Glycoprotein N subtypes of human cytomegalovirus induce a strain-specific antibody response during natural infection

Abstract

Human cytomegalovirus (HCMV) encodes several highly polymorphic envelope glycoproteins; however, the biological relevance of this polymorphism is unclear. Glycoprotein N (gN) is one member of this polymorphic protein family. Four major gN genotypes (gN1-4) have been identified. We have tested the hypothesis that the gN polymorphism represents a mechanism to evade a neutralizing antiviral antibody response. Four recombinant viruses that differed only in the expression of the gN genotype were constructed on the genetic background of HCMV strain AD169. Exchange of gN genotypes had a minor detectable influence on virus replication, gN expression and gN-gM complex formation. Randomly selected human sera were analysed for neutralizing activity against the recombinant viruses. Of these, 70 % showed no difference in neutralizing titre between the viruses, whereas 30 % showed strain-specific neutralization. Differences in 50 % neutralization titre reached .8-fold. Viruses expressing the gN4 genotype were neutralized significantly better than those expressing the other gN genotypes. Strain specificity, or lack thereof, could not be attributed to the presence or absence of anti-gN antibodies, as all sera contained antibodies reacting with gN (as determined by ELISA). Thus, polymorphism of gN could contribute to evasion of an efficient neutralizing-antibody response and facilitate reinfection in previously seropositive individuals. INTRODUCTIONHuman cytomegalovirus (HCMV) is a significant cause of morbidity and mortality in immunocompromised individuals, such as transplant recipients, AIDS patients and newborns . A puzzling aspect of HCMV biology is the fact that a large number of genetically distinct HCMV strains circulate in the population (Chandler & McDougall, 1986;Chou, 1990;Rasmussen et al., 2002Rasmussen et al., , 2003Murphy et al., 2003;Pignatelli et al., 2003). The presence of more than one strain has been observed in immunocompetent persons, indicating the possibility of simultaneous coinfection with multiple different virus strains or reinfection in the presence of a functional immune response (Chandler et al., 1987;Bale et al., 1996;Schoppel et al., 1997;Boppana et al., 2001). In immunocompromised patients, reinfection may represent a clinically important problem, as a de novo adaptive immune response against the reinfecting strain is impaired. Clinical studies in transplant patients have supported the importance of HCMV reinfection in these patients (Grundy et al., 1988; Coaquette et al., 2004;Ishibashi et al., 2007). Moreover, in women who are seropositive for HCMV, reinfection with a different strain can lead to intrauterine transmission and symptomatic congenital infection (Boppana et al., 2001). In the closely related murine cytomegalovirus (MCMV), simultaneous or sequential infection with different virus strains results in mixed infections in immunocompetent mice (Farroway et al., 2005;Gorman et al., 2006). Thus, reinfection with different strains of cytomegalovirus is frequent in both immunocompetent and ...

Strain-Specific Neutralizing Antibody Responses against Human Cytomegalovirus Envelope Glycoprotein N

“…In a previous study from our laboratory, we demonstrated that the majority of study subjects were infected with multiple viruses (15). In addition, the current study included a larger number of HCMV-seropositive individuals than the 20 subjects in the study of Burkhardt et al (5). We found that sera from some seropositive women neutralized all four recombinant viruses with comparable efficiencies, while clear differences in neutralizing capacity against individual gN recombinant viruses were seen in sera from others.…”

“…Recombinant HCMV strains containing different genomic variants of UL73 (gN) coding sequences (gN genotypes 2, 3, and 4) were constructed using the AD169 bacterial artificial chromosome (BAC) as described previously (5). The four gN recombinant viruses differed only with respect to the gN genotype.…”

“…A strainspecific neutralizing antibody response was defined as a Ͼ3-fold difference in neutralizing titers against at least two different gN recombinant viruses in a serum specimen (5). Overall, sera from 61% (49/80 women) of the study women showed evidence of strain-specific virus neutralization activity against recombinant viruses.…”

Deep Sequencing Reveals Highly Complex Dynamics of Human Cytomegalovirus Genotypes in Transplant Patients over Time

“…Furthermore, the relative frequencies of the individual genotypes within a patient did not remain stable over time, a finding which has also been described for Epstein-Barr virus strains in mixed infections (44) and which makes it even more unlikely that a specific polymorphism at a specific viral genomic region might have influenced the level of replication of a particular genotype. As has already been demonstrated for the four major gN and two gH genotypes (2,4,20), host factors, such as differences in genotype-specific immune responses, could also have a certain influence on the rate of replication of individual strains, but from our data it does not seem that this effect would be strong enough to provide a constant selection of major genotypes over time. This holds true of course only for the HCMV genes tested in the present study.…”

Virion Glycoprotein-Mediated Immune Evasion by Human Cytomegalovirus: a Sticky Virus Makes a Slick Getaway

“…The potential for emergence of gH escape mutants was also demonstrated by use of the human-derived antibody MSL- Finally, CMV-seropositive individuals also display strain-specific neutralizing antibodies to gN, suggesting that a broad gNneutralizing activity may be required to impart protection when an individual is infected with multiple CMV strains (147,149). Indeed, CMV-seropositive sera from various donors displayed varied neutralizing activities against four recombinant viruses that differed only in their gN genotype, thus demonstrating that gN polymorphism may contribute to antibody evasion and facilitate superinfection of CMV-positive individuals (150).…”