Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Mon, 03 Dec 2018 21:29:17 Human cytomegalovirus serum neutralizing antibodies block virus infection of endothelial/ epithelial cells, but not fibroblasts, early during primary infection Giuseppe Gerna, 1 Antonella Sarasini, 1 Marco Patrone, 2 Elena Percivalle, 1 Loretta Fiorina, 1 Giulia Campanini, 1 Andrea Gallina, 2 Fausto Baldanti 1,3 and M. Grazia Revello 1 Correspondence Giuseppe Gerna g.gerna@smatteo.pv.it 1 Servizio di Virologia, Fondazione IRCCS Policlinico San Matteo, 27100 Pavia, Italy 2 Dipartimento di Medicina, Chirurgia e Odontoiatria, Universita ` degli Studi di Milano, 20142 Milano, Italy 3 Laboratori Sperimentali di Ricerca, Fondazione IRCCS Policlinico San Matteo, 27100 Pavia, Italy Received 16 October 2007 Accepted 12 December 2007 A panel of human sera exhibited a ¢128-fold higher neutralizing potency against a human cytomegalovirus (HCMV) clinical isolate propagated and tested in endothelial (or epithelial) cells than against the same virus infecting human fibroblasts. In a group of 18 primary infections, the reverse geometric mean titre was in the range of 10–15 in human fibroblasts within the first 3 months after the onset of infection, whereas the endothelial cell infection-neutralizing activity was already present within the first 10 days, reaching median levels of 122, 320 and 545 at respectively 30, 60 and 90 days after onset, then declining slowly. This difference was also confirmed in the majority of reactivated and remote HCMV infections, as well as in a hyperimmune globulin preparation. The antibody response to HCMV pUL131A, pUL130 and pUL128 locus products, which are required for endothelial/epithelial cell infection, provided a potential molecular basis for such a differential neutralizing activity. In addition, monoclonal/monospecific antibodies raised against the pUL131A, pUL130 and pUL128 proteins were found to display an inhibitory activity on HCMV plaque formation and HCMV leukocyte transfer from HCMV-infected cells. Hence, conventional determination of the neutralizing activity of human sera in fibroblasts is misleading. Antibodies to pUL131A, pUL130 and pUL128 appear to display a major HCMV-neutralizing and dissemination-inhibiting activity. INTRODUCTION Neutralizing antibodies are a major component of the humoral immune response and, following primary infec- tion, confer protection against several viral infections. However, in herpesvirus infections, and particularly in those caused by human cytomegalovirus (HCMV), the protective role of neutralizing antibody remains substan- tially undefined. In this type of infection, a major role in protection is provided by the T-cell-mediated immune response, whilst the role of neutralizing antibody has been claimed repeatedly, but never documented conclusively. Epidemiological surveys indicate that primary HCMV infections occurring in seronegative pregnant women in the absence of neutralizing antibody (which are conven- tionally defined as appearing late) carry a high risk (about 40 %) of HCMV transmission to the fetus (Stagno et al., 1986; Revello & Gerna, 2002). On the other hand, although at a much lower rate, vertical transmission may also occur in seropositive pregnant women in the presence of neutralizing antibody (Fowler et al., 2003). Similarly, in immunocompromised patients, clinical syndromes occur- ring in seronegative individuals are more severe than those observed in seropositive subjects (Grossi et al., 1995; Gerna et al., 1998). However, reactivated infections occur in seropositive patients, even in the presence of high levels of neutralizing antibody (Mun ˜oz et al., 2001). In addition, in these patients, HCMV infections are controlled only after reconstitution of cellular immunity (Quinnan et al., 1982; Reusser et al., 1991; Sester et al., 2005; Gerna et al., 2006a; Lilleri et al., 2006). HCMV was recovered for the first time in 1956 in human fibroblasts and, since then, neutralizing antibodies have been evaluated in this cell system (Smith, 1956). Determination of neutralizing antibody has been proposed as a parameter for differentiating primary from reactivated HCMV infections, in that neutralizing antibodies appear Journal of General Virology (2008), 89, 853–865 DOI 10.1099/vir.0.83523-0 0008-3523 G 2008 SGM Printed in Great Britain 853