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Problem: Preeclampsia (PE), new-onset hypertension during pregnancy accompanied by organ dysfunction, is associated with chronic inflammation including elevated IL- 17, CD4+ T cells, B cells and natural killer (NK) cells. IL-17 can serve as a signal for either the adaptive or innate immune activation.We have previously shown that IL-17 contributes to increased blood pressure in association with elevated TH17 cells, NK cells and B cells secreting angiotensin II type 1 receptor agonistic autoantibodies (AT1- AA) during pregnancy. Moreover, we have shown an important role for CD4+T cells and AT1-AA in multiorgan dysfunction as measured by mitochondrial oxidative stress (mt ROS).However, we do not know the role of adaptive immune cells such as T cells or B cells secreting AT1-AA in mediating the PE phenotype in response to elevated IL-17. Method of study: In order to answer this question, we infused IL-17 (150 pg/day i.p.) into either SpragueDawley (SD) or athymic nude rats via mini-osmotic pump from gestational day (GD) 14--19 of pregnancy. On GD 19, blood pressure was determined and NK cells,mtROS and respiration and AT1-AA production from B cells were measured. Results: Infusion of IL-17 increased blood pressure in the presence or absence of T cells. Mean arterial pressure (MAP) increased with IL-17 from 98 ±2mmHg (n = 12) to 114 ± 2 (n = 12) in SD rats and from 99 ± 4 mmHg (n = 7) versus 115 ± 2 mmHg (n = 7) in athymic nude rats. Similar trends were seen in NK cells and placental mt ROS. Knowing that IL-17 stimulates AT1-AA in SD pregnant rats, we included a group of SD and athymic nude pregnant rats infused with IL-17 and the AT1-AA inhibitor peptide ('n7AAc'). The inhibitor attenuated blood pressure (104.9 ± 3.2, p = .0001) and normalized NK cells andmt function in SD pregnant rats. Importantly, the AT1-AA was not produced in pregnant nude IL-17 treated rats, nor did 'n7AAc' effect MAP, in nude athymic rats. Conclusion: These findings suggest two conclusions; one is that IL-17 causes hypertension and multiorgan dysfunction in the absence of T cells and AT1-AA, possibly through its activation of innate cells and secondly, in the presence of T cells, blockade of the AT1-AA attenuates the effect of IL-17. This study indicates the critical effects of elevated IL-17 during pregnancy and suggest treatment modalities to consider for PE women. [ABSTRACT FROM AUTHOR]