Genetic landscape of pediatric acute liver failure of indeterminate origin.

BACKGROUND AND AIMS: Pediatric acute liver failure (PALF) is a life-threatening condition. In Europe, the main causes are viral infections (12%-16%) and inherited metabolic diseases (14%-28%). Yet, in up to 50% of cases the underlying etiology remains elusive, challenging clinical management, including liver transplantation. We systematically studied indeterminate PALF cases referred for genetic evaluation by whole-exome sequencing (WES), and analyzed phenotypic and biochemical markers, and the diagnostic yield of WES in this condition. APPROACH AND RESULTS: With this international, multicenter observational study, patients (0-18 y) with indeterminate PALF were analyzed by WES. Data on the clinical and biochemical phenotype were retrieved and systematically analyzed. RESULTS: In total, 260 indeterminate PALF patients from 19 countries were recruited between 2011 and 2022, of whom 59 had recurrent PALF. WES established a genetic diagnosis in 37% of cases (97/260). Diagnostic yield was highest in children with PALF in the first year of life (41%), and in children with recurrent acute liver failure (64%). Thirty-six distinct disease genes were identified. Defects in NBAS (n=20), MPV17 (n=8), and DGUOK (n=7) were the most frequent findings. When categorizing, the most frequent were mitochondrial diseases (45%), disorders of vesicular trafficking (28%), and cytosolic aminoacyl-tRNA synthetase deficiencies (10%). One-third of patients had a fatal outcome. Fifty-six patients received liver transplantation. CONCLUSIONS: This study elucidates a large contribution of genetic causes in PALF of indeterminate origin with an increasing spectrum of disease entities. The high proportion of diagnosed cases and potential treatment implications argue for exome or in future rapid genome sequencing in PALF diagnostics.

Long-Term Evaluation of Gastroesophageal Reflux in Neonates with and without Preventive Anti-reflux Surgery at the Time of Congenital Diaphragmatic Hernia Repair.

One potential comorbidity after congenital diaphragmatic hernia (CDH) is gastroesophageal reflux (GER), which can have a substantial effect on patients' quality of life, thriving, and complications later in life. Efforts have been made to reduce gastroesophageal reflux with a preventive anti-reflux procedure at the time of CDH repair. In this follow-up study of neonates participating in a primary RCT study on preventive anti-reflux surgery, symptoms of GER were assessed longitudinally. Long-term data with a median follow-up time of ten years was available in 66 patients. Thirty-one neonates received an initial fundoplication. Secondary anti-reflux surgery was necessary in 18% and only in patients with large defects. It was required significantly more often in patients with intrathoracic herniation of liver (p = 0.015) and stomach (p = 0.019) and patch repair (p = 0.03). Liver herniation was the only independent risk factor identified in multivariate regression analysis. Primary fundopexy and hemifundoplication did not reveal a protective effect regarding the occurrence of GER symptoms, the need for secondary antireflux surgery or the gain of body weight regardless of defect size neither in the short nor in the long term. Symptoms of GER must be assessed carefully especially in children with large defects, as these are prone to require secondary anti-reflux surgery in the long-term. Routine evaluation of GER including endoscopy and impedance measurement should be recommended especially for high-risk patients.

Invasion of the choroid plexus epithelium by Neisseria meningitidis is differently mediated by Arp2/3 signaling and possibly by dynamin dependent on the presence of the capsule.

Neisseria meningitis (Nm) is a human-specific bacterial pathogen that can cause sepsis and meningitis. To cause meningitis Nm must enter the central nervous system (CNS) across one of the barriers between the blood and the brain. We have previously shown that a capsule-depleted Serogroup B strain of Nm displays enhanced invasion into human choroid plexus (CP) epithelial papilloma (HIBCPP) cells, which represent an in vitro model of the blood-cerebrospinal fluid barrier (BCSFB). Still, the processes involved during CNS invasion by Nm, especially the role of host cell actin cytoskeleton remodeling, are not investigated in detail. Here, we demonstrate that invasion into CP epithelial cells by encapsulated and capsule-depleted Nm is mediated by distinct host cell pathways. Whereas a Serogroup B wild-type strain enters HIBCPP cells by a possibly dynamin-independent, but actin related protein 2/3 (Arp2/3)-dependent mechanism, invasion by a capsule-depleted mutant is reduced by the dynamin inhibitor dynasore and Arp2/3-independent. Both wild-type and mutant bacteria require Src kinase activity for entry into HIBCPP cells. Our data show that Nm can employ different mechanisms for invasion into the CP epithelium dependent on the presence of a capsule.

