ScienceDaily (Nov. 19, 2008) — "Foamy" macrophage formation may be the key to persistence of infection by Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis, explains a new study. These immunity-related cells are shown to be a safety reservoir where the bacterium can hide for years in infected individuals, before inducing an active disease.

According to the research group led by Frederic Altare, the tubercle bacillus circumvents the host immune response by inducing the transformation of aggressive immune cells into a non-aggressive refuge where it is able to survive and have access to large sources of nutrients.

Mtb is responsible for a dramatic global health problem. The World Health Organization has estimated that this pathogen infects one third of the human population and causes three million deaths annually. Most individuals remain asymptomatic for several years before developing an active disease. In such individuals, it is generally admitted that the bacilli are not cleared but rather persist in a dormant state. One of the main goals of TB research is to understand how and where the bacilli survive within infected hosts.

Using a recently developed in vitro assay mimicking the human host immune response, the researchers observed that Mtb uses some of its cell surface constituents to induce the transformation of macrophages (which are supposed to internalize and kill infecting bacteria), into "foamy" cells. These cells have lost their killing ability and have accumulated large amounts of lipids, the main nutrient for internalized Mtb. They further observed that Mtb remained alive within these cells, and switched into a dormant state.

This observation may direct novel research towards the elucidation of tubercle bacillus survival mechanisms. This study also helps explain the role of a previously uncharacterized cell population participating in the human response to Mtb. "Foamy" macrophages may prove to be a useful tool for the development of new antimicrobial drugs targeted to kill the bug directly within its natural shelter.

Journal reference:

1. Peyron et al. Foamy Macrophages from Tuberculous Patients' Granulomas Constitute a Nutrient-Rich Reservoir for M. tuberculosis Persistence. PLoS Pathogens, 2008; 4 (11): e1000204 DOI: 10.1371/journal.ppat.1000204

Related Stories

Tuberculosis Bacillus Hides From Immune System In Host's Fat Cells (Dec. 24, 2006) — 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 ...  > read more

Air Pollution, Smoking Affect Latent Tuberculosis (May 14, 2008) — A toxic gas present in air pollution and tobacco smoke plays a significant role in triggering tuberculosis infection, according to a new study. The study shows for the first time how carbon monoxide ...  > read more

Researchers Discover Ancient Origins Of Tuberculosis-causing Bacteria (Aug. 20, 2005) — In the new open access journal PLoS Pathogens, researchers report that M. tuberculosis and related strains recently emerged from a much more ancient bacterial ...  > read more

One Secret To How TB Sticks With You (July 13, 2009) — Mycobacterium tuberculosis is arguably the world's most successful infectious agent because it knows how to avoid elimination by slowing its own growth to a crawl. Now, scientists offer new insights ...  > read more

Search ScienceDaily

Bacteria-Killing Bandage