The potential of a monocyte cell surface marker as an indicator of endotoxin exposure

Endotoxin is common in workplaces such as farms, grain processing plants and cotton mills, and exposure can lead to a wide variety of respiratory symptoms including organic toxic dust syndrome and chronic bronchitis. We developed an in vitro model to enable us to determine the use of lipopolysaccharide receptor (CD14) expression to act as a biomarker of endotoxin exposure. Whole blood was incubated with endotoxin, human serum albumin (HSA) or phosphate buffered saline (PBS) at 37 C to determine the time course of CD14 expression following in vitro stimulus. Fluorescent-labelled antibodies were used to label CD14 on monocytes, and CD45 on monocytes and lymphocytes. Levels of CD14 and CD45 expression were measured by flow cytometry. Levels of expression were determined on eight different samples at the optimum time point and concentration of endotoxin. CD14 expression on monocytes was upregulated in response to endotoxin exposure (p < 0 0001) and could be measured easily in whole blood samples using flow cytometry 4 h afterexposure. CD45 upregulation in response to endotoxin was monocytespecific (p < 0 0001), there was no significant difference in expression of CD45 on lymphocytes between the PBS and HSA controls and endotoxin-exposed cells (p= 0 6). We have shown that the expression of cell surface CD14 and CD45 was significantly increased following in vitro exposure to endotoxin, and that this response was specific for monocytes. We suggest that the measurement of CD14 on monocytes by flow cytometry may be a useful biomarkerof endotoxin exposure.