CD79a, a 32-33KD membrane glycoprotein, is a member of Ig superfamily. It heterodimerizes with CD79b and is non-covalently cross-linked with surface Ig thus forming the BCR complex. It is expressed all stages of differentiation in mature B-cells and is required for cell surface expression and signal transduction by the BCR complex. Upon antigen binding, CD79a/b heterodimer interacts with Tyrosine kinase (Lyn) and gets phosphorylated, resulting in the inititation of intracellular signaling cascade. Pathological role of CD79a has been suggested in B-cell lymphomas and acute lymphoblastic leukemia. CD79a is often used along with CD20 in the detection of normal and neoplastic B-cells in tissue sections.