The Impact of Small Extracellular Vesicles on Lymphoblast Trafficking across the Blood-Cerebrospinal Fluid Barrier In Vitro.

Central nervous System (CNS) disease in pediatric acute lymphoblastic leukemia (ALL) is a major concern, but still, cellular mechanisms of CNS infiltration are elusive. The choroid plexus (CP) is a potential entry site, and, to some extent, invasion resembles CNS homing of lymphocytes during healthy state. Given exosomes may precondition target tissue, the present work aims to investigate if leukemia-derived exosomes contribute to a permissive phenotype of the blood-cerebrospinal fluid barrier (BCSFB). Leukemia-derived exosomes were isolated by ultracentrifugation from the cell lines SD-1, Nalm-6, and P12-Ichikawa (P12). Adhesion and uptake to CP epithelial cells and the significance on subsequent ALL transmigration across the barrier was studied in a human BCSFB in vitro model based on the HiBCPP cell line. The various cell lines markedly differed regarding exosome uptake to HiBCPP and biological significance. SD-1-derived exosomes associated to target cells unspecifically without detectable cellular effects. Whereas Nalm-6 and P12-derived exosomes incorporated by dynamin-dependent endocytosis, uptake in the latter could be diminished by integrin blocking. In addition, only P12-derived exosomes led to facilitated transmigration of the parental leukemia cells. In conclusion, we provide evidence that, to a varying extent, leukemia-derived exosomes may facilitate CNS invasion of ALL across the BCSFB without destruction of the barrier integrity.

Experience with Stent Placement for Benign Pancreaticobiliary Disorders in Children.

Purpose: There is a lack of experience with stenting for benign pancreaticobiliary disorders in children. Materials and Methods: Fifteen children (9 male and 6 female) with a median age of 7.1 years (range 0.7-14.2 years) who underwent treatment with a plastic stent for a benign disorder of the pancreaticobiliary system between May 2003 and September 2017 were recruited to this retrospective study. Results: Biliary and/or pancreatic plastic stents were inserted into 5 patients with congenital, 4 with post-traumatic, and 6 with idiopathic pathologies. Median duration of individual stent placement was 111 days (range 14-1569 days). Eleven children (73%) were treated with one stent only. In 4 cases, up to 22 stents were successively placed over time. There were no complications during stent insertion or stent removal. Seven patients (47%) experienced adverse effects during stenting, including choledocholithiasis, pancreaticolithiasis, cholangitis, acute pancreatitis, stent obstruction, and stent fracture. At follow-up, in 11 cases (73%), the underlying condition was resolved. In 4 children, all of whom suffered from congenital pancreaticobiliary disorders, stent therapy was considered as a temporary treatment before definite surgery. Conclusions: Patients with congenital anomalies of the pancreaticobiliary tree often require surgery for definitive management. However, temporary stent placement can be accomplished safely and successfully and this serves as a bridge to temporize their obstructive process while awaiting surgical intervention. Children with post-traumatic or idiopathic disorders can frequently be managed definitively by stenting alone and many of these require only one single stent insertion.

Virulence factor-dependent basolateral invasion of choroid plexus epithelial cells by pathogenic Escherichia coli in vitro.

Escherichia coli is the most common Gram-negative causative agent of neonatal meningitis and E. coli meningitis is associated with high morbidity and mortality. Previous research has been carried out with regard to the blood-brain barrier and thereby unveiled an assortment of virulence factors involved in E. coli meningitis. Little, however, is known about the role of the blood-cerebrospinal fluid (CSF) barrier (BCSFB), in spite of several studies suggesting that the choroid plexus (CP) is a possible entry point for E. coli into the CSF spaces. Here, we used a human CP papilloma (HIBCPP) cell line that was previously established as valid model for the study of the BCSFB. We show that E. coli invades HIBCPP cells in a polar fashion preferentially from the physiologically relevant basolateral side. Moreover, we demonstrate that deletion of outer membrane protein A, ibeA or neuDB genes results in decreased cell infection, while absence of fimH enhances invasion, although causing reduced adhesion to the apical side of HIBCPP cells. Our findings suggest that the BCSFB might constitute an entry point for E. coli into the central nervous system, and HIBCPP cells are a valuable tool for investigating E. coli entry of the BCSFB.

Capsule and fimbriae modulate the invasion of Haemophilus influenzae in a human blood-cerebrospinal fluid barrier model.

