Persistent polyclonal B-cell lymphocytosis – an important differential diagnosis of B-cell chronic lymphocytic leukemia

Over the last 17 years, 83 cases of polyclonal B-cell lymphocytosis (PPBL) have been published. This rare hematological disorder of unknown etiology is characterized by morphologically atypical lymphocytes, polyclonal immunoglobulin M production in association with smoking, female gender, and HLA-DR7 phenotype. We studied another male patient with PPBL. In contrast to normal B-cells, PPBL cells showed no response to interleukin-4 with regard to CD23 and human leukocyte antigen-DR expression. F2μ antibodies failed to co-stimulate interleukin-4-mediated CD23 expression. Crosslinking membrane immunoglobulin M receptors by F2μ resulted in elevated human leukocyte antigen-DR expression but did not induce in vitro proliferation of PPBL cells. This indicates a different activation and differentiation status than normal B-cells.