Differential response of BDCA-1+ and BDCA-3+ myeloid dendritic cells to respiratory syncytial virus infection

Background: Respiratory syncytial virus (RSV) is the leading cause of respiratory infections in children, elderly, and immunocompromised individuals. Severe infection is associated with short-and long-term morbidity including pneumonia, recurrent wheezing, and abnormal pulmonary function, and several lines of evidence indicate that impaired adaptive immune responses during infection are critical in the pathophysiology of RSV-mediated disease. Myeloid Dendritic cells (mDCs) play a pivotal role in shaping antiviral immune responses in the respiratory tract; however, few studies have examined the interactions between RSV and individual mDC subsets. In this study, we examined the effect of RSV on the functional response of primary mDC subsets (BDCA-1(+) and BDCA-3(+)) isolated from peripheral blood. Methods: BDCA-1(+) and BDCA-3(+) mDCs were isolated from the peripheral blood of healthy adults using FACS sorting. Donor-matched BDCA-1(+) and BDCA-3(+) mDCs were infected with RSV at a multiplicity of infection (MOI) of 5 for 40 hours. After infection, cells were analyzed for the expression of costimulatory molecules (CD86, CD80, and PD-L1), cytokine production, and the ability to stimulate allogenic CD4(+) T cell proliferation. Results: Both BDCA-1(+) and BDCA-3(+) mDCs were susceptible to infection with RSV and demonstrated enhanced expression of CD86, and the inhibitory costimulatory molecules CD80 and PD-L1. Compared to BDCA-3(+) mDCs, RSV-infected BDCA-1(+) mDC produced a profile of cytokines and chemokines predominantly associated with pro-inflammatory responses (IL-1 beta, IL-6, IL-12, MIP-1 alpha, and TNF-alpha), and both BDCA-1(+) and BDCA-3(+) mDCs were found to produce IL-10. Compared to uninfected mDCs, RSV-infected BDCA-1(+) and BDCA-3(+) mDCs demonstrated a reduced capacity to stimulate T cell proliferation. Conclusions: RSV infection induces a distinct pattern of costimulatory molecule expression and cytokine production by BDCA-1(+) and BDCA-3(+) mDCs, and impairs their ability to stimulate T cell proliferation. The differential expression of CD86 and pro-inflammatory cytokines by highly purified mDC subsets in response to RSV provides further evidence that BDCA-1(+) and BDCA-3(+) mDCs have distinct roles in coordinating the host immune response during RSV infection. Findings of differential expression of PD-L1 and IL-10 by infected mDCs, suggests possible mechanisms by which RSV is able to impair adaptive immune responses.