Conditional ablation of STAT3 in murine hematopoietic cells or congenital STAT3 dysfunction in humans results in decreased basal NKG2D surface expression and decreased upregulation by STAT3-activating cytokines. (A) NK cells were isolated from the spleens of STAT3 conditional knockout and WT mice. The expression of NKG2D on NK1.1⁺ CD3⁻ splenocytes was determined by flow cytometry. PBMCs were isolated from NDs and patients with HIE and NK cells (gated on CD56⁺ CD3⁻ lymphocytes), and were assessed for baseline expression of NKG2D by flow cytometry and expressed in panel (B) as MFI, or in panel (C) as % of positive cells compared with isotype controls. (D) PBMCs were then cultured with 20 ng/mL of IL10 or IL21, and NKG2D expression determined at 24 and 48 hours. Data were obtained in 2 separate experiments by different investigators, the results of which were pooled after normalization of the 2 experiments to mean expression at 48 hours. P values for 1-tailed unpaired Student t tests are shown or designated as *P < .05; **P < .01. NS, no statistical significance. HIE sample numbers from Table 1 are indicated at the far right.