Serotonin and immune response: Effect of the amine on in vitro proliferation of rat lymphocytes

Objective: The effect of serotonin (5-hydroxytryptamine; 5HT) on the in vitro proliferation of mitogen-stimulated lymphocytes was studied in primary cultures of rat spleen cells. Methods: 5HT was added to the cultures 1 h prior to the mitogen, at final concentrations from 10(-13) Up to 10(-2) M. T and B cell mitogens (concanavalin A, pokeweed mitogen and lipopolysaccharide) were used at suboptimal and optimal concentrations. The cell proliferation was measured 24-72 h after the addition of mitogen. The effect of each 5HT concentration was studied on a group of 6-12 animals and was expressed as a percentage of the control values obtained with mitogen alone. Results: No significant effect of 5HT at concentrations from 10(-13) to 10(-5) M was found. At concentrations of greater than or equal to 10(-4) M, a regular dose-dependent inhibition of the lymphocyte proliferation appeared, the concentration producing the half-maximal effect being 6 x 10(-4) M. The observed suppression was not due to 5HT cytotoxicity toward spleen cells. Conclusion: With the experimental system used, we failed to confirm an immunostimulatory effect of 5HT in the range of concentrations of its receptor sensitivities or lower, but found a clear-cut immunoinhibitory effect at higher concentrations. Copyright (C) 2001 S. Karger AG, Basel.