Limited Effector Memory B-Cell Response to Envelope Glycoprotein B During Primary Human Cytomegalovirus Infection.

BACKGROUND: Following primary human cytomegalovirus (HCMV) infection, the production of antibodies against envelope glycoprotein B (gB) is delayed, compared with production of antibodies against tegument proteins, and this likely reduces the control of HCMV dissemination. METHODS: The frequency and the phenotype of gB-specific and tegument protein-specific B cells were studied in a cohort of pregnant women with primary HCMV infection. Healthy adults who had chronic HCMV infection or were recently immunized with tetanus toxoid (TT) were included as controls. RESULTS: Primary HCMV infection was associated with high and similar frequencies of gB-specific and tegument protein-specific B cells following primary HCMV infection. During primary infection, tegument protein-specific B cells expressed an activated (CD21(low)) memory B-cell (MBC) phenotype. Activated MBCs were also induced by TT booster immunization, indicating that the expansion of this subset is part of the physiological B-cell response to protein antigens. In contrast, gB-specific B cells had a predominant classical (CD21(+)) MBC phenotype during both primary and chronic infections. CONCLUSIONS: The delayed production of gB-specific immunoglobulin G (IgG) during primary HCMV infection is associated with a limited induction of MBCs with effector potential. This novel mechanism by which HCMV may interfere with the production of neutralizing antibodies could represent a target for therapeutic immunization.

Sequestration of human cytomegalovirus by human renal and mammary epithelial cells.

Urine and breast milk represent the main routes of human cytomegalovirus (HCMV) transmission but the contribution of renal and mammary epithelial cells to viral excretion remains unclear. We observed that kidney and mammary epithelial cells were permissive to HCMV infection and expressed immediate early, early and late antigens within 72 h of infection. During the first 24 h after infection, high titers of infectious virus were measured associated to the cells and in culture supernatants, independently of de novo synthesis of virus progeny. This phenomenon was not observed in HCMV-infected fibroblasts and suggested the sequestration and the release of HCMV by epithelial cells. This hypothesis was supported by confocal and electron microscopy analyses. The sequestration and progressive release of HCMV by kidney and mammary epithelial cells may play an important role in the excretion of the virus in urine and breast milk and may thereby contribute to HCMV transmission.

Primary human cytomegalovirus infection induces the expansion of virus-specific activated and atypical memory B cells.

BACKGROUND: Although neutralizing antibodies play a central role in the control of cytomegalovirus (CMV) dissemination, little is known about the response of B lymphocytes to primary human CMV infection. METHODS: The proportion, phenotype, specificity, and functionality of B-cell subsets were studied in a cohort of pregnant women with primary CMV infection. CMV-seronegative pregnant women, as well as CMV-seronegative and CMV-seropositive healthy adults, were included as controls. RESULTS: Primary CMV infection was associated with a sustained expansion of activated (CD27(+)CD20(+)CD21(low)) and atypical (CD27(-)CD20(+)CD21(low)) memory B cells (MBCs). Both subsets expressed an effector phenotype, and their proportions were correlated with viremia. Activated MBCs expressed high levels of activation markers and included high frequencies of tumor necrosis α (TNF-α)-producing cells, whereas atypical MBCs expressed high levels of inhibitory receptors and had low TNF-α responses. Fluorescent-labeled antigen experiments indicated that activated and atypical MBCs were enriched in CMV-specific cells. CONCLUSIONS: Primary CMV infection mobilizes a large pool of memory B cells that includes activated and atypical MBCs. The functional regulation of CMV-specific MBCs may limit the production of antibodies and the control of viral dissemination.