B. anthracis PGA and B. licheniformis PGA elicit signal in a human TLR4 assay. (A) 50, 250, and 500 μg/ml B. anthracis PGA, B. licheniformis PGA, or B. subtilis PGA were tested in a TLR4 assay. Mean data for four experiments are presented as ligand/vehicle ratios ± SEM (n = 4). Statistical significance of signal for each dose of PGA above its vehicle was determined by t test comparing the mean treatment/background ratios. Statistical significance of the difference between the responses to 500 μg/ml B. anthracis PGA and μg/ml B. licheniformis PGA was determined by t test. No significant responses to B. subtilis PGA were observed (data not shown). *p < 0.05, ***p < 0.001, ****p < 0.0001. (B) Mean ligand/vehicle ratios for TLR2 (n = 4 experiments) and TLR4 (n = 4 experiments) and their p values are shown. Ba, B. anthracis; Bl, B. licheniformis; Bs, B. subtilis; NR, no response.