To further dissect target cells of RVFV replication in Ifnar1deficient mice, we used the recombinant virus rZHDNSs-GFP that carries GFP in place of the NSs gene. We have shown previously that cells infected in vitro with rZHDNSs-GFP are fluorescent upon excitation at 488 nm [24] . Ifnar1-deficient mice were either infected i.p. with 10 4 PFU rZHDNSs-GFP (N = 6) or mocktreated (N = 5). At 24 h post-infection, the spleen was dissected and single-cell suspensions were analyzed by flow cytometry for GFP expression. At this time point, 0.54% (range 0.14-1.53%) of the total hematopoietic cell population of the spleen from rZHDNSs-GFP-infected mice expressed GFP whereas no GFP-positive cells were found in splenocytes after mock infection ( Figure 7A ). We examined the expression of GFP in various subsets of antigen presenting cells based on the surface expression patterns of CD45.2, CD11b, CD11c, Ly6G, CD19, CD3, NKp46, CD115 and MHCII class II by multicolor flow cytometric analysis. Among the CD11b + CD115 + Ly6G 2 (macrophages), CD11c + CD11b + MHC II + (dendritic cells) [44] and CD11b + CD11c 2 Ly6G + (granulocytes), on average 5.58% (range 2.15-8.71%), 4.5% (range 0.82-8.49%) and 1.96% (range 0.05-6.07%) cells expressed GFP, respectively ( Figure 7C [left panels], B [right panels], and C [right panels], respectively). The percentage of GFP-expressing cells within the total cell population of spleen varied from one infected mice to another, indicating that the dynamics of RVFV infection progression was not identical in all individuals. However, each of the three subsets of immune cells was infected with the same efficiency in the different mice. This is shown by the fact that the ratio of GFP-expressing macrophages, dendritic cells or granulocytes was highly correlated with the ratio of GFP-expressing cells in the total cell population from the spleen (Pearson correlation coefficient 0.97, 0.85 and 0.79, respectively) . These findings suggest a distinct pattern of susceptibility to infection by the RVFV-GFP for different immune cells in the following order: CD11b + CD115 + Ly6G 2 (macrophages).CD11c + CD11b + MHC II + (dendritic cells).CD11b + CD11c 2 Ly6G + (granulocytes). On average, less than 0.4% (range 0-1.19%) of NKp46 + CD3 2 natural killer (NK) cells were positive for GFP ( Figure 7E, left panel) . Finally, GFP fluorescence was seen on average in only 0.25% (range 0.07-0.57%) of CD19 + CD3 2 (B lymphocytes) cells and 0.20% (range 0.05-0.43%) NKp46 2 CD3 + (T lymphocytes) cells ( Figure 7D and E, right panels). Thus, at 24 h post-infection, RVFV replicated in cells of the myeloid lineage, primarily in mononuclear phagocytic cells, such as macrophages, dendritic cells and granulocytes.