Figure 5. IL-6 deficiency hampers macrophage recruitment to the lung and increases virus-induced cell death during influenza infection.

(a) Immunohistochemical examination of NP-positive cells in thioglycollate-elicited macrophages infected with IAV at an MOI of 1 for 24 h. Representative images are shown (original magnification ×100, scale bar = 200 μm). (b) NP-positive macrophages were quantified by averaging the number of positively stained cells in four randomly selected fields (n = 3). (c) Titers of IAV produced from the infected macrophages were quantified by the plaque assay (n = 3). (d) Immunohistochemical detection of macrophages in the lung with anti-Mac-3 antibody at day 7 p.i. in WT and IL-6^−/− mice infected with 10⁵ PFU of IAV. Macrophages in the lung were quantified by averaging the number of Mac-3-positive cells in three randomly selected fields in each section (n = 4). (e) Immunohistochemical detection of macrophages in the BAL fluid with anti-F4/80 antibody at day 7 p.i. in WT and IL-6^−/− mice infected with 10⁵ PFU of IAV. Total numbers of macrophages in the BAL fluid were quantified by counting F4/80-positive cells (n = 4). (f). Total numbers of thioglycollate-elicited peritoneal macrophages collected from WT and IL-6^−/− mice were counted using a hemocytometer (n = 3 for WT, n = 5 for IL-6^−/−). (g) Migratory capability of thioglycollate-elicited peritoneal macrophages from WT and IL-6^−/− mice determined by the Boyden chamber assay. The number of migrating cells was the average of the cells counted from four randomly selected fields in each section (n = 6). (h) Cytotoxicity of thioglycollate-elicited peritoneal macrophages from WT and IL-6^−/− mice infected with IAV at an MOI of 1 for 24 h, as assessed by the LDH release assay (n = 4).