Eosinophils are cellular targets of the novel uteroplacental heparin-binding cytokine decidual/trophoblast prolactin-related protein D Wang 1 , R Ishimura 1 , D S Walia 1 , H Müller 1 , G Dai 1 , J S Hunt 2 , N A Lee 3 , J J Lee 3 and M J Soares 1 1 Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas 66160, USA 2 Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, Kansas 66160, USA 3 Department of Biochemistry and Molecular Biology, Mayo Clinic Scottsdale, Scottsdale, Arizona 85259, USA (Requests for offprints should be addressed to M J Soares; Email: msoares@kumc.edu) (R Ishimura is now at Laboratory of Cellular Biochemistry, Veterinary Medical Sciences, The University of Tokyo, 1–1–1 Yayoi, Bunkyo-ku, Tokyo 113, Japan) (H Müller is now at Department of Obstetrics and Gynecology, Universitats-Frauenklinik, Doberaner Str. 142, PF 10 08 88, 18055 Rostock, Germany) Abstract The uterus and placenta of the mouse and rat produce a member of the prolactin (PRL) family referred to as decidual/trophoblast PRL-related protein (d/tPRP). This cytokine/hormone has been hypothesized to regulate decidual cell activities needed for the establishment and maintenance of gestation. An alkaline phosphatase (AP)- tagging strategy was used to identify d/tPRP target cells. AP–d/tPRP bound to virtually all cells and tissues to which it was exposed, consistent with our earlier evidence that d/tPRP binds to heparin-containing molecules. Moreover, we found that co-incubation with heparin or pretreatment with heparitinase greatly decreased the bind- ing of AP–d/tPRP to tissue sections. In addition, we observed that the AP–d/tPRP probe bound to the surface of Chinese hamster ovary (CHO) cells but not to heparan sulfate-deficient CHO-pgsD-677 cells. Potential unique non-heparin d/tPRP binding sites within mouse and rat uteroplacental tissues were identified by consecutively incubating sections with AP–d/tPRP followed by heparin. This strategy led to the identification of d/tPRP target cells associated with the uterus and the labyrinth zone of the chorioallantoic placenta. Within the uterus, d/tPRP specifically bound to eosinophils. d/tPRP-binding and eosinophil peroxidase activity were co-localized and showed similar patterns of distribution during the estrous cycle, pregnancy, and following hormonal manipulation. d/tPRP interactions with eosinophils were further dem- onstrated in the lung and intestine, with eosinophils isolated from the peritoneum, and in mice with gen- eralized tissue eosinophilia. Collectively, these findings suggest that intercellular d/tPRP targeting is mediated through associations with heparin-containing molecules which help direct d/tPRP to specific interactions with eosinophils within the uterus and with the labyrinthine compartment of the chorioallantoic placenta. Journal of Endocrinology (2000) 167, 15–28 Introduction The establishment of pregnancy requires numerous concomitant maternal uterine changes, including those related to the vasculature and immune cells. Hemo- chorial placentation occurs in both primates and rodents, resulting in the establishment of a close connection between maternal and fetal tissues (Enders & Welsh 1993). This close connection facilitates the exchange of nutrients and wastes at the expense of an increased risk of maternal immune system recognition of the genetically disparate embryo. Decidual and tropho- blast cells, and their secretory products, likely provide the signaling system that coordinates the activities of the maternal uterine compartment. Decidual cells arise from uterine stroma, forming intimate relationships with placental structures that facilitate the development of the embryo (DeFeo 1967, Bell 1983, Parr & Parr 1989). Among the important functions of decidual cells are their hormone/cytokine producing capabilities. In the mouse and rat, decidual cell production of a hormone related to pituitary prolactin (PRL) is of particular interest. This hormone, referred to as decidual/trophoblast PRL-related protein (d/tPRP), has been implicated in directing early changes in the utero- placental compartment required for the establishment of pregnancy (Roby et al. 1993, Rasmussen et al. 1996). d/tPRP was originally isolated during a search for a putative decidual luteotropin (Roby et al. 1993). Although d/tPRP exhibits significant structural similarities to PRL, 15 Journal of Endocrinology (2000) 167, 15–28 0022–0795/00/0167–015  2000 Society for Endocrinology Printed in Great Britain Online version via http://www.endocrinology.org