title: Surface-bound myeloperoxidase is a ligand for recognition of late apoptotic neutrophils by human lung surfactant proteins A and D.
abstract: Surfactant proteins A (SP-A) and D (SP-D), both members of the collectin family, play a well established role in apoptotic cell recognition and clearance. Recent in vitro data show that SP-A and SP-D interact with apoptotic neutrophils in a distinct manner. SP-A and SP-D bind in a Ca(2+)-dependent manner to viable and early apoptotic neutrophils whereas the much greater interaction with late apoptotic neutrophils is Ca(2+)-independent. Cell surface molecules on the apoptotic target cells responsible for these interactions had not been identified and this study was done to find candidate target molecules. Myeloperoxidase (MPO), a specific intracellular defense molecule of neutrophils that becomes exposed on the outside of the cell upon apoptosis, was identified by affinity purification, mass-spectrometry and western blotting as a novel binding molecule for SP-A and SP-D. To confirm its role in recognition, it was shown that purified immobilised MPO binds SP-A and SP-D, and that MPO is surface-exposed on late apoptotic neutrophils. SP-A and SP-D inhibit binding of an anti-MPO monoclonal Ab to late apoptotic cells. Fluorescence microscopy confirmed that anti-MPO mAb and SP-A/SP-D colocalise on late apoptotic neutrophils. Desmoplakin was identified as a further potential ligand for SP-A, and neutrophil defensin as a target for both proteins.
authors.affiliation: Department of Pharmacology, University of Oxford, Mansfield Road, Oxford OX1 3QT, UK.
authors.forename: Anne
authors.initials: A
authors.lastname: Jäkel
authors.forename: Howard
authors.initials: H
authors.lastname: Clark
authors.forename: Kenneth B M
authors.initials: KB
authors.lastname: Reid
authors.forename: Robert B
authors.initials: RB
authors.lastname: Sim
mesh_terms: D017209:Apoptosis; D001667:Binding, Competitive; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D009504:Neutrophils / Q000737:chemistry / Q000166:cytology / Q000378:metabolism*; D009195:Peroxidase / Q000302:isolation & purification / Q000378:metabolism*; D011485:Protein Binding; D037662:Pulmonary Surfactant-Associated Protein A / Q000302:isolation & purification / Q000378:metabolism*; D037663:Pulmonary Surfactant-Associated Protein D / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D037662:Pulmonary Surfactant-Associated Protein A; D037663:Pulmonary Surfactant-Associated Protein D; D009195:Peroxidase