Relationship of lymph node CD38 expression with tumor proliferation and the microvasculature. (A) View (original magnification ×630) of a CLL lymph node from a patient with a peripheral blood CD38 level of 13% stained with CD38 (green), Ki-67 (blue), and CD23 (red). All proliferating CLL cells stain for both CD23 and CD38 (yellow). Identical appearances were observed in all CD38⁺ lymph nodes, defined by the presence of detectable CD38 staining as detailed in “Distribution of CD38 expression in CLL lymph nodes.” (B) View (original magnification ×200) of a CLL lymph node stained with CD31 (white) and CD23 (red), illustrating the larger number of vessels in a CD38⁺ compared with a CD38⁻ case. (C) Quantification of the difference in lymph node vascular density assessed by the number of CD31⁺ pixels in CD38⁻ and CD38⁺ cases of CLL. Significantly increased vessel density is apparent in the CD38⁺ cases. Results shown are the mean CD31 pixel index plus or minus SEM with the unpaired t test result. (D) View (original magnification ×630) of a CD38⁺ CLL lymph node, illustrating the relationship between proliferating CLL cells stained for Ki-67 (blue) and CD23 (red), T cells stained for CD3 (green), and a microvessel detected by CD31 (white). (E) View (original magnification ×400) of a CLL lymph node frozen section stained for CD38 and shown as a rainbow palette image in which different levels of expression are assigned a different color. The level of CD38 expression varies markedly within the lymph node and is most dense in areas around vascular structures. This image is representative of 12 frozen sections.