Interleukin-33 in the human placenta

Abstract

Objective: Interleukin-33 (IL-33) is the newest member of the IL-1 cytokine family, a group of key regulators of inflammation. The purpose of this study was to determine whether IL-33 is expressed in the human placenta and to investigate its expression in the context of acute and chronic chorioamnionitis.

Methods: Placental tissues were obtained from five groups of patients: 1) normal pregnancy at term without labor (n = 10); 2) normal pregnancy at term in labor (n = 10); 3) preterm labor without inflammation (n = 10); 4) preterm labor with acute chorioamnionitis and funisitis (n = 10); and 5) preterm labor with chronic chorioamnionitis (n = 10). Immunostaining was performed to determine IL-33 protein expression patterns in the placental disk, chorioamniotic membranes, and umbilical cord. mRNA expression of IL-33 and its receptor IL1RL1 (ST2) was measured in primary amnion epithelial and mesenchymal cells (AECs and AMCs, n = 4) and human umbilical vein endothelial cells (HUVECs, n = 4) treated with IL-1β (1 and 10 ng/ml) and CXCL10 (0.5 and 1 or 5 ng/ml).

Results: 1) Nuclear IL-33 expression was found in endothelial and smooth muscle cells in the placenta, chorioamniotic membranes, and umbilical cord; 2) IL-33 was detected in the nucleus of CD14+ macrophages in the chorioamniotic membranes, chorionic plate, and umbilical cord, and in the cytoplasm of myofibroblasts in the Wharton's jelly; 3) acute (but not chronic) chorioamnionitis was associated with the presence of IL-33+ macrophages in the chorioamniotic membranes and umbilical cord; 4) expression of IL-33 or IL1RL1 (ST2) mRNA in AECs was undetectable; 5) IL-33 mRNA expression increased in AMCs and HUVECs after IL-1β treatment but did not change with CXCL10 treatment; and 6) IL1RL1 (ST2) expression decreased in AMCs and increased in HUVECs after IL-1β but not CXCL10 treatment.

Conclusions: IL-33 is expressed in the nucleus of placental endothelial cells, CD14+ macrophages, and myofibroblasts in the Wharton's jelly. IL-1β can induce the expression of IL-33 and its receptor. Protein expression of IL-33 is detectable in macrophages of the chorioamniotic membranes in acute (but not chronic) chorioamnionitis.

Figure 1. IL-33 protein expression in the placenta and chorioamniotic membranes of normal term pregnancies

(A) IL-33 is expressed in the nuclei of endothelial (arrowhead) and smooth muscle cells (arrow) of blood vessels in the chorionic plate and chorionic villi. CP = chorionic plate; CV = chorionic villi. x200 magnification. (B) Immunofluorescence staining of CD31 (red), IL-33 (green) and DAPI (blue) shows nuclear IL-33 staining of vascular endothelial cells in chorionic villi. x900 magnification. (C) IL-33 is expressed in the nuclei of decidual endothelial cells (arrowhead) in blood vessels in chorioamniotic membranes. AE = amnion epithelium; AM = amnion mesoderm; CM = chorionic mesoderm; CT = chorionic trophoblast layer; DP = decidua parietalis. x200 magnification. (D) Immunofluorescence staining of CD31 (red), IL-33 (green) and DAPI (blue) show nuclear IL-33 staining in endothelial cells of decidual blood vessels. x400 magnification. (E) Immunofluorescence staining of CD14 (red), IL-33 (green) and DAPI (blue) shows nuclear IL-33 staining in macrophages in the mesodermal layer. x1500 magnification.

Figure 2. IL-33 protein expression in the umbilical cord of normal term pregnancies

(A) IL-33 is expressed in the umbilical artery (B) and Wharton’s jelly (C). x100 magnification. (B) IL-33 is expressed in the nuclei of endothelial (arrowhead) and smooth muscle cells (arrow) in the umbilical vessels. x200 magnification. (C) IL-33 is expressed in the nuclei of stromal cells in the Wharton’s jelly (inset). x100 magnification. (D) Immunofluorescence staining of procollagen (red), IL-33 (green) and DAPI (blue) shows cytoplasmic IL-33 staining in myofibroblasts in the Wharton’s jelly. x630 magnification. (E) Immunofluorescence staining of CD14 (red), IL-33 (green) and DAPI (blue) shows cytoplasmic IL-33 staining in macrophages in the Wharton’s jelly. x630 magnification. UA = umbilical artery; WJ = Wharton’s jelly.

Figure 3. IL-33 expression in pathologic pregnancies

(A) IL-33 is expressed in the nuclei of endothelial cells of decidual blood vessels in patients with preterm labor. IL-33 is not expressed in the mesodermal layer of the amnion. x200 magnification. (B) IL-33 is expressed in the nuclei of macrophages in the chorioamniotic membranes of patients with preterm labor and acute chorioamnionitis. x200 magnification. (C) IL-33 is not expressed in macrophages in the chorioamnionic membranes of patients with preterm labor and chronic chorioamnionitis. x200 magnification. Arrowheads are endothelial cells and thick arrows are macrophages for all. AE = amnion epithelium; AM = amnion mesoderm; CM = chorionic mesoderm; CT = chorionic trophoblast layer; DP = decidua parietalis.

Figure 4. IL-33 and IL1RL1 (ST2) mRNA expression in amnion mesenchymal cells

(A) Amnion mesenchymal cells (AMCs) treated with IL-1β expressed significantly increased IL-33 mRNA (p<0.001 for both 1 ng/ml and 10 ng/ml) and significantly decreased IL1RL1 (ST2) mRNA (p=0.007 for 1 ng/ml and p=0.003 for 10 ng/ml). (B) IL-33 and IL1RL1 (ST2) mRNA expression did not change in AMCs treated with CXCL10 (p>0.05 for both concentrations).

Figure 5. IL-33 and IL1RL1 (ST2) mRNA expression in HUVECs

(A) HUVECs treated with IL-1β expressed significantly increased IL-33 mRNA at a concentration of 1 ng/ml (p=0.02) and a slight increase at 10 ng/ml although this difference was not significant (p=0.11). IL1RL1 (ST2) mRNA expression significantly increased with IL-1β treatment (p=0.001 for 1 ng/ml and p=0.003 for 10 ng/ml. (B) IL-33 and IL1RL1 (ST2) mRNA expression did not change in HUVECs treated with CXCL10.