Identification of MDSC and myeloid cell types in tumour-bearing mice. A) PMN-MDSC expressed high levels of Gr-1, CD11b. MO-MDSC have a slightly higher expression of Ly6c. A third population was identified showing a low expression of Gr-1. Based on FSC/SSC this population was further subdivided into two subsets; SSClow expressing high Ly6c and SSChigh expressing low Ly6c. ROS production was measured for each subtype. B) Histology on tumour sections showed Gr-1+ (red) at the rim of the tumour in close contact with COX-2 expressing cells (blue). [Magnification: 200× (left) and 400× (right)]. C) Inhibition of COX-2 activity was tested in vitro by adding celecoxib to AB1 cell cultures. AB1 cells were cultured for 24 hours with medium, 10 μg/ml, or 100 μg/ml celecoxib and stained with anti-COX-2 and anti-COX-1 (as control) antibodies.