Plasma cell light and heavy chains can be knocked down with siRNA. (A) The flow cytometry plots in the upper row (si[-]) show that ALMC1 and EJM cells both produce intact IgGλ immunoglobulins but that EJM cells contain a subpopulation producing IgL without IgH. In the plots in the lower row, cells at 24 hours after si[IGLC] treatment showed a leftward shift when compared with si[-] controls (top). This shift represents a marked decrease in IgL MFI. MFI values for IgL and IgH are shown for each plot, demonstrating that MFI for IgL decreases and for IgH increases with IgL knockdown. (B) In these flow cytometry histograms, the IgL and IgH in ALMC1 cells are shown at 24 hours after treatment with si[IGLC] or si[IGH]. The MFI is markedly reduced (arrows) in both instances consistent with a marked reduction in intracellular protein. (C) ALMC1 and EJM cells produce intact IgGλ and IgL. Specific interference with IgL or IgH mRNA leaves residual intracellular IgL or IgH staining as a percent of si[-] control. Plots reflect 3 independent repeats (median, range). Intracellular IgL MFI was reduced by a median of 72% in ALMC1 and 40% in EJM cells. (D) Reduction of IgL but not IgH or combined IgL and IgH production was associated with significantly reduced cell proliferation and viability by MTT assay at 24 hours (mean ± standard deviation [SD]). *P < .01 by 2-tailed paired Student t test in both cases (ALMC1, n = 14; EJM, n = 9). (E) In ALMC1, ALMC2 (a sister cell line), and EJM cells, reduction of IgL but not IgH or IgL and IgH production was associated with significantly increased levels of caspase 3/7 activity at 24 hours (mean ± SD). *P < .01 by 2-tailed paired Student t test; n = 4 for each cell line. (F) In ALMC1 cells producing intact IgGλ, specific interference with IgL mRNA is associated with increased intracellular IgH staining as this histogram demonstrates. In this typical example, MFI for IgH is increased by 41%.