The CD79 antigen is a heterodimer consisting of two phosphoproteins designated CD79a (mb-1; 47 kDa) and CD79b (B29; 37 kDa). CD79 associates to membrane-bound Ig to create the B-cell complex allowing signal transduction to be transmitted to the interior of the cell. CD79a is specific for B-cells, appearing before the pre-B cell stage, still being present at the plasma cell stage.
CD79a is detected in the large majority of B-cell neoplasms. However, among plasma cell neoplasms, only about 50% are stained. CD79a has been reported in up to 10% cases of precursor T-cell lymphoblastic lymphoma but very rarely in mature T-cell lymphomas. In nodular lymphocyte predominant Hodgkin lymphoma, CD79a is found in of L&H cells in the large majority of cases, while in the other types, Reed-Sternberg cells are only stained in 20% of the cases. Among myeloid leukaemias, CD79a positivity has been described in type M3.
Together with CD20, CD79a is one of the most important markers for the identification of B-cell neoplasms as outlined above.
Tonsil and colon/appendix are recommended as positive and negative tissue controls for CD79a. In tonsil, the protocol must be calibrated to provide a distinct and strong membranous staining reaction in all mantle zone B-cells. Virtually all germinal centre B-cells must at least display a moderate and distinct membranous staining reaction. Plasma cells and late stage activated B-cells must show a strong cytoplasmic staining reaction. No staining reaction must be seen in T-cells and squamous epithelial cells.
In colon/appendix, plasma cells in lamina propria mucosa must show a strong cytoplasmic staining reaction. No staining reaction should be seen in the epithelial cells.
Jaffe ES, Harris NL, Stein H, Vardiman JW (Eds.) WHO Classification of Tumours. Pathology and Genetics of Tumours of Haematopoietic and Lymphoid Tissues. Lyon, IARC Press 2001. Korkolopoulou P, Cordell J, Jones M, Kaklamanis L, Tsenga A, Gatter KC, Mason DY. The expression of the B-cell marker mb-1 (CD79a) in Hodgkin's disease. Histopathology. 1994 Jun;24(6):511-5. Kurtin PJ, Hobday KS, Ziesmer S, Caron BL. Demonstration of distinct antigenic profiles of small B-cell lymphomas by paraffin section immunohistochemistry. Am J Clin Pathol. 1999 Sep;112(3):319-29. Mason DY, Cordell JL, Brown MH, Borst J, Jones M, Pulford K, Jaffe E, Ralfkiaer E, Dallenbach F, Stein H, et al. CD79a: a novel marker for B-cell neoplasms in routinely processed tissue samples. Blood. 1995 Aug 15;86(4):1453-9. Pilozzi E, Pulford K, Jones M, Muller-Hermelink HK, Falini B, Ralfkiaer E, Pileri S, Pezzella F, De Wolf-Peeters C, Arber D, Stein H, Mason D, Gatter K. Co-expression of CD79a (JCB117) and CD3 by lymphoblastic lymphoma. J Pathol. 1998 Oct;186(2):140-3. Toth B, Wehrmann M, Kaiserling E, Horny HP. Immunophenotyping of acute lymphoblastic leukaemia in routinely processed bone marrow biopsy specimens. J Clin Pathol. 1999 Sep;52(9):688-92. Vasef MA, Alsabeh R, Medeiros LJ, Weiss LM. Immunophenotype of Reed-Sternberg and Hodgkin's cells in sequential biopsy specimens of Hodgkin's disease: a paraffin-section immunohistochemical study using the heat-induced epitope retrieval method. Am J Clin Pathol. 1997 Jul;108(1):54-9. Yao X, Teruya-Feldstein J, Raffeld M, Sorbara L, Jaffe ES. Peripheral T-cell lymphoma with aberrant expression of CD79a and CD20: a diagnostic pitfall. Mod Pathol. 2001 Feb;14(2):105-10.