Knocking meningitis bacteria on the head
Sun, 22nd Feb 2009
Scientists have uncovered the chemical trick used by meningitis bacteria to evade the immune system.
The body has a system called complement, which comprises a cascade of enzymic reactions that are triggered off by the presence of foreign cells in the body. This cascade culminates in the production of molecules which lock onto foreign tissue such as bacterial cells, earmarking them for destruction, and also punching holes in their membranes. The body's own cells protect themselves from attack by adding to their surfaces a chemical marker called factor H, which allows the complement system to tell friend from foe. But Neisseria meningitidis, the commonest cause of bacterial meningitis in adults, has evolved a mechanism to cover itself in this same factor H, which it scavenges from the bloodstream using a molecule called FHbp - factor H binding protein.
As a result the bug slips under the body's immunological radar making it much harder to kill. Worse still, as the bacteria grow and spread in the bloodstream they can take up so much factor H that there isn't enough for the body's own cells and so they can become vulnerable to immune attack themselves, which might contribute to the dramatic haemorrhagic rash seen in some meningitis cases.
But now, writing in Nature, a team of researchers at Oxford University and Imperial College London have solved the 3D structure of the fhBP molecule to show how it locks on to factor H by pretending to be a marker on our own cells.
'It's like the bacteria have stolen someone's coat and put it on in an effort to look like them,' explains Oxford researcher and team member Professor Susan Lea. 'This protein enables the meningococcal bacteria to pass themselves off as human cells, and the disguise is good enough to fool the immune system.' The new work should help to guide researchers towards an effective vaccine for group B Neisseria meningitidis which can target this evasion system.