Microarray analysis was used to investigate the effects of Bacillus anthracis lethal toxin (LT) on human neutrophil-like NB-4 cells to identify markers of intoxication. Genes down-regulated after a 2 h LT exposure included those encoding chemokines and transcription factors. Significant decreases in the mRNA of interleukin-8, CCL20, CCL3 and CCL4. which are important chemoattractants for immune cells, were observed using real-time PCR (12.3, 4.0, 4.1 and 2.2-fold (p<0.05), respectively). The decreases were more pronounced at 4 and 8 h and were LT-specific. Decreases in chemokine protein levels were evident after 24 h and were sensitive to low concentrations of LT. Co-incubation with an anti-lethal factor mAb at 500 and 250 ng/ml restored levels of interleukin-8 to 100% and 50%, respectively. The results reveal that LT suppresses the cellular immune response and that this assay is a useful tool for the analysis of toxin-neutralising antibody activity in a biologically relevant system. (C) 2008 Elsevier Inc. All rights reserved.