LEUKEMIA-ASSOCIATED CHANGES IDENTIFIED BY QUANTITATIVE FLOW-CYTOMETRY.2. CD5 OVER-EXPRESSION AND MONITORING IN B-CLL

The CD5 antigen density on B cells was studied on fetal spleen, cord b lood, and adult peripheral blood (after immunomagnetic bead purificati on) using an indirect immunofluorescence technique. In fetal spleen, t here was a continuum in CD5 expression, whereas all cord blood and les s than 20% adult peripheral blood B cells were CD5(+). Mean CD5 antige n density on these normal cells was low (3-6 x 10(3) molecules/cell); eight to 20 times lower than on normal T lymphocytes. In adult blood, less than 10% B cells expressed more than 3 x 10(3) CD5 molecules/cell . In chronic malignancies, 34/35 cases had a CD5 antigen density lower than on residual T cells, but mean antigen density was higher (14.8 /- 2.1 x 10(3) molecules/cell) than on normal B cells. Sixteen cases o f chronic lymphocytic leukemia (50%) expressed a CD5 density above 10 x 10(3) molecules/cell. This aberrantly high CD5 expression was used t o detect neoplastic cells after dilution in normal lymphocytes, with a limit of detection between 1 :100 and 1:1000. Quantitation of the CD5 antigen allows better characterization of the Bm population and shoul d be used for the monitoring of chronic malignancies.