CD11b Is Useful in the Diagnosis of Chronic Lymphocytic Leukemia/Prolymphocytic Leukemia, Mixed Chronic Lymphocytic Leukemia, and Prolymphocytic Leukemia.

CD11b is well known as an integrin, Mac-1, is often complexed with CD18, and is found on monocytes, granulocytes, and natural killer cells. It also serves as a receptor for iC3b. However, its occurrence in B cell chronic lymphoproliferative disorders is not generally recognized and has not been fully evaluated. To address this issue, a series of B cell leukemias and lymphomas referred for primary diagnosis was evaluated for the presence of CD11b. The purpose was to determine the frequency of its expression on these tumors and to evaluate its diagnostic value. Consecutive cases referred for flow cytometry as possible lymphoproliferative disease were analyzed. Included were bone marrow, peripheral blood, and lymph nodes. All cases were diagnosed according to the WHO classification based on immunophenotypic, morphologic, and clinical findings. The morphologic criteria of Melo (1986) and Bennett (1989) were used for classification of chronic lymphocytic leukemia (CLL), CLL/prolymphocytic leukemia (CLL/PLL), mixed CLL, and PLL. Cases identified as not related to chronic lymphocytic leukemia or prolymphocytic leukemia were recorded but not further analyzed. Similarly, lymph node and spleen-based tumors were excluded from the final analysis. CD11b was present on cells from 32 of 123 cases, including occasional follicular lymphoma, (5/35); mantle cell lymphoma, (1/8); diffuse large B cell lymphoma, (3/9); hairy cell leukemia, (3/5); multiple myeloma, (1/2); lymphoplasmacytic lymphoma, (2/2); nodal marginal zone lymphoma, 0/1); and splenic marginal zone lymphoma, (1/1). However, it was most consistently expressed on CLL that contained increased numbers of prolymphocytes or large cells and on PLL. A total of 16 such cases were found. Morphologic assessment showed them to include 8 CLL/PLL, 3 mixed CLL, 4 PLL, and 1 typical CLL. The typical CLL case included both large cells and prolymphocytes but did not have more than 10% PLs. Five of the 16 cases (31%) were negative for CD5, CD23, and CD38 but were positive for FMC-7. In contrast, the other 11 cases were all CD5(+) and CD23(+); 3/11 were positive for CD38; and 5/11 were positive for FMC-7. Forty-five CLLs also were identified during the study, of which 27 had sufficient data for comparison. Twenty-six of the 27 CLLs were morphologically typical. The remaining case was mixed CLL. All of the CLLs were CD11b(−), CD5(+) and CD23(+); 15/43 were CD38(+), and 6/43 were FMC-7(+). The findings show that CD11b is expressed on chronic B cell lymphoproliferative disorders. In particular, it is expressed on almost all CLL cases that contain large cells or prolymphocytes and on PLL. Inclusion of CD11b in routine screening panels of possible chronic B cell leukemiaa will improve diagnosis of these disorders.