At this time we can only speculate on a potential role of the nonneutralizing antibodies on the infection in vivo. Besides being irrelevant for the infection, non-neutralizing antibodies might have positive or negative effects. Effector functions mediated via the Fcportion of the antibodies such as ADCC and/or complement fixation may contribute to elimination of infected cells and thus could lead to enhanced clearance of these cells. That such mechanisms are operative in vivo has been shown in different viral systems, including herpesviruses, but not for HCMV [54, 55] . On the other hand, infection-enhancing effects could be contributed by mechanisms such as competition of non-neutralizing antibodies for binding to neutralizing epitopes or enhanced infection of Fcreceptor bearing cells such as monocytes, which is one of the major target cell population for HCMV infection in vivo [56] .