Interleukin-1 receptor accessory protein is constitutively expressed in human endometrium throughout the menstrual cycle.

Interleukin-1 (IL-1) is one of the principal cytokines that participate in endocrine and local regulation of many endometrial and reproductive functions. The cellular response to IL-1 principally implicates receptor type 1 (IL-1R tI) and, according to recent data, an accessory protein (IL-1R-AcP) that seems to play an essential function in signal transduction. In the present study, we examined the expression of IL-1R-AcP in the endometrium of 39 normal fertile women throughout the menstrual cycle. As studied by immunohistochemistry, IL-1R-AcP was detected across endometrial tissue, but more noticeably in the glands and luminal epithelium. The intensity of IL-1R-AcP immunostaining was consistently high throughout the menstrual cycle, and this was confirmed by Western blot analysis of the protein and corroborated by reverse transcription-polymerase chain reaction analysis of the mRNA. To our knowledge, this is the first report showing that IL-1R-AcP is expressed in endometrial tissue, and without any noticeable variation throughout the menstrual cycle. This suggests that the accessory protein, whose co-expression is critical for IL-1R tI-mediated cell activation, is, in contrast to the functional receptor, constitutively expressed and not subject to similar cycle-dependent regulation.