Human cytomegalovirus serum neutralizing antibodies block virus infection of endothelial/epithelial cells, but not fibroblasts, early during primary infection.

A panel of human sera exhibited a >or=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.