IPS-1 Is Essential for the Control of West Nile Virus Infection and Immunity

Suthar, Mehul S.; Ma, Daphne Y.; Thomas, Sunil; Lund, Jennifer M.; Zhang, Nu; Daffis, Stephane; Rudensky, Alexander Y.; Bevan, Michael J.; Clark, Edward A.; Kaja, Murali-Krishna; Diamond, Michael S.; Gale, Michael

To characterize the immune parameters associating with the dysregulated inflammatory and humoral responses in WNV infected IPS-1 2/2 mice, we analyzed the immune cell composition in draining lymph node and spleen tissues. Wild type and IPS-1 2/2 mice were challenged with diluent alone or with WN-TX, and draining popliteal lymph node (DLN) and the spleen were harvested at 1 and 6 days pi, respectively. Analysis of the popliteal DLN provides insight into how IPS-1 modulates the inflammatory response immediately after infection whereas assessment of the spleen elucidates characteristics of the adaptive immune response prior to the infection endpoint. Immune cells were isolated from the popliteal DLN and were characterized by flow cytometry (Fig 6) . Analysis of CD8a DC subsets, which are phenotypically the major antigen presenting cells within lymphoid tissues and are implicated in eliciting virus-specific CD8 T cell in response to acute WNV infection [41] , showed that infected wild type and IPS-1 2/2 mice exhibited similar increases in the numbers of CD8a + and CD8a 2 DCs compared to mock-infected mice (Fig 6A, B) . However, a significant increase (,3-fold; p,0.05) of a proinflammatory DC subset, characterized as CD11c + CD11b hi Ly6C + , was observed within the popliteal DLNs of IPS-1 2/2 infected mice (Fig 6C) . This DC subset is monocytederived and typically recruited to sites of acute inflammation where they propagate the inflammatory response [42] . We found that these DC subsets were not significantly expanded and showed no differences in their recruitment to the DLN in either wild type or IPS-1 2/2 infected mice at 12 hours pi (data now shown). Thus, as early as 24 hours pi, an elevated cellular inflammatory response is initiated in the IPS-1 2/2 mice. In contrast, similar increases in plasmacytoid DCs were observed within infected wild type and IPS-1 2/2 infected mice (Fig 6D) , demonstrating that an absence of IPS-1 did not directly affect expansion and/or recruitment of this DC subset. Within the popliteal DLNs, mock-infected IPS-1 2/2 mice compared to wild type mice generally showed elevated numbers of B cells, CD4+ T cells (p,0.05), and CD8+ T cells (Fig 6E, F, and G) .