Journal of Reproductive Immunology 66 (2005) 127–140 Presence of the P2X 7 purinergic receptor on immune cells that invade the rat endometrium during oestrus Rachel Koshi a , Robson Coutinho-Silva b,e , Cynthia Machado Cascabulho d , Andrea Henrique-Pons d , Gillian E. Knight b , Andrzej Loesch c , Geoffrey Burnstock b,∗ a Department of Anatomy, Christian Medical College, Vellore 632002, India b Autonomic Neuroscience Centre, Royal Free and University College Medical School, Rowland Hill Street, London NW3 2PF, UK c Department of Anatomy and Developmental Biology, Royal Free and University College Medical School, Rowland Hill Street, London NW3 2PF, UK d Departamento de Ultraestrutura e Biologia Celular, Instituto Oswaldo Cruz-Fiocruz, Rio de Janeiro, Brasil e Instituto de Biof´ ısica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil Received 27 August 2004; received in revised form 19 April 2005; accepted 26 April 2005 Abstract Eosinophils, macrophages and other leucocytes invade the uterine endometrium during oestrus and play a role in the tissue remodeling and immune responses that occur prior to implantation of the fertilized ovum. Adenosine 5 ′ -triphosphate (ATP) and its metabolites influence uterine function via ATP receptors. In this study, we investigated the presence and localisation of the P2X 7 nucleotide receptor in the cells that infiltrate the uterine endometrium of adult female rats during oestrus at the electron microscope level, using gold–silver pre-embedding immunocytochemical techniques. P2X 7 receptor expression was found in the cytoplasm and the cell membrane of eosinophils, macrophages and fibroblasts in the endometrium during oestrus. These results suggest that ATP-mediated responses may be important in uterine preparation and remodeling before implantation and that this may involve several types of cells. In particular, the presence of P2X 7 receptors on endometrial stromal cells may indicate their involvement in apoptosis and immune and inflammatory responses. © 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Implantation; Oestrus; Purinergic receptor; Signal transducer; Uterus ∗ Corresponding author. Tel.: +44 20 7830 2948; fax: +44 20 7830 2949. E-mail address: g.burnstock@ucl.ac.uk (G. Burnstock). 0165-0378/$ – see front matter © 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.jri.2005.04.006