CD2 distribution on bovine NK cells in peripheral blood and during cell culture. (A) CD2 expression by PBMCs from healthy cattle, and in NKp46-selected cells cultured for the indicated time in the presence of 100U/ml rbIL-2. Results were obtained by two-colour flow cytometry, gating for viable lymphocytes. Data shown are from one animal representative of 19. (B) Monitoring of cell divisions of CD2- and CD2+ NK cell populations during three and six days of rbIL-2 (100U/ml) stimulation. NKp46-selected cells were labelled with CFSE the day after isolation and CFSE intensity (filled histograms) measured in flow cytometry on the indicated days, gating for CD2- or CD2+ viable cells. Solid line open histograms show non-dividing NK cells, cultured in the presence of 1U/ml rbIL-2, while broken line open histograms show unlabeled stimulated NK cells. Data shown are from one animal representative of five. (C) Stability of CD2 expression in NK cell subsets cultured separately. NK cells separated with immunomagnetic beads for absence or presence of CD2 were cultured separately for eleven days in the presence of IL-2, monitoring CD2 expression at three different time points (filled histograms). Day 1 corresponds to the day of separation, 24 h after primary NK cell isolation. Open histograms show secondary mAb controls. Data shown are from one animal representative of eight.