multiprotein complex. This complex may be heterogeneous within a single cell and among different cell types. The goal of this study was to elucidate the role of the EGF receptor (EGFR) as a component of the uPAR-signaling machinery. uPA activated extracellular signal-regulated kinase (ERK) in COS-7 cells and in COS-7 cells that overexpress uPAR, and this response was blocked by the EGFR inhibitor, tyrphostin AG1478, implicating the EGFR in the pathway that links uPAR to ERK. By contrast, Rac1 activation, which occurred as a result of uPAR overexpression, was EGFR-independent. COS-7 cell migration was stimulated, in an additive manner, by uPAR-dependent pathways leading to ERK and Rac1. AG1478 inhibited only the ERK-dependent component of the response. CHO-K1 cells do not express EGFR; however, these cells demonstrated ERK activation in response to uPA, indicating the presence of an EGFR-independent alternative pathway. As anticipated, this response was insensitive to AG1478. When CHO-K1 cells were transfected to express EGFR or a kinase-inactive mutant of EGFR, ERK activation in response to uPA was unchanged; however, the EGFR-expressing cells acquired sensitivity to AG1478. We conclude that the EGFR may function as a transducer of the signal from uPAR to ERK, but not Rac1. In the absence of EGFR, an alternative pathway links uPAR to ERK; however, this pathway is apparently silenced by EGFR expression.

Interactions of fungi with phagocytes

Recent advances have broadened our knowledge of the unique role that dendritic cells, macrophages and neutrophils play in protecting the host against fungal infections and the mechanisms by which fungal pathogens attempt to subvert phagocytic defenses. In this article, the interplay between phagocytes and fungi is reviewed.