ULBP-4 expression by monocytes regulates NKG2D surface expression by autologous NK cells. Monocytes and NK cells purified from the same individual were cocultured for 18 to 20 hours. (A) The percent of NK cells expressing NKG2D cultured in the presence or absence of autologous monocytes (AVG ± SEM) (n = 6). (B) The mean fluorescent intensity (MFI) (AVG ± SEM) of anti-NKG2D staining on the surface of NK cells cultured in the presence or absence of autologous monocytes (n = 6). (C) NKG2D expression on NK cells cultured with autologous monocytes or monocyte culture supernatant. These results are representative of results from 4 independent experiments. (D) Lysis of Jurkats by NK cells cultured in the absence of monocytes, or isolated from NK-monocyte coculture at an effector:target cell ratio of 1:1. These results are combined results from 2 independent experiments. (E) NK cells were cultured in the presence or absence of autologous monocytes along with NKG2D-Fc or control Fc. Twenty hours later, NKG2D surface expression on the NK cells was determined by flow cytometry. The level of anti-NKG2D staining is expressed as percent of anti-NKG2D staining on NK cells cultured in the absence of monocytes and with control Fc, which is defined as 100% expression (AVG ± SEM) (n = 5). (F) NK cells were cultured in the presence or absence of autologous monocytes and IL-12 (10 ng/mL), IL-15 (10 ng/mL), and IL-18 (10 ng/mL). Twenty hours later, NKG2D surface expression on the NK cells was determined by flow cytometry. The MFI (AVG ± SEM) of anti-NKG2D staining on the surface of NK cells is shown (n = 9). *P < .04 in 2-tailed Wilcoxon matched-pairs signed rank test. **P < .03 in 1-tailed Student t test. ns, not statistically significant.