The Gram-negative bacterium Haemophilus influenzae (H. influenzae) can commensally colonize the upper respiratory tract, but also cause life threatening disease including epiglottitis, sepsis and meningitis. The H. influenzae capsule protects the bacteria against both phagocytosis and opsonization. Encapsulated H. influenzae strains are classified into serotypes ranging from a to f dependent on their distinct polysaccharide capsule. Due to the implementation of vaccination the incidence of invasive H. influenzae type b (Hib) infections has strongly decreased and infections with other capsulated types, including H. influenzae type f (Hif), are emerging. The pathogenesis of H. influenzae meningitis is not clarified. To enter the central nervous system (CNS) the bacteria generally have to cross either the blood-brain barrier (BBB) or the blood-cerebrospinal fluid barrier (BSCFB). Using a cell culture model of the BCSFB based on human choroid plexus papilloma (HIBCPP) cells and different H. influenzae strains we investigated whether Hib and Hif invade the cells, and if invasion differs between encapsulated vs. capsular-deficient and fimbriated vs. non-fimbriated variants. We find that Hib can adhere to and invade into HIBCPP cells. Invasion occurs in a strongly polar fashion, since the bacteria enter the cells preferentially from the basolateral "blood "side. Fimbriae and capsule attenuate invasion into choroid plexus (CP) epithelial cells, and capsulation can influence the bacterial distribution pattern. Finally, analysis of clinical Hib and Hif isolates confirms the detected invasive properties of H. influenzae. Our data point to roles of capsule and fimbriae during invasion of CP epithelial cells.

Weibel-Palade Body Localized Syntaxin-3 Modulates Von Willebrand Factor Secretion From Endothelial Cells.

OBJECTIVE: Endothelial cells store VWF (von Willebrand factor) in rod-shaped secretory organelles, called Weibel-Palade bodies (WPBs). WPB exocytosis is coordinated by a complex network of Rab GTPases, Rab effectors, and SNARE (soluble NSF attachment protein receptor) proteins. We have previously identified STXBP1 as the link between the Rab27A-Slp4-a complex on WPBs and the SNARE proteins syntaxin-2 and -3. In this study, we investigate the function of syntaxin-3 in VWF secretion. APPROACH AND RESULTS: In human umbilical vein endothelial cells and in blood outgrowth endothelial cells (BOECs) from healthy controls, endogenous syntaxin-3 immunolocalized to WPBs. A detailed analysis of BOECs isolated from a patient with variant microvillus inclusion disease, carrying a homozygous mutation in STX3(STX3-/-), showed a loss of syntaxin-3 protein and absence of WPB-associated syntaxin-3 immunoreactivity. Ultrastructural analysis revealed no detectable differences in morphology or prevalence of immature or mature WPBs in control versus STX3-/- BOECs. VWF multimer analysis showed normal patterns in plasma of the microvillus inclusion disease patient, and media from STX3-/- BOECs, together indicating WPB formation and maturation are unaffected by absence of syntaxin-3. However, a defect in basal as well as Ca2+- and cAMP-mediated VWF secretion was found in the STX3-/- BOECs. We also show that syntaxin-3 interacts with the WPB-associated SNARE protein VAMP8 (vesicle-associated membrane protein-8). CONCLUSIONS: Our data reveal syntaxin-3 as a novel WPB-associated SNARE protein that controls WPB exocytosis.

Loss of syntaxin 3 causes variant microvillus inclusion disease.

Microvillus inclusion disease (MVID) is a disorder of intestinal epithelial differentiation characterized by life-threatening intractable diarrhea. MVID can be diagnosed based on loss of microvilli, microvillus inclusions, and accumulation of subapical vesicles. Most patients with MVID have mutations in myosin Vb that cause defects in recycling of apical vesicles. Whole-exome sequencing of DNA from patients with variant MVID showed homozygous truncating mutations in syntaxin 3 (STX3). STX3 is an apical receptor involved in membrane fusion of apical vesicles in enterocytes. Patient-derived organoid cultures and overexpression of truncated STX3 in Caco-2 cells recapitulated most characteristics of variant MVID. We conclude that loss of STX3 function causes variant MVID.

In vitro transcriptome analysis of porcine choroid plexus epithelial cells in response to Streptococcus suis: release of pro-inflammatory cytokines and chemokines.

