Acquisition of human cytomegalovirus (CMV) usually occurs by contact between contaminated bodily fluids, such as urine and saliva, and host mucosal cells. Langerhans-type dendritic cells (LC) are the only type of immune cells found in the outermost layers of the oral mucosae, where they not only provide a first line of defense against CMV but can easily be targeted by orally administered vaccines, while their bone marrow resident progenitors are important sites of virus latency. In this work, we tracked the progress of infection in CD34 ؉ progenitor cells, immature LC (iLC), and mature LC (mLC) exposed to the clinicallike strain TB40-BAC4 or to the vaccine strain AD169varATCC, prior to their long-term maintenance under either immature or mature conditions. We show that the genomes of both strains are efficiently maintained in CD34؉ cells during their differentiation into iLC, although this requires the presence of larger amounts of input AD169varATCC DNA. Lipopolysaccharide-and CD40 ligand-induced maturation of iLC derived from latently infected progenitors was not associated with robust viral genome replication and progeny production, while maturation of directly infected iLC increased and prolonged expression of the viral immediate early proteins. While effective replication of viral genomes from both strains occurred only in mLC, both iLC and mLC produced viral progeny, suggesting that both types of LC may contribute to CMV horizontal transmission in vivo. H uman cytomegalovirus (CMV), a major cause of disease and death in immunocompromised and in congenitally infected individuals, is normally acquired by contact between infected bodily fluids such as urine and saliva and host mucosal surfaces, particularly those lining the oral and nasal cavities. IMPORTANCE Human CMV is usually acquired via the oral and nasal mucosae. Langerhans-type dendritic cells (LC) are the only type of immune cells found in the outermost layers of these tissues. Understanding how CMV interacts with LC and their hematopoietic progenitors is thus essential to develop innovative means of defense against this virus. Here we show that the genomes of a viru-From these peripheral sites, CMV is thought to reach the circulation and hence the bone marrow, where latency is established in myeloid cells, including CD34 ϩ hematopoietic progenitors (1-5). Reactivation from latency in the myeloid progeny of these cells is then believed to be the source of newly produced viral particles, which upon amplification in oral epithelial cells are released in the saliva and contribute to CMV horizontal transmission in vivo (6-8).Immature Langerhans-type dendritic cells (iLC) are the only professional antigen-presenting cells located in the outermost layers of the oral mucosa (9-14). As such, iLC are bound to be the first immune cells to encounter invading pathogens that access their hosts via the oral cavity, such as CMV. Upon contact with "danger" signals, iLC migrate toward the draining lymph nodes and begin the process of maturation, which culmina...

Oral mucosal Langerhans cells (LC) are likely to play important roles in host defense against infection by human cytomegalovirus (CMV). We previously showed that in vitro-differentiated immature LC (iLC) populations contain smaller amounts of infected cells but produce higher yields than mature LC (mLC) cultures, obtained by iLC stimulation with fetal bovine serum (FBS), CD40 ligand (CD40L) and lipopolysaccharide (LPS). Here, we sought to determine if exposure to select stimuli can improve LC permissiveness to infection, if specific components of the mLC cocktail are responsible for lowering viral yields, if this is due to defects in progeny production or release, and if these restrictions are also effective against reactivated virus. None of the stimuli tested extended the proportion of infected cells to 100%, suggesting that the block to infection onset cannot be fully removed. While CD40L and FBS exerted positive effects on viral progeny production per cell, stimulation with LPS alone or in combination with CD40L was detrimental. Reductions in viral titers were not due to defects in progeny release, and the permissive or restrictive intracellular environment established upon exposure to each stimulus appeared to act in a somewhat similar way toward lytic and latent infections.