Characterization of human metapneumovirus infection of myeloid dendritic cells.

Recent in vivo studies suggest that hMPV is a poor inducer of inflammatory cytokines and that clinical symptoms may not be related to immune-mediated pathogenesis as it has been proposed for respiratory syncytial virus (RSV) and human parainfluenza 3 (HPF3). Dendritic cells (DCs) are specialized antigen presenting cells, and very effective at inducing specific CTLs after encountering invading viruses. Interactions of hMPV with DCs have not been characterized. We hypothesized that the relatively mild inflammatory responses observed in vivo after hMPV infection might be at least in part due to hMPV's poor ability to stimulate and activate DCs. hMPV actively infected immature monocyte-derived CD11c+/HLA-DR+ DCs. However, in contrast to RSV or HPF3, hMPV caused no gross cytopathic effects such as syncytia, lytic infection, or massive apoptosis. DCs exposed to hMPV show no cytopathic effects under tissue culture conditions permissive for viral replication. The surface maturation markers CD83 and CD86 were not significantly up-regulated in infected DCs as compared to uninfected controls, while expression of CD80 appeared increased. Stimulation of hMPV-infected DCs with LPS resulted in the enhanced expression of all these surface markers indicating that hMPV is not generally suppressing DC maturation. Overall, cytokine expression remained low. These results indicate that hMPV does not induce effective DC maturation in vitro and suggest that the weak stimulation of DCs may account for the overall low immunogenicity of this virus observed in vivo.