Anthrax toxins inhibit neutrophil signaling pathways in brain endothelium and contribute to the pathogenesis of meningitis

BACKGROUND

Anthrax meningitis is the main neurological complication of systemic infection with Bacillus anthracis approaching 100% mortality. The presence of bacilli in brain autopsies indicates that vegetative bacteria are able to breach the blood-brain barrier (BBB). The BBB represents not only a physical barrier but has been shown to play an active role in initiating a specific innate immune response that recruits neutrophils to the site of infection. Currently, the basic pathogenic mechanisms by which B. anthracis penetrates the BBB and causes anthrax meningitis are poorly understood.

METHODOLOGY/PRINCIPAL FINDINGS

Using an in vitro BBB model, we show for the first time that B. anthracis efficiently invades human brain microvascular endothelial cells (hBMEC), the single cell layer that comprises the BBB. Furthermore, transcriptional profiling of hBMEC during infection with B. anthracis revealed downregulation of 270 (87%) genes, specifically key neutrophil chemoattractants IL-8, CXCL1 (Gro alpha) and CXCL2 (Gro beta), thereby strongly contrasting hBMEC responses observed with other meningeal pathogens. Further studies using specific anthrax toxin-mutants, quantitative RT-PCR, ELISA and in vivo assays indicated that anthrax toxins actively suppress chemokine production and neutrophil recruitment during infection, allowing unrestricted proliferation and dissemination of the bacteria. Finally, mice challenged with B. anthracis Sterne, but not the toxin-deficient strain, developed meningitis.

CONCLUSIONS/SIGNIFICANCE

These results suggest a significant role for anthrax toxins in thwarting the BBB innate defense response promoting penetration of bacteria into the central nervous system. Furthermore, establishment of a mouse model for anthrax meningitis will aid in our understanding of disease pathogenesis and development of more effective treatment strategies.

Iatrogenic (para-) spinal abscesses and meningitis following injection therapy for low back pain

Low back pain is often treated with paraspinal injections of analgesics and steroids. Infectious complications of these techniques are rare but they can potentially hold high risks for the patients. History and clinical data of all patients admitted to a neurological unit suffering from community acquired purulent meningitis were prospectively analyzed during an 8 year interval (1992 and 2000) with special regard to the previous medical history. One hundred and twenty eight patients were included in the study. Eight out of 128 patients (6.25%) had a history of single or repeated paravertebral (4/8), facet-joint (2/8), peridural (1/8) or spinal (1/8) injections 2-21 days before admission to the hospital. In six out of eight patients either Staphylococcus aureus (4/8) or coagulase-negative staphylococci (2/8) were found in the cerebro spinal fluid (CSF), in two patients no causative organism was detected. One patient died, three survived with sequel. Repeated paraspinal, peridural or spinal injections with analgesic drugs in combination with corticosteroids hold a risk for parameningeal inoculation of bacteria resulting in paraspinal, spinal, and epidural abscesses or meningitis. The absolute frequency of these complications may be rare but they are responsible for a considerable proportion of community acquired purulent CNS infections.

Impaired anti-pneumococcal polysaccharide antibody production and invasive pneumococcal infection following heart transplantation

An increased risk of invasive pneumococcal infection has been described among adult heart transplant (HT) recipients. Vaccination has been recommended before HT but the appropriate time for revaccination is not known. In a preliminary analysis of a prospective study involving a cohort of 32 HT recipients receiving daclizumab and triple immunosuppresion therapy, a progressive decline in pneumococcal polysaccharide antibody (anti-PPS) levels was observed during the first year after HT. One of the patients who was found to have a decrease in the levels of anti-PPS developed severe pneumococcal meningitis 20 months after HT. Before HT he had received non-conjugated 23-valent pneumococcal vaccine and showed a normal post-immunization anti-PPS production. The data suggest that long-term immunologic monitoring might be useful to recognize impairment of antibody responses under immunosuppressive therapy in HT.

Implication of long non-coding RNA NEAT1 in the pathogenesis of bacterial meningitis-induced blood-brain barrier damage

PURPOSE

Blood-brain barrier (BBB) damage is closely related to various neurological disorders, including bacterial meningitis (BM). Determining a reliable strategy to prevent BBB damage in the context of infection would be highly desirable. In the present study, we investigated the implications of the long non-coding RNA (lncRNA) nuclear paraspeckle assembly transcript 1 (NEAT1) in moderating BBB damage.

METHODS

In vitro BBB models were developed by co-culturing hCMEC/D3 cells with glioma cells, whereupon the glioma-exposed endothelial cells (GECs) were treated with a series of mimics, inhibitors, overexpression plasmids, and shRNAs for evaluating whether NEAT1, microRNA-135a (miR-135a) and hypoxia-inducible factor 1α (HIF1α) mediated BBB integrity and permeability. Furthermore, the in vivo biological function of NEAT1 was validated in a mouse model of BBB damage.

RESULTS

NEAT1 and HIF1α were determined to be up-regulated, while miR-135a was under-expressed in GECs. As demonstrated by chromatin immunoprecipitation and dual-luciferase reporter assays, NEAT1 could bind to miR-135a, and HIF1α was confirmed as a target of miR-135a. Either overexpression of NEAT1 or depletion of miR-135a impaired the integrity and augmented the permeability of BBB. However, HIF1α silencing could reverse the BBB damage induced by NEAT1 overexpression or by inhibition of miR-135a. In vivo experiments substantiated that knockdown of NEAT1 could alleviate BBB damage in living mice.

CONCLUSIONS

Hence, NEAT1 knockdown prevents BBB disruption and exerts promise as a potential target for BM treatment.

Fatal Disseminated Mycobacterium chelonae Infection in an Immunocompromised Host--A Unique Presentation

Disseminated disease due to rapidly growing non tuberculous mycobacteria especially in the immunocompromised host is being increasingly reported. The usual manifestations of disease being skin and soft tissue infection, post operative wound infection and pulmonary disease. We present a case of a disseminated infection due to Mycobacterium chelonae with features of chronic meningitis and knee joint arthritis in a patient with systemic lupus erythematosus on systemic steroids and mycophenolate. M chelonae was isolated from both synovial and cerebrospinal fluid and anti microbial therapy was initiated as per sensitivity results. However the patient's clinical condition continued to worsen and she succumbed to her illness.