BCA-1 is expressed by B lymphocytes and vascular endothelium in PNCSL.

Double immunostaining confirms expression of BCA-1 by CD20⁺B cells in panel A (DAB, BCA-1; Fast Red, CD20; no counterstain, original magnification × 1000) and CD31⁺ vascular endothelium in panel B (DAB, BCA-1; Fast Red, CD31; no counterstain, original magnification × 1000). Brain biopsy specimen from a patient with PCNSL does not contain CD21⁺ cells (C), whereas, in panel D, CD21⁺ cells are detected in a lymphoid follicle of a normal tonsil (Fast Red, hematoxylin counterstain, original magnification × 600).