Morphology and phenotype of SP37A3 cells. SP37A3 cells were kept at an immature proliferative state by addition of GM-CSF and M-CSF. To induce maturation, cells were cultivated for 3 days with GM-CSF and proinflammatory cytokines IL-1β and TNF-α. (A) Images of immature (left panel) and mature (right panel) SP37A3 cells were taken at room temperature with cells kept in the respective culture medium (see above) at ×20 magnification (UPlanFI 20×/0.50, 40×/0.75; Olympus Optical, Hamburg, Germany) using an Olympus IX70 inverted microscope (Olympus Optical) equipped with a DXC-950P digital camera (Sony Electronics, NJ) and AnalySIS 3.00 software (Olympus Soft Imaging Solutions, Münster, Germany). Representative sections are shown at ×40 magnification (UPlanFI 40×/0.75; Olympus Optical) in the inserts. Colors, brightness, and contrast of images were adjusted using PhotoShop 5.0 (Adobe Systems, Saggart, Ireland). (B) Cells were stained with mAbs specific for the indicated cell-surface markers. Histograms represent specific mAb binding to immature (thin line) and mature (thick line) SP37A3 cells, as well as binding of isotype-matched control mAb (dotted line). Graphs are representative of at least 2 independent experiments.