Local injury of the endometrium induces an inflammatory response that promotes successful implantation

Abstract

Objective: To study whether an injury-induced inflammation might be the mechanism underlying the favorable effect of endometrial biopsy on the implantation rate in in vitro fertilization (IVF) patients.

Design: Controlled clinical study.

Setting: A medical center IVF unit and a research institute.

Patient(s): Women undergoing IVF who had previous failed treatment cycles.

Intervention(s): Endometrial samples were collected from two groups of patients on day 21 of their spontaneous menstrual cycle. The experimental, but not the control group underwent prior biopsy treatment on days 8 or/and 11 to 13 of that same cycle.

Main outcome measure(s): Abundance of immune cells, cytokines/chemokines level, correlation between these parameters and pregnancy outcome.

Result(s): A statistically significantly higher amount of macrophages/dendritic cells (HLA-DR+ CD11c+ cells) and elevated proinflammatory cytokines, tumor necrosis factor-α (TNF-α), growth-regulated oncogene-α (GRO-α), interleukin-15 (IL-15), and macrophage inflammatory protein 1B (MIP-1B), were detected in day-21 endometrial samples of the experimental group. A direct stimulatory effect of TNF-α on MIP-1B, GRO-α, and IL-15 messenger RNA (mRNA) expression was demonstrated. A positive correlation was found between the levels of macrophages/dendritic cells, MIP-1B expression, and TNF-α expression and the pregnancy outcome.

Conclusion(s): A biopsy-induced inflammatory response may facilitate the preparation of the endometrium for implantation. Increased MIP-1B expression could possibly serve for prediction of implantation competence.

FIGURE 1

Evaluation of the cytokine/chemokine profile in the endometrial samples. Protein levels of (A) growth-regulated oncogene-α (GRO-α), (B) interleukin-15 (IL-15), (C) macrophage inflammatory protein 1B (MIP-1B) were determined by multiple cytokine Luminex analysis. (D, E) Relative MIP-1B and tumor necrosis factor-α (TNF-α) messenger RNA (mRNA) levels were tested by quantitative real-time polymerase chain reaction. The box plot horizontal lines represent the median and the 25th to 75th percentile. Comparison between days 8 to 12 and 21 within the experimental group was performed by Wilcoxon’s signed rank test. Comparison between day-21 samples of the experimental and control groups was performed using Mann-Whitney test (**P<.01, *P<.05). The effect of TNF-α on the expression of MIP-1B, MUC1, Gro-α, and IL-15 was tested in (F) freshly isolated endometrial stromal cells (ESC) from day-21 control samples and in (G) epithelial cell line ECC-1. Results of in vitro experiments are mean ± standard error of the mean from three independent experiments. Endometrial stromal cells were prepared from three different tissues. *, #, and † are significantly different from their respective control (P<.05; student t-test).

FIGURE 2

Characterization of macrophages/dendritic cells (DCs) in the endometrial samples by flow cytometry. Leukocytes region was defined using (A) characteristic size (FSC) and granularity (SSC) parameters (R1) as well as by positive staining with (B) anti-CD45 (R2). (C) The HLA-DR⁺CD56⁻ cells (R3) within leukocyte region (R1 and R2) that exhibited a positive staining for (D) CD11c were defined as macrophages/DCs. (E) HLA-DR⁺CD11c⁺ cells (R4) were separated to (F) macrophages and DCs according to CD14 staining. (G) A representative analysis of HLA-DR⁺CD11c⁺ cells in endometrial samples from days 8 to 12 and day 21 of the experimental group and the day-21 sample of the control group. (H) The abundance of HLA-DR⁺CD11c⁺ cells was calculated of total leukocytes (R1 and R2). The box plot horizontal lines represent the median and the 25th to 75th percentile. Comparison between days 8 to 12 and 21 within the experimental group was performed by Wilcoxon’s test signed rank test. Comparison between the day-21 samples of the experimental and control groups was performed using Mann-Whitney test. ***P<.001.

FIGURE 3

Expression of osteopontin (OPN) and vascular endothelial growth factor (VEGF) in the endometrial samples. The box plot horizontal lines represent the median and the 25th to 75th percentile of (A) VEGF messenger RNA (mRNA) levels, (B) OPN mRNA, and (C) protein levels. *P<.05, **P<.01 (Mann-Whitney test).

FIGURE 4

Comparison of the abundance of (A) macrophages/dendritic cells (HLA-DR⁺CD11c⁺ cells), (B) messenger RNA (mRNA) levels of macrophage inflammatory protein 1B (MIP-1B), (C) tumor necrosis factor-α (TNF-α), and (D) osteopontin (OPN) between pregnant (+) and not pregnant (−) IVF patients. The box plot horizontal lines represent the median and the 25th to 75th percentile. *P<.05 (Mann-Whitney test).