By Anita Srikameswaran and Tim Betler The
presence of a certain molecule allows the immune system to effectively police
tuberculosis (TB) of the lungs and prevent it from turning into an active and
deadly infection, according to a new multicenter study led by Shabaana A.
Khader, Ph.D., an assistant professor of pediatrics at the University of Pittsburgh School of
Medicine and Children’s
Hospital of Pittsburgh of UPMC. The study was published today in the online
version of the Journal of Clinical Investigation. It’s
akin to reporting a break-in, Dr. Khader said. If a person calls 911 because of
a robbery, but doesn’t give a specific address, the police could come to the
neighborhood but don’t know for certain which home was invaded. In the body, a
molecule called CXCR5 can tell the immune cells which lung cells contain TB
bacteria so that they can surround them in a structure called a granuloma to
thwart further spread of the infection. For
the study, which was funded by the National
Institutes of Health, the researchers studied human TB-infected cells as
well animal models of the disease. They found that granulomas that contain
ectopic lymphoid structures, which resemble lymph nodes, are associated with
effective suppression of TB, and that granulomas that don’t contain them are
associated with active TB. They also learned that immune cells called T cells that
had a surface marker molecule called CXCR5 were associated with the presence of
ectopic lymphoid structures. “The
protective power of CXCR5 points us in a novel direction for future management
of TB,” Dr. Khader said. “These findings have powerful implications for the
development of vaccines to prevent infection.” More
than 2 billion people or one-third of the world’s population are infected with
mycobacterium tuberculosis, the bacterium that causes TB, Dr. Khader said. The
infection is challenging to treat partly because the bacillus is able to enter
cells and linger for years without causing symptoms, known as latent TB. Then,
typically when the immune system becomes impaired due to other reasons such as
age or HIV, the infection becomes active and causes the cough, night sweats,
fever and weight loss that characterize the disease.