The CD79a antigen (Immunoglobulin binding protein-1, IGBP-1) is an alpha/beta heterodimer cell membrane protein required in cooperation with CD79b for the initiation of the signal transduction cascade activated by binding of antigen to the B-cell antigen receptor complex (BCR). This cascade leads to BCR complex internalization, trafficking to late endosomes and antigen presentation. CD79a is also required for BCR surface expression and efficient differentiation of pro- and pre-B-cells. CD79a interacts with numerous kinases such as SYK, BLNK, Src-family tyrosine kinases. Defects in CD79a are a cause of non-Bruton type agammaglobulinemia, an immunodeficiency disease of the B-cell maturation pathway.