Large-scale testing of human serum to determine cytomegalovirus neutralising antibody

Association of human cytomegalovirus (HCMV) neutralizing antibodies with antibodies to the HCMV glycoprotein complexes

Background

Human cytomegalovirus (HCMV) causes asymptomatic infections, but also causes congenital infections when women were infected with HCMV during pregnancy, and life-threatening diseases in immunocompromised patients. To better understand the mechanism of the neutralization activity against HCMV, the association of HCMV NT antibody titers was assessed with the antibody titers against each glycoprotein complex (gc) of HCMV.

Methods

Sera collected from 78 healthy adult volunteers were used. HCMV Merlin strain and HCMV clinical isolate strain 1612 were used in the NT assay with the plaque reduction assay, in which both the MRC-5 fibroblasts cells and the RPE-1 epithelial cells were used. Glycoprotein complex of gB, gH/gL complexes (gH/gL/gO and gH/gL/UL128–131A [PC]) and gM/gN were selected as target glycoproteins. 293FT cells expressed with gB, gM/gN, gH/gL/gO, or PC, were prepared and used for the measurement of the antibody titers against each gc in an indirect immunofluorescence assay (IIFA). The correlation between the IIFA titers to each gc and the HCMV-NT titers was evaluated.

Results

There were no significant correlations between gB-specific IIFA titers and the HCMV-NT titers in epithelial cells or between gM/gN complex-specific IIFA titers and the HCMV-NT titers. On the other hand, there was a statistically significant positive correlation between the IIFA titers to gH/gL complexes and HCMV-NT titers.

Conclusions

The data suggest that the gH/gL complexes might be the major target to induce NT activity against HCMV.

Pediatric roots of cytomegalovirus recurrence and memory inflation in the elderly

The establishment of a lifelong latent infection after resolution of primary infection is a hallmark of cytomegalovirus (CMV) biology. Primary infection with human CMV is possible any time in life, but most frequently, virus transmission occurs already perinatally or in early childhood. Many years or even decades later, severe clinical problems can result from recurrence of infectious virus by reactivation from latency in individuals who undergo immunocompromising medical treatment, for instance, transplant recipients, but also in septic patients without canonical immunosuppression, and in elderly people with a weakened immune system. The diversity of disease manifestations, such as retinitis, pneumonia, hepatitis, gastrointestinal disease, and others, has remained an enigma. In clinical routine, seropositivity for IgG antibodies against human CMV is taken to indicate latent infection and thus to define a qualitative risk of recurrence, but it is insufficient as a predictor for the quantitative risk of recurrence. Early experimental studies in the mouse model, comparing primary infection of neonatal and adult mice, led to the hypothesis that high load of latent viral genomes is a better predictor for the quantitative risk. A prolonged period of virus multiplication in the immunologically immature neonatally infected host increased the risk of virus recurrence by an enhanced copy number of latent virus genomes from which reactivation can initiate. In extension of this hypothesis, one would predict today that a higher incidence of reactivation events will also fuel the expansion of virus-specific T cells observed in the elderly, a phenomenon known as "memory inflation". Notably, the mouse model also indicated a stochastic nature of reactivation, thus offering an explanation for the diversity and organ selectivity of disease manifestations observed in patients. As the infection history is mostly undefined in humans, such predictions from the mouse model are difficult to verify by clinical investigation, and moreover, such questions were actually rarely addressed. Here, we have surveyed the existing literature for reports that may help to retrospectively relate the individual infection history to the risk of virus recurrence and recrudescent organ disease.

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.

Protection from CMV infection in immunodeficient hosts by adoptive transfer of memory B cells

Severe disease associated with cytomegalovirus (CMV) infection is still a major problem in patients who undergo transplantation. Support of the patients' immune defense against the virus is a major goal in transplantation medicine. We have used the murine model of CMV (MCMV) to investigate the potential of a cell-based strategy to support the humoral antiviral immune response. Immunocompetent C57BL/6 mice were infected with MCMV, and memory B cells from the immune animals were adoptively transferred into T-cell- and B-cell-deficient RAG-1(-/-) mice. Following MCMV infection, a virus-specific IgG response developed within 4 to 7 days in the recipient animals. Concomitantly, a significant reduction in viral titers and DNA copies in several organs was observed. In addition, the memory B-cell transfer provided long-term protection from the lethal course of the infection that is invariably seen in immunodeficient animals. Transfer of memory B cells was also effective in protecting from an already ongoing viral infection, indicating a therapeutic potential of virus-specific memory B cells. T cells were not involved in this process. Our data provide evidence that a cell-based strategy to support the humoral immune response can be effective to combat infectious pathogens in severely immunodeficient hosts.

The epidemiology of childhood cytomegalovirus infections in a large city of southern Italy

The present study was undertaken to determine the prevalence of cytomegalovirus infections among 4,790 infants and children living in the Bari area. Serum antibodies were measured by a microneutralization test. IgM antibodies were measured with a capture immunoenzymatic test. A high incidence of maternally derived antibody was found during the first 6 months of life (92.8%). The positivity rate declined during the second 6 months (86.9%) and between 1 and 4 years (86.6%) and increased again between 4 and 7 years (89.1%), between 7 and 10 years (90.6%) and between 10 and 15 years (91.7%). IgM-specific antibodies were found at a titer of 1:30 or greater in 42 subjects (0.9%) who also exhibited neutralizing antibody titers > or = 1:256. Infection in Bari is characteristic of cytomegalovirus-endemic areas where maternally derived immunity is immediately replaced by immunity due to primary infection.