The involvement of multiple cell types along with the possible role of non-infected cells in the secretion of cytokines further complicates the analysis of existing data. Primary human monocytes and macrophages are activated by MARV infection inducing the secretion of cytokines. Induction of cytokines has also been described using UV-inactivated MARV, suggesting that viral replication might not be needed for the observed cytokine increase [200] . In contrast, MARV-infected mDCs show no upregulation of activation markers, do not secrete cytokines, and fail to stimulate T cells [146] . mDCs treated with VLPs containing MARV VP40 and GP show functional mDC responses including cytokine secretion indicating that MARV replication is required to inhibit mDC activation [216] . However, infection of mDCs with MARV did not prevent LPS-induced TNFα production whereas dsRNA-dependent IFNα secretion was inhibited [146] , suggesting differential regulation of cytokines by MARV. Interestingly, pDCs in the spleen were identified as the major source of secreted IFNα in MARV infected NHPs, but secretion most likely occurs from non-infected cells [193] . It has been shown for EBOV that pDCs are not productively infected due to impairment of viral entry [217] .