2B4 and CD48 are critical for macrophage-mediated activation of NK cell proliferation and IFN-γ secretion. (A) Proliferation and (B) IFN-γ secretion of NK cells during 48 hours of coincubation alone or with monocytes, DCs, macrophages, and macrophages activated with 100 ng/mL (macrophages^{low LPS}) or 200 ng/mL (macrophages^{high LPS}) LPS at a 10:1 ratio. NK cells were pulsed with anti-2B4, anti-LFA1, anti-CD40L, anti-NKp30 (F252, IgM), or isotype-matched control mAbs prior to coculture with APCs for 48 hours. Alternatively, APCs were pulsed with anti-CD48 or isotype-matched control mAb (IgM; APC) prior to coculture with NK cells for 48 hours. *P < .05, **P < .01 by Student t test for unpaired values. The results are expressed as the mean ± SE of at least 3 independent experiments using cells from different donors.