Prolactin stimulates the internalization of Staphylococcus aureus and modulates the expression of inflammatory response genes in bovine mammary epithelial cells Angelina Gutie ´rrez-Barroso a,1 , Jose ´ L. Anaya-Lo ´pez a,1 , Leticia Lara-Za ´rate a , Pedro D. Loeza-Lara b , Joel E. Lo ´pez-Meza a , Alejandra Ochoa-Zarzosa a, * a Centro Multidisciplinario de Estudios en Biotecnologı ´a-Facultad de Medicina Veterinaria y Zootecnia, Universidad Michoacana de San Nicola ´s de Hidalgo, Apdo. Postal 53, Administracio ´n Chapultepec, C.P. 58262, Morelia, Michoaca ´n, Me ´xico b Facultad de Biologı ´a., Universidad Michoacana de San Nicola ´s de Hidalgo, Morelia, Michoaca ´n, Me ´xico Received 27 March 2007; received in revised form 11 July 2007; accepted 26 September 2007 Abstract The incidence of mastitis in dairy cattle is highest at the drying off period and parturition, which are characterized by high levels of the lactogenic hormone prolactin (PRL). One of the most frequently isolated contagious pathogens causing mastitis is Staphylococcus aureus. However, the role of PRL on S. aureus infection in mammary epithelium has not been studied. In this work we evaluated the effect of bovine PRL (bPRL) on S. aureus internalization in a primary culture of bovine mammary epithelial cells (bMEC) and on the expression of cytokine and innate immune response genes. Our data show that 5 ng/mL bPRL enhances 3-fold the internalization of S. aureus (ATCC 27543) into bMEC. By RT-PCR analysis, we showed that bPRL is able to up- regulate the expression of tumor necrosis factor-a (TNF-a), interleukin-1b (IL-1b) and inducible nitric oxide synthase (iNOS) mRNAs. However, bPRL together with S. aureus did not modify the expression of TNF-a and iNOS mRNAs, while it down- regulated the expression of b-defensin and IL-1b mRNAs, as well as nitric oxide production, suggesting that infection and bPRL together can inhibit elements of the host immune response. To our knowledge, this is the first report that shows a role of bPRL during the internalization of S. aureus into bMEC. # 2007 Elsevier B.V. All rights reserved. Keywords: Prolactin; Mastitis; Mammary epithelium; Staphylococcus aureus; Cytokines; iNOS 1. Introduction Bovine mastitis is the most important infectious disease of dairy cattle, affecting both the quality and quantity of milk produced in the world. This disease is characterized by an inflammatory response of the mammary tissue caused by bacterial and fungal infections. The highest incidence of udder infection and the establishment of mastitis occur during the drying off period and around calving (Burvenich et al., 1999; Burton and Erskine, 2003). These periods are characterized by important physiological changes related to milk production and metabolism. However, the functions of lactogenic hormones such as prolactin (PRL) during the udder infection and the establishment of mastitis remain unclear. Recently, it has been www.elsevier.com/locate/vetimm Available online at www.sciencedirect.com Veterinary Immunology and Immunopathology 121 (2008) 113–122 * Corresponding author. Tel.: +52 443 295 8029; fax: +52 443 295 8029. E-mail addresses: ochoaz@zeus.umich.mx, aleocho@hotmail.com (A. Ochoa-Zarzosa). 1 These authors contributed equally to this work. 0165-2427/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.vetimm.2007.09.007