Mondo Description Persistent polyclonal B-cell lymphocytosis (PPBL) is a rare, generally benign, lymphoproliferative hematological disease characterized by: chronic, stable, persistent, polyclonal lymphocytosis of memory B-cell origin, the presence of binucleated lymphocytes in the peripheral blood, and a polyclonal increase in serum immunoglobulin M (IgM). Patients are most frequently asymptomatic or may present with mild splenomegaly.