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 (Fig 1), 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 (Fig 2). 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.
For formalin fixed, paraffin embedded material, mAb JCB117 is one of the most frequently used clones. For optimal epitope retrieval, HIER is needed, and an alkaline buffer is preferred. mAb HM57 cannot be recommended for paraffin sections because of cross reactivity with smooth muscle cells and various epithelia (see assessment, run 6). For control tissue, lymph node or tonsil is appropriate. B-cells in both the follicle centre and mantle zone as well as plasma cells should be stained.
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