The interaction of human peripheral blood eosinophils with bacterial lipopolysaccharide is CD14 dependent

Bacterial lipopolysaccharide (LPS, endotoxin) is a ubiquitous component of dust and air pollution and is suspected to contribute after inhalation to a n activation of eosinophils in bronchial tissues of asthmatic patients, pro voking inflammatory and allergic processes. We were therefore interested in the interaction of eosinophil granulocytes with LPS and have examined the activation of and uptake to human peripheral blood eosinophils by LPS, Eosi nophils were stimulated by LPS and the endotoxic component lipid A and the release of tumor necrosis factor alpha (TNF-alpha) and of the eosinophil-sp ecific granule protein eosinophil cationic protein (ECP) was estimated. The results show induction of TNF-alpha and ECP-release by LPS and lipid A in a dose-dependent manner. Anti-CD14 monoclonal antibody (moAb) (clone MEM-18 ) and the synthetic lipid A partial structure 406 blocked the release of TN F-alpha and ECP by LPS-stimulated eosinophils, Studies with radioactively l abeled LPS showed dose-dependent uptake of H-3-LPS to eosinophils. The 3H-L PS uptake was found to be specific because preincubation with unlabeled LPS , compound 406 and also anti-CD14 antibodies inhibited uptake of 3H-LPS to eosinophil granulocytes, By flow cytometry using anti-CD14 moAb and by reve rse transcriptase-polymerase chain reaction (RT-PCR) technique, CD14 expres sion was detectable. Furthermore, messenger RNA (mRNA) expression of Toll-l ike receptors (TLR)2 and TLR 4 was detected, indicating the presence of the se CD14 coreceptors, The results indicate that eosinophils can take up LPS and can be stimulated by LPS in a CD14-dependent manner. Hence, in addition to allergens, eosinophils interact with endotoxin,a process that possibly exacerbates ongoing inflammatory and allergic processes. (C) 2001 by The Am erican Society of Hematology.