IL-2 induces further proliferation and differentiation of KIL. (A) Growth curve of KIL stimulated with human IL-2 (20 ng/mL) alone. The vertical axis is plotted on a logarithmic scale. Each point represents the mean of triplicates. (B) Wright-Giemsa–stained KIL. Note the fine azurophilic granules in the cytoplasm. Bar = 20 μm. (C) Wright-Giemsa–stained KIL stimulated with IL-2 (20 ng/mL) alone for 6 days. Note the larger cell size, ruffled cell membrane, and prominent azurophilic granules. Bar = 20 μm. (D) Western analysis of the expression of granzyme B by KIL stimulated with IL-2 alone for 0, 3, 6, 9, and 11 days. The 32-kDa granzyme B is indicated. Low-level granzyme B expression was detectable in the day 0 sample on the original film. The same blot was reprobed with an anti–β-actin antibody. (E) Northern and Western analyses of Notch-1 expression in KIL stimulated with IL-2 alone for 0 and 6 days and in the promyelocyte cell line, MPRO (negative control).³¹  The Northern blot (top) was hybridized to a cDNA probe encoding the intracellular domain of mNotch1. The ethidium bromide–stained gel is shown in the middle row. The bottom row is a Western blot probed with affinity-purified antibodies against the carboxy terminus of mNotch1. The 120-kDa fragment of mNotch1 is indicated. (F) Cytolytic activity of KIL. KIL cells were incubated with monolayers of OP-9S at 1:1 to 4:1 effector-to-target ratios in a 12-well plate in growth medium containing IL-7 and SCF. KIL lysed the OP-9S monolayers in 24 to 48 hours. The OP-9S monolayers were then fixed and stained with Coomassie blue. Lysed or denuded areas (†) of the OP-9S monolayers appear clear whereas the intact areas (^*) appear blue. (G) The relationship between the degree of cell lysis and the effector-to-target ratio.