To determine the effect of hMPV infection on co-stimulatory molecule expression by primary mDCs and to assess whether RSV and hMPV differentially regulate co-stimulatory molecule expression, the expression of CD86, CD80, and PD-L1 on hMPV- and RSV-infected BDCA-1+ and BDCA-3+ mDCs was examined using flow cytometry (Fig. 2A). Here, CD86 is linked to infection.