Compared with the vehicle controls, the protein and mRNA expression levels of Nr4a2 were significantly elevated after transfection with Nr4a2-overexpressing plasmid into the CD4+ T cells (1.453 ± 0.179 vs. 1.000 ± 0.018, p = 0.0192; 2.602 ± 0.775 vs. 1.000 ± 0.000, p = 0.001, respectively; Figure 5A–5C), and downregulated the mRNA expression level of GATA3, IL-4, and IL-13 in CD4+ T cells from patients with PV, compared with the vehicle controls (0.554 ± 0.090 vs. 1.000 ± 0.000, p < 0.001; 0.448 ± 0.105 vs. 1.000 ± 0.000, p < 0.001; 0.483 ± 0.097 vs. 1.000 ± 0.000, p < 0.001; Figure 5D). Here, NR4A2 is linked to acquired polycythemia vera.