Quantitative analysis of neutralizing antibody response to human cytomegalovirus in natural infection

Naturally acquired immunity significantly reduces the risk of congenital cytomegalovirus (CMV) infection in future pregnancies. An immune response comparable to that of natural infection has been used as a benchmark for CMV vaccine efficacy; however, the magnitude and persistence of the neutralizing antibody responses in naturally infected women are not completely understood. In this study, we quantitatively analyzed a panel of 375 female CMV convalescent sera ranging in age from 18 to 84 years, for its ability to block virus entry into epithelial cells and fibroblasts, as well as its binding potential to CMV particles. The geometric mean titer of the sera in this panel to neutralize 50% of the virus entry into epithelial cells was 7491, compared to 802 for entry into fibroblasts. The epithelial neutralizing titers were statistically indistinguishable among different age groups, and conformed to a normal distribution. There was a weak correlation between the levels of neutralization and the binding activities to viral particles. Our data confirmed that natural CMV infection in healthy women induces potent neutralizing antibodies against infection of both fibroblasts and epithelial cells. The serum neutralizing activities were maintained at high levels throughout the child bearing age. The corresponding titers may serve as a biomarker for CMV vaccine efficacy.