Factors affecting SP-A-mediated phagocytosis in human monocytic cell lines.
Surfactant protein-A enhances the phagocytosis and killing of many pathogens, although studying this effect in an assortment of models and different experimental protocols has sometimes yielded conflicting results. In this report, using the human THP-1 cell line as the primary phagocytic cell, we systematically examined several models where microspheres, Staphylococcus aureus and Escherichia coli were used for targets. We found that SP-A derived from human lavage appeared to enhance phagocytosis by two different mechanisms; by SP-A binding of the target to enhance its recognition and subsequent phagocytosis and by a direct SP-A stimulatory effect on the phagocyte itself. Both SP-A mechanisms occurred with different targets in the same experimental system and the SP-A effects were qualitatively (but not quantitatively) comparable in several human cell lines (THP-1, U937, Mono-Mac-6). We also found that the SP-A effects were abrogated when SP-A was combined with surfactant lipids, but the lipids did not affect the basal level of phagocytosis or phagocytosis by mechanisms not involving SP-A. Moreover, the stimulatory effect of SP-A was pH-dependent and appeared to be independent of several other phagocytic mechanisms, including those mediated by Fc receptors and mannose receptor.
Ding
Jianqiang
J
Department of Cellular Physiology, Pennsylvania State College of Medicine, P.O. Box 850, Hershey, PA 17033, USA.
Umstead
Todd M
TM
Floros
Joanna
J
Phelps
David S
DS
D001688:Biological Products / Q000494:pharmacology; D018929:Cell Culture Techniques / Q000379:methods; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000502:physiology; D006801:Humans; D008024:Ligands; D008863:Microspheres; D009000:Monocytes / Q000187:drug effects*; D009895:Opsonin Proteins / Q000494:pharmacology; D010587:Phagocytosis / Q000187:drug effects*; D037662:Pulmonary Surfactant-Associated Protein A / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000502:physiology
D001688:Biological Products; D008024:Ligands; D009895:Opsonin Proteins; D037662:Pulmonary Surfactant-Associated Protein A; C072197:beractant