002 for 8 h, p = 0.04 for 16 h, and p = 0.03 for 24 h). Figure 5 Labile iron pool in macrophages during infection with Francisella and Salmonella. RAW264.7 macrophages were infected for 2 h, 8 h, 16 h, and 24 h with wild Francisella (FT), wild-type Salmonella (ST), spiA Salmonella (ST/spiA), or spiC Salmonella RG7420 concentration (ST/spiC). Labile iron pool
was determined with the calcein method as described in detail in Materials and Methods. Measurements were in arbitrary fluorescence units standardized to uninfected samples. Data shown are the deviation in percentage from uninfected samples from triplicate experiments. Results are expressed as means +/- 1 standard error of mean (SEM). We also measured changes in the labile iron pool during infection with two isogenic mutant Salmonella strains, spiA and spiC,
which have intracellular trafficking deficits associated with reduced intracellular proliferation and avirulence in mice. These strains carry two different deletions in the SPI-2 type III secretion system (spiA and spiC) [32, 33]. The rationale for using these strains in our experiments was to investigate if different subcellular localizations of a given pathogen can lead to different patterns in iron acquisition. After two hours of infection, the labile iron pool was increased similar to macrophages infected with wild-type Salmonella (Figure 5; p = 0.001 for spiA Salmonella, p = 0.002 for spiC Salmonella). After twenty-four hours, spiC Salmonella gradually decreased the iron pool similar to infection with wild type (Figure 5; p = 0.02 for 8 h, p = 0.02 for 16 h, p = 0.001 for 24 h). In contrast, the labile iron pool initially A-1210477 decreased and then remained unchanged during infection with spiA Salmonella (Figure 5; p = 0.02 for 8 h, p = 0.45 for 16 h, p = 0.56 for 24 h). Iron-related gene expression in macrophages infected with Salmonella or Francisella Acquisition of iron through TfR1 requires expression of accessory gene products (Steap3, Dmt1) and can be countered by increased iron export (Fpn1) or scavenging of iron by the lipocalin system (Lcn2, LcnR). Induction of innate immune responses during infection can modulate
iron homeostasis pathways through induction of hepcidin (Hamp1) and Lcn2. The expression of such genes and selected other genes that are involved in the homeostasis Florfenicol of host cell iron levels were investigated by real-time RT-PCR during infection with Francisella and compared to the expression profile of host cells during infection with Salmonella. There are two main eukaryotic iron-regulatory proteins, IRP1 and IRP2, which sense changes in the labile iron pool and secondary signals associated with redox active species. They both act post-translationally by stabilizing their respective target mRNA and by affecting initiation of translation. While expression of IRP-2 is increased by Salmonella and Francisella (p = 0.003 and p = 0.