The immunophenotype of amniotic fluid leukocytes in normal and complicated pregnancies

Abstract

Problem The immune cellular composition of amniotic fluid is poorly understood. Herein, we determined the immunophenotype of amniotic fluid: 1) immune cells during the second and third trimester; 2) T cells and innate lymphoid cells (ILCs); and 3) immune cells during intra-amniotic infection/inflammation. Method of Study Amniotic fluid samples (n=57) were collected from women from 15-40 weeks of gestation 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. Results In the absence of intra-amniotic infection/inflammation, the amniotic fluid contained several immune cell populations from 15-40 weeks. Among these immune cells: 1) T cells and ILCs were greater than B cells and NK cells between 15 to 30 weeks; 2) T cells were most abundant between 15 to 30 weeks; 3) ILCs were most abundant between 15 to 20 weeks; 4) B cells were scarce between 15 to 20 weeks; yet, they increased and were constant after 20 weeks; 5) NK cells were greater between 15 to 30 weeks than at term; 6) ILCs expressed high levels of RORγt, CD161, and CD103 (i.e. Group 3 ILCs); 7) T cells expressed high levels of RORγt; 8) neutrophils increased as gestation progressed; and 9) monocytes/macrophages emerged after 20 weeks and remained constant until term. All of the amniotic fluid immune cells, except ILCs, were increased in the presence of intra-amniotic infection/inflammation. Conclusions The amniotic fluid harbors a diverse immune cellular composition during normal and complicated pregnancies.

Human β‐defensin‐1: A natural antimicrobial peptide present in amniotic fluid that is increased in spontaneous preterm labor with intra‐amniotic infection

“…This is in line with the evidence showing that in midtrimester; most of the innate immune cells that participate in host defense mechanisms against infection (e.g. neutrophils) are low in number 46 . Therefore, amniotic fluid HBD-1 may serve as an innate soluble component that protects the fetus against invading pathogens during midtrimester when neutrophils are rare.…”

“…It contains soluble components such as electrolytes, carbohydrates, lipids, and peptides which can act as a defense against pathogens invading the amniotic cavity 10–30 . The amniotic fluid also contains cellular components 31–45 that have been recently characterized using immunophenotyping 46 . It is now clear that amniotic fluid includes both innate and adaptive immune cells such as monocytes/macrophages, neutrophils, innate lymphoid cells, B cells, natural killer cells, and T cells 46 .…”

“…It is now clear that amniotic fluid includes both innate and adaptive immune cells such as monocytes/macrophages, neutrophils, innate lymphoid cells, B cells, natural killer cells, and T cells 46 . Most of these immune cells are more abundant in women with intra-amniotic infection and/or inflammation 46 . Among innate immune cells, neutrophils are considered a marker of intra-amniotic inflammation since their number is increased in women with intra-amniotic infection 47, 48 .…”

“…The amniotic fluid also includes cellular components [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] that have been recently characterized using immunophenotyping. 46 It is now clear that amniotic fluid contains both innate and adaptive immune cells such as monocytes/macrophages, neutrophils, innate lymphoid cells, B cells, natural killer cells, and T cells. 46 Most of these immune cells are more abundant in women with intra-amniotic infection and/or inflammation.…”

Inflammasome activation during spontaneous preterm labor with intra‐amniotic infection or sterile intra‐amniotic inflammation

“…We propose that the adaptive immune system may participate in such an inflammatory process. This concept is supported by the following observations: 1) effector T cells can activate the NLRP3 inflammasome in antigen-presenting cells, amplifying adaptive immune responses, 157 2) T cells are present in the amniotic fluid 128 and chorioamniotic membranes, 158,159 and 3) maternal and fetal T-cell activation is associated with preterm labor and birth. 160–162 …”