Expression of IGF-IR by ALK⁺ ALCL cell lines. (A) Immunohistochemical staining demonstrates the expression of IGF-IR protein in 5 ALK⁺ ALCL cell lines: Karpas 299, SU-DHL-1, SUP-M2, SR786, and DEL. The cell lines R⁻ and P6 were used as negative and positive controls, respectively. The expression of IGF-IR is limited to the cell membrane and cytoplasm, whereas the nuclei are negative (original magnification, ×400). (B) WB studies confirm the results. It is important to note that the overexpression of IGF-IR in P6 cells does not represent a physiologic level. (C) RT-PCR shows the presence of IGF-IR mRNA in the ALK⁺ ALCL cell lines as well as in the P6 cell line. Although IGF-IRα mRNA is not detectable in R⁻ cells, these cells appear to express very low levels of IGF-IRβ mRNA. (D) Quantitative flow cytometric analysis shows that the ALK⁺ ALCL cell lines express significantly higher levels of IGF-IR compared with normal human T lymphocytes. R⁻ and P6 cell lines were used as negative and positive controls for the expression of IGF-IR, respectively. The estimated numbers of IGF-IR molecules/cell are shown.