Microscopical examination of a peripheral-blood smear revealed abnormal lymphocytes (lambda positive, monocolonal B-cell population, 4% of peripheral blood leukocytes) and immunophenotyping using the immunofluorescence with flow cytometry was positive for CD45, CD19, CD20, CD22, CD79b, CD200, CD10, CD11c,CD103, CD305 and CD25 (Fig. 2), and a diagnosis of hairy cell leukemia (HCL) was made. Here, CD19 is linked to hairy cell leukemia.