Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited. Natural mucosal antibodies reactive with first extracellular loop of CCR5 inhibit HIV-1 transport across human epithelial cells Morgane Bomsel a , Claudia Pastori b , Daniela Tudor a , Chiara Alberti b , Severine Garcia b , Davide Ferrari c , Adriano Lazzarin b and Lucia Lopalco b Objective: The genital mucosa represents the major site for initial host-HIV-1 contact. HIV-1-protective mucosal immunity has been identified either in subjects who despite repeated sexual exposure, remain seronegative (ESN) or in long-term non-progressor HIV-1-seropositive individuals (LTNP). As a subset of ESN and LTNP produce anti-CCR5 antibodies both at systemic and mucosal level, we studied the role of anti-CCR5 antibodies in blocking HIV transfer through human epithelial cells. Design and methods: To evaluate HIV-1-inhibitory activity by anti-CCR5 antibodies, a two-chambers system was established to model HIV-1 infection across the human mucosal epithelium. Moreover, peripheral blood mononuclear cells (PBMC) and a CCR5 transfected cell line were also used in a classical HIV-infectivity assay. CCR5- specific IgG and IgA were used to inhibit HIV replication. Results: Either serum or mucosal IgA to CCR5 were able to specifically block trans- cytosis of CCR5- but not CXCR4-HIV strains across a tight epithelial cell layer by interacting with the first extracellular loop of the receptor (amino acids YAAAQWDFGNTMCQ). Monoclonal antibodies against other regions of CCR5 had no effect on HIV transcytosis. Moreover, mucosal CCR5-specific IgA neutralized CCR5- tropic strains and SOS–JRFL pseudovirus replication in PBMC and CCR5 transfected cell lines respectively, with a mechanism different than that observed for transcytosis. Conclusions: Anti-CCR5 Abs shed light on the immunological mechanisms involved in the control of HIV-1 infection in a model that can be considered an experimentum naturae for resistance to HIV. They could be useful in the design of new strategies against HIV infection at mucosal sites. ß 2007 Lippincott Williams & Wilkins AIDS 2007, 21:13–22 Keywords: CCR5, HIV, neutralizing antibodies, mucosal IgA, transcytosis, anti-CCR5 antibodies Introduction Mucosal humoral immunity is mainly mediated by secretory IgA which inhibit HIV-1 transport across epithelium by capturing the transcytosing virions and redirecting them to the serosal pole [1–4]. IgA also inhibit binding of HIV to the glycosphingolipid galactosyl ceramide (Gal–Cer) [5,6] and thereby HIV transcytosis in mucosae [2,4]. Transcytosis, specific for epithelial cells [7], may allow translocation of HIV-1 across mono- stratified mucosa that cover endo-cervix, gastro-intestinal tract and rectum [8]. The monostratified transition zone in HIV infection represents one main portal of HIV entry [9], emphasizing the role of transcytosis in HIV mucosal From the a Institut Cochin, INSERM, CNRS, Paris, France, the b Infectious Diseases Clinic, San Raffaele Scientific Institute, Milano, Italy, and the c Department of Obstetrics and Gynecology, San Raffaele Scientific Institute, Milano, Italy. Correspondence to L. Lopalco, Infectious Diseases Clinic, San Raffaele Scientific Institute, Via Stamira D’Ancona 20, Milano 20127; Italy. Tel: +39 02 2643 7936; fax: +39 02 2643 7989; e-mail: lopalco.lucia@hsr.it Received: 6 April 2006; revised: 11 August 2006; accepted: 18 September 2006. ISSN 0269-9370 Q 2007 Lippincott Williams & Wilkins 13