Cellular Immunology 233 (2005) 61–71 www.elsevier.com/locate/ycimm 0008-8749/$ - see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.cellimm.2005.04.003 Immunology ellular Interleukin-8 mRNA synthesis and protein secretion are continuously up-regulated by respiratory syncytial virus persistently infected cells Rocio Tirado a , Arturo Ortega b , Rosa Elena Sarmiento a , Beatríz Gómez a,¤ a Departamento de Microbiología y Parasitología, Facultad de Medicina, Universidad Nacional Autónoma de México, Cd. Universitaria, Mexico D.F. 04510, Mexico b Departamento de Genética y Biología Molecular, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Mexico D.F. 07300, Mexico Received 23 February 2005; accepted 15 April 2005 Available online 4 June 2005 Abstract The aim of this study was to investigate whether respiratory syncytial virus persistence regulates interleukin 8 (IL-8) mRNA syn- thesis and protein secretion in a human lung epithelial cell line (A549). Therefore, we established RSV persistence in these cells (A549per) and determined the levels of interleukin-8 mRNA by RT-PCR and of protein through ELISA. Interleukin-8 mRNA syn- thesis and protein secretion were continuously up-regulated in A549per cells during passages and in A549 cells that had been incu- bated with supernatants (cA549per) obtained from A549per passages. These results suggested that the enhancement of interleukin-8 was stimulated either by the presence of the RSV genome in the cell or by soluble mediator(s) induced by RSV, which, in turn, increased interleukin-8 mRNA synthesis and protein secretion. Soluble RSV F and G proteins were identiWed as mediators. More- over, interleukin-8 enhancement was observed after 1-min incubation with the soluble mediators, thus suggesting that interleukin-8 up-regulation was triggered by receptor–ligand interaction.  2005 Elsevier Inc. All rights reserved. Keywords: Interleukin-8; Up-regulation; Extra-cellular RSV proteins; Human airway epithelial cells 1. Introduction Respiratory syncytial virus (RSV) is the most impor- tant respiratory pathogen in infancy; by age 2 virtually 100% of children have been infected. The infection is rarely subclinical and mostly presents as an upper or lower tract infection. RSV infection in the lower respira- tory tract in infants typically causes bronchiolitis and pneumonia; furthermore, clinical and epidemiological data show that early severe infection is associated with increased risk of long-term problems such as recurrent chronic obstructive pulmonary disease [1–8]. The mecha- nisms, by which this infection leads to airway dysfunc- tion that persists long after the acute disease has been resolved, are not well deWned. However, involvement of RSV persistence in long-term respiratory problems has been suggested [1,9–12]. RSV is a member of the Paramixoviridae (genus Pneumovirus), a large group of non-segmented, nega- tive-strand RNA virus, which includes several viruses that persist in humans and in human cell lines [13,14]. RSV codes for 11 proteins, three being transmembrane surface glycoproteins (F, G, and SH), two of which, F and G, can be secreted [13,15,16]. Although RSV persistence in humans (the natural host of RSV) has not been clearly demonstrated, some circumstantial evidences suggest it: RSV was isolated from the nasopharynx of apparently healthy children [17]; viral antigens in osteoclasts and cells from patients * Corresponding author. Fax: +52 55 5623 23 82/5623 23 86. E-mail address: begomez@servidor.unam.mx (B. Gómez).