The Gram-positive zoonotic bacterium Streptococcus suis (S. suis) is responsible for a wide range of diseases including meningitis in pigs and humans. The blood-cerebrospinal fluid (CSF) barrier is constituted by the epithelial cells of the choroid plexus, which execute barrier function also after bacteria have entered the central nervous system (CNS). We show that the bacterial capsule, a major virulence factor, strongly attenuates adhesion of S. suis to the apical side of porcine choroid plexus epithelial cells (PCPEC). Oligonucleotide microarray analysis and quantitative PCR surprisingly demonstrated that adherent wild-type and capsule-deficient S. suis influenced expression of a pronounced similar pattern of genes in PCPEC. Investigation of purified capsular material provided no evidence for a significant role of the capsule. Enriched among the regulated genes were those involved in "inflammatory response", "defense response" and "cytokine activity". These comprised several cytokines and chemokines including the interleukins 6 and 8, which could be detected on protein level. We show that after infection with S. suis the choroid plexus contributes to the immune response by actively producing cytokines and chemokines. Other virulence factors than the bacterial capsule may be relevant in inducing a strong inflammatory response in the CNS during S. suis meningitis.

Therapy-refractory gastrointestinal motility disorder in a child with c-kit mutations.

Constipation and fecal impaction are frequent and distressing complaints in pediatric gastroenterology. Especially in neurologically handicapped children, treatment of severe forms of slow-transit constipation (STC) can be difficult. In the majority of cases, STC is of unknown etiology. However, in recent years, there is growing evidence that interstitial cells of Cajal (ICCs), which serve as electrical pacemakers and generate spontaneous electrical slow waves in the gastrointestinal tract, might play an important role in the pathophysiology of STC. It remains unclear whether morphological ICC alterations seen in affected patients are based on congenital developmental anomalies, or whether they are a consequence of long-term constipation with secondary damage of the gastrointestinal nervous system. To the best of our knowledge, we present the first case of a patient with histological alterations in ICC morphology who displayed multiple alterations of c-kit at the level of mRNA. The protein encoded by c-kit is the receptor tyrosine kinase Kit (CD117), which is crucial for development and function of ICCs. Therefore, these findings provide a new explanation for congenital alterations of ICC development that result in gastrointestinal motility disorders.

Polar bacterial invasion and translocation of Streptococcus suis across the blood-cerebrospinal fluid barrier in vitro.

Previous experimental studies in a standard Transwell culture system have shown Streptococcus suis ability to compromise barrier function of porcine choroid plexus epithelial cells (PCPEC). The development of an 'inverted' Transwell filter system of PCPEC enables us now for the first time to investigate bacterial invasion and translocation from the physiologically relevant basolateral (blood) to the apical (cerebrospinal fluid) side. Most importantly, we observed specific invasion and translocation of S. suis across the PCPEC exclusively from the basolateral side. During this process, bacterial viability and the presence of a capsule as well as cytoskeletal regulation of PCPEC seemed to play an important role. No loss of barrier function was observed. Bacterial translocation could be significantly inhibited by the phosphatidylinositol 3-kinase inhibitor LY294002, but not by its inactive analogue Ly303511 or dexamethasone. Apotome imaging as well as electron microscopy revealed intracellular bacteria often in cell vacuoles. Thus, possibly regulated by the presence of a capsule, S. suis induces signals that depend on the lipid kinase phosphatidylinositol 3-kinase pathway, which paves the way for cellular uptake during the bacterial transcellular translocation process. Taken together, our data underline the relevance of the blood-cerebrospinal fluid barrier as a gate for bacterial entry into the central nervous system.

Dexamethasone prevents alteration of tight junction-associated proteins and barrier function in porcine choroid plexus epithelial cells after infection with Streptococcus suis in vitro.

Apart from antibiotic treatment in bacterial meningitis supportive therapy including dexamethasone is widely used. In investigations on the pathogenesis of bacterial meningitis we previously demonstrated that Streptococcus suis (S. suis), a relevant cause of bacterial meningitis in pigs and humans, affects porcine choroid plexus epithelial cell (PCPEC) barrier function. The choroid plexus epithelium constitutes the structural basis of the blood-CSF barrier. Now, we investigated the role of tight junction proteins and the actin cytoskeleton of PCPEC in correlation to barrier function after S. suis infection and analyzed the influence of dexamethasone. S. suis caused massive rearrangement of the tight junction proteins ZO-1, occludin and claudin-1, caused loss of actin at the apical cell pole and induced basolateral stress fiber formation. Moreover, tight junctions were shifted from the Triton X insoluble to the Triton X soluble fraction, and additionally occludin was dephosphorylated and degraded. Infection with S. suis leads to an inflammatory response exemplified by the induction of tumor necrosis factor (TNF) alpha and matrix metalloproteinase (MMP)-3 gene activation, which correlated with phosphorylation of extracellular signal regulated kinases (ERKs). Importantly, dexamethasone significantly prevented S.suis-induced protein and morphological tight junction alterations and attenuated ERK activation and MMP-3 expression. It especially improved the barrier function by preventing tight junction protein reorganization and degradation. In the pathogenesis of bacterial meningitis protection of blood-CSF barrier by dexamethasone may prevent the penetration of bacteria and leukocytes into the CSF.

