Immunocytochemical analysis of vimentin expression in PMA-induced U937 cells co-incubated with WIN55212-2. Differentiation of U937 cells was induced by 25 nM PMA with or without co-incubation with WIN55212-2. The experimental groups were: 1.) Vehicle control = treatment with 0.1% DMSO only (a, b, c, d), 2.) Differentiation control = treatment with 25 nM PMA (e, f, g, h), 3.) Experimental groups were treated additionally with 3 μM (I, j, k, l) or 5 μM (m, n, o, p) WIN55212-2, respectively. Cells were stain against vimentin (a, e, i, m), actin (b, f, j, n) and DAPI (c, g, k, o) and analysed by confocal laser scanning microscopy. Merged pictures are shown (d, h, l, p). Scale bar = 15 μM.