Figure 2

MDSCs promote B-cell proliferation and IgA production. (a) MDSCs (5 × 10⁶) were intravenously transferred into naive wild-type mice. These mice and untreated wild-type mice were immunized with OVA (100 μg). After 2 days, spleen sections were stained for Ki67 (green) and B220 (red). The nuclei were counterstained with DAPI (blue). The cLSM images are representative of two independent experiments with 2 mice per group. Original magnifications: 1st to 3rd rows. The bottom row shows an enlarged image of the marked area in the 3rd row: scale bars, 50 μm. (b) MDSCs (5 × 10⁶) were intravenously transferred into naive wild-type mice. Two days later, these mice and wild-type mice that did not receive MDSCs were immunized with OVA (100 μg). The MDSC transfer was repeated once weekly for 3 weeks. Each mouse was challenged with OVA (10 μg) 14 days later. (c) Wild-type mice subcutaneously received MCA205 (5 × 10⁵) tumor cells in PBS or PBS alone. After 20 days, half of the MCA205 tumor-bearing mice were treated with ATRA. The mice from all groups were immunized with OVA (100 μg) and challenged with OVA (10 μg) 14 days later. For b and c, the OVA-specific IgM and IgA antibody serum concentrations were assessed at day 7 and 14 during the primary immunization (1st) as well as 7 days after the challenge (2nd). Shown are representative results of two independent experiments with 8 mice per group. *P<0.05 and **P<0.01, as determined with the Mann-Whitney test. ATRA, all-trans retinoic acid; cLSM, confocal laser scanning microscope; Ig, immunoglobulin; MDSCs, myeloid-derived suppressor cells; OVA, ovalbumin; PBS, phosphate-buffered saline.