β₂M-specific mAbs activate the JNK signaling pathway. (A) Western blot analysis and (B) densitometric data (AVG) showing protein levels of phosphorylated (p) and nonphosphorylated ASK1, MLK3, MEKK1, MKK4, MKK7, and JNK in β₂M-specific mAb (D1)–treated myeloma cells. Results obtained with D1 mAb on MM.1S myeloma cells from 1 representative experiment of 3 performed are shown. Similar results were obtained with β₂M-specific mAb E6 with this and other myeloma cell lines. Error bars indicate SD.