IL-16 is constitutively present in peripheral blood monocytes and spontaneously released during apoptosis.
Constitutive expression of the pro-molecule of IL-16 has been found in T cells, mast cells, eosinophils, epithelial cells, fibroblasts, and dendritic cells. Here we show that IL-16 is also constitutively present in >98% of freshly isolated human CD14-positive peripheral blood monocytes when analyzed by flow cytometry. Because pro-IL-16 is cleaved to its bioactive mature form by caspase-3, and caspase-3 is also the pivotal effector of apoptosis in monocytes, we asked whether IL-16 release occurs in monocytes that undergo spontaneous apoptosis. As expected, freshly isolated, unstimulated monocytes underwent spontaneous caspase-3 activation. This apoptosis was paralleled by the loss of intracellular IL-16, as detected by flow cytometry, and the concurrent release of IL-16, as detected by ELISA. In contrast, stimulation with bacterial LPS inhibited caspase-3 activation and significantly inhibited the release of IL-16. As a specificity control, IL-1beta and IL-8 were not released during spontaneous monocyte apoptosis. In summary, our data demonstrate that monocytes contain IL-16 that is released during spontaneous apoptosis.
Elssner
Andreas
A
The Dorothy M. Davis Heart and Lung Research Institute, Ohio State University, 473 West 12th Avenue, Columbus, OH 43210, USA.
Doseff
Andrea I
AI
Duncan
Michelle
M
Kotur
Mark
M
Wewers
Mark D
MD
D017209:Apoptosis; D001773:Blood Cells; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002478:Cells, Cultured; D006801:Humans; D018836:Inflammation Mediators / Q000494:pharmacology; D019410:Interleukin-16 / Q000032:analysis / Q000378:metabolism*; D007700:Kinetics; D018950:Lipopolysaccharide Receptors / Q000032:analysis; D008070:Lipopolysaccharides / Q000494:pharmacology; D009000:Monocytes / Q000737:chemistry / Q000378:metabolism*
D018836:Inflammation Mediators; D019410:Interleukin-16; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases