Influence of antidepressants on mitogen stimulation of human lymphocytes

Exposure to antidepressants inhibited mitogen stimulation of cultured human lymphocytes. The lowest concentration that cause total inhibition of mitogen (phytohaemagglutinin, PHA) stimulation (the minimum inhibitory concentration, MIC) was 20, 30, 40, 60 and 120 mumol/litre for fluoxetine, clomipramine, amitriptyline, imipramine and citalopram, respectively. The lymphocytes were more sensitive to all of the antidepressants when stimulated with concanavalin A than with PHA. When the lymphocytes were preincubated with the drugs at the MIC for 24 hr before mitogen stimulation, amitriptyline, citalopram and imipramine did not suppress mitogen (PHA) stimulation whereas fluoxetine and clomipramine caused 50 and 60% inhibition. For all of the antidepressants, preincubation at 2.5 x MIC for 24 hr completely inhibited mitogen stimulation. The results show that antidepressants can affect lymphocytes by inhibiting blastogenesis and that there were large differences in potency between the drugs.