BCR and B-cell chronic lymphocytic leukemia: Chronic lymphocytic leukemia (CLL) is a mature B-lymphocyte clonal proliferative neoplasm, characterized by lymphocyte aggregation in the peripheral blood, bone marrow, spleen and lymph nodes.155 The B cell receptor (BCR) is an immunoglobulin expressed on the membrane surface of B lymphocytes during B lymphocyte development, and is a specific receptor for B lymphocytes to recognize and bind antigens.