Identification of HBP and LL-37 as principal mediators of PMN-induced mobilization of inflammatory monocytes. (A) Extravasation of Gr1⁺ inflammatory monocytes in the air pouch of neutropenic mice after stimulation with PAF and individual PMN granule fractions. ** indicates significant difference compared with both ctrl and PMN depl + primary or secondary granule fraction. (B) Immunodepletion of LL-37, HBP, HNP1-3, and cathepsin G from the PMN secretion, renders the secretion nonfunctional. * indicates significant difference compared with ctrl. (C) Extravasation of Gr1⁺ inflammatory monocytes in the air pouch of neutropenic mice after stimulation with PAF combined with recombinant/isolated forms of LL-37 (10 μg/mL), HBP (10 μg/mL), HNP1-3 (5 μg/mL), or cathepsin G (10 μg/mL). ** indicates significant difference compared with both ctrl and PMN depl + LL37/HBP/cathepsin G. (D) Extravasation of Gr1⁺ inflammatory monocytes in the air pouch of neutropenic mice after stimulation with PAF combined with crude PMN secretion or PMN secretion immunodepleted of LL-37, HBP, and cathepsin G, respectively. * indicates significant difference compared with PMN depl + PMN-sec. Data are expressed as means (± SD) n = 5 for each bar.