The immunophenotype of amniotic fluid leukocytes in normal and complicated pregnancies

ProblemThe immune cellular composition of amniotic fluid is poorly understood. Herein, we determined: 1) the immunophenotype of amniotic fluid immune cells during the second and third trimester in the absence of intra-amniotic infection/inflammation; 2) whether amniotic fluid T cells and ILCs display different phenotypical characteristics to that of peripheral cells; and 3) whether the amniotic fluid immune cells are altered in women with intra-amniotic infection/inflammation. Method of StudyAmniotic fluid samples (n=57) were collected from 15 to 40weeks of gestation in women without intra-amniotic infection/inflammation. Samples from women with intra-amniotic infection/inflammation were also included (n=9). Peripheral blood mononuclear cells from healthy adults were used as controls (n=3). Immunophenotyping was performed using flow cytometry. ResultsIn the absence of intra-amniotic infection/inflammation, the amniotic fluid contained several immune cell populations between 15 and 40 weeks. Among these immune cells: (i) T cells and ILCs were greater than B cells and natural killer (NK) cells between 15 and 30weeks; (ii) T cells were most abundant between 15 and 30weeks; (iii) ILCs were most abundant between 15 and 20weeks; (iv) B cells were scarce between 15 and 20weeks; yet, they increased and were constant after 20weeks; (v) NK cells were greater between 15 and 30weeks than at term; (vi) ILCs expressed high levels of RORt, CD161, and CD103 (ie, group 3 ILCs); (vii) T cells expressed high levels of RORt; (viii) neutrophils increased as gestation progressed; and (ix) monocytes/macrophages emerged after 20weeks and remained constant until term. All of the amniotic fluid immune cells, except ILCs, were increased in the presence of intra-amniotic infection/inflammation. ConclusionThe amniotic fluid harbors a diverse immune cellular composition during normal and complicated pregnancies.