(A) Bacillus anthracis endospores are taken up by human PMNs but do not germinate efficiently within. Human PMNs were incubated for 1, 3 and 6 h in the presence of B. anthracis endospores at an MOI of 1:1. Germination was determined by counting the colony-forming units at time 0 and after 1, 3 and 6 h with and without heating the endospores at 65°C. (B) Vegetative 34F2 B. anthracis were incubated for 1 h in the presence of human PMNs at an MOI of 1:1, either in the presence or absence of 10% normal human serum (NHS). (C) Vegetative 34F2 B. anthracis were incubated without NHS in the presence and absence of PMN (MOI 1:1) and samples obtained and counted at 10, 20 30, 40 and 60 min. (D) Vegetative 34F2 B. anthracis were incubated for 1 h in the presence of human PMNs at an MOI of 1:1, 3:1 or 5:1. Means and standard deviation of three different experiments are shown.