Localization of hCAP-18 in resting human neutrophils by immunogold labeling of ultrathin cryosections. (A) hCAP-18 (large gold particles) is shown to colocalize with lactoferrin (small gold particles) in many of the specific granules (arrows). Some lactoferrin positive granules did not label for hCAP-18 (arrowhead). The large dense peroxidase-positive granules (*) were rarely labeled with either antibody. Biotinylated hCAP-18 antibodies were labeled with streptavidin gold (10 nm) and lactoferrin antibodies were labeled with goat antirabbit gold (5 nm). The cells were reacted enzymatically for peroxidase before being frozen to identify the azurophil granules (*), while the specific granules were identified by immunogold labeled lactoferrin. Original magnification [OM] × 78,000. (B) Anti-hCAP-18 antibody was labeled with goat antirabbit gold (15 nm) and biotinylated antilactoferrin antibody was labeled with streptavidin gold (10 nm). No peroxidase reaction was performed before immunogold labeling. Arrows point to specific granules with both sizes of gold, and arrow heads to granules that label only for lactoferrin. OM × 77,500.