A team from the Institut Pasteur has recently shown that the tuberculosis bacillus hides from the immune system in its host's fat cells. This formidable pathogen is protected against even the most powerful antibiotics in these cells, in which it may remain dormant for years. This discovery, published in PLoS ONE, sheds new light on possible strategies for fighting tuberculosis. Attempts to eradicate the bacillus entirely from infected individuals should take these newly identified reservoir cells into account.

Mycobacterium tuberculosis, the bacillus responsible for tuberculosis can hide, in a dormant state, in adipose cells throughout the body. The bacterium is protected in this cellular environment, to which the natural immune defences have little access, and is inaccessible to isoniazid, one of the main antibiotics used to treat tuberculosis worldwide. These results were obtained by Olivier Neyrolles* and his colleagues from the Mycobacterial Genetics Unit directed by Brigitte Gicquel at the Institut Pasteur, in collaboration with Paul Forns, a pathologist from Hpital Europen Georges Pompidou. They raise questions of considerable importance in the fight against tuberculosis.

Tuberculosis kills almost two million people worldwide every year and is considered by the World Health Organisation to represent a global health emergency. However, the bacillus is much more prevalent in the world's population than the statistics would lead us to believe, because only 5 to 10% of those infected actually develop tuberculosis. The bacillus may be present in a significant proportion of the population, remaining in a "dormant" state in the body, sometimes for years, and may be "reactivated" at any time. The risk of rea ctivation is particularly high in immunocompromised individuals, such as those infected with AIDS: the HIV virus and the tuberculosis bacillus make a formidable team, with each infectious agent facilitating the progression of the other.