Cytokine Production of In Vitro Stimulated Peripheral Lympho- cytes During the Course of Pregnancy and Pseudopregnancy in the Rat M. M. Faas, R. Eenling, G. van der Schaaf, H. Moes, M. J. Heineman, P. de Vos Transplantation Biology and Immunoendocrinology, Division of Medical Biology, Department of Pathology and Laboratory Medicine and Department of Obstetrics and Gynecology, University Medical Centre Groningen and University of Groningen, Groningen, The Netherlands Introduction Disturbances of the Th1/Th2 balance have been shown to have a strong effect on the success of reproduction. Various in vivo studies have shown that peripheral injection of the Th1 cytokine inter- feron-c (IFNc) during pregnancy in experimental animals results in increased abortion and fetal abnor- malities. 1–3 Therefore, Th1 cytokines were consid- ered harmful for pregnancy. However, more recently, it has been shown that Th1 cytokines, for instance IFNc and tumor necrosis factor-a (TNFa) Keywords Cytotoxic lymphocytes, helper lymphocytes, interferon-c, interleukin-4, NK cells, pregnancy Correspondence M. M. Faas, PhD, Transplantation Biology and Immunoendocrinology, Division of Medical Biology, Department of Pathology and Laboratory Medicine, University of Groningen, PO Box 30.001, 9700 RB Groningen, The Netherlands. E-mail: m.m.faas@med.umcg.nl Submitted October 13, 2005; revised November 29, 2005; accepted December 6, 2005. Citation Faas MM, Eenling R, van der Schaaf, Moes H, Heineman MJ, de Vos P. Cytokine production of in vitro stimulated peripheral lymphocytes during the course of pregnancy and pseudopregnancy in the rat. Am J Reprod Immunol 2006; 55:282–290 doi:10.1111/j.1600-0897.2005.00361.x Problem Does maternal lymphocyte cytokine production after in vitro stimulation vary with the stage of pregnancy in the rat? Method of study Blood samples were taken during the estrus cycle in rats (n ¼ 11). Thereafter, rats were rendered pregnant (n ¼ 6) or pseudopregnant (n ¼ 5) and blood samples were taken at days 4, 8, 11, 15, and 20 of pregnancy and pseudopregnancy. White blood cell (WBC) count was measured and whole blood was stimulated with phorbol 12-myristate 13-acetate and calcium ionophore; interferon-c (IFNc) and interleukin-4 (IL-4) production as well as (sub)populations of lymphocytes were measured using flow cytometry. Results We observed an increase of WBC in the second week of pregnancy and a slowly decreasing percentage of lymphocytes during the course of pregnancy. The percentage IFNc producing T-lymphocytes after in vitro stimulation was increased during pregnancy (for Th-lymphocytes only in the second week of pregnancy, for Tc-lymphocytes at all days). This increased IFNc production in pregnant T-lymphocytes was accompanied by an increase during pseudopregnancy, and therefore may result from increased sex hormone concentrations. The percentage IFNc producing natural killer (NK) cells after in vitro stimulation was decreased on day 20 of pregnancy. No effect of pregnancy or pseudopregnancy was seen on percentage IL-4 producing lymphocytes after in vitro stimulation. Conclusion In the rat the IFNc production after in vitro stimulation varies during pregnancy and is increased, rather than decreased, during pregnancy. ORIGINAL ARTICLE American Journal of Reproductive Immunology 55 (2006) 282–290 ª 2006 The Authors 282 Journal compilation ª 2006 Blackwell Munksgaard