Figure 1.

CD137 mRNA expression is upregulated by hypoxia in mouse tumor cell lines. Quantitative RT-PCR assessment of CD137 mRNA expression under 21% and 1% O₂ (hypoxia) in the indicated cell lines cultured under these conditions for 48h. A representative direct immunofluorescence staining for CD137 surface expression analyzed flow cytometry is presented in a corresponding histogram showing the discrepancy between the mRNA levels and the weak or dim surface protein staining. *p < 0.05, **p < 0.01.