Figure 6: POP2 limits acute inflammation and increases IFN-γ in pulmonary tularaemia.

(a) Mean total numbers±s.d. of Ly6G⁺ neutrophils and F4/80⁺ macrophages in lungs of POP2 (n=4) and LMC (n=4) mice infected with F. tularensis (Ft) LVS (MOI=100). (b) Mean total numbers±s.d. of polymorphonucleated-MDSC (pMDSC) and mono-nucleated-MDSC (mMDSC) in lungs of POP2 (n=4) and LMC (n=4) mice infected with Ft LVS (MOI=100). (c) Representative histologic lung sections from mice infected with Ft LVS showing inflammatory foci and necrosis (‘necrotizing inflammation’) at 6 dpi in LMC mice (top panel) and POP2 mice (bottom panel) (haematoxylin and eosin; Scale bar, 100 μm). Lung pathology scores for LMC (n=6) and POP2 (n=6) mice infected with Ft LVS (1,000 c.f.u.; LD100) (right graph) were calculated by analysis of lung sections for location, type and extent of inflammation and necrosis (see ‘Methods’ section). (d–g) POP2 (n=6) and LMC (n=6) mice were infected with Ft LVS (1,000 c.f.u.; LD100) and shown are (d) mean levels±s.d. of IL-1β, IL-18, IL-6 and TNF from lung homogenates, (e) bacterial burden in lungs, (f) mean levels±s.d. of IFN-γ measured from lung homogenates and (g) mean total numbers±s.d. of IFN-γ⁺ immune cells in lungs. (h) Mean bacterial count (c.f.u.)±s.d. from POP2 (n=4) and LMC (n=4) BMDM infected with Ft LVS (MOI=100) with and without administration of recombinant IFN-γ (100 IU). (i) Per cent survival of POP2 (n=12) and LMC (n=12) mice treated with 300 μg anti-IFN-γ antibody (catalogue number BE0055, BioXCell) on days −1, 2 and 4 or isotype control (catalogue number BE0088, BioXCell) and infected with Ft LVS (500 c.f.u., LD50). Survival of infected POP2 mice receiving isotype control differs significantly from that of POP2 mice receiving anti-IFN-γ (P<0.001) To determine significance, for a,b,d and h, Student’s t-test was used (*P<0.05); for c, scores were evaluated using the Mann–Whitney test (*P<0.05); for e–g, Student’s t-test was used (*P<0.05, **P<0.01), and for i, the Log-rank test, was used.