PMNs from PGRP-S^-/- mice are deficient in killing of B subtilis, M luteus, and L acidophilus but not S aureus, E coli, and P vulgaris, and this defect is reversed by exogenous recombinant PGRP-S. Peritoneal (A) or bone marrow (B) PMNs or peritoneal macrophages (C) from PGRP-S^+/+ (light gray bars) or PGRP-S^-/- (dark gray bars) mice were incubated in vitro with the indicated bacteria, and the numbers of viable bacteria were determined as described in “Materials and methods.” (D) Bacteria were first incubated with 50 μg recombinant PGRP-S/mL (or buffer control) for 10 minutes, and then peritoneal PMNs were added to yield 10 μg PGRP-S/mL. The killing assay was then performed as in panel A. The results are means ± SE of the following number of experiments: (A) 21 (B subtilis), 4 (M luteus and L acidophilus), 10 (S aureus), 11 (E coli), and 8 (P vulgaris); (B) 12 (B subtilis and M luteus), 6 (E coli), and 12 (P vulgaris); (C) 6; and (D) 4. The significance of differences was calculated using the Student t test.