Determination of NK cell phenotypes in whole blood samples. NK cell phenotypes, CD56dimCD16+ and CD56brightCD16-NK cells were determined by flow cytometry after separation from whole blood from CFS patients (white bars; n = 10) and control subjects (black bars; n = 10). The plots shown are gated on NK lymphocyte population. Data are the mean ± SEM. the symbol (*) denotes statistical significance.