Tracheostomy Timing During Pediatric Cardiac Intensive Care: Single Referral Center Retrospective Cohort.

OBJECTIVES: To describe associations between the timing of tracheostomy and patient characteristics or outcomes in the cardiac ICU (CICU). DESIGN: Single-institution retrospective cohort study. SETTING: Freestanding academic children's hospital. PATIENTS: CICU patients with tracheostomy placed between July 1, 2011, and July 1, 2020. INTERVENTIONS: We compared patient characteristics and outcomes between early and late tracheostomy based on the duration of positive pressure ventilation (PPV) before tracheostomy placement, fitting a receiver operating characteristic curve for current survival to define a cutoff. MEASUREMENTS AND MAIN RESULTS: Sixty-one patients underwent tracheostomy placement (0.5% of CICU admissions). Median age was 7.8 months. Eighteen patients (30%) had single ventricle physiology and 13 patients (21%) had pulmonary vein stenosis (PVS). Primary indications for tracheostomy were pulmonary/lower airway (41%), upper airway obstruction (UAO) (31%), cardiac (15%), neuromuscular (4%), or neurologic (4%). In-hospital mortality was 26% with 41% survival at the current follow-up (median 7.8 [interquartile range, IQR 2.6-30.0] mo). Late tracheostomy was defined as greater than or equal to 7 weeks of PPV which was equivalent to the median PPV duration pre-tracheostomy. Patients with late tracheostomy were more likely to be younger, have single ventricle physiology, and have greater respiratory severity. Patients with early tracheostomy were more likely to have UAO or genetic comorbidities. In multivariable analysis, late tracheostomy was associated with 4.2 times greater mortality (95% CI, 1.9-9.0). PVS was associated with higher mortality (adjusted hazard ratio [HR] 5.2; 95% CI, 2.5-10.9). UAO was associated with lower mortality (adjusted HR 0.2; 95% CI, 0.1-0.5). Late tracheostomy was also associated with greater cumulative opioid exposure. CONCLUSIONS: CICU patients who underwent tracheostomy had high in-hospital and longer-term mortality rates. Tracheostomy timing decisions are influenced by indication, disease, genetic comorbidities, illness severity, and age. Earlier tracheostomy was associated with lower sedative use and improved adjusted survival. Tracheostomy placement is a complex decision demanding individualized consideration of risk-benefit profiles and thoughtful family counseling.

"New Trach Mom Here ": A qualitative study of internet-based resources by caregivers of children with tracheostomy.

OBJECTIVE: Decision-making around tracheostomy placement and chronic respiratory support in children is complicated. Families often seek support and advice from outside the medical care team, including from social media. We undertook this study to characterize the content and nature of online resources created and managed primarily by caregivers of children living with tracheostomy and chronic mechanical ventilation. DESIGN/SETTING: We used a "grey literature" search methodology to identify internet resources created by caregivers of children with tracheostomy. We included only publicly available, nonindustry associated, English language, North American websites updated at least once in 2019. We then applied inductive content analysis to establish central themes, patterns and associations. MEASUREMENTS/MAIN RESULTS: We identified six blogs/forums that met our search criteria. We identified four main themes: (1) Uncertainty, (2) Lived experience-wants, needs, and emotions, (3) Seeking context and meaning, and (4) Advice/information sharing/support. Two patterns of coping were identified on the basis of the relationships between codes. The "Acceptance pathway" is associated with a sense of self-actualization, mastery, satisfaction, return to normalcy, and ultimately acceptance. The "Resignation pathway" is associated with a sense of lack of control, frustration, burnout and stress, persistent lack of normalcy, and resignation to the tracheostomy as a negative but necessary outcome. CONCLUSION: Caregivers often come to see themselves as experts in the care of children with tracheostomy, though many still express ambivalence about their knowledge and skills. Those early in the experience express a desire for community and can potentially benefit from online resources.

WITHDRAWN: Complete Heart Block, Severe Ventricular Dysfunction and Myocardial Inflammation in a Child with COVID-19 Infection.

