The involvement of interleukin (IL)-15 in regulating the differentiation of granulated metrial gland cells in mouse pregnant uterus

Abstract

Previous studies have suggested that granulated metrial gland (GMG) cells are bone marrow-derived lymphoid cells, which differentiate in situ in the mouse pregnant uterus into natural killer (NK)-like cells. Similar to NK cells, GMG cells express an abundant level of cytolytic mediators such as perforin. The factor(s) regulating the differentiation of GMG cells remain(s) to be identified, although cytokines previously implicated in the stimulation/activation of NK cells (e.g., IL-2, IL-6, IL-7, and IL-12) can be considered as potential candidates. Recently, IL-15, a novel cytokine, which displays biological activities similar to IL-2, has also been shown to be capable of activating NK cells. Using reverse transcription-polymerase chain reaction (RT-PCR) analysis, we have demonstrated in the present study that IL-15 and its cognate receptor, but not the other cytokines, are expressed in the mouse pregnant uterus, with a time course concomitant with those of cytolytic mediators in differentiated GMG cells. Moreover, IL-15, though not IL-2, is capable of inducing the expression of perforin and granzymes in pregnant uterine tissues explanted in vitro. Data obtained from in situ hybridization study have suggested that the macrophages present in the pregnant uterus may be responsible for the production of IL-15. These results suggest that IL-15 is involved in regulating the differentiation of GMG cells during mouse pregnancy.

Figure 1

Expression of mRNAs encoding lymphocyte cytolytic mediators, cytokines, and cytokine receptors in the pregnant uterus, investigated by RT-PCR analysis (see Materials and Methods).

Figure 2

Effects of IL-15 and IL-2 on the expression of perforin mRNA in pregnant uterus. The explants of pregnant uterus prepared on the indicated days of gestation were cultured for 24 h in medium alone, or in medium supplemented with either IL-15 or IL-2. The RNAs prepared from the cultured explants were subjected to RT-PCR and PhosphorImager analysis. The level of the expression of perforin mRNA in the explants obtained on the indicated day of gestation was determined based on the ratio of the PCR product specific for perforin to that for β-actin. The perforin/β-actin ratios obtained in the RNAs prepared from the explants cultured in the presence of cytokines were then normalized against those obtained from the explants cultured in medium alone.

Figure 3

Effects of IL-15 and IL-2 and the production of perforin protein in pregnant uterus. Proteins extracted from the cultured explants of pregnant uterus were subjected to Western blot analysis using an anti-perforin antiserum. Lanes 1, with medium; lane 2, with IL-15; lane 3, with IL-2; lane 4, with IL-15 and anti-IL-15.

Figure 4

Expression of IL-15 in the pregnant uterus analyzed by in situ hybridization. Sections of an implantation site in a pregnant uterus of day 9 of gestation were hybridized with dioxygenin-labeled antisense (A and C) or sense (B and D) riboprobe specific for murine IL-15. Some cells residing in the decidua basalis (DB) (arrows) appeared to hybridize specifically with the antisense probe, indicating the expression of IL-15 mRNA in these cells.