ERK1/2 and STAT5 phosphorylation levels in CD56⁺ cells costimulated with HC. Total CD56⁺ cells were stimulated with IL-15 in the absence (filled symbols) or presence of 10^–4 M HC (open symbols) for a 17-day period and tested at the indicated time points for (A) phospho-ERK1/2 and (B) phospho-STAT5 staining by FACS analysis on gated CD3^– (squares) and CD3⁺ cells (circles). Mean fluorescence intensity (MFI) values (mean ± SD) from 3 different donors are presented.