In summary, the repertoire analysis revealed that most anti-gB IgG antibodies derived from memory B cells are non-neutralizing. Among those antibodies that neutralized HCMV in vitro, most antibodies reacted against two previously uncharacterized regions of the gB protein. Addition of complement had no influence on the neutralizing capacity of the recombinant antibodies. Moreover, when a selected set (n = 10) of non-neutralizing antibodies directed against different antigenic domains of gB was tested in concentrations up to 5 mg/ml in the presence of complement we observed no significant increase in neutralization capacity which is in agreement with previous reports on gB-specific human mabs (data not shown) [35] . However, we cannot completely rule out a moderate enhancing effect of complement for some antibodies, especially those of the IgG3 subtype.