Case report: severe gastrointestinal inflammation and persistent HHV-6B infection in a paediatric cancer patient.

Lymphotropic herpesviruses such as human herpesvirus type 6 (HHV-6) have enhanced pathogenicity in some immunocompromised hosts, such as transplant recipients and HIV-infected patients. The clinical relevance of HHV-6 infections in cancer patients undergoing conventional cytotoxic therapy is undetermined, however. Here we report on a 10-month-old boy with an anaplastic astrocytoma, who acquired an HHV-6 variant B infection during chemotherapy. HHV-6B infection caused or triggered severe gastrointestinal inflammation with intractable diarrhoea and failure to thrive over several months. The clinical symptoms were associated with pronounced (CD4) lymphopenia and a marked increase in serum immunoglobulin A levels. After unsuccessful therapy with ganciclovir and foscarnet, combined antiviral and anti-inflammatory treatment with cidofovir and prednisolone controlled the HHV-6 infection and enabled resolution of clinical symptoms.

How to prevent small stature in Rett syndrome-associated collapsing spine syndrome.

Severe scoliosis in Rett syndrome is an important orthopedic, neurologic, and pediatric problem. The curve in Rett syndrome is of a neurologic type, has its highest incidence during early childhood, and shows rapid progression. In this study, the authors report the results of a 4-year follow-up of a 10-year-old Rett syndrome female patient with early onset and severe rapid progressive thoracolumbar scoliosis. The first signs of spinal deformity were documented at age 3 years. During adolescence, the patient developed a 115-degree thoracolumbal scoliosis with reduced respiratory volume due to a collapsing spine syndrome. To stop this life-threatening progression of the curve, the patient was treated by a 2-stage surgical procedure. The combination of an anterior release, halo traction, and posterior instrumented fusion from Th3 to L5 using a computer-assisted technique was performed. An excellent reduction of the deformity was achieved (postoperative 24-degree Cobb angle). After 4 years, the authors found a radiologically solid spinal fusion and no progression of the deformity. Operative treatment regimes and etiology of severe spinal deformities in Rett syndrome were discussed. The high perioperative risks in Rett syndrome patients who underwent spinal surgery may be reduced by an early cooperation between orthopedic and pediatric specialists. When considering recent data from literature, it can be concluded that an early correction of spine deformities in Rett syndrome patients may prevent a life-threatening collapsing spine syndrome.

Cell death, caspase activation, and HMGB1 release of porcine choroid plexus epithelial cells during Streptococcus suis infection in vitro.

The choroid plexus epithelium constitutes the structural basis of the blood-cerebrospinal fluid barrier. We previously demonstrated that Streptococcus suis (S. suis), a relevant cause of bacterial meningitis in pigs and humans, affects porcine choroid plexus epithelial cell (PCPEC) barrier function and integrity. We now characterized PCPEC cell death and investigated whether apoptosis or necrosis is responsible for the cytotoxicity after infection with different S. suis isolates. We found S. suis strain-dependent histone associated DNA-fragments quantified by ELISA. This response could partially be inhibited by cylcoheximide, cytochalasin D, dexamethasone, herbimycin A, but most effectively by the pan-caspase inhibitor zVAD-fmk. We further detected caspase-3 and -9 activation after infection with all tested S. suis isolates that could also be blocked by zVAD-fmk. However, we found a significantly stronger caspase activity with the protein kinase inhibitor staurosporine. All tested S. suis isolates induced loss of cell viability in PCPEC as shown with the Live/Dead assay, but strain dependent lactate dehydrogenase-release. Both parameters could not be influenced by zVAD-fmk. Immunostaining showed release of high-mobility group box 1 (HMGB1) protein from the nucleus, indicative of necrosis. Transmission electron microscopy showed cell swelling, cytoplasmic vacuolization, loss of membrane integrity, nuclear fermentation but no nuclear condensation, indices for a primarily necrotic cell morphology. Taken together, our findings indicate that S. suis causes cell death in PCPEC by different mechanisms. Although apoptosis may be involved in the process of PCPEC cell death, necrosis seems to be the predominant mechanism. Through inflammation in the choroid plexus during bacterial meningitis, the blood-cerebrospinal fluid barrier function will be compromised.

