High levels of NK cells in the peripheral blood of patients affected with anti-phospholipid syndrome and recurrent spontaneous abortion: a potential new hypothesis

Objectives. No data regarding phenotypic assets of circulating lymphocytes in anti-phospholipid syndrome (APS) are reported in the literature. Role of anti-phospholipid antibodies (aPL) in recurrent spontaneous abortion (RSA) remains uncertain, while natural killer (NK)-cells are involved in RSA pathogenesis. In this study, patients affected with APS without RSA, APS with RSA and RSA without aPL were studied for NK-cell subpopulation to evaluate its role in abortive events typical of APS. Methods. NK-cell levels in peripheral blood of APS patients without RSA (n=28) and in APS-RSA patients (n=25) were evaluated by means of flow cytofluorimetry. NK-cells levels were evaluated also in RSA without aPL associated with either endocrine (n=86), anatomic (n = 30) or idiopathic (n = 77) conditions and in 42 healthy women. Results. High NK levels were found in 14/25 (56%) APS-RSA patients. Among these patients, all except one aborted before the 10th gestational week (GW), while among the remaining patients all except one aborted after the 10th GW. NK mean levels were significantly higher in APS-RSA than in all the other conditions studied, including healthy subjects, except idiopathic RSA. Conclusions. Our results demonstrate that the numbers and proportions of NK-cells are significantly higher in patients with RSA with APS than in APS without RSA. Increased numbers of NK-cells correlate with reduced gestational age at abortion in patients with APS-RSA. These data lead to a hypothesis that NK-cells contribute to the development of RSA in patients with APS. NK-cells might precipitate damage initiated by aPL or they might cause pathology in RSA independent of aPL.