Cted on the apical surface of the luminal epithelium (Figure 2A) and glandular PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/20460822 epithelium (Figure 2B), but weakly on the myometrium (Figure 2C). In contrast, the protein signal in stromal cells was dispersedly distributed on some unidentified cells, parts of which may be macrophage as judged by cell morphology (Figure 2B). In addition, SERPINE2 was detected on endothelial cells of the vessel (Figure 2C) as demonstrated by a previous PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/13485127 study [23]. When slides were immunostained with control antiserum, no signal was detected (data not shown). To further evaluate the expression of the SERPINE2 protein in various sub-phases of the menstrual cycle, we examined endometrial slides prepared from early-, mid-, and late-proliferative as well as secretory phases by immunohistochemistry. The results showed that the signal was relatively weaker during the proliferative phase (Figure 3A-C), while it was strongly detected in the glandular epithelium during the secretory phase (Figure 3D-F), especially in the mid- and late-secretory phase (Figure 3E, F). Positively stained cells in the endometrial gland were quantified to analyze expression levels of the SERPINE2 protein. The signal intensity was determined by quantitative software. Scattergrams of the staining intensity (Figure 4B) indicated strongly and weakly stained cells in the glandular epithelium (Figure 4A). The results implied that weakly stained cells in the gland wereLee et al. Reproductive Biology and Endocrinology 2011, 9:38 http://www.rbej.com/content/9/1/Page 4 ofFigure 1 Antibody specificity and presence of the Methyl 5-amino-2,4-difluorobenzoate SERPINE2 protein in human uterine fluid. (A) Four hundred nanograms of recombinant human SERPINE2 was resolved on 10 SDS-PAGE and followed by Western blotting using anti-mouse SERPINE2 antiserum (lane 1), an antihuman SERPINE2 antibody (R D) (lane2), or another anti-human SERPINE2 antibody (Abnova) (lane 3). (B) One hundred micrograms of the extract of endometrial curettage was analyzed by anti-mouse SERPINE2 antiserum (lanes 1 and 2) and an anti-human SERPINE2 antibody (R D) 4,4,5,5-Tetramethyl-2-(2-methylprop-1-en-1-yl)-1,3,2-dioxaborolane (lanes 3 and 4). (C) Fifty micrograms of uterine fluid proteins collected from each individual patient (n = 7) was Western-blotted using antimouse SERPINE2 antiserum (1:3000) (upper panel). EP, MP, and LP indicate early-, mid-, and late-proliferative phases, and ES and MS indicate early- and mid-secretory phases, respectively. The blot was also overexposed to clearly display the staining signal (lower panel).mostly derived from the proliferative phase, while strongly stained cells were predominantly from the secretory phase (Figure 4C). Thus, SERPINE2 was primarily expressed in secretory-phase endometrial glandular cells from which it was secreted into the lumen of the uterus.Discussion In this study, we demonstrated that the SERPINE2 protein, an inhibitor of PAs, is highly expressed in the human uterus during the secretory phase. However, its levels are low in the uterus during the proliferative phase. It is primarily expressed in the luminal and glandular epithelium, weakly expressed in the myometrium, and dispersedly expressed by certain stromal cells. Proteases are known to be involved in extracellular matrix degradation required for implantation, including cysteine, serine, and matrix metalloproteinases [24]. PA serine proteases and their cognate inhibitors are involved in implantation [1,3]. Tissue remodeling is an important biological event for many reproductive processes that occur in the ovary, uteru.