Meningitis affects about 3000 people every year in the UK and in those patients presenting with severe shock, the death rate may be as high as 50%. Although meningitis can occur at any age, it mainly affects babies and younger children who have less natural immunity. Recent studies have indicated that a protein, mannose binding lectin (MBL) is important in our natural defence against Neisseria meningitidis, a bacterium which causes meningitis and septicaemia. This proposal aims to explore the mechanisms by which this protein may control our defence against these bacteria. This should provide considerable insight into the role of MBL in meningitis and establish a rationale for its use as a method of treatment.