Meningitis bacteria ‘dress up as human cells to evade body's defences’

Researchers at the University of Oxford and Imperial College London have shown the way meningitis bacteria masquerade as human cells to evade our body's defences.

The Nature study could pave way for the development of new vaccines that give better protection against meningitis B.

Meningitis involves an inflammation of the membranes covering the brain and the spinal cord as the result of an infection. The infection can be due to a virus or bacteria, but bacterial meningitis is much more serious with approximately 5 percent of cases resulting in death.

The most common cause of bacterial meningitis is the bacterium Neisseria meningitides. It comes in different forms, causing different strains of the disease.

To reach the conclusion, the researchers looked at how one protein in the outside coat of Neisseria meningitidis enables the bacteria to avoid being attacked and killed by the complement system, part of the body''s innate immune system.

The complement system is designed to attack all foreign bodies that come into contact with the blood. We have particular sugar molecules on the surface of our own cells that flag them as being part of our body and stop them from being attacked and killed.

This system works through factor H, a molecule that circulates in the blood and binds to the sugars on the surface of our cells, preventing any immune response.

Critically, the protein on the outside of Neisseria bacteria also binds factor H. Called factor H binding protein, it makes the bacteria appear like human cells and so prevents any attack from the innate immune system.

The researchers, led by Professor Susan M. Lea of the Sir William Dunn School of Pathology at the University of Oxford and Professor Christoph M. Tang of the Centre for Molecular Microbiology and Infection at Imperial College London, determined the structure of human factor H attached to factor H binding protein on the meningitis bacterium.

They found that the protein in the bacterial coat mimicked the sugars on the surface of human cells precisely, enabling the bacteria to bind factor H in the same way as human cells.

"It''s like the bacteria have stolen someone''s coat and put it on in an effort to look like them," says Professor Lea of Oxford University, who led the work.

"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 researcher added.