Hp and lactoferrin colocalize in specific granules of neutrophils. Cryosections of peripheral-blood neutrophils were labeled with rabbit anti-human Hp antibodies followed by a 10-nm protein A-gold probe (left). In addition, cryosections (right) were double-labeled, first with a rabbit anti-human Hp antibody and a 10-nm protein A-gold probe and subsequently with a rabbit anti-human Lf antibody and a 15-nm protein A-gold probe. Immunoelectron microscopy demonstrates the ultrastructural colocalization of Hp (arrows) and Lf in specific granules.