CD14⁺CD16⁻monocytes acquire stable IFN-γ signature only after cell-cell contact with NK cells. CD14⁺CD16⁻ monocytes and in vitro preactivated NK cells were isolated from HD blood and cocultured for 18 hours (NK-Mo). Monocytes alone (Mo) or cocultured with NK cells through a Transwell membrane (NK//Mo) were used as controls. In some experiments, controls included monocytes treated with IFN-γ (Mo + IFN-γ). Some coculture experiments were done in the presence of anti-IFN-γ (NK-Mo + α-IFN-γ) or IgG1,κ isotype control (NK-Mo + IgG1,κ). After coculture, the transcriptional, phenotypical, and functional profiles of monocytes were assessed. (A) Main gene signatures induced in monocytes after coculture with NK cells, assessed by microarray. (B-C) Validation by real-time PCR of JAK2, STAT1, IRF1, CXCL10, and CXCL9 gene expression in monocytes after coculture with NK cells. (D) Validation of FCGRA1 gene expression and CD64 protein expression in monocytes after coculture with NK cells assessed by real-time PCR and flow cytometry, respectively. (E) Histograms for phenotypical characterization of monocytes after coculture with NK cells; frequency of CCR2⁺CX₃CR1⁺ monocytes assessed by flow cytometry. (F) Expression (MFI) of CX₃CR1 in monocytes after coculture with NK cells, assessed by flow cytometry. (G) Frequency of TNF-α⁺ and IL-23p19⁺ monocytes after LPS stimulation, assessed by flow cytometry. Error bars represent standard deviation. Data are representative of at least 2 or more independent experiments combined; n = 2-3 HDs per experiment. Statistical comparisons were performed with the unpaired Student t test with Welch correction. *P < .05, **P < .01, ***P < .001. NS, not significant.