Evaluation of the effect of selective serotonin-reuptake inhibitors on lymphocyte subsets in patients with a major depressive disorder Maria Eugenia Hernandez a,b , Daniel Martinez-Fong c , Mayra Perez-Tapia d , Iris Estrada-Garcia d , Sergio Estrada-Parra d , Lenin Pavón a, ⁎ a Department of Psychoimmunology, National Institute of Psychiatry “Ramón de la Fuente”, Mexico b Doctorado en Ciencias Biológicas, UAM, Mexico c Department of Physiology, Biophysics and Neuroscience, CINVESTAV-IPN, Mexico d Department of Immunology, National School of Biological Sciences, National Polytechnic Institute, Mexico Received 22 May 2009; received in revised form 2 November 2009; accepted 12 November 2009 KEYWORDS CD4+ cells; CD8+ cells; B lymphocyte; NK cells; 5-HT; Major Depressive Disorder Abstract To date, only the effect of a short-term antidepressant treatment (b 12 weeks) on neuroendocrinoimmune alterations in patients with a major depressive disorder has been evaluated. Our objective was to determine the effect of a 52-week long treatment with selective serotonin-reuptake inhibitors on lymphocyte subsets. The participants were thirty-one patients and twenty-two healthy volunteers. The final number of patients (10) resulted from selection and course, as detailed in the enrollment scheme. Methods used to psychiatrically analyze the participants included the Mini-International Neuropsychiatric Interview, Hamilton Depression Scale and Beck Depression Inventory. The peripheral lymphocyte subsets were measured in peripheral blood using flow cytometry. Before treatment, increased counts of natural killer (NK) cells in patients were statistically significant when compared with those of healthy volunteers (312 ± 29 versus 158 ± 30; cells/mL), but no differences in the populations of T and B cells were found. The patients showed remission of depressive episodes after 20 weeks of treatment along with an increase in NK cell and B cell populations, which remained increased until the end of the study. At the 52nd week of treatment, patients showed an increase in the counts of NK cells (396± 101 cells/mL) and B cells (268 ± 64 cells/mL) compared to healthy volunteers (NK, 159 ± 30 cells/ mL; B cells, 179 ± 37 cells/mL). We conclude that long-term treatment with selective serotonin- reuptake inhibitors not only causes remission of depressive symptoms, but also affects Abbreviations: BDI, Beck Depression Inventory; BMI, body mass index; CD, cluster differentiation; FITC, fluorescein-isothiocyanate; HDRS, Hamilton Depression Rate Scale; HPA, hypothalamus–pituitary–adrenal axis; HVs, healthy volunteers; IFN-γ, interferon-gamma; MDD, major depressive disorder; NK, natural killer; PE, R-phycoerythrin; W, week; SSRIs, selective serotonin-reuptake inhibitors; 5-HT, serotonin. ⁎ Corresponding author. Instituto Nacional de Psiquiatría “Ramón de la Fuente”, Calzada México-Xochimilco 101, Col San Lorenzo Huipulco, Tlalpan CP 14370, México DF, Mexico. Tel.: +52 55 41605082; fax: +52 55 56559980. E-mail address: lkuriaki@imp.edu.mx (L. Pavón). 0924-977X/$ - see front matter © 2009 Elsevier B.V. and ECNP. All rights reserved. doi:10.1016/j.euroneuro.2009.11.005 www.elsevier.com/locate/euroneuro European Neuropsychopharmacology (2010) 20, 88–95