uPA can recruit MDSCs. (A) DA-3/TM tumor-bearing mice were injected intraperitoneally with saline as control or 1 μg recombinant uPA. Two hours later, peritoneal lavages (IP) were performed and spleens were harvested for staining MDSCs and analyzing by flow cytometry. (B) Normal BALB/c mice were injected intraperitoneally 8 times every other day with either saline as control, or 1 μg recombinant uPA. Two hours after the last injection, the BM, spleen, blood, and IP cells were harvested and stained for MDSC analysis by flow cytometry. (C) Normal BALB/c mice were injected 2 times every other day with uPA intraperitoneally, and then 2 hours after the last injection IP cells were purified for MDSCs using an antibody to GR-1. Splenic MDSCs from DA-3/TM tumor-bearing mice were also purified. DO11.10 splenocytes were then cocultured with MDSCs at various ratios and activated with OVA. T-cell proliferation (counts per million [CPM]) was measured after providing cultures [³H]thymidine. Error bars representing SEM and P values are provided. Results are representative of at least 3 experiments.