Abstract
Monoclonal B cell lymphocytosis (MBL) is now recognized as the B‐lymphocyte analogue of a monoclonal gammopathy of unknown significance. MBL can be the precursor of chronic lymphocytic leukemia or associated with non‐Hodgkin's lymphoma. It may be associated with an autoimmune abnormality or be related to aging (immunosenescence). The combination of available new fluorochrome‐conjugated monoclonal antibody reagents, multilaser instrumentation, and improved software tools have led to a new level of multicolor analysis of MBL. Presently, several centers, including the University of Salamanca (Spain), Duke University (Durham, NC), Mayo Clinic (Rochester, MN), and the National Cancer Institute (Bethesda, MD) in conjunction with the Genetics and Epidemiology of Familial chronic lymphocytic leukemia Consortium, the Food and Drug Administration (Bethesda, MD), and the Centers for Disease Control and Prevention/Agency for Toxic Substances and Disease Registry (Atlanta, GA) in collaboration with Saint Luke's Hospital (Kansas City, MO), the Università Vita‐Salute San Raffaele in Milan (Italy), and Leeds Teaching Hospital (UK) are all actively conducting studies on MBL. This commentary is an updated summary of the current methods used in these centers. It is important to note the diversity of use in reagents, instruments, and methods of analysis. Despite this diversity, there is a consensus in what constitutes the diagnosis of MBL and its subtypes. There is also an emerging consensus on what the next investigative steps should be. Published 2010 Wiley‐Liss, Inc.