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 i s characterized by morphologically atypical lymphocytes, polyclonal immunog lobulin M production in association with smoking, female gender, and HLA-DR 7 phenotype. We studied another male patient with PPBL. In contrast to norm al B-cells, PPBL cells showed no response to interleukin-4 with regard to C D23 and human leukocyte antigen-DR expression. F2 mu antibodies failed to c o-stimulate inter leukin-4-mediated CD23 expression. Crosslinking membrane immunoglobulin M receptors by F2 mu resulted in elevated human leukocyte an tigen-DR expression but did not induce in vitro proliferation of PPBL cells . This indicates a different activation and differentiation status than nor mal B-cells.