* Section of Oral Biology, School of Dentistry, and
Division of Infectious Diseases, Cedars-Sinai Medical Center, University of California, Los Angeles, and
Department of Medicine, Division of Hematology, Oncology and Bone Marrow Transplantation, University of Minnesota, Minneapolis
Correspondence: Rekha K. Murthy, M.D., Division of Infectious Diseases, Cedars-Sinai Medical Center, 8700 Beverly Blvd., MOT 1130E, Los Angeles, CA 90048. E-mail: armurthy{at}ucla.edu
Calprotectin is an abundant cytosolic protein complex of human neutrophils with in vitro extracellular antimicrobial activity. Studies suggest that calprotectin may be actively secreted from intact HL-60 cells and that it can be translocated to polymorphonuclear neutrophil (PMN) cell membranes. To examine whether calprotectin is secreted extracellularly, we incubated soluble and particulate stimuli, including live and heat-inactivated Candida albicans, with whole blood and measured calprotectin levels in the plasma. We compared the release of calprotectin to that of lactoferrin, a protein known to be secreted by PMNs. Extracellular lactoferrin was detected after incubation with any of the particulate stimuli. In contrast, a significant increase in extracellular calprotectin was found only after incubation with live C. albicans. Specifically, the increase in extracellular calprotectin correlated directly with a proportional decrease in PMN viability. Our results indicate that human PMN calprotectin is not secreted extracellularly except as a result of cell disruption or death.
Key Words: MRP8 • MRP14 • granulocytes • L1
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