Role of human brain microvascular endothelial cells during central nervous system infection. Significance of indoleamine 2,3-dioxygenase in antimicrobial defence and immunoregulation.

The cerebral endothelium is involved both in regulating the influx of immune cells into the brain and in modifying immunological reactions within the CNS. A number of human pathogens may cause encephalitis or meningitis when this important protective barrier is impaired. We have previously shown that interferon-gamma activated human brain microvascular endothelial cells (HBMEC) restrict the growth of bacteria and parasites. We now provide evidence that HBMEC are also capable of inhibiting viral replication after stimulation with IFN-gamma, an effect further augmented by costimulation with IL-1. This antiviral effect was completely blocked in the presence of L-tryptophan, indicating the induction of the tryptophan degrading enzyme indoleamine 2,3-dioxygenase (IDO) to be responsible for the observed antiviral effect. Apart from exerting antimicrobial effects tryptophan depletetion has also been described as a regulatory mechanism in T cell responses to both allo- and autoantigens. We were able to demonstrate that IDO mediated degradation of L-tryptohan in HBMEC is responsible for a significant reduction in T lymphocyte proliferation. Resupplementation of L-tryptophan and restoration of initial T cell responses demonstrated the central role of this essential amino acid in the reduction of T-cell proliferation. Brain endothelial cells appear to limit microbial expansion in the CNS by local degradation of tryptophan, thus acting in concert with other IDO-positive cell populations on the parenchymal side of the blood-brain barrier such as astrocytes, microglia and neurons. Since all dietary tryptophan must cross the blood-brain barrier, the microvascular endothelial cells may play a key role in restricting tryptophan influx from the bloodstream into the brain. As deleterious effects of brain infections can often be attributed to subsequently invading immune cells, an IDO-mediated reduction of lymphocyte proliferation may be beneficial for preventing collateral brain damage.

Strain-dependent disruption of blood-cerebrospinal fluid barrier by Streptoccocus suis in vitro.

Streptococcus suis capsular type 2 is an important agent of diseases including meningitis among pigs worldwide, and is also a zoonotic agent. The barrier function of the choroid plexus epithelium that constitutes the structural basis for the blood-cerebrospinal fluid (CSF) barrier has not been elucidated yet in bacterial meningitis. We investigated the influence of various S. suis isolates on the barrier function of cultured porcine choroid plexus epithelial cells with respect to the transepithelial resistance and paracellular [(3)H]-mannitol flux. Preferentially apical application of S. suis isolates significantly decreased transepithelial resistance and significantly increased paracellular [(3)H]-mannitol flux in a time-, dose- and strain-dependent manner. Viable S. suis isolates caused cytotoxicity determined by lactate dehydrogenase assay and electron microscopy, whereas S. suis sonicates and UV-inactivated S. suis did not cause cytotoxicity. The observed effects on porcine choroid plexus epithelial cells barrier function could not exclusively be ascribed to known virulence factors of S. suis such as suilysin. In conclusion, S. suis isolates induce loss of blood-cerebrospinal fluid barrier function in an in vitro model. Thus, S. suis may facilitate trafficking of bacteria and leucocytes across the blood-cerebrospinal fluid barrier. The underlying mechanisms for the barrier breakdown have yet to be determined.

Porcine choroid plexus epithelial cells induce Streptococcus suis bacteriostasis in vitro.

The involvement of the choroid plexus in host defense during bacterial meningitis is unclear. Aiming to elucidate possible antibacterial mechanisms, we stimulated primary porcine choroid plexus epithelial cells (pCPEC) with proinflammatory cytokines and challenged them with various Streptococcus suis strains. In the supernatant of gamma interferon (IFN-gamma)-stimulated pCPEC, streptococcal growth was markedly suppressed. Costimulation with tumor necrosis factor alpha enhanced this bacteriostatic effect, while supplementation of L-tryptophan completely eliminated it. We also demonstrate that an activation of indoleamine 2,3-dioxygenase in the pCPEC seems to be responsible for the IFN-gamma-induced bacteriostasis. This supports the hypothesis of an active role of the choroid plexus in host defense against bacterial meningitis.