CD200 expression constitutes a major immunological marker in the differential diagnosis of CD5+ small B-cell lymphomas; for example, mantle cell lymphoma is CD200-negative (in contrast to SMZL) and also in small B-cell lymphomas with villous cytoplasm; SDRPL is dimly CD200-positive, whereas HCL is strongly CD200-positive [25]. This evidence concerns the gene CD5 and mantle cell lymphoma.