Blood NLC protect CLL B cells from spontaneous apoptosis in vitro.

(A) Determination of CLL B-cell viability by staining with DiOC₆ and PI. Presented are contour maps of CLL B cells from a representative patient defining the relative green (DiOC₆) and red (PI) fluorescence intensities of the leukemia cells on the horizontal and vertical axes, respectively. The vital cell population (DiOC₆^bright, PI exclusion) was determined for CLL cells cultured in the presence (left box) or absence (right box) of NLC. Vital cells were gated as indicated by the polygons with the broken lines. Relative percentage numbers of vital cells are displayed above each of these gates. (B) Determination of CLL B-cell viability as assessed by light scatter. These contour plots show the relative forward-light scatter (or FSC) or granularity (side-light scatter, or SSC) of CLL cells from the same patient sample as displayed in A, cultured with (left box) or without (right box) NLC. Vital cells were gated as indicated by the circles with the broken lines, and the relative percentage numbers of vital cells are indicated above each of these gates. (C) Viability of CLL cells in the presence or absence of NLC. CLL cells from 6 patients were removed from NLC in long-term CLL B-cell cultures 14 days after seeding, and the leukemia cells were plated in either wells with NLC (squares) or without NLC (diamonds). Displayed are the mean percentage viability values (±SEM) of leukemia cells assessed at the indicated time points relative to those noted at initiation of culture on day 0.