Infection and maturation of monocyte-derived human dendritic cells by human respiratory syncytial virus, human metapneumovirus, and human parainfluenza virus type 3

Human respiratory syncytial virus (HRSV), human metapneumovirus (HMPV), and human parainfluenza virus type 3 (HPIV3) are common, important respiratory pathogens, but HRSV has a substantially greater impact with regard to acute disease, long-term effects on airway function, and frequency of re-infection. It has been reported to strongly interfere with the functioning of dendritic cells (DC). We compared HRSV to HMPV and HPIV3 with regard to their effects on human monocyte-derived immature DC (IDC). Side-by-side analysis distinguished between common effects versus those specific to individual viruses. The use of GFP-expressing viruses yielded clear identification of robustly infected cells and provided the means to distinguish between direct effects of robust viral gene expression versus bystander effects. All three viruses infected inefficiently based on GFP expression, with considerable donor-to donor-variability. The GFP-negative cells exhibited low, abortive levels of viral RNA synthesis. The three viruses induced low-to-moderate levels of DC maturation and cytokine/chemokine responses, increasing slightly in the order HRSV, HMPV, and HPIV3. Infection at the individual cell level was relatively benign, such that in general GFP-positive cells were neither more nor less able to mature compared to GFP-negative bystanders, and cells were responsive to a secondary treatment with lipopolysaccharide, indicating that the ability to mature was not impaired. However, there was a single exception, namely that HPIV3 down-regulated CD38 expression at the RNA level. Maturation by these viruses was anti-apoptotic. Inefficient infection of IDC and sub-optimal maturation might result in reduced immune responses, but these effects would be common to all three viruses rather than specific to HRSV.