Neutralization of cytomegalovirus virions: the role of complement

Complement provides a key immunologic defense against invading pathogens; thus, a clear understanding of the interactions between cytomegalovirus (CMV) and complement may permit the development of strategies to enhance CMV neutralization. In the presence of specific anti-CMV antibodies, complement enhanced the neutralizing ability of serum by 2- to 3-fold. However, in the absence of specific anti-CMV antibodies, complement was ineffective in neutralizing CMV virions by plaque assay. Although complement alone did not mediate any neutralizing effect, CMV consumed complement activity from seronegative serum, resulting in the deposition of C3 on the virion. However, only in the presence of specific anti-CMV antibody did complement activation continue to the deposition of C9 on the virions. These results strongly suggest complement regulation by CMV virions that is modulated by anti-CMV antibody; this regulation may be attributed to three host complement regulators on the virions: CD55, CD46, and CD59. Complement provides a main line of immunologic defense tent persons also results in a normal humoral response and the subsequent generation of stable levels of anti-CMV IgGagainst invading pathogens. The complement system consists of at least 22 immunologically non–cross-reactive and distinct antibodies. The antibodies generated have been reported to be directed against both CMV early (nonstructural) and CMV lateplasma proteins. Together they represent a significant propor