IL-21, IL-21R, and common γ chain receptor expression on WM cells. (A) Immunohistochemical staining of IL-21 (brown) in bone marrow sections obtained from 5 consenting patients with WM (WM1-WM5) was performed with a polyclonal anti–IL-21 antibody as described in “Methods.” Slides were visualized on an Olympic Provus AX70 light microscope, and images shown are with original magnification of ×400. (B) PCR for IL-21R, IL-21, and GADPH was performed on cDNA generated from either CD19⁺CD138⁺ cells obtained from patients with WM (n = 8; nos. 6-14) or the WM cell line, MWCL-1. RNA was extracted from previously frozen WM cells; therefore, the sample numbers are not consistent with those noted in other figures. The T-cell line Karpas299 was used as a positive control for both IL-21 and IL-21R. (C) IL-21R and common γ chain receptor coexpression was determined on CD19⁺CD138⁺ cells from patients with WM and the MWCL-1 cell line with the use of FACS analysis. Three representative histograms obtained from a total of 8 patient samples are shown (WM14-WM16). Gray histograms represent the appropriate isotype controls.