Bortezomib-mediated long-lived plasma cell (LLPC) depletion is transient. Twelve- to 16-wk-old NZB/W F1 mice were treated with one bortezomib cycle consisting of two bortezomib injections within 36 h and analyzed 12 h and 3, 7 and 15 days after the last bortezomib injection. (A) Representative gating strategy for plasma cell analysis by flow cytometry. Lymphocytes were gated according to their position in forward and sideward scatter, and doublets were excluded from the analysis (not shown). Plasma cells were identified as CD138+ and intracellular kappa light chain + cells both in spleen and bone marrow. Within the plasma cells population, plasmablasts and newly generated plasma cells were identified as cells with a higher expression of MHC-II. Conversely, MHC-IIlow plasma cells were regarded as LLPCs. A representative plot of the expression of MHC-II on the plasma cell population is shown for spleen and bone marrow 15 days after bortezomib treatment. (B) Absolute numbers of all CD138+/intracellular kappa light chain + plasma cells (white bars) and the subgroups of short-lived, MHChigh (gray bars) and long-lived, MHC-IIlow (black bars) plasma cells in spleens (left) and bone marrows (right) 12 h (0.5 days), 3, 7 and 15 days after one cycle of bortezomib measured by flow cytometry. n = 7 mice per time point. (C) Frequencies of the remaining anti-double-stranded DNA (dsDNA) antibody-secreting cells (ASCs) (immunoglobulin G (IgG) and immunoglobulin M (IgM) combined) in spleen (left) and bone marrow (right) calculated by comparison with untreated mice (day 0), as detected by enzyme-linked immunospot (ELISPOT). n = 4 mice per time point. Data are presented as mean and standard error of the mean (SEM). n.s., nonsignificant. P >0.05, *
P ≤0.05, **
P ≤0.01 by two-tailed unpaired t test.