The Publisher regrets that this article is an accidental duplication of an article that has already been published, https://doi.org/10.1016/j.jaccas.2020.05.023>. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Complete Heart Block, Severe Ventricular Dysfunction, and Myocardial Inflammation in a Child With COVID-19 Infection.

A young child presented with severe ventricular dysfunction and troponin leak in the setting of coronavirus disease-2019. He developed intermittent, self-resolving, and hemodynamically insignificant episodes of complete heart block that were diagnosed on telemetry and managed conservatively. This report is the first description of coronavirus disease-2019-induced transient complete heart block in a child. (Level of Difficulty: Intermediate.).

Factors Impacting Physician Recommendation for Tracheostomy Placement in Pediatric Prolonged Mechanical Ventilation: A Cross-Sectional Survey on Stated Practice.

OBJECTIVES: To characterize the stated practices of qualified Canadian physicians toward tracheostomy for pediatric prolonged mechanical ventilation and whether subspecialty and comorbid conditions impact attitudes toward tracheostomy. DESIGN: Cross sectional web-based survey. SUBJECTS: Pediatric intensivists, neonatologists, respirologists, and otolaryngology-head and neck surgeons practicing at 16 tertiary academic Canadian pediatric hospitals. INTERVENTIONS: Respondents answered a survey based on three cases (Case 1: neonate with bronchopulmonary dysplasia; Cases 2 and 3: children 1 and 10 years old with pediatric acute respiratory distress syndrome, respectively) including a series of alterations in relevant clinical variables. MEASUREMENTS AND MAIN RESULTS: We compared respondents' likelihood of recommending tracheostomy at 3 weeks of mechanical ventilation and evaluated the effects of various clinical changes on physician willingness to recommend tracheostomy and their impact on preferred timing (≤ 3 wk or > 3 wk of mechanical ventilation). Response rate was 165 of 396 (42%). Of those respondents who indicated they had the expertise, 47 of 121 (38.8%), 23 of 93 (24.7%), and 40 of 87 (46.0%) would recommend tracheostomy at less than or equal to 3 weeks of mechanical ventilation for cases 1, 2, and 3, respectively (p < 0.05 Case 2 vs 3). Upper airway obstruction was associated with increased willingness to recommend earlier tracheostomy. Life-limiting condition, severe neurologic injury, unrepaired congenital heart disease, multiple organ system failure, and noninvasive ventilation were associated with a decreased willingness to recommend tracheostomy. CONCLUSION: This survey provides insight in to the stated practice patterns of Canadian physicians who care for children requiring prolonged mechanical ventilation. Physicians remain reluctant to recommend tracheostomy for children requiring prolonged mechanical ventilation due to lung disease alone at 3 weeks of mechanical ventilation. Prospective studies characterizing actual physician practice toward tracheostomy for pediatric prolonged mechanical ventilation and evaluating the impact of tracheostomy timing on clinically important outcomes are needed as the next step toward harmonizing care delivery for such patients.

Serpins: Development for Therapeutic Applications.

Serine protease inhibitors, or serpins, function as central regulators for many vital processes in the mammalian body, maintaining homeostasis for clot formation and breakdown, immune responses, lung function, and hormone or central nervous system activity, among many others. When serine protease activity or serpin-mediated regulation becomes unbalanced or dysfunctional, then severe disease states and pathogenesis can ensue. With serpinopathies, genetic mutations lead to inactive serpins or protein aggregation with loss of function. With other disorders, such as sepsis, atherosclerosis, cancer, obesity, and the metabolic syndrome, the thrombotic and thrombolytic cascades and/or inflammatory responses become unbalanced, with excess bleeding and clotting and upregulation of adverse immune responses. Returning overall balance can be engineered through introduction of a beneficial serpin replacement as a therapeutic or through blockade of serpins that are detrimental. Several drugs have been developed and are currently in use and/or in development both to replace dysfunctional serpins and to block adverse effects induced by aberrant protease or serpin actions.With this chapter, we provide a general overview of the development of a virus-derived serpin, Serp-1, and serpin reactive center loop (RCL) peptides, as therapeutics. Serp-1 is a virus-derived serpin developed as a new class of immune modulator. We will use the development of Serp-1 as a general introduction to serpin-based drug development.

