Demonstration of Src-kinase activation in ALCL-derived cell lines expressing NPM-ALK by immunocytochemistry. Cytospins from FEPD (A,D), SU-DHL₁ (B,E), and COST (C,F) cells were fixed in acetone and immunostained. Src-kinase activation was assessed using a streptavidin-biotin-peroxidase method with anti-Src pTyr418 polyclonal Ab and biotin-conjugated pig antirabbit IgG (A-C). The same protocol without anti-Src pTyr418 polyclonal Ab was performed in order to assess background nonspecific immunostaining (D-F). Original magnification, × 400.