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M. Nairz et al.
However, C3 levels were not affected by high serum or parenchymal iron (Figure 6A). IL-6, the key cytokine for the initiation of the acute-phase response, was reduced in the serum (Figure 6B) but not in the liver (Online Supplementary Figure 4E) of AlfpCre+ Hfefl/fl mice (Figure 6B). This and the unaltered production of hepcidin-1 (Figure 3E and Table 2) suggest that the acute-phase response is intact in AlfpCre+ Hfefl/fl mice. Moreover, glutamate-pyru- vate transaminase (GPT) was reduced in AlfpCre+ Hfefl/fl mice, ruling out increased iron-induced hepatic injury (Online Supplementary Figure S4A). Rather, a specific defect in the pro-inflammatory cytokine output was associated
with the poor outcome of Salmonella-infected AlfpCre+ Hfefl/fl mice. Specifically, serum IFN-g concentrations (Figure 6C) were significantly lower in AlfpCre+ Hfefl/fl mice and may have contributed to the insufficient induc- tion of cellular effector mechanisms such as Nos2 in the spleen (Table 1).
Increased serum iron due to dietary iron overload enhances extracellular Salmonella growth and reduces IFN-g levels
In order to further investigate whether the reduced cytokine production in AlfpCre+ Hfefl/fl mice and may have
A
Figure 4. Bacterial proliferation is affected by Hfe. RPMI was spiked with 10% sera of naïve mice of the indicated genotypes. Spiked RPMI was inoculated with wild-type (WT) S. enterica Typhimurium (S. Tm.) and its isogenic derivatives mutated in one of three or all three iron uptake systems (entC, sitABCD, feo). Where applicable, deferasirox (DFX), ferrous sulfate (FeSO4) and recombi- nant murine Lcn2 (rmuLcn2) was added. Liquid cultures were assessed for extracellular bacterial proliferation (G to I) using the optical density at 600 nm (OD600). **P<0.01, ***P<0.001 for the comparison between mouse genotypes, #P<0.05, ##P<0.01 and ###P<0.001 for the comparison to solvent (Ctrl) or the S. Tm. WT strain as applicable. n=4-6 independent experiments.
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haematologica | 2021; 106(12)