Endotoxin potency in the A549 lung epithelial cell bioassay and the limulus amebocyte lysate assay

The purpose of this study was to elucidate to what extent the potency of en dotoxins measured by the limulus amebocyte lysate (LAL) assay is reflected in the potency in an in vitro assay based on release of interleukin-8 (IL-8 ) from a lung epithelial cell Line, A549. Lipopolysaccharides (LPS) from Es cherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Salmonella e nteritidis and detoxified LPS from E. coli were applied in serial dilutions in the LAL assay and in the A549 bioassay. Also 19 organic dust samples fr om waste recycling plants were tested. The A549 cells were incubated for 24 h with LPS or dust, and the IL-8 secretion was determined by ELISA. The me thod for evaluation of the LAL assay showed linearity for the four endotoxi ns. Using the slope as a measure of the potency factor (PF), LPS from E. co li and S. enteritidis was about four times more potent than that for LPS fr om K. pneumoniae and P. aeruginosa. In the A549 bioassay each of the differ ent types of endotoxin had characteristic and very different dose-response curves. The potency of the LPS, in the A549 bioassay, ranked as follows K, pneumoniae > P. aeruginosa > E. coli greater than or equal to S. enteritidi s. The content of endotoxin in the dust samples did not correlate with thei r potency in the A549 bioassay. The present study indicates a poor correlat ion between the potency of endotoxin in the LAL assay compared with the A54 9 bioassay. The lack of correlation when organic dust samples are tested ma y reflect the fact that these samples contain biological active compounds, which are non-reactive in the LAL-assay but stimulate IL-8 secretion from e pithelial cells. (C) 1999 Elsevier Science B.V. All rights reserved.