Ann. Méd. Vét., 2009, 153 (3), pp 135-144 Endotoxins in asthma : friends or foes?BEDORET D., LEKEUX P., BUREAU F.Abstract :
Respiratory mucosal surfaces are
constantly exposed to a broad range of non-pathogenic environmental antigens. In the absence of proinflammatory signals, inhalation of harmless antigens results in immunological tolerance. Indeed, lung dendritic cells stimulate the development of antigen-specific regulatory T cells. Nevertheless, epidemiological studies have shown that ambient air contains not
only inert antigens but also immunostimulatory molecules of microbial
origin. Of particular interest are
endotoxins, a cell wall component
of gram-negative bacteria that is
ubiquitous in the environment. In
spite of the fact that high levels
of endotoxin exposure in early life
protect against allergic sensitization,
most evidence indicates that exposure to house-dust endotoxin is a significant risk factor for increased asthma prevalence and severity. When the respiratory tract is stimulated with airborne endotoxins, lung dendritic cells lose their tolerogenic properties and rather promote the development of an allergic response directed against concomitant aeroantigens.
Although endotoxins are omnipresent
in the environment and favour airway allergy, only a minority of people develops asthma. These contradictory observations imply the existence of unknown mechanisms capable of preventing endotoxin-triggered allergic responses to inhaled antigens. Get the PDF Contact person : denis.bedoret@ulg.ac.be |