Crystal Structure of Cleaved Serp-1, a Myxomavirus-Derived Immune Modulating Serpin: Structural Design of Serpin Reactive Center Loop Peptides with Improved Therapeutic Function.

The Myxomavirus-derived protein Serp-1 has potent anti-inflammatory activity in models of vasculitis, lupus, viral sepsis, and transplant. Serp-1 has also been tested successfully in a Phase IIa clinical trial in unstable angina, representing a "first-in-class" therapeutic. Recently, peptides derived from the reactive center loop (RCL) have been developed as stand-alone therapeutics for reducing vasculitis and improving survival in MHV68-infected mice. However, both Serp-1 and the RCL peptides lose activity in MHV68-infected mice after antibiotic suppression of intestinal microbiota. Here, we utilize a structure-guided approach to design and test a series of next-generation RCL peptides with improved therapeutic potential that is not reduced when the peptides are combined with antibiotic treatments. The crystal structure of cleaved Serp-1 was determined to 2.5 Å resolution and reveals a classical serpin structure with potential for serpin-derived RCL peptides to bind and inhibit mammalian serpins, plasminogen activator inhibitor 1 (PAI-1), anti-thrombin III (ATIII), and α-1 antitrypsin (A1AT), and target proteases. Using in silico modeling of the Serp-1 RCL peptide, S-7, we designed several modified RCL peptides that were predicted to have stronger interactions with human serpins because of the larger number of stabilizing hydrogen bonds. Two of these peptides (MPS7-8 and -9) displayed extended activity, improving survival where activity was previously lost in antibiotic-treated MHV68-infected mice (P < 0.0001). Mass spectrometry and kinetic assays suggest interaction of the peptides with ATIII, A1AT, and target proteases in mouse and human plasma. In summary, we present the next step toward the development of a promising new class of anti-inflammatory serpin-based therapeutics.

Return visits to the pediatric emergency department: A multicentre retrospective cohort study.

OBJECTIVE: Return visits to the emergency department (RTED) for the same clinical complaint occur in 2.7% to 8.1% of children presenting to pediatric emergency departments (PEDs). Most studies examining RTEDs have focused solely on PEDs and do not capture children returning to other local emergency departments (EDs). Our objective was to measure the frequency and characterize the directional pattern of RTED to any of 18 EDs serving a large geographic area for children initially evaluated at a PED. METHODS: We conducted a retrospective cohort study of all visits to a referral centre PED between August 2012 and August 2013. We compared demographic variables between children with and without an RTED, measures of flow and disposition outcomes between the initial (index) visit and RTED, and between RTED to the original PED versus to other EDs in the community. RESULTS: Among all PED visits, 7.6% had an RTED within 7 days, of which 13% were to a facility other than the original PED. Children with an RTED had higher acuity and longer length of stay on their index visit. They were also more likely to be admitted on a subsequent visit than the overall PED population. RTED to the original PED had a longer waiting time (WT), length of stay, and more frequently resulted in hospitalization than RTED to a general ED. CONCLUSIONS: A significant proportion of RTED occur at a site other than where the original ED visit occurred. Examining RTED to and from only PEDs underestimates its burden on emergency health services.

Serpin treatment suppresses inflammatory vascular lesions in temporal artery implants (TAI) from patients with giant cell arteritis.

