Quantum dot IHC for expression of CD20, MHC II (HLA-DR), and PRDM1/Blimp1 in tonsil, DLBCL, and PBL. (A) Tonsil control. (B) MHC II(+) DLBCL. (C) MHC II(−) DLBCL. (D) PBL. Multiplexed quantum dot IHC was performed as described in “Quantum dot fluorescent IHC.” Images (original magnification ×40) demonstrate the composite wavelength image (overlay), followed by 2-color overlays of the unmixed spectral components (CD20, HLA-DR, and PRDM1/Blimp1) depicting individual quantum dot analytes and nuclear counterstain (DAPI). It should be noted that the imaging software artificially increases intensity to match the dynamic range of the display, so that some proteins scored as negative by eye demonstrate an artifactual dusting in the overlay images. For detailed methods on image acquisition, please see supplemental Methods (available on the Blood Web site; see the Supplemental Materials link at the top of the online article).