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

Abstract

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 (DCs). We compared HRSV to HMPV and HPIV3 with regard to their effects on human monocyte-derived immature DCs (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.

Surface expression of the hRSV nucleoprotein impairs immunological synapse formation with T cells

“…Because DCs are poorly permissive for hRSV replication and produce only limited viral progeny (ref. 17 and Fig. S3D), our data suggest that inoculated viral particles attached to the cell surface could be responsible for the N + signal observed in HEp-2 as soon as 1 hpi by flow cytometry.…”

“…To address whether localization of the hRSV N at the cell surface requires active viral replication, we used a recombinant hRSV A2 strain encoding the green fluorescent protein (hRSV GFP ). Because GFP translation from the viral genome is regulated by the hRSV large RNA-dependent RNA polymerase, GFP synthesis serves as reporter for viral replication (17,30). Also, because the GFP displays a half-life of 26 h (31), accumulation of GFP over time [and the increase in its mean fluorescence intensity (MFI)] serves to track the progression of the viral replication cycle in infected cells.…”

“…Several studies have shown that hRSV infects human and mouse DCs, impairing their capacity to activate both naïve (14) and antigen-experienced CD4 + T cells (15,16). Furthermore, hRSV infection reduces the capacity of DCs to induce the expansion of antiviral Th1 effector cells (17)(18)(19). It has been shown that hRSV inhibits naïve T-cell priming by preventing the assembly of the immunological synapse (IS) with DCs (20), which is a supramolecular structure required for the activation of T cells by DCs and other antigen-presenting cells (APCs) (21).…”

Human metapneumovirus keeps dendritic cells from priming antigen‐specific naive T cells

“…These results are in agreement with recent reports showing modest-to-null DC maturation in response to hMPV infection. 10,27 Although we observed poor DC maturation in response to hMPV, the phenotype acquired by these cells could potentially lead to T-cell activation because of increased MHC class II expression and mild up-regulation of co-stimulatory molecules.…”

“…12,27,44 However, another study showed no inhibition of human T-cell activation when stimulated with hMPVinoculated monocyte-derived DCs pulsed with a superantigen 9 . Because the quality of the TCR ligand and TCR/ pMHC binding kinetics can deeply influence the outcome of T-cell activation, 24,45 here we used an antigenic peptide that is presented to T cells bound to MHC-II molecules in a physiological context.…”