Neutralizing antibody response to cytomegalovirus in seropositive pregnant women

Risk factors associated with the vertical transmission of cytomegalovirus in seropositive pregnant women

Congenital cytomegalovirus infection (cCMV) is the leading cause of childhood disabilities. More recent data indicates that cCMV following maternal nonprimary infection occurs frequently and can cause similar rates of sequelae as those following maternal primary infection. However, the risks associated with cCMV especially in CMV-seropositive women remain unclear. This review summarizes potential risk factors of cCMV in seropositive women with perspectives on the causal link including sociodemographic factors, virological characteristics, the host immune system, genomics, metabonomics and proteomics. These observations and some new molecular markers, although not yet validated as a reliable tool predictive of cCMV, could be the basis for designing future prospective studies.

Antigenic domain 1 of human cytomegalovirus glycoprotein B induces a multitude of different antibodies which, when combined, results in incomplete virus neutralization

Glycoprotein B (gB, gpUL55) is the major antigen for the induction of neutralizing antibodies against human cytomegalovirus (HCMV), making it an attractive molecule for active and passive immunoprophylaxis. The region between aa 552 and 635 of HCMV gB (termed AD-1) has been identified as the immunodominant target for the humoral immune response following natural infection. AD-1 represents a complex domain which requires a minimal continuous sequence of more than 70 aa for antibody binding. Neutralizing as well as non-neutralizing antibodies can bind to AD-1 in a competitive fashion. The fine specificity of AD-1-binding monoclonal antibodies (MAbs) and affinity-purified human polyclonal antibodies was analysed by using recombinant proteins containing single amino acid substitutions spanning the entire AD-1 domain. Our results revealed that all MAbs had individual patterns of binding to the mutant proteins indicating the presence of a considerable number of distinct antibody-binding sites on AD-1. The neutralization capacity of antibodies could not be predicted from their binding pattern to AD-1 mutant proteins. Polyclonal human antibodies purified from different convalescent sera showed identical binding patterns to the mutant proteins suggesting that the combined antibody specificities present in human sera are comparable between individuals. Neutralization capacities of polyclonal human AD-1 antibodies did not exceed 50% indicating that, during natural infection, a considerable proportion of non-neutralizing antibodies are induced and thus might provide an effective mechanism to evade complete virus neutralization.

The pathogenicity of cytomegalovirus

Human cytomegalovirus is ubiquitous, yet causes little illness in immunocompetent individuals. Disease is evident in immunodeficient groups such as neonates, transplant recipients and AIDS patients either following a primary infection or reactivation of a latent infection. Little is known of the mechanisms underlying the pathogenicity of the virus. The recent determination of the nucleotide sequence of both human cytomegalovirus (strain AD169) and murine cytomegalovirus (murine cytomegalovirus strain Smith) has allowed an analysis of the biological importance of several virus genes. Studies with human cytomegalovirus have indicated that many viral genes are non-essential for replication in vitro which are thus assumed to be important in the pathogenesis of the virus. This is being examined in the murine model where the role of the gene and its product in disease can be directly examined in vivo using viral mutants in which the relevant gene has been interrupted or deleted. Current information on the role of cytomegalovirus genes in tissue tropism, immune evasion, latency, reactivation from latency and damage is described.

Human cytomegalovirus neutralizing antibody-resistant phenotype is associated with reduced expression of glycoprotein H

We have characterized a neutralizing antibody-resistant mutant human cytomegalovirus (HCMV) obtained from a patient treated with a human monoclonal antiglycoprotein H (gH; unique long region 75) antibody. This virus exhibited resistance to several different neutralizing anti-gH murine monoclonal antibodies (MAbs), as well as to a polyvalent anti-gH serum. The resistant phenotype was unstable and could be maintained only by passage of plaque-purified virus under neutralizing MAb selection. In the absence of a MAb, the resistant phenotype reverted to a neutralizing antibody-sensitive phenotype within one passage. The predicted amino acid sequences of gH from the MAb-resistant and -susceptible parent viruses were identical. Biochemical analysis of the MAb-resistant and -susceptible parent viruses revealed a marked decrease of gH expression in the envelope of the MAb-resistant virus. Furthermore, propagation of the virus in various MAb concentrations resulted in the production of extracellular virions with various levels of resistance to the neutralizing activity of the MAb. These results suggest a mechanism for the generation of neutralizing antibody-resistant viruses which could evade host-derived antiviral antibody responses. In addition, our findings indicate that the stoichiometry of gH in the envelope of infectious HCMV virions is not rigidly fixed and therefore offer a simple explanation for production of phenotypic variants of HCMV through an assembly process in which the content of gH in the envelope of progeny virions varies randomly.