MyD88-dependent pathways in MM plasma cells. (A) Real-time polymerase chain reaction analysis of MyD88 RNA levels in 20 primary MM CD138-selected cell samples incubated for 24 hours with 500 IU/mL IFN-γ. (B) Western Blot analysis of MyD88 expression in RPMI 8226 MM cells exposed for 24 hours to 500 IU/mL IFN-γ with or without 1-hour pretreatment with 20 μM UO126 and in CD138-selected samples from MM and MGUS patients. (C) MyD88 expression in RPMI 8226 cells stably transfected with an expression plasmid carrying a human MyD88 cDNA (hMyD88) or a dominant-negative mutant (DN-hMyD88), or with MyD88 siRNA. (D) ERK1/2 and STAT1 phosphorylation in RPMI 8226 cells transfected with MEK1, MyD88, TRAF6 siRNAs, or DN-hMyD88 cDNA and exposed to 500 IU/mL IFN-γ.