A human cytomegalovirus-neutralizing monoclonal antibody recognizes a normal cell protein

A monoclonal antibody (MAb), N2, neutralized human cytomegalovirus (HCMV) infectivity in the absence of complement and recognized a normal cell protein. By immunofluorescence, MAb N2 detected antigens in uninfected human cells, but not in cells of non-human origin. Antigens were present at the membrane and were dispersed diffusely within the cytoplasm. MAb N2 immunoprecipitated a glycoprotein with an Mr of 94K from uninfected and infected cells. In infected cells only, it also recognized a protein of Mr 34K which was not linked to the 94K Mr glycoprotein by disulphide bonds. N2 neutralized both laboratory and field isolates of HCMV. A study of the distribution of the N2 neutralization epitope recognized among fresh isolates of HCMV showed that only 67% of the isolates could be neutralized by this antibody. There was no correlation between the number of in vitro passages and the level of neutralization. The 34K Mr polypeptide was present in cells infected by all isolates. It thus appears that, during virus assembly, HCMV acquires a normal cell protein that bears a neutralization epitope.