Quantitative expression of CD23 and its ligand CD21 in chronic lymphocytic leukemia

Cells from the great majority of patients with chronic lymphocytic leukemia (CLL) express CD23. A recent histologic study has shown that CD23 is expressed more strongly in the proliferating centers of the lymph nodes, where the large prolymphocytoid cells are located. The aim of our study was to quantify the expression of CD23 and CD21 in small and prolymphocytoid cells from patients with CLL and B-cell lymphomas, and correlate this expression with clinical parameters.

Using quantitative flow cyto-metry we analyzed the antigen density of CD23 and CD21 in: 1) 101 cases of chronic lymphocytic leukemia, 84 typical, 14 with increased prolymphocytes (CLL/PL) and 3 atypical, 2) 15 cases of CD23 positive B-cell lymphoma with circulating lymphoma cells and 3) 8 normal subjects. The results were correlated with morphology and clinical staging.

Cells from CLL and CLL/PL have a significantly higher number of CD23 molecules than normal and lymphoma B-cells (p<0.001 and p<0.001, respectively). Differences were not significant for CD21. CLL and CLL/PL cases had similar values of CD23 and CD21 molecules, but analysis at a single level showed that prolymphocytes in typical CLL and CLL/PL expressed significantly higher CD23 (p=0.001, p=0.006) and CD21 (p=0.001, p=0.001) than small lymphocytes. There was no correlation between CD23 or CD21 antigen density and clinical stages although there was a trend for a brighter CD23 in stage C patients.

Since interaction between CD23 and CD21 is important for B-cell activation, proliferation and tumor formation, findings that both molecules are upregulated in prolymphocytes suggest that this is the proliferating cell component in CLL and underline the association between progression and increased prolymphocytes in typical CLL and CLL/PL.