TLR expression on human neutrophils measured by flow cytometry. Human neutrophils were incubated in RPMI 1640 with or without GM-CSF (50 ng/mL) for 90 minutes. Cells were stained with antibodies specific for human TLR1 (A), TLR2 (B), TLR4 (C), and TLR9 (D) (solid lines indicate untreated; dotted lines, GM-CSF treated) or their isotype controls (gray histogram). Neutrophils stained with antibodies to TLR9 were first permeabilized. Representative of experiments performed on 3 donors.