CD32B expression by clonal plasma cells in AL-amyloidosis. (A) The log_e-transformed quantitative expression levels (Ln(QLE)) for the clonal and nonclonal light-chain constant region genes are shown (horizontal lines are mean values). The clonal genes were expressed at significantly higher levels than the nonclonal, indicating that clonal plasma cells were purified (paired t test, P = .006). (B) The Ln(QLE) values of lineage-specific genes are depicted. Comparisons of the Ln(QLE) of plasma cell versus other markers were highly significant (paired t test, P < .001) except for comparisons with CD14 where the P values were .002 for CD38 and .01 for XBP-1 and CD138. CD14 levels may reflect aberrant expression of CD14 by clonal plasma cells or monocyte contamination. (C) The Ln(QLE) values of Fcγ receptor family member genes are shown (paired t test, P < .001 for CD32B compared with each of the others). (D) The CD32B1 isoform is expressed by RT-PCR using B-B4–double-enriched plasma cells at diagnosis (n = 6) and relapse (n = 6). (E) Typical flow cytometry dot plots are shown, displaying that nearly all CD138⁺ cells are also CD32B⁺. A median of 99% of the CD138⁺ cells in samples from 31 patients (B-B4–double-enriched cells = 11, marrow aspirate mononuclear cells = 20) coexpressed CD32B⁺ at diagnosis and relapse. Marrows at relapse contained a median of 8% plasma cells (range, 4%-15%).