Monocyte-Mediated Suppression of IL-2-Induced NK-Cell Activation.

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Abstract
In the present study, the effects of serotonin on human natural killer (NK)-cell responsiveness to interleukin 2 (IL-2) was investigated. Concomitant treatment of human lymphocytes, enriched for NK effector cells by Percoll density-gradient centrifugation, with serotonin and/or IL-2 yielded a synergistic activation of NK-cell cytotoxicity (NKCC) in the presence but not in the absence of monocytes. The monocyte-dependent. regulatory effects of serotonin and/or IL-2 were prosta-glandin-independent and could be reconstituted when monocytes, recovered by countercurrent centrifugal elutriation (CCE), were added to purified NK effector cells. The effects of serotonin on baseline and IL-2-activalcd NK cells were mimicked by the 5-HT1A receptor-specific agonists 8-OH-DPAT and (+)-ALK. Our data suggest that serotonin regulates NK-cell responsiveness to IL-2 via 5-HT1a receptors.