Expression of IGF-I by ALK⁺ ALCL cell lines. (A) Immunohistochemical staining of ALK⁺ ALCL cell lines demonstrates the expression of IGF-I in 4 cell lines: SU-DHL-1, SUP-M2, SR786, and DEL. Karpas 299 cells are negative for IGF-I. RSC96 and EJM cells served as negative and positive controls, respectively. The expression of IGF-I is cytoplasmic, and the cell membranes and nuclei are negative (400×). (B) WB shows similar findings. (C) RT-PCR shows the presence of IGF-I mRNA in SUP-M2, SR786, DEL (low level), and EJM, and its absence in Karpas 299, SU-DHL-1, and RSC96. (D) ELISA supports autocrine release of IGF-I. SUP-M2, SR786, and DEL cell lines demonstrate the presence of IGF-I in cell culture supernatants. The EJM cell line was included because it expresses IGF-I protein and mRNA. IGF-I is almost undetectable in cell culture supernatants from Karpas 299 and RSC96 cells. The experiment was repeated 3 times, and the results are shown as the mean ± SD. P < .01 for SUP-M2, SR786, and DEL compared with other cell lines.