Interleukin-15 (IL-15) is a potent regulator of T-, B-, and natural killer cell proliferation and displays unusually tight controls of secretion. Even though IL-15 mRNA is constitutively expressed in monocytes/macrophages and is upregulated by a variety of stimuli, evidence for IL-15 cytokine secretion is only found exceptionally, eg, conditions of pathological, chronic inflammation. This raises the possibility that monocytes express membrane-bound IL-15 rather than secrete it. The current study explores this hypothesis. We demonstrate here that biologically active IL-15 is indeed detectable in a constitutively expressed, membrane-bound form on normal human monocytes, as well as on monocytic cell lines (MONO-MAC-6, THP-1, and U937), but not on human T or B cells (MT4, M9, C5966, JURKAT, DAUDI, RAJI, and Epstein-Barr virus-immortalized B-cell clones). Furthermore, cell surface-bound IL-15 is upregulated upon interferon-gamma stimulation. Interestingly, monocyte/macrophage inhibitory cytokines such as IL-4 and IL-13 fail to downregulate both constitutive and induced cell-surface expression of IL-15. Membrane-bound IL-15 does not elute with acetate buffer or trypsin treatment, suggesting that it is an integral membrane protein and that it is not associated with the IL-15 receptor complex. Finally, membrane-bound IL-15 stimulates T lymphocytes to proliferate in vitro, indicating that it is biologically active. These findings enlist IL-15 in the fairly small family of cytokines for which the presence of a biologically active membrane-bound form has been demonstrated (eg, IL-1, tumor necrosis factor-alpha, and IL-10) and invites the speculation that most of the biological effects of IL-15 under physiological conditions are exerted by the cell surface-bound form.
This research output has an Altmetric Attention Score of 11. This is our high-level measure of the quality and quantity of online attention that it has received. This Attention Score, as well as the ranking and number of research outputs shown below, was calculated when the research output was last mentioned on 04 August 2026.
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#3,591,910
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#3,488
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Outputs of similar age from Blood
#8
of 181 outputs
Altmetric has tracked 28,584,465 research outputs across all sources so far. Compared to these this one has done well and is in the 87th percentile: it's in the top 25% of all research outputs ever tracked by Altmetric.
So far Altmetric has tracked 38,479 research outputs from this source. They typically receive more attention than average, with a mean Attention Score of 8.1. This one has done well, scoring higher than 85% of its peers.
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We're also able to compare this research output to 181 others from the same source and published within six weeks on either side of this one. This one has done particularly well, scoring higher than 95% of its contemporaries.