Giant cell arteritis (GCA) and Takayasu's disease are inflammatory vasculitic syndromes (IVS) causing sudden blindness and widespread arterial obstruction and aneurysm formation. Glucocorticoids and aspirin are mainstays of treatment, predominantly targeting T cells. Serp-1, a Myxomavirus-derived serpin, blocks macrophage and T cells in a wide range of animal models. Serp-1 also reduced markers of myocardial injury in a Phase IIa clinical trial for unstable coronary disease. In recent work, we detected improved survival and decreased arterial inflammation in a mouse Herpesvirus model of IVS. Here we examine Serp-1 treatment of human temporal artery (TA) biopsies from patients with suspected TA GCA arteritis after implant (TAI) into the aorta of immunodeficient SCID (severe combined immunodeficiency) mice. TAI positive for arteritis (GCApos) had significantly increased inflammation and plaque when compared to negative TAI (GCAneg). Serp-1 significantly reduced intimal inflammation and CD11b+ cell infiltrates in TAI, with reduced splenocyte Th1, Th17, and Treg. Splenocytes from mice with GCApos grafts had increased gene expression for interleukin-1 beta (IL-1ß), IL-17, and CD25 and decreased Factor II. Serp-1 decreased IL-1ß expression. In conclusion, GCApos TAI xenografts in mice provide a viable disease model and have increased intimal inflammation as expected and Serp-1 significantly reduces vascular inflammatory lesions with reduced IL-1ß.

Suppression of collagen-induced arthritis with a serine proteinase inhibitor (serpin) derived from myxoma virus.

Many viruses encode virulence factors to facilitate their own survival by modulating a host's inflammatory response. One of these factors, secreted from cells infected with myxoma virus, is the serine proteinase inhibitor (serpin) Serp-1. Because Serp-1 had demonstrated anti-inflammatory properties in arterial injury models and viral infections, it was cloned and evaluated for therapeutic efficacy in collagen-induced arthritis (CIA). Clinical severity was significantly lower in the Serp-1 protocols (p<0.0001) and blinded radiographs indicated that the Serp-1 group had significantly less erosions than the controls (p<0.01). Delayed-type hypersensitivity was lower in the Serp-1 group but antibody titers to type II collagen were not significantly altered. Recipients had minimal histopathologic synovial changes and did not develop neutralizing antibodies to Serp-1. These results indicate that Serp-1 impedes the pathogenesis of CIA and suggests that the therapeutic potential of serine proteinase inhibitors in inflammatory joint diseases, such as rheumatoid arthritis, should be investigated further.

Myxomavirus-derived serpin prolongs survival and reduces inflammation and hemorrhage in an unrelated lethal mouse viral infection.

Lethal viral infections produce widespread inflammation with vascular leak, clotting, and bleeding (disseminated intravascular coagulation [DIC]), organ failure, and high mortality. Serine proteases in clot-forming (thrombotic) and clot-dissolving (thrombolytic) cascades are activated by an inflammatory cytokine storm and also can induce systemic inflammation with loss of normal serine protease inhibitor (serpin) regulation. Myxomavirus secretes a potent anti-inflammatory serpin, Serp-1, that inhibits clotting factor X (fX) and thrombolytic tissue- and urokinase-type plasminogen activators (tPA and uPA) with anti-inflammatory activity in multiple animal models. Purified serpin significantly improved survival in a murine gammaherpesvirus 68 (MHV68) infection in gamma interferon receptor (IFN-γR) knockout mice, a model for lethal inflammatory vasculitis. Treatment of MHV68-infected mice with neuroserpin, a mammalian serpin that inhibits only tPA and uPA, was ineffective. Serp-1 reduced virus load, lung hemorrhage, and aortic, lung, and colon inflammation in MHV68-infected mice and also reduced virus load. Neuroserpin suppressed a wide range of immune spleen cell responses after MHV68 infection, while Serp-1 selectively increased CD11c(+) splenocytes (macrophage and dendritic cells) and reduced CD11b(+) tissue macrophages. Serp-1 altered gene expression for coagulation and inflammatory responses, whereas neuroserpin did not. Serp-1 treatment was assessed in a second viral infection, mouse-adapted Zaire ebolavirus in wild-type BALB/c mice, with improved survival and reduced tissue necrosis. In summary, treatment with this unique myxomavirus-derived serpin suppresses systemic serine protease and innate immune responses caused by unrelated lethal viral infections (both RNA and DNA viruses), providing a potential new therapeutic approach for treatment of lethal viral sepsis.

