Secretion of IL-16 (lymphocyte chemoattractant factor) from serotonin-stimulated CD8+ T cells in vitro

At sites of inflammation, mononuclear cells are in close contact with aggregated platelets. Although the physiologic role of this association is not clear, this proximity suggests that platelet-derived mediators may play a role in chemoattraction of T lymphocytes. In the current study we investigated serotonin receptor-bearing lymphocyte modulation of T cell migration. Serotonin-stimulated human blood mononuclear cells secrete lymphocyte chemoattractant activity with selective activity for CD4+ T cells. This chemoattractant activity was observed within 2 h of exposure to serotonin and was blocked by serotonin type 2 receptor antagonists. Molecular sieve chromatography of supernatant from serotonin-stimulated PBMCs revealed a single peak of T cell chemoattractant activity with an apparent molecular mass of 56 kDa and a pl of 9.1. Neutralizing experiments with specific mAbs indicated that the serotonin-induced chemotactic factor was the previously characterized lymphocyte chemoattractant factor (LCF), recently designated IL-16. Serotonin induced secretion of IL-16 from CD8+, not CD4+, T cells which did not require the de novo protein synthesis. These studies suggest that serotonin, via serotonin type 2 receptors, may promote the recruitment of CD4+ T lymphocytes into an inflammatory focus.