Expression of thrombospondin receptor (CD36) in B-cell chronic lymphocytic leukemia as an indicator of tumor cell dissemination.

BACKGROUND AND
OBJECTIVE: The expression of CD36 antigen has not been conclusively associated with human B-lymphocytes although CD36 was recently detected in a human B-cell angiotropic lymphoma where it might be involved in lymphoblast-endothelial cell adhesion. We investigated the expression of CD36 in B-cell chronic lymphocytic leukemia (CLL) by multiparameter flow cytometry; results were correlated with clinical features. DESIGN AND METHODS: CD36 expression was evaluated on peripheral blood and bone marrow samples from 24 patients affected by CD5+ B-CLL. Mononuclear cells were isolated by Ficoll-Hypaque density gradient centrifugation, were labeled with fluorochrome-conjugated monoclonal antibodies under standard experimental conditions and were analyzed by flow cytometry. CD36 expression was quantified both in terms of frequency of CD19+CD36+ cells and of mean fluorescence intensity (MFI-R) of CD36+ cell populations. The intensity of CD36 expression was arbitrarily classified as weak (MFI-R ranging from 3 to 6; score 0), moderate (MFI-R ranging from 6 to 9; score 1), intermediate (MFI-R ranging from 9 to 11; score 2) or strong (MFI-R ranging from 11 to 17; score 3).
RESULTS: CD36 could be detected on 3% (range 2-5) of normal CD19+ B-lymphocytes and on 45% (range 30-75) of neoplastic CD19+ B-cells. When CLL patients were stratified according to CD36 staining intensity, higher hemoglobin levels (Hb) were recorded in patients assigned to score 0 (Hb = 14.3 g/dL; range 13.9-15.1) compared to patients scoring 1-2 (Hb = 11.2; range 10.3-12.2) or 3 (Hb = 9.8; range 9.6-11.6; p=0.0053). Similarly, higher platelet counts (Plt) were found in patients scoring 0 (Plt = 282x10(3)/microL; range 244-319), compared to patients with intermediate (Plt = 175x10(3)/microL; range 144-238) and high scores (Plt = 149x10(3)/microL; range 103-230; p=0.044); lymphocyte count (Ly) was significantly higher in patients assigned to score 3-4 (Ly = 23.3x10(3)/microL, range 13-30) compared to score 0-2 (Ly = 9.8x10(3)/microL, range 8.5-10.8; p=0.045). CLL patients expressing CD36 at intermediate-to-strong intensity (MFI-R = 14, range 9-16) were more frequently assigned to Rai stages III-IV than stages I-II (CD36 MFI-R = 9, range 6.5-11; p=0.005) and stage 0 (CD36 MFI-R = 6, range 4-7.3; p<0.001). Interestingly, bone marrow diffuse histology was strongly associated with higher CD36 expression (MFI-R = 8.7; range 4.7-13.9) compared to non-diffuse patterns of bone marrow infiltration (MFI-R = 6.7; range 5.2-9.3; p=0.0019). In multivariate regression analysis, CD36 staining intensity significantly and independently correlated with diffuse BM histology (p=0.033). INTERPRETATION AND
CONCLUSIONS: The present report provides the first evidence of CD36 expression on CD19+ B-cells from CLL; the correlations with clinical parameters strongly support the view that CD36 might favor tumor cell spreading. Whether high CD36 expression levels on CLL CD19+ B-cells identify an aggressive disease subset remains to be further confirmed in larger series of patients.