Nonuniform distribution of contacts from noradrenergic and serotonergic boutons on the dendrites of cat splenius motoneurons.

The input-output properties of motoneurons are dynamically regulated. This regulation depends, in part, on the relative location of excitatory and inhibitory synapses, voltage-dependent and -independent channels, and neuromodulatory synapses on the dendritic tree. The goal of the present study was to quantify the number and distribution of synapses from two powerful neuromodulatory systems that originate from noradrenergic (NA) and serotonergic (5-HT) neurons. Here we show that the dendritic trees of motoneurons innervating a dorsal neck extensor muscle, splenius, in the adult cat are densely, but not uniformly innervated by both NA and 5-HT boutons. Identified splenius motoneurons were intracellularly stained with Neurobiotin. Using 3D reconstruction techniques we mapped the distributions of contacts formed by NA and 5-HT boutons on the reconstructed dendritic trees of these motoneurons. Splenius motoneurons received an average of 1,230 NA contacts (range = 647-1,507) and 1,582 5-HT contacts (range = 1,234-2,143). The densities of these contacts were 10 (NA) to 6 (5-HT)-fold higher on small compared to large-diameter dendrites. This relationship largely accounts for the bias of NA and 5-HT contacts on distal dendrites and is partially responsible for the higher density of NA contacts on dendrites located more than 200 µm dorsal to the soma. These results suggest that the neuromodulatory actions of NA and 5-HT are compartmentalized and regulate the input-output properties of motoneurons according to precisely arranged interactions with voltage-dependent and -independent channels that are primarily located on small-diameter dendrites.

Viral serpin therapeutics from concept to clinic.

Over the past 19 years, we have developed a novel myxoma virus-derived anti-inflammatory serine protease inhibitor, termed a serpin, as a new class of immunomodulatory therapeutic. This review will describe the initial identification of viral serpins with anti-inflammatory potential, beginning with preclinical analysis of viral pathogenesis and proceeding to cell and molecular target analyses, and successful clinical trial. The central aim of this review is to describe the development of two serpins, Serp-1 and Serp-2, as a new class of immune modulating drug, from inception to implementation. We begin with an overview of the approaches used for successful mining of the virus for potential serpin immunomodulators in viruses. We then provide a methodological overview of one inflammatory animal model used to test for serpin anti-inflammatory activity followed by methods used to identify cells in the inflammatory response system targeted by these serpins and molecular responses to serpin treatment. Finally, we provide an overview of our findings from a recent, successful clinical trial of the secreted myxomaviral serpin, Serp-1, in patients with unstable inflammatory coronary arterial disease.

A randomized controlled, phase 2 trial of the viral serpin Serp-1 in patients with acute coronary syndromes undergoing percutaneous coronary intervention.

BACKGROUND: Vascular inflammation can lead to plaque instability and acute coronary syndromes (ACS). Viruses produce potent immunomodulating proteins that regulate key inflammatory pathways. A myxoma virus-derived serpin Serp-1 reduces inflammatory cell invasion and plaque growth in vascular injury models. Our objective was to evaluate the safety and efficacy of Serp-1 in patients with ACS undergoing percutaneous coronary intervention. METHODS AND RESULTS: This double-blind pilot trial included 48 ACS patients undergoing percutaneous coronary intervention randomly assigned to Serp-1 at doses of 5 µg/kg (n=19) or 15 µg/kg (n=17) or to placebo (n=12). Serp-1 was given by intravenous bolus immediately before intervention and 24 and 48 hours later. Patients were assessed for safety (primary objective) and efficacy outcomes, including biomarker analysis. In-stent neointimal hyperplasia was evaluated by intravascular ultrasound at 6 months. Key safety outcomes including coagulation parameters and adverse events did not differ between Serp-1 and placebo groups. A dose-dependent reduction in troponin I levels was observed with Serp-1 at 8, 16, 24, and 54 hours (P<0.05) and in creatine kinase-MB levels at 8, 16, and 24 hours after dose (P<0.05). The composite of death, myocardial infarction, or coronary revascularization occurred in 2 of 12 patients with placebo, 5 of 19 in the low-dose group, and none of 17 patients with the high-dose (P=0.058). Intravascular ultrasound did not detect changes in neointimal hyperplasia among groups. CONCLUSIONS: This is the first study of a viral serpin demonstrating its safety in ACS patients. The significant reduction in myocardial damage biomarkers supports further assessment of Serp-1 in ACS patients undergoing stent deployment. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT00243308.

