Decreased expression of the decoy interleukin-1 receptor type II in human endometriosis

Abstract

Many of the biological changes occurring in the endometrium during the menstrual cycle bear a striking resemblance to those associated with inflammatory and reparative processes. Hence, it would not be surprising to find that cytokines known for their pro-inflammatory properties, such as interleukin-1 (IL-1), could play a key role in the physiology of this tissue and that their action would be tightly controlled by local mechanisms. In the present study, immunohistochemical and Western blot analyses show that in normal women (n = 39), the endometrial tissue expresses, in a cycle-dependent manner, the IL-1 receptor type II (IL-1RII), a molecule of which the only biological property known to date is that of capturing IL-1, inhibiting thereby its binding to the functional type I IL-1 receptor. IL-RII immunostaining was particularly intense within the lumen of the glands and at the apical side of surface epithelium. Interestingly, the intensity of staining was markedly less pronounced in the endometrium of women with endometriosis (n = 54), a disease believed to arise from the abnormal development of endometrial tissue outside the uterus, especially in the early stages of the disease (stages I and II). This study is the first to show the local expression in endometrial tissue of IL-1RII, a potent and specific down-regulator of IL-1 action and its decreased expression in women suffering from endometriosis.

Figure 1.

Representative illustration of IL-1RII immunostaining in the human endometrium. Sections of endometrial tissue were incubated with mouse monoclonal anti-IL-1RII antibody (A, proliferative day 13; B, secretory day 24; original magnification, ×68) or with an equivalent concentration of normal mouse IgGs (C and D, respectively; original magnification, ×68). Sections were then incubated successively with biotinylated goat anti-mouse polyclonal antibody and avidin-biotinylated horseradish peroxidase complex. The immunoreaction was revealed with diaminobenzidine (brown staining) and hematoxylin was used for counterstaining (blue staining). Note the brown fine positive staining in stromal and epithelial cells (cellular staining) (E–H; original magnification, ×268), and the brown deposit (arrow) that is primarily located at the apical side of glandular (E, secretory phase day 24) and surface (F, secretory phase day 16) epithelium, or more spread within the glands lumen (G, secretory phase day 16). Positive immunostaining is also detected in isolated stromal cells (c) (G, secretory phase day 16) and microvessels (v) (H, secretory phase day 24) found in the stroma in the secretory phase of the menstrual cycle. s = stroma, g = gland.

Figure 2.

Dual immunofluorescent staining of IL-1RII (A) and IL-1β (B) in the endometrial tissue of normal women. Tissue sections were successively incubated with mouse monoclonal anti-IL-1RII antibody, rabbit polyclonal anti-IL-1 antibody, and biotinylated goat anti-rabbit antibody before being incubated simultaneously with rhodamine-conjugated goat anti-mouse antibody and fluorescein isothiocyanate-conjugated streptavidin. Serial sections incubated with normal mouse and normal rabbit IgGs instead of the primary antibodies were included as negative controls (C and D) (original magnification, ×160). Note the co-expression of IL-1RII (red color) and IL-1β (green-yellow color) within the luminal deposit in endometrial glands. Data from a normal woman in the secretory phase of the menstrual cycle (day 23).

Figure 3.

Representative illustration of IL-1RII immunostaining in the endometrium of women with and without endometriosis. A: Normal secretory day 24, luminal staining score 3, cellular staining score 2 in stromal and epithelial cells. B: Endometriosis stage secretory day 26, luminal staining score 0, cellular staining score 2 in stromal and epithelial cells. Note the lack of staining within the lumen of endometrial glands in B. Original magnification, ×160.

Figure 4.

Western blot analysis of IL-1RII expression in the endometrial tissue. A: Normal women: day 10 (lanes 1 and 3) and day 24 (lanes 2 and 4). B: Women with endometriosis: stage II, day 13 (lanes 1 and 3) and stage II, day 25 (lanes 2 and 4). Equal amounts of endometrial proteins (100 μg/lane) were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred to nitrocellulose membranes. IL-1RII was detected using a mouse monoclonal antibody (lanes 1 and 2) and the immunocomplex was revealed by chemiluminescence. No immunoreaction was observed in negative controls where the anti-IL-1RII antibody was replaced by an equal concentration of mouse immunoglobulins of the same isotype (lanes 3 and 4).