The role of non-endotoxin components of the meningococcus and of mannose binding lectin (MBL) in the pathogenesis of acute meningococcal infections

Fulminant meningococcal sepsis (FMS) is considered the prototypic gram-negative human infection. Much of our knowledge on gram-negative sepsis is based on studies of patients with Neisseria meningitides sepsis. FMS is a frightening disease that can kill mainly healthy young children within 24 hours. It is caused by the overwhelming outgrowth of meningococci in the bloodstream. This leads to release of endotoxin i.e. lipopolysaccharide (LPS) and induces shock via activation of inflammatory mediators like complement-proteins and cytokines, i.e. interleukin-1ß (IL-1ß) and tumour necrosis factor-a (TNFa). So far, all trials with LPS-blocking drugs turned out to be negative and therefore the question is raised whether non-LPS moieties contribute to the pathogenesis more than previously thought. Improvement of therapy for FMS (or other types of Gram-negative sepsis) requires better insight in the mechanisms that permit the outgrowth of bacteria in the bloodstream and processes that lead to activation of inflammatory mediators. This is the principal objective of the present study. More precisely, the first aim of the study is to define to what extent non-LPS components of N. meningitides contribute to the activation of pro-inflammatory mediators. Second, the study aims to unravel the role of Mannose Binding Lectin (MBL) and MBL-polymorphism in the outgrowth of meningococci and the induction of cytokines. The third aim of the study is to determine in patients with meningococcal disease the time course of LPS, MBL and proinflammatory mediators in plasma and bound to blood cells. To achieve these goals the study comprises in-vitro laboratory studies, in-vivo studies with mice and observational studies in patients. The analytical work will be done in the laboratory of General Internal Medicine in Nijmegen by the AGIKO-candidate with analytical support by laboratory technicians. MBL assays are done in co-operation with the Institute of Child Health in London (Prof M Turner). LPS-analysis in patient samples and complement assays will be done in co-operation with the Department of Pediatrics, Ullevâl University, Oslo (Prof P Brandtzaeg). Cell-bound cytokines will be measured in cooperation with Dr Jean-Marc Cavaillon of the Institute Pasteur in Paris. The in-vitro laboratory studies include cytokine production studies with human peripheral blood cells or cell-lines stimulated with various types of meningococcal LPS, complete meningococci and mutant meningococci deficient for LPS or other virulence factors. These mutant strains were constructed for vaccine development purposes by the National Institute of Environmental Health (RIVM). In these experiments the role of serum-proteins like MBL and LPS-binding protein (LBP) and the signalling pathways (via CD 14, TLR2, TLR4) will be assessed. In experiments with mice deficient for these receptors, the disease inducing potency of the various types of LPS and non-LPS will be determined in-vivo. For the patient studies, data and blood samples are obtained from patients admitted to the ICU of the UMC-St. Radboud (± 20 patients yearly). To facilitate the start of the study samples collected during the last 10 years at the ICU in Nijmegen and Oslo are available. Patient samples will be analysed for MBL-plasma-concentrations and MBL-polymorphisms.