Inhibition of chemokine-glycosaminoglycan interactions in donor tissue reduces mouse allograft vasculopathy and transplant rejection.

BACKGROUND: Binding of chemokines to glycosaminoglycans (GAGs) is classically described as initiating inflammatory cell migration and creating tissue chemokine gradients that direct local leukocyte chemotaxis into damaged or transplanted tissues. While chemokine-receptor binding has been extensively studied during allograft transplantation, effects of glycosaminoglycan (GAG) interactions with chemokines on transplant longevity are less well known. Here we examine the impact of interrupting chemokine-GAG interactions and chemokine-receptor interactions, both locally and systemically, on vascular disease in allografts. METHODOLOGY/PRINCIPAL FINDINGS: Analysis of GAG or CC chemokine receptor 2 (CCR2) deficiency were coupled with the infusion of viral chemokine modulating proteins (CMPs) in mouse aortic allograft transplants (n = 239 mice). Inflammatory cell invasion and neointimal hyperplasia were significantly reduced in N-deacetylase-N-sulfotransferase-1 (Ndst1(f/f)TekCre(+)) heparan sulfate (GAG)-deficient (Ndst1(-/-), p<0.044) and CCR2-deficient (Ccr2(-/-), p<0.04) donor transplants. Donor tissue GAG or CCR2 deficiency markedly reduced inflammation and vasculopathy, whereas recipient deficiencies did not. Treatment with three CMPs was also investigated; Poxviral M-T1 blocks CC chemokine receptor binding, M-T7 blocks C, CC, and CXC GAG binding, and herpesviral M3 binds receptor and GAG binding for all classes. M-T7 reduced intimal hyperplasia in wild type (WT) (Ccr2(+/+), p< or =0.003 and Ccr2(-/-), p

10 M-T7: measuring chemokine-modulating activity.

Chemokines are important for activation of a host of cellular immune and inflammatory responses including cell signaling, activation, and communication. M-T7, a myxoma virus protein, inhibits the activity of chemokines by direct binding to chemokines and/or with glycosaminoglycans (GAGs). To study the effects of this chemokine-modulating protein (CMP), we use a variety of in vitro and in vivo techniques to evaluate M-T7 inhibition of inflammatory cells. To quickly analyze the effects of M-T7, changes in cell adhesion and membrane fluidity are measured as well as cell migration in mouse ascites. For more physiological analyses, an aortic transplant model in rodents is used to assess change in inflammatory cell infiltrates and vascular plaque growth (rejection). Utilization of the combination of these in vitro and in vivo techniques allows for a more complete study of the chemokine-modulating activity of M-T7, and can be used to study other immune and inflammation-modulating proteins.

The serpin saga; development of a new class of virus derived anti-inflammatory protein immunotherapeutics.

