Table 2 ALO-mediated lysis of human monocytes by B. anthracis is inhibited by 10% FBS. Percent viable THP-1s in the presence of B. anthracis Sterne strain 7702 (ALO+), UT231 (ALO-) and the complemented over-producer, UT231 (pUTE544) (ALO++) at an MOI of 1000 in the presence of 10 % FBS. At various time points, aliquots were mixed with 0.25 % trypan blue to measure viability. Native ALO expressed by 7702, at all time points, and UT231 (pUTE544), at 5 min, is inhibited by cholesterol present in heat-inactivated 10% FBS. Results are average ± standard deviations of two experiments.