A review of the use of CD14: a biomarker for workplace airborne endotoxin exposure?

Occupational exposure to endotoxin, a component of Gram-negative bacteria, causes short-term illness and contributes to long-term illness. There are currently no recognised objective markers of endotoxin exposure. Such a biomarker could be used to distinguish between symptoms caused by inhaled endotoxin or by other contaminants of organic aerosols and to demonstrate a cause and effect relationship between endotoxin exposure and impairment of respiratory function. Flow cytometry has been used to measure CD14, an endotoxin receptor on monocytes, which may be a useful biomarker of endotoxin exposure. An in vitro model was developed, CD14 expression on monocytes was significantly upregulated in response to endotoxin. In cotton dust workers exposed to 1–400 EU/m3 air, CD14 expression significantly increased after 6 h and at 72 h levels had fallen to baseline or lower. We propose that CD14 expression on monocytes may be used to monitor workers exposure to endotoxin.