Serine proteinase inhibitors, also called serpins, are an ancient grouping of proteins found in primitive organisms from bacteria, protozoa and horseshoe crabs and thus likely present at the time of the dinosaurs, up to all mammals living today. The innate or inflammatory immune system is also an ancient metazoan regulatory system, providing the first line of defense against infection or injury. The innate inflammatory defense response evolved long before acquired, antibody dependent immunity. Viruses have developed highly effective stratagems that undermine and block a wide variety of host inflammatory and immune responses. Some of the most potent of these immune modifying strategies utilize serpins that have also been developed over millions of years, including the hijacking by some viruses for defense against host immune attacks. Serpins represent up to 2-10 percent of circulating plasma proteins, regulating actions as wide ranging as thrombosis, inflammation, blood pressure control and even hormone transport. Targeting serpin-regulated immune or inflammatory pathways makes evolutionary sense for viral defense and many of these virus-derived inhibitory proteins have proven to be highly effective, working at very low concentrations--even down to the femptomolar to picomolar range. We are studying these viral anti-inflammatory proteins as a new class of immunomodulatory therapeutic agents derived from their native viral source. One such viral serpin, Serp-1 is now in clinical trial (conducted by VIRON Therapeutics, Inc.) for acute unstable coronary syndromes (unstable angina and small heart attacks), representing a 'first in class' therapeutic study. Several other viral serpins are also currently under investigation as anti-inflammatory or anti-immune therapeutics. This chapter describes these original studies and the ongoing analysis of viral serpins as a new class of virus-derived immunotherapeutic.

Heparin alters viral serpin, serp-1, anti-thrombolytic activity to anti-thrombotic activity.

Serine protease inhibitors (serpins) regulate coagulation and inflammation. Heparin, a glycosaminoglycan, is an important cofactor for modulation of the inhibitory function of mammalian serpins. The secreted myxoma viral serpin, Serp-1 exerts profound anti-inflammatory activity in a wide range of animal models. Serp-1 anti-inflammatory and anti-atherogenic activity is dependent upon inhibition of the uPA / uPA receptor thrombolytic complex. We demonstrate here that heparin binds to Serp-1 and enhances Serp-1 inhibition of thrombin, a human pro-thrombotic serine protease, in vitro, altering inhibitory activity to a more predominant anti-thrombotic activity. Heparin also facilitates the simultaneous thrombin-mediated cleavage of Serp-1 and prevents formation of a serpin-typical SDS-resistant complex, implying mutual neutralization of Serp-1 and thrombin. In a cell-based assay, heparin facilitates Serp-1 reversal of cellular activation by stabilizing cellular membrane fluidity in thrombin-activated monocytes. In conclusion, heparin and other GAGs serve as cofactors enhancing Serp-1 regulation of local thrombotic and inflammatory pathways.

Induction of indefinite cardiac allograft survival correlates with toll-like receptor 2 and 4 downregulation after serine protease inhibitor-1 (Serp-1) treatment.

BACKGROUND: Innate immunity provides obstacles to successful organ transplantation, which cannot be prevented by cyclosporine (CsA). Here we have determined the potential of a myxoma viral serpin, Serp-1, with proven anti-inflammatory and antiatherogenic actions, to modulate innate immunity and contribute synergistically with CsA in the prevention of acute cardiac allograft rejection. METHODS: Brown-Norway rat hearts were heterotopically transplanted into Lewis rats and given either a monotherapy treatment of Serp-1, a subtherapeutic dose of CsA, or the two drugs in combination. RESULTS: A brief treatment of Serp-1 alone, or a subtherapeutic dose of CsA, resulted in a marked decrease in intragraft macrophage infiltration and downregulation of toll-like receptor (TLR)-2, TLR4 and MyD88 at 48 hours posttransplantation, which was associated with significantly reduced numbers of mature dendritic cells. A significant reduction in intragraft T-lymphocyte infiltration was observed with both Serp-1 monotherapy and Serp-1 and CsA combination therapy, with the combination treatment achieving indefinite graft survival (>100 days) with normal histology. The CsA monotherapy group displayed partially reduced lymphocyte infiltration compared to the untreated controls, but failed to inhibit early innate immune graft recognition events such as macrophage infiltration and TLR 2, TLR4, and MyD88, and was ultimately unsuccessful in preventing rejection (36.3+/-7.8 days). CONCLUSION: Observed suppressive effects of Serp-1 on early innate immune response components such as TLR-2 and 4, and on adaptive responses such as T-cell intragraft infiltration suggests that Serp-1 may modulate the transition from innate to adaptive immunity, exhibiting a synergistic effect on allograft survival when used in combination with a subtherapeutic dose of CsA.