IL-6 is required for bacterial clearance and survival during pneumococcal pneumosepsis. (A to H) Pneumococcal loads of lungs (A, n = 12 to 18/group; E, n = 6/group), heart blood (B, n = 6 to 9/group; F, n = 5 to 6/group), spleens (C, n = 5 to 16/group; G, n = 4 to 6/group), and livers (D, n = 5 to 11/group; H, n = 5 to 6/group) of IL-6−/− and WT mice following intranasal infection with 1 × 108 CFU D39 from 1 to 3 dpi (A to D) or following intranasal treatment with exogenous recombinant mouse IL-6 protein (10 μg/30 μL/mouse) during pneumococcal pneumosepsis (E to H). (I to J) Dynamic changes of IL-6 in lungs of WT mice (I, n = 5/group, by enzyme-linked immunosorbent assay [ELISA]) and clinical scores (J, n = 6/group) of IL-6−/− and WT mice from 1 to 3 dpi. (K to L) Mortality (K, n = 6 to 10/group) and weights (L, n = 6/group) following D39 infection, as indicated.