Anaplastic plasmacytomas: relationships to normal memory B cells and plasma cell neoplasms of immunodeficient and autoimmune mice

Abstract

Anaplastic plasmacytomas (APCTs) from NFS.V(+) congenic mice and pristane-induced plasmacytic PCTs from BALB/c mice were previously shown to be histologically and molecularly distinct subsets of plasma cell neoplasms (PCNs). Here we extended these comparisons, contrasting primary APCTs and PCTs by gene expression profiling in relation to the expression profiles of normal naïve, germinal centre, and memory B cells and plasma cells. We also sequenced immunoglobulin genes from APCT and APCT-derived cell lines and defined surface phenotypes and chromosomal features of the cell lines by flow cytometry and by spectral karyotyping and fluorescence in situ hybridization. The results indicate that APCTs share many features with normal memory cells and the plasma cell-related neoplasms (PLs) of FASL-deficient mice, suggesting that APCTs and PLs are related and that both derive from memory B cells. Published in 2010 by John Wiley & Sons, Ltd.

Figure 1

Comparisons of the expression profiles for genes that distinguish PCTs and APCTs with genes that distinguish subsets of normal B-cell-lineage cells. (A) Genes that differ significantly for PCTs and APCTs determined from microarray analyses (Supporting information, Supplementary Table 1) and that overlap with non-redundant genes from the microarray data set of Battacharya et al [24] were compared with genes from the latter set that distinguish normal memory and plasma cells (top row), normal naïve and plasma cells (middle row), and normal germinal centre (GC) and plasma cells (bottom row). Odds ratio indicates the enrichment of genes differentially expressed in memory, naïve, and GC B cells compared with plasma cells. (B) Relationships between genes that distinguish PCTs from APCTs quantified by qPCR (X axis) and genes that distinguish normal memory and plasma cells quantified by microarrays (Y axis). Genes that characterize APCTs and memory B cells were assigned positive values, while genes that characterize PCTs and plasma cells were assigned negative values. The scale for each axis is fold change in log₂.

Figure 2

Immunohistochemical and western blot analyses of protein expression in PCTs and APCTs. (A) Comparative analyses of APCTs and PCTs on sections stained with H+E and with antibodies to proteins that differed significantly for expression between the tumour subsets. Immunohistochemical analyses show the significant difference between PCT and APCT. By H+E staining, PCT comprises almost all mature cells with a central nucleolus in a clock-face nucleus, basophilic cytoplasm, and a discernible Golgi. APCT is made up of a mixture of immunoblasts and anaplastic cells, as well as some plasmablasts. By IHC staining, higher levels of IRF4, BLNK, and MATK proteins are seen in PCT, and BLK and HCK in APCT. (B) Western blotting of protein extracts from the two tumour subsets using antibodies to the indicated proteins.

Figure 3

Flow cytometric analyses of cell lines derived from primary APCTs. Single cell suspensions of the B6-207 and B6-1710 cell lines were stained with the indicated antibodies. Green, unstained cells; red, stained cells.

Figure 4

Chromosomal aberrations in cell lines derived from primary anaplastic PCTs detected by spectral karyotyping (SKY) studies of the B6-1710 and B6-207 cell lines. The Del(6E) is presumably the T(6;12) that could not be resolved by SKY.

Figure 5

Chromosomal studies of the B6-207 cell line. Top left: fluorescence in situ hybridization (FISH) using probes for Igh (green) and Igk (red) showing the translocation involving chromosome 12 and chromosome 6 (left side) that was present in all cells. Bottom left: FISH showing IgH (red) and Cμ (green) in abnormal locations. Diagrammatic structures of normal chromosome 12 and normal chromosome 6 with positions of probes for Igh, Cμ, and Igk and break-point positions give rise to the T(12;6) (right side).