SAT0068 CIRCADIAN RHYTHMS OF IMMUNE SYSTEM IN HEALTHY INDIVIDUALS AND PATIENTS WITH RHEUMATOID ARTHRITIS
Authors: Siska Wilantri, Cindy Strehl, Dimas Abdirama, Timo Gaber, Frank Buttgereit
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background</h3> Chronobiological aspects play an important role in rheumatoid arthritis (RA), with major symptoms such as joint pain and stiffness follow a day-night-cycle that peak in the early morning. The circadian behavior of symptoms has been attributed to the rhythmic expression of cytokines and hormones<sup>1</sup>,<sup>2</sup>. Animal models of autoimmune inflammation demonstrated that immune cells, which belong to the vast producers of such cytokines, circulate in a circadian manner and that the circadian rhythm of circulating immune cell is different in health and disease<sup>3</sup>. Moreover, coordinating timing of glucocorticoid therapy (chronotheraphy) results in a greater reduction of morning stiffness and pain compared with the same glucocorticoid dose taken in the morning<sup>4</sup>. <h3>Objectives</h3> Here, we aim to analyse the circadian rhythms of circulating immune cell populations in the periphery of healthy individuals and RA patients in order to optimize treatment strategies. <h3>Methods</h3> We performed a 24-hours study involving 14 eligible RA patients and 12 healthy individuals to monitor the dynamic occurrence of diverse immune cells in the periphery. A week prior to study day, the biological rhythms were synchronized by scheduled activities and food intakes. On the study day, blood was drawn every 2 hours throughout 24 hours using peripheral venous catheter. The participants were provided with regular meal, allowed to eat snacks ad libitum and carry passive activities. Blood samples were subsequently analyzed by flow cytometry using TruCount Beads to count absolute cell numbers. RNA from CD14<sup>+</sup> monocytes was analyzed by real-time PCR to monitor the circadian clock genes expression. <h3>Results</h3> We investigated major immune populations and found chronobiological differences in NK T cells, NK cells, CD8 T cells, CD4 T cells and regulatory T cells (Tregs) of healthy individuals and patients with RA. In RA Tregs showed a lag phase of 5 hours, while CD8 and CD4 T cells showed a mild reduction of the amplitude. NK T cells and NK cells did not circulate in a circadian manner in healthy individuals, but they exhibited circadian pattern in RA. In addition, the qPCR data also indicated a disrupted circadian rhythm on RNA level. Among ten clock genes that were examined, <i>REVERBα</i>, <i>PER1</i>, and <i>PER3</i> showed altered expression in RA patients. The expression of <i>REVERBα</i> was suppressed by 50% and the rhythm of <i>PER1</i> was diminished in RA patient. Furthermore, the rhythm of <i>PER3</i> was present exclusively in RA patients, but not in healthy participants. <h3>Conclusion</h3> Taken together, we conclude that the circadian rhythms of immune cells in RA patients are different from that in healthy individuals. The alteration can be observed on both cellular and RNA level. We postulate that the alterations in circadian rhythms may contribute to disease manifestations and may have impact for optimizing diagnosis and therapy in RA. Further analysis is required to expand the data set. It is also of interest to investigate the functionality of circadian clock genes in immune cells. <h3>References</h3> [1] Cutolo M, et al. Ann. Rheum. Dis. 67, 905–8 (2008). [2] Straub RH, et al. Arthritis Rheum. 56, 399–408 (2007). [3] Druzd D, et al. Immunity. 46(1),120-132 (2017). [4] Buttgereit, et al. Lancet. 371: 205–14 (2008). <h3>Acknowledgement</h3> We thank our study team; R. Biesen, E. Wiebe, K-N. Zeiner, D. Freier, M. Jakstadt, L. Ehlers, A. Damerau, A. Lang, M. Pfeiffenberger, G. May, P-L. Krauß, M. Ibach, F. Heinsohn, A. Brinkman, Y. Chen and J. Pienczykowski for their contribution. <h3>Disclosure of Interests</h3> None declared