CLINICAL RESEARCH Bariatric Surgery Reverses Natural Killer (NK) Cell Activity and NK-Related Cytokine Synthesis Impairment Induced by Morbid Obesity Cristiane Martins Moulin & Ivo Marguti & Jean Pierre Schatzmann Peron & Alfredo Halpern & Luiz Vicente Rizzo Published online: 28 August 2010 # Springer Science+Business Media, LLC 2010 Abstract Background Obesity is related to a higher rate of infections and some types of cancer. Here we analyzed the impact of obesity and weight loss induced by Roux-en-Y gastric bypass (RYGB) on immunological parameters, i.e., cytokine productions and natural killer cell function. Methods We analyzed 28 morbidly obese patients before and 6 months after RYGB. Biochemical parameters were analyzed in plasma. The percent of natural killer (NK) cells, their cytotoxicity, and the production of cytokines by peripheral blood mononuclear cells were analyzed. The percent of NK cells was determined by flow cytometry and cytokine production determined by enzyme-linked immu- nosorbent assay. NK cytotoxicity was determined by the lactate dehydrogenase release assay. Results The weight loss 6 months following surgery was 35.3±4.5 kg. RYGB also improves biochemical parameters. No significant difference was found in the percent of NK cells after surgery. We found an increase in the production of interferon-γ, interleukin (IL)-12 and IL-18, but not in IL-2, 6 months after RYGB. Cytotoxic activity of NK cells was significantly enhanced 6 months after RYGB [17.1±14.7% before RYGB vs 51.8±11.3% at 6 months after, at 40:1 effector to target cell ratio; p <0.001]. We observed signif- icant post-surgical improvement in the cytotoxic activity curve in 22 out of 28 patients (78.6%), irrespective of the target to effector cell ratio. Conclusions The weight loss induced by RYGB modifies the production of cytokines related with NK cell function and improves its activity. Keywords Morbid obesity . Bariatric surgery . Immunity . Natural killer cells . Weight reduction Introduction Obesity is a worldwide public health problem associated with several comorbidities including cardiovascular diseases, reproductive disorders, osteoarthritis, gallstones, and respira- tory disease [1]. Furthermore, obesity has also been linked to decreased immunocompetence [2]. Epidemiological data indicate that the incidence and severity of infections are higher in obese individuals [3]. Results from meta-analysis show the association between high body mass index (BMI) and an increased incidence of many types of cancer [4]. The Alfredo Halpern and Luiz Vicente Rizzo contributed equally to this work. C. M. Moulin : A. Halpern Obesity and Metabolic Syndrome Group, Endocrinology Department, University of São Paulo Medical School General Hospital, São Paulo, Brazil I. Marguti : J. P. S. Peron : L. V. Rizzo Department of Immunology, Biomedical Sciences Institute, University of São Paulo, São Paulo, Brazil L. V. Rizzo (*) Hospital Israelita Albert Einstein, Av. Albert Einstein 627/701, São Paulo, SP, Brazil, CEP 05652-000 e-mail: lvrizzo@einstein.br Present Address: I. Marguti Instituto Gulbenkian de Ciência, Apartado 14, Oeiras, Portugal OBES SURG (2011) 21:112–118 DOI 10.1007/s11695-010-0250-8