TB-causing bacteria appear to mask their identity to avoid recognition by infection-killing cells in the upper airways. The bacteria call up more permissive white blood cells in the deeper regions of the lungs and hitch a ride inside them to get into the host's body.
Details on this finding are reported Dec. 16 in the advanced online edition of the journal Nature. The research was a collaboration between the University of Washington and the Seattle Biomedical Research Institute.
Dr. Lalita Ramakrishan, who studies how TB evades the body's immune system and manipulates the body's defenses for its own ends, is the senior author. She is a UW professor of microbiology, medicine and immunology. The lead author is C.J. Cambier of the UW Department of Immunology.
Ramakrishnan noted that the recent study also suggests an explanation for the longstanding observation that tuberculosis infections begin in the comparatively sterile lower lungs. In the upper respiratory tract, resident microbes and inhaled microbes of a variety of species signal their presence.
These tip-offs alert and attract many infection-fighting cells to the upper airways. The presence of other microbes in the upper airway may thereby help to keep TB infections at bay by creating a hostile environment.
Their presence may explain why TB is a less contagious disease than those caused by several other respiratory pathogens.
To cause disease, TB bacteria must sneak through this well-patrolled area and head for parts of the lungs where fewer microbiocidal cells are policing.
Almost like intruders wearing a stocking over their faces to keep surveillance cameras from clearly recording their features, the TB pathogens produce particular types of fatty substances, or lipids, on their cell surfaces.
These lipids, abbreviated as PDIM, are already known to be associated with bacterial virulence. The researchers showed that P
|Contact: Leila Gray|
University of Washington