AB0025 Pregnancy results in the selective modulation of platelet tissue factor expression independently of the presence of antiphospholipid antibodies or of other autoimmune features

Background Neutrophils and platelets are key innate immune cells that productively interact upon activation, generating/releasing moieties that can damage the bystander tissue and prompt vasculogenesis. Successful pregnancy critically depends on a tight regulation of the latter events. Conversely pregnancy complications are associated with alteration/damage of the vasculature associated to the placenta. Blood-born tissue factor (TF) due to the expression of the moiety by platelets and leukocytes has been involved in the pro-thrombotic diathesis associated with sustained human autoimmunity, including that associated with anti-phospholipid syndrome (APS). Objectives To test the modulation of parameters related to blood-born TF during normal and pathological pregnancy Methods The expression of TF by platelets, monocytes and neutrophils has been studied in 40 women at the 12th week of gestation (wg) including twelve healthy women, 14 patients with insulin-dependent diabetes mellitus (IDDM) and 14 patients with a previous history of pregnancy complications, six of them with APS. 30 healthy age-matched non-pregnant women served as controls. When possible, patients were studied again at least one year after the pregnancy completion. Blood samples were collected and processed as described1,2. Other features reflecting cell activation were assessed in parallel1,2. Results The expression of platelet TF was significantly higher in pregnant women compared with age-matched controls. Platelet P-selectin was as well significantly up-regulated. Neutrophils circulating in all pregnant women were mildly degranulated. The content of the neutrophil secondary granules was depleted in particular in subiects with previous pregnancy complications sine causa. Conclusions Our data support the contention that the activation of the innate immune system is a key feature of pregnancy, regardless of the presence of features of systemic or organ-specific autoimmunity. This implies an important modulation of the machinery involved in the reciprocal activation of platelets and neutrophils and in the pro-thrombotic phenotype of circulating cells. The analysis of the potential modulation of these parameters by ongoing treatment is currently being carried out. References Manfredi A & al. Ann Rheum Dis. 2016;75(8):1511–20. doi: 10.1136/annrheumdis-2015-208442. Maugeri N et al. Blood. 2011 Sep 22;118(12):3359–66. doi: 10.1182/blood-2011-02-337337. Disclosure of Interest None declared