CD200 Expression in B-Cell Chronic Lymphoproliferative Disorders

Background: Flow cytometry immunophenotyping (FCIP) is used for rapid, specific diagnosis of B-chronic lymphoproliferative disorders (BCLPDs). However, cases may deviate from the typical immunophenotype; therefore, there is a need for adding new marker(s) for differentiating BCLPDs. Lately, few researches highlighted CD200 expression in some BCLPDs. Our aim was to evaluate CD200 expression in different BCLPDs and whether adding CD200 to BCLPD-FCIP routine panels could improve the ability of their differential diagnosis. Methods: We evaluated CD200 expression in 49 BCLPD patients and 26 age-and sex-matched control subjects. Flow cytometry immunophenotyping first panel included CD5, CD19, sIg, CD23, CD22, CD79b, and FMC7; for BCLPDs other than chronic lymphocytic leukemia (CLL) and mantle cell lymphoma, CD11c, CD103, CD25, and CD10 were evaluated. Results: Using tricolor FCIP, CD200 showed high bright expression on CD5/19-positive clone in all B-CLL patients (100%), with a mean of 94% (SD, 11%); in the 2 cases of hairy cell leukemia, CD200 was brightly expressed on 96% and 99% of cells. In all other BCLPDs including mantle cell lymphoma, follicular lymphoma and splenic marginal zone lymphoma, CD200 expression (on CD19/22-positive cells) was less than 20% with a mean of 10% (SD, 8%) and a dim pattern. CD200 expression was significantly higher in CLL compared with non-Hodgkin lymphoma groups (P < 0.001). Conclusions: Evaluating CD200 expression has a great impact on accurate BCLPDs diagnosis and could be added to the BCLPD routine panels. The high expression of CD200 in B-cell CLL and hairy cell leukemia could open the option for targeted immune (anti-CD200) therapy.