The mb-1 gene codes for a phosphoprotein, designated CD79a, that, together with the related CD79b protein, forms a dimer associated with membrane-bound immunoglobulin in B-cells. The CD79a/CD79b dimer is closely associated with the B-cell antigen receptor, in a similar manner to the association of CD3 with the T-cell receptor, and enables the cell to respond to the presence of antigens on its surface. The CD79a protein is present on the surface of B-cells throughout their life cycle, and is absent on all other healthy cells, making it a highly reliable marker for B-cells in immunohistochemistry