Stimulation of splenic T-lymphocyte function by endogenous serotonin and by low-dose exogenous serotonin.

The modulatory effects of endogenous serotonin on splenic T-cell activity were investigated using two distinct approaches. The first approach showed that pretreatment of mice with p-cholorphenylalanine (PCPA) to deplete intracellular stores of serotonin reduced the capacity of their splenic T cells to proliferate and to express interleukin-2 receptor (IL-2R) in response to concanavalin A (Con A). These responses could be restored by the addition of serotonin to the spleen cell cultures. In contrast, PCPA treatment did not effect stimulation of spleen cells to produce IL-2. The second approach showed that T-cell proliferation to Con A as well as to IL-2 was diminished by the presence of antagonists to the serotonin-2 receptor (5-HT2R). The effects of low doses (100 ng/ml) of exogenously added serotonin on functions of normal spleen cells were also examined. At this low dose, serotonin stimulated splenic T-cell proliferation in response to IL-2, and enhanced both proliferation and IL-2 production in response to a suboptimal concentration of Con A. These results show autologous serotonin to be required for T-cell activation and that the activation of suboptimally stimulated T cells can be augmented with low doses of exogenously added serotonin. These data also suggest that the positive regulation of T-cell function by serotonin is mediated through 5-HT2R.