FLOW CYTOMETRIC DETECTION OF CD44 (H-CAM) IN HAIRY-CELL LEUKEMIA

Hairy cell leukemia (HCL) is a rare clonal B-cell disorder characteriz ed by a distinctive pattern of infiltration of hairy cells (HCs) in th e bone marrow (BM), hepatic sinusoids and splenic red pulp. HCs expres s a wide spectrum of matrix-binding integrins, which influence their m igratory behaviour and subsequent tissue localization. CD44 distributi on and staining intensity on HCs from the BM and peripheral blood (PB) were investigated using dual-color flow cytometry. HCs from all cases expressed CD44, but the staining intensity of the positive population was significantly higher than normal residual lymphocytes (p < 0.0005 ) and medullary HCs in those patients exhibiting additional hairy cell dissemination in the peripheral blood. It is of interest to speculate that the BM microenvironmental may deliver signals which down-regulat e CD44 expression on resident HCs compared to HCs recirculating in per ipheral blood. CD44 expression on HCs may help clarify their homing me chanisms in the bone marrow and to define phenotypic subsets with diff erent clinical and pathological behaviours.