Spiked gene expression corresponds to protein expression in MM.

(A) GeneChip HuGeneFL analysis of MS4A2 (CD20)gene expression. The normalized AD value of fluorescence intensities of streptavidin-PE–stained biotinylated cRNA as hybridized to 2 independent probe sets (accession numbers M27394 [blue] andX12530 [red]) located in different regions of the MS4A2gene is on the vertical axis and samples are on the horizontal axis. Note relatively low expression in 31 normal PCs (NPCs) and spiked expression in 5 of 74 MM samples (MM PCs) Also note similarity in expression levels detected by the 2 different probe sets. (B) Immunohistochemistry for CD20 expression on clonal MM PCs: (i) bone marrow biopsy section showing asynchronous type MM cells (hematoxylin and eosin; original magnification × 500); (ii) CD20⁺ MM cells (original magnification × 100; inset, original magnification × 500); (iii) biopsy from a patient with mixed asynchronous and Marschalko-type MM cells (hematoxylin and eosin; original magnification × 500); and (iv) CD20⁺ single lymphocyte and CD20⁻ MM cells (original magnification × 200). CD20 immunohistochemistry was examined without knowledge of clinical history or gene expression findings.