Fig. 1.

MDSCs originate from both the bone marrow and extramedullary sites in S. aureus chronic infection. a Bacterial load in the tibia and spleen of mice after intravenous inoculation with 10⁶ CFU of S. aureus 6850. b Photographs showing splenomegaly in S. aureus-infected mice. c Absolute numbers of CD11b⁺, B cells (B220⁺), and CD4⁺ and CD8⁺ T cells in the spleen of S. aureus-infected mice at progressing times after bacterial inoculation. d Absolute numbers of CD11b⁺Ly6C⁺Ly6G⁺ in the spleen of S. aureus-infected mice. e Flow cytometry analysis showing the frequency of CD11b⁺ cells (upper panels) and the frequency of Ly6C⁺Ly6G⁺ cells within the CD11b⁺ population (lower panels) in the spleen of S. aureus-infected mice. Gating strategies are shown in online suppl. Figure 5. f Proliferation of CD4⁺ T cells unstimulated (black line histograms) or stimulated with anti-CD3ε/anti-CD28 antibodies (red line histograms) for 72 h in the absence (left panel) or presence (right panel) of Ly6C⁺Ly6G⁺ cells isolated from the spleen of S. aureus-infected mice at day 21 of infection at a 1:1 ratio. g Flow cytometry analysis showing the frequency of CD11b⁺ cells (upper panels) and the frequency of Ly6C⁺Ly6G⁺ cells within the CD11b⁺ population (lower panels) in the bone marrow of S. aureus-infected mice. h Percentage of CD11b⁺Ly6C⁺Ly6G⁺ cells in the bone marrow of S. aureus-infected mice. i Representative flow cytometry analysis showing LK and LSK in the spleen of uninfected (T.0) or S. aureus-infected mice at progressing times of infection. j Representative hematoxylin and eosin-stained histological sections of formalin-fixed and paraffin-embedded spleen sections from an uninfected (left) and from a S. aureus-infected (right) mouse at day 21 of infection (M indicates megakaryocytes). Original magnification ×40. Results are presented as the mean ± SD of biological replicates (N = 5 for a and N = 4 for e–h) and are representative of 3 independent experiments. Statistical significance: **p < 0.01; ***p < 0.001. LK, Lin⁻IL-7Rα⁻c-Kit⁺Sca-1⁻ lineage-committed progenitors; LSK, Lin⁻IL-7Rα⁻Sca-1⁺c-Kit⁺ myeloid progenitors.