Description: The monoclonal antibody L26 recognizes human CD20, a two transmembrane spanning protein found on precursor and mature B lymphocytes. Expression is lost upon differentiation to plasma cells. The levels of CD20 are critical in evaluating malignant B lymphocytes including Non-Hodgkin’s Lymphoma, and Acute B cell, Chronic Lymphocytic and Hairy-Cell Leukemias. CD20 plays a role in B cell differentiation and activation. The structure of the protein shows a small extracellular loop with the carboxy and amino termini in the cytoplasmic compartment. The L26 antibody recognizes an epitope in the cytoplasmic domain and therefore requires permeabilization of the tissue for staining applications. Unlike many anti-CD20 antibodies that recognize the extracellular domain, the epitope recognized by L26 will not be blocked by therapeutic antibodies to CD20, like Rituximab.