Evidence for a role for the adaptive immune response in human term parturition

Abstract

Problem: Spontaneous labor at term involves leukocyte recruitment and infiltration into the choriodecidua; yet, characterization of these leukocytes and their immunological mediators is incomplete. The purpose of this study was to characterize the immunophenotype of choriodecidual leukocytes as well as the expression of inflammatory mediators in human spontaneous parturition at term.

Method of study: Choriodecidual leukocytes were analyzed by FACS, immunohistochemistry, and RT-PCR in three different groups: (i) preterm gestation delivered for medical indications without labor; (ii) term pregnancy without labor; and (iii) term pregnancy after spontaneous labor.

Results: Two T-cell subsets of memory-like T cells (CD3(+) CD4(+) CD45RO(+) and CD3(+) CD4(-) CD8(-) CD45RO(+) cells) were identified in the choriodecidua of women who had spontaneous labor. Evidence for an extensive immune signaling network composed of chemokines (CXCL8 and CXCL10), chemokine receptors (CXCR1-3), cytokines (IL-1β and TNF-α), cell adhesion molecules, and MMP-9 was identified in these cells during spontaneous labor at term.

Conclusions: The influx of memory-like T cells in the choriodecidua and the evidence that they are active by producing chemokines and cytokines, and expressing chemokine receptors, cell adhesion molecules, and a matrix-degrading enzyme provides support for the participation of the adaptive immune system in the mechanisms of spontaneous parturition at term.

Figure 1

Number and phenotype of choriodecidual leukocytes. PTG, white; TNL, gray; TL, black bars. (a) Number of leukocytes per cm² of tissue. Leukocyte density increased at term of pregnancy. (b) Leukocyte subsets were analyzed within the CD45⁺ gate. While T cells increased, granulocytes decreased from PTG to TL. Monocytes were greater in TNL than in PTG. (c) T-cell subsets were analyzed within the CD3⁺ gate. TNL and TL included a high proportion of CD4⁺ T cells. CD3⁺CD4⁻CD8⁻ DN T cells were higher in TL cells were higher in TL than in TNL. Data shown are means ± SEM, with five to seven tissues per group.

Figure 2

Tissue localization of choriodecidual leukocytes. Photomicrograph of amniochorion (left panel) and choriodecidua (right panel) in each group. A, amnion; C, chorion; D, decidua. Leukocytes (CD45⁺) were greater in choriodecidua than in amniochorion, and their density seemed to increase from PTG to TL. T cells (CD45⁺CD3⁺) and granulocytes (CD45⁺CD3⁻CD14⁻CD56⁻CD19⁻) increased from PTG to TL. Bar, 20 μm. Confocal microscopy: magnification x200. Data are representative of three or more independent experiments with five tissues per group.

Figure 3

Tissue localization of CD45RO⁺ memory-like T cells. (a) Photomicrograph of choriodecidua identifying CD4⁺ T cells in each group. (b) Photomicrograph of choriodecidua identifying CD4⁺ CD45RO⁺ memory-like T cells in each group. Merge shows the co-localization of both markers. CD45RO⁺ memory-like T cells seemed to increase from PTG to TL. Bar, 20 μm. Confocal microscopy: magnification x200. Data are representative of three or more independent experiments with five tissues per group.

Figure 4

Chemokine expression. Relative expression of CXCL8 and CXCL10 and its receptors CXCR1-3 in choriodecidual leukocytes from each group. CXCL8 was higher in TL than in TNL, and lower in TNL than in PTG. CXCL10, CXCR1, CXCR2, and CXCR3 were higher in TL than in TNL and PTG. Data are expressed as relative expression using ACTB gene as the reference. Data shown are means ± SEM, with five to seven tissues per group.

Figure 5

Cell adhesion moelcules expression. Relative expression of ICAM1, ICAM2, ICAM3, VCAM, SELP, SELE, ITGAL and ITGAM were higher in TNL than in PTG. ITGAL was higher in TL than in TNL. Data are expressed as relative expression using ACTB gene as the reference. Data shown are means ± SEM, with five to seven tissues per group.

Figure 6

Labor mediators. (a) Expression of labor mediators. IL-1β, TNF-α, and MMP-9 in choriodecidual leukocytes from each group. All three mediators increased from PTG and TL. Data are expressed as relative expression using ACTB gene as the reference. Data shown are means ± SEM, with five to seven tissues per group. (b) Photomicrograph of choriodecidua from each group. IL-1β, TNF-α, and MMP-9 increased from PTG to TL. Merge shows the co-localization of both markers. Bar, 20 μm. Confocal microscopy: magnification x200. Data are representative of three or more independent experiments with five tissues per group.

Figure 7

Localization of MMP-9 in choriodecidual leukocytes. Photomicrograph of choriodecidua identifying MMP-9⁺CD45⁺ cells or MMP-9⁺CD3⁺ T cells in each group. Both MMP-9⁺ total leukocytes and T cells increased from PTG to TL. Merge shows the co-localization of both markers. Bar, 20 μm. Confocal microscopy: magnification x200. Data are representative of three or more independent experiments with five tissues per group.

Figure 8

Conceptual framework. Choriodecidual tissues express chemokines to recruit maternal circulating leukocytes at term pregnancy. Before the onset of labor, choriodecidual memory-like CD4⁺ T cells and other leukocytes such as granulocytes express cell adhesion molecules to remain into this anatomical space. Infiltrating leukocytes release CXCL10 to recruit double-negative (DN) T cells. Together they release labor mediators (e.g., CXCL8, IL-1β, TNF-α and MMP-9) to participate in